WeatherRouting

1.1 What the app does and what it needs

The app runs on the boat's computer. You use it in a web browser: on that computer, or on a tablet connected to the boat's network. Everything it uses is stored on the boat's computer, so once the data is on board you can plan, calculate and follow routes without any internet connection.

An internet connection is needed only to fetch data. While you are online — in the marina, or over a mobile connection — the app downloads:

• wind and current forecasts for the areas you sail in (see chapter 2); at sea you can also import forecast files you received by e-mail;
• the zones: traffic separation schemes, wind farms, restricted and protected areas (see chapter 3);
• the tide data for the tidal atlas (see chapter 9);
• the chart tiles of the map, and the coastlines the router keeps clear of (see chapter 10).

To calculate a route you need three things: forecasts for the area, a boat with its polar, and a route drawn on the map. The passage in 1.3 takes you through them in that order.

1.2 The screen

The map fills most of the window. Over it lie:

• the area chip, top left — the light and name of the area you are working in, and the weather model and run shown (for example GFS 06Z). Tap it to open the Areas tab;
• the run caption next to it — which wind and current forecasts the map shows. Tap it to choose others (see 8.2);
• the instruments of the routes on the map, under the chip (see 7.3);
• the colour scale, top right — the wind speed (or current rate) of the colour shading, in knots;
• the ☰ map menu, in the top right corner — Split screen, Stream and how the map looks (see 8.6).

The time bar runs under the map, on top of the route panel — the time the map shows, with play, the step buttons and a scale with days and hours (see 7.1).

The route panel under the map appears as soon as a calculation is on the map: a graph or table of the route, or a comparison when several routes are shown (see 7.6).

The side panel on the right has six tabs, in the order you usually need them:

• Areas — your areas and their weather models; downloading forecasts and zones;
• Routes — drawing routes and calculating them;
• Results — the calculations: showing them on the map, comparing, recalculating;
• Boats — your boats and their polars;
• Atlas — the tidal atlas of each area;
• Settings — routing defaults, zone rules, position, offline map and more.

At the top of the side panel the light next to online shows that the page is connected to the app on the boat's computer; it turns red and reads offline when that connection is lost. (It says nothing about the internet.) While downloads or calculations run, it also counts them, for example online · 2 jobs. Tap it to see what is running, how far it got, and a Cancel button for each. A small red dot on the Settings tab means a program the app needs is missing on the computer; Settings → About says which.

The » button at the top right folds the side panel away, see 1.4.

All times are shown in the local time of the device you are using, often with the UTC time next to it in grey. Model runs are named by their UTC hour, as the weather services do: 06Z.

1.3 A first passage, step by step

This is the whole route from an empty app to a route you can follow. Each step has its own chapter.

1. Make an area and download forecasts. In the Areas tab, tap + New area (or Create an area the first time), draw a box around your sailing waters, tick the weather models you want and save. Then tap Refresh all to download the newest run of each model, and download the area's zones. See chapter 2 and chapter 3.
2. Add your boat. In the Boats tab, import a polar into the polar library and make a boat with it: its motoring speed, the speed below which you start the engine, and the time a tack or gybe costs. See chapter 4.
3. Draw a route. In the Routes tab, tap + New route and click the map to set your waypoints: the start, any marks you must pass, and the destination. The router finds the best way between them. Save. See chapter 5.
4. Calculate. Select the route in the Routes tab. Its Calculate card appears: tick the boat, check the wind model, the currents and the departure time, and tap Calculate. The app switches to the Results tab while it works.
5. Look at the result. The new calculation is shown on the map, with its details in the Results tab (see chapter 6). Press ▶ in the time bar to sail the route: the boat moves along it and the instruments show the wind, speed and current you will meet (see chapter 7).

1.4 Using it on a tablet

On a tablet in the cockpit you want as much map as possible. The app keeps the same layout as on the computer, with a few things that help:

• Fold the side panel. The » button at the top of the side panel folds it into a narrow strip of tab icons. Tap an icon to open the panel on that tab, or « to open it where you left it.
• Narrow screens. On a tablet held upright (or a phone) the side panel moves under the map, and the map takes a little over half the screen height.
• Move and size the instruments. Drag the instrument panel by its title bar to where it hides the least, and drag its bottom-right corner to make it smaller or larger; both work with a finger. See 7.3.
• Stack the cards. With several routes on the map, ⇆ puts their instrument cards under each other instead of side by side.
• Numbers only. Digital shows the instruments as plain numbers, which take less room and read well in bright light.

These choices — the folded panel, the display settings of the map, the instrument style, size and position — are remembered by each device separately. The tablet keeps its own layout, and the computer at the chart table its own.

2.1 What an area is

An area is a box on the map, for example the Southern North Sea or the Channel, with everything the router needs for it:

• its wind models (GFS, ECMWF, ICON-EU, Météo-France, Met Office) and current models (Copernicus), each with its own forecast length and time step;
• the runs of each model: the forecasts downloaded so far, newest first, of which it keeps a number you choose;
• a reference port for the tides (see 9.5);
• its zones: traffic separation schemes, wind farms and restricted areas (see chapter 3);
• its tidal atlas (see chapter 9).

Make the box large enough for the passages you plan, with some sea room around them: the router only knows the wind inside the box. A larger box takes longer to download, especially for the fine models.

2.2 The list of areas

At the top of the Areas tab, Your areas lists every area with its size in degrees (width × height). Tap an area's name to open it: its card (see 2.4) appears right under the name, and the area is selected: the map, the Routes tab and the Results tab then work in that area. One area is open at a time: opening another closes the first. Tap the open name again to close it; the area stays selected. While the Areas tab is open the map shows the outlines of all areas; tapping an outline selects that area too.

The light and badge of each area sum up its state:

up to date

Every enabled model has its newest run and the zones are downloaded.

25 behind

Newer runs have been published than the ones downloaded: the number adds up the runs missing over all models. Refresh all fetches them (see 2.6).

too short

A model's newest run ends before the length you set for it, for example after you raised ICON-EU from 78 to 120 hours. Refresh all downloads it again at the full length.

zones incomplete

The zones were downloaded, but part of them is missing: the box was made larger afterwards, or not all protected areas could be fetched.

model missing

An enabled model has no run at all yet.

no zones

The zones of this area were never downloaded. The router then ignores traffic separation schemes and wind farms.

checking…

The app is still asking which runs have been published.

The app checks which runs are out when you open the tab, when you select another area, and every 15 minutes while the tab stays open. Without an internet connection it estimates this from each model's timetable instead, and says so at the bottom of the tab.

2.3 Making a new area

1. Tap + New area at the top of the Areas tab (or Create an area when you have none yet).
2. Give the area a Name, up to 60 characters.
3. Tap Select box on map and click two opposite corners on the map. A bar at the top of the map reminds you what to do; Cancel or Esc stops without a box. The editor then shows the box's edges and size. Change box on map draws it again.
4. Set Runs to keep per model (1 to 50, 8 by default): after a refresh, older runs beyond this number are deleted. Keep a few if you like to compare how the forecast changed.
5. Choose the Reference port, or leave it on Automatic, the nearest standard port (named in the list). The list offers tide gauges within 150 nm of the box centre, nearest first.
6. Tick the wind models and current models you want. For each ticked model set the forecast length in hours (its maximum is shown) and the time step. Longer and finer means more to download.
7. Tap Save, then Refresh all on the new area's card to download its first runs.

Models that cannot serve your box say Does not cover this box. under their name — for example Météo-France AROME for a box reaching north of about 55° N, or the Met Office UKV model for a box reaching beyond the waters around the British Isles. If you tick one anyway, the editor names the part of the world it covers and Save stays unavailable until the box fits or the model is unticked. Other problems (no name, no box, a length beyond the maximum) are listed above the buttons in the same way.

Untick enabled to keep a model and its runs but skip it when you refresh, for example a slow model you only want now and then. Unticking a model altogether removes it from the area when you save; its runs are kept, but become unassigned (see 2.8).

Copernicus currents need the free Copernicus Marine tool installed and logged in on the computer that runs the app; the editor shows the commands when you tick the model. Météo-France needs an API key (see 2.7).

To change an area later, choose Edit in its ⋯ menu: the same editor opens in place of the area's card, with the area's settings. A new area's editor opens at the top of the list.

2.4 The area card

An open area shows its card under its name, marked by a line on the left. The card's top line has Refresh all and the ⋯ menu (Area actions):

• Edit opens the area editor (see 2.3);
• Saildocs requests shows request texts to get GRIB files by e-mail (see 2.9);
• Import files… imports GRIB or NetCDF files straight into this area (see 2.8);
• Delete… deletes the area (see 2.10).

Under that line the card repeats the area's size and how many runs it keeps per model. If the map still shows wind from another area, it says so: tap a model name below to switch. Then follow three groups: Wind, Current (with the tidal atlas at its end, see 9.2) and Zones (see 3.2).

2.5 Weather models and their runs

Every model of the area has a line:

• a light and the model's name. Tap the name to show its newest run on the map; for a wind model this also makes it the wind the Routes tab starts with for this area. The name of the model on the map is coloured;
• the run tag, for example 06Z: the hour (UTC) of the newest run downloaded. Hold the pointer over it to see the run's date and age;
• a badge: recent when the newest published run is downloaded, 3 behind when three newer runs are out, shorter than set when the newest run ends before the model's length (refresh to fetch it longer), not downloaded when there is no run yet, and a grey disabled for a model you switched off. Hold the pointer over the badge for the full text, including when the latest run was published — or estimated, when the app could not check online;
• the cadence line, for example every 6 h · 120 h · downloaded Mon 12 Oct, 13:43: how often the model brings out a new run, the forecast length you asked for, and when the newest run was downloaded;
• the last result of a refresh: ✓ run Mon 12 Oct, 08:00 when it went well, or ✗ with the reason when it did not, for example a missing key or a server that did not answer.

The ⋯ menu of a model (Runs of GFS) lists every stored run as Show run …, the newest marked (newest) and the one on the map with ●. Choose an older run to see how the forecast looked before; the line then says map shows the older run …. For a current model the menu also has Automatic (newest, or the route's), which goes back to the newest run, or to the run a calculation in focus used. Delete runs… is described in 2.10.

Files you imported into the area without choosing a model appear as an extra model called Imported, with a grey imported badge. Its runs are never deleted by the area's run limit.

2.6 Refreshing: downloading new runs

Tap Refresh all on the area card to download the newest run of every enabled model. The button reads Refreshing… while it works, and every model line shows its own progress:

• waiting, then checking for a new run…;
• downloading with a progress bar and the step being fetched, then importing…;
• ✓ done when a new run came in, or ✓ up to date when the newest run was already there;
• ✗ with the reason when it failed, or skipped when, for example, no run is available yet.

All models download at the same time, and one that fails never holds up the others: the lines turn to their result one by one as each model finishes. Afterwards the badges, lights and run tags are updated, a map showing a model's newest run moves on to the new one, and runs beyond the area's limit are deleted. Results calculated with an older run get a newer run label in the Results tab (see 6.4).

Refreshing needs an internet connection. Do it in harbour or wherever you have a good connection: a large area with several fine models can take a while. Disabled models are skipped.

2.7 Météo-France API keys

Météo-France AROME, AROME HD and ARPEGE are free, but need an API key from the Météo-France API portal. Without one, the area card and the model line say, for example, Météo-France: API key missing in config.json (sources.meteofrance.aromeApiKey).

The keys cannot be entered in the app: type them into the file config.json on the computer that runs WeatherRouting, under sources → meteofrance:

• aromeApiKey — the key for AROME; AROME HD uses the same key;
• arpegeApiKey — the key for ARPEGE;
• apiKey — a shared key, used for a model that has no key of its own.

The app reads the file again by itself; reload the page to clear the message.

2.8 Importing GRIB and NetCDF files

You can also load forecasts you got some other way, for example by e-mail (see 2.9) or from a USB stick. Import files at the top of the Areas tab accepts GRIB1 and GRIB2 files with 10 m wind and/or surface currents, and NetCDF current files such as Copernicus; tap ? next to it for the same summary. Files copied into the folder data/gribs/inbox/ on the boat computer are imported by themselves.

After an import each new run is listed with Belongs to: an area, a model and Save. The app suggests the model the file came from (a GFS file to the GFS model, and so on); choose Imported (no model) when it fits none. Later leaves the run unassigned for now. A new wind run is shown on the map straight away.

Import files… in an area's ⋯ menu does the same, with that area already chosen.

Runs that belong to no area — imports you put off, files from the inbox, and runs of models you removed from an area — wait at the bottom of the tab under N unassigned files. Each shows its model, run, times, box and file name; Move to area… assigns it, ✕ deletes it.

2.9 Saildocs: forecasts by e-mail

Offshore, with only e-mail — for example over a satellite phone — you can still get GRIB files from the free Saildocs service. Choose Saildocs requests in the area's ⋯ menu: the card shows one request line each for GFS, ECMWF and ICON wind and for RTOFS currents, for the area's box rounded out to whole degrees and as long as the area's longest wind model allows.

1. Tap Copy next to a line and send it, one line per e-mail, to query@saildocs.com. The app never sends mail itself.
2. The GRIB file comes back by reply. Import it with Import files and assign it to the area (see 2.8).

Saildocs changes its model codes from time to time: send an e-mail with send help first to check them. Close hides the requests again.

2.10 Deleting runs and areas

Old runs are deleted by themselves after each refresh, beyond the area's Runs to keep per model. To delete runs yourself, choose Delete runs… in a model's ⋯ menu: the line lists its stored runs with their age, times and number of steps, each with a ✕. Close hides the list again.

To delete an area, choose Delete… in its ⋯ menu. Tick also delete runs to delete its downloaded runs too; otherwise they are kept as unassigned files. The area's tidal atlas and downloaded zones are deleted either way; your own zones are not (see 3.6).

Every ✕ asks Delete? Yes / No in place before anything is deleted; tapping elsewhere or waiting a few seconds cancels.

3.1 What zones are

The zones come from the sea marks in OpenStreetMap:

• traffic separation schemes (TSS): traffic lanes, separation zones, roundabouts, junctions and crossing areas;
• wind farms;
• restricted areas, such as military areas and areas where entry is prohibited, and protected areas and nature reserves at sea;
• precautionary areas and inshore traffic zones.

The app groups the parts of a TSS into schemes, for example Dover Straits TSS area, each with its traffic axis, and gives every lane its traffic direction.

3.2 Downloading zones for an area

The Zones group at the bottom of the area card has one line. Its title counts the zones and schemes, for example 1,675 zones · 17 TSS; below it a line counts the wind farms, restricted and protected areas and your own zones (mine).

Its badge says how current they are: downloaded today or downloaded 3 d ago, amber with · incomplete when part is missing, or with · 59 holes when the app found gaps in the schemes (see 3.7). Red not downloaded means the area has no zones yet; until you download them, calculations in the area ignore schemes and wind farms, and their results warn no zone data for this area — exclusions and TSS not applied.

The ⋯ menu of the line has:

• Download — fetches the zones from OpenStreetMap for the area's box, with a progress bar (Cancel download stops it). Download again after you made the box larger, or now and then to pick up corrections. Your rules, flipped lanes and own zones are kept.
• Zone list and TSS settings — opens the list below the line (see 3.4).
• Add zone — draws a zone of your own (see 3.6).

Warnings appear under the line, for example covers part of the area — download again after the box was changed. For a very large area the protected areas are left out, and the zone list says so.

3.3 Rules: how the router treats a zone

Every zone has one of four rules:

no-go

Avoided like land: the route never enters it. Wind farms and areas where entry is prohibited are no-go by default.

warn

Crossed freely, but the calculation lists the warn zones it passes. Other restricted areas, protected areas, precautionary areas, inshore traffic zones and TSS crossing areas are warn by default.

TSS rules

The traffic rules below, for the parts of a traffic separation scheme.

allowed

Ignored by the router. Use it to switch off a zone you know is wrong.

Under TSS rules the router tests the boat's heading, not its track over the ground, against the scheme, within a tolerance (15° by default; set it under Settings › Routing defaults and per calculation in the Options of the Calculate card, see 5.5):

• Separation zones are only crossed at right angles to the traffic, within the tolerance, in one go.
• Traffic lanes are crossed the same way. With cross or follow the route may also follow a lane in its traffic direction, within the tolerance, which includes joining and leaving it at a small angle. A lane is never sailed against its traffic. One passage through a lane is either a crossing or a following: the route never switches between the two halfway. A following can end in a roundabout or junction, after which another lane may be crossed.
• Roundabouts are avoided like a no-go zone with avoid. With transit the route may go through them counter-clockwise: any heading that keeps the centre on the port side, so it may cut across the ring as long as the centre stays to port. The tolerance does not apply here. The central zone keeps its own rule: the centre of one of your roundabouts is a no-go.
• Junctions (and precautionary areas that are part of a scheme) may be crossed on any heading except against the traffic arriving from a lane that ends there: a heading within 45° of straight against it is refused (Settings › Zone rules, see 3.8).

A calculation reports the schemes it passed and the warn zones it crossed (see 6.3 and chapter 7).

3.4 The zone list and TSS settings

Choose Zone list and TSS settings in the Zones menu. At the top, the status line says how many zones were fetched, how many are yours, how many were skipped (for example inland features) and when; any warnings follow. Download again downloads them again.

The two TSS settings of the area apply to all its schemes:

• Traffic lanes: cross only or cross or follow;
• Roundabouts: avoid or transit.

Under Traffic separation schemes each scheme is listed with its traffic axis and a menu to set its lanes (and roundabout, when it has one) differently from the area, for example to follow the lanes of one scheme only. lanes: area (cross only) means it follows the area. A scheme with one of your own roundabouts in it defaults to lanes: follow (roundabout) and roundabout: transit (roundabout), since a roundabout is there to be used.

Below follow My zones (all areas), Holes found, the button Add zone, and all zones grouped by kind: traffic lanes, separation zones, roundabouts, junctions, crossing areas, precautionary areas, inshore traffic zones, wind farms, restricted and protected areas. The groups start closed; tap one to open it. The field Filter zones by name or type narrows them to the zones whose name, kind or scheme contain every word you type.

Each zone shows a small square in the colour of its rule, its name and scheme, and a menu with its rule: default (…), naming the rule it gets by default, or a rule of your own: no-go, TSS rules (TSS parts only), warn or allowed. Your choice stays when the zones are downloaded again.

Traffic lanes also show their traffic direction (→ 065°). If OpenStreetMap has it the wrong way round — check the arrows on the map against your chart — tap flip direction; tap again to go back. A lane whose direction is unknown says direction unknown and cannot be followed. A roundabout that is avoided says no-go while roundabouts are avoided.

3.5 Zones on the map

The zones of the selected area are drawn on the map, coloured by rule: no-go red, warn orange, TSS purple and hatched, allowed grey and dashed. Junctions are outlined orange. Lanes carry arrows in their traffic direction when you zoom in, and roundabouts an arrow showing the way round. Hold the pointer over a zone for its name, kind and rule.

Click a zone to open a small window listing every zone under that spot — zones often overlap, like a lane and its separation zone. Each has its name, kind and rule, with (changed) when you changed it, and:

• a menu to change its rule right there — no-go, warn, allowed (TSS zones also TSS rules) or back to the default, the same as in the zone list (see 3.3). Changed rules apply to new calculations: recalculate to use them;
• Show in list, which opens the zone list in the Areas tab at that zone, highlighted for a few seconds;
• for one of your own zones (see 3.6) an Edit button instead of the rule menu: it opens the zone in the editor on the map;
• for a roundabout, Roundabout: transit lets the route go round it counter-clockwise, as the rules require, keeping the centre to port; avoid keeps the route out of it. It is set for the roundabout's scheme — or, for a roundabout in no scheme, for the whole area — the same setting as in the zone list.

While the window is open its zones are outlined thick black on the map; hold the pointer over one zone in the window to outline just that one. Zone clicks are ignored while you edit a route, draw a zone or use the Stream tool.

The ☰ map menu switches the zones layer on and off, and shows or fades each kind of zone (see 8.7). This only changes the picture: the router applies every zone by its rule, shown or not.

3.6 Adding your own zones

OpenStreetMap often misses exactly the parts that matter: a roundabout at a light vessel, a junction, the end of a lane. You can add them yourself, together with no-go and warn areas of your own. Your zones form one layer shared by all areas: a zone counts in every area whose box it lies in, and is never touched when zones are downloaded again.

Choose Add zone in the Zones menu or in the zone list. A bar opens at the top of the map. Choose the kind — No-go zone, Warn zone, Traffic lane, Separation zone, Roundabout or Junction — and how you give its shape:

• on the map: click the corners. A click within a few pixels of a corner of another zone snaps onto it, so your zone joins the existing ones without a gap. Undo point removes the last corner; click the first corner or tap Finish to close the outline. Once closed, drag a corner to move it, or tap Back to points to add more.
• typed positions: one position per line, latitude first, in decimal degrees (51.3725, 1.9761) or degrees and minutes (51°22.35'N 001°58.57'E), then Use positions. Lines it cannot read are named.
• GPX file: a route, track or waypoint, for example from your chart plotter. When the file holds several, choose one, then Use it.

The kinds have their own fields:

• Traffic lane: the Traffic direction (°), typed, or with set on the map: click where the traffic comes from, then where it goes.
• Roundabout: click its centre (the light vessel), then type the Centre zone (nm) — the radius of the central separation zone, which is no-go — and the Outer edge (nm), at most 10 nm. One typed position or one GPX waypoint also gives a roundabout centre.
• Lanes, separation zones, roundabouts and junctions join the nearest scheme within 2 nm, and follow its rules and settings. Further away they form a scheme of their own, named after the zone or after what you type under Scheme.

Every zone needs a name; a note is optional. Tap Save zone, or Cancel (or press Esc) to drop it. The bar says what is still missing, for example an outline that crosses itself or an outer edge smaller than the centre zone. Drawing stops by itself when you start editing a route or an area, or select another area.

Your zones are listed under My zones (all areas) in the zone list, with their kind, the areas they lie in and the scheme they joined. edit opens the same bar (Save changes), show moves the map to the zone, ✕ deletes it after Delete? Yes / No.

Where one of your zones overlaps an OpenStreetMap zone, both apply and the stricter rule wins. To replace a wrong OpenStreetMap zone, set its rule to allowed and draw your own.

3.7 Holes in the zone data

The app looks for places where a scheme is probably incomplete, and lists them under Holes found in the zone list:

• Gap in Dover Straits TSS area · 3.2 nm² — water enclosed by the parts of a scheme that no zone covers, such as a wedge between a lane and a separation zone. The router treats a gap as a warn zone, so a route through it is reported.
• Lanes end without a junction — lane ends close together with nothing between them, where a junction or roundabout is probably missing.

show moves the map to the hole; on the map holes are dashed orange. Add the missing zone with Add zone, or ignore the hole if your chart shows it is open water. The area's zones badge counts the holes.

3.8 Default rules in Settings

The default rule of each kind of zone is set in Settings › Zone rules (see 10.2), for all areas: wind farms, restricted areas with entry prohibited, other restricted areas, nature reserves and protected areas, precautionary areas, inshore traffic zones and TSS crossing areas, each no-go, warn or allowed. A rule you set on a single zone in the zone list wins over the default. TSS parts follow the area's TSS settings instead.

The same section holds Junction: against arriving traffic within (°), 45° by default: in a junction, a heading this close to straight against a lane ending there is refused. Settings saves itself as soon as you change a value.

4.1 The Boats tab

The tab has two parts:

• The boats, each with the name of its polar. Tap a boat's name to open it: its card, with its values and its polar chart, appears right under the name. One boat is open at a time; tap the name again to close it. Edit on the card opens the values for changing (see 4.2); ✕ deletes the boat after you answer Yes to Delete?. Calculations made with a deleted boat stay in the Results tab.
• The polar library, with every polar you imported (see 4.4).

To add a boat, tap + New boat. A new card opens for editing at the top of the list, named My boat, with the first polar of the library and these starting values: minimum sailing speed 3 kn, motoring speed 6 kn, tack and gybe penalty 60 s each, sail ↔ motor penalty 0 s. Change what you need and tap Save; Close drops the new boat. A boat needs a polar, so import one first; the app says so if the library is empty. When you import your very first polar and have no boat yet, the app starts a new boat with that polar by itself.

4.2 A boat's settings

Open the boat and tap Edit on its card. The values, and what they do in the routing:

Name

The name you see in the Calculate card and in the Results tab.

Polar

Which polar of the library the boat sails to.

Polar efficiency (%)

Every polar speed is multiplied by this before the router uses it: at 90 % a polar speed of 6 kn becomes 5.4 kn. Polars are usually made for a clean hull, new sails and a crew that trims all the time. A cruising boat with gear on deck, a shorthanded crew or a foul bottom does not reach them; 85–95 % is a common choice. Between 10 and 150 %.

Minimum sailing speed (kn)

When the polar (with the efficiency) gives less than this on a heading, the router motors on that heading instead. This is your “engine on” rule: if you start the engine when the boat sails slower than 3 kn, put 3 here. Set it to 0 for a boat that never motors.

Motoring speed (kn)

Your speed through the water under engine. The router uses it on every heading where it motors; current is added to it as to the sailing speed.

Tack penalty (s) and Gybe penalty (s)

The time a tack or a gybe costs you. Each time the router puts the wind on the other side — upwind for a tack, downwind for a gybe — it takes this time off the distance sailed in that step. Higher penalties give routes with fewer, longer boards; shorthanded, you may want to make them larger.

Sail ↔ motor penalty (s)

The time lost each time you switch between sailing and motoring (furling or hoisting sails, starting the engine). A value here keeps the router from switching back and forth in fickle wind.

Tap Save to keep the changes, or Close to leave them. The card then shows the values in short: Polar (with the efficiency), Motor below, Motoring speed, Tack / gybe and Sail ↔ motor.

A calculation stores a copy of the boat as it was, so changing a boat later does not change earlier results. For a single calculation you can also change the minimum sailing speed and the motoring speed, or sail without engine, in the Calculate card's options (see 5.5), without touching the boat.

4.3 The polar chart

The chart on the boat's card shows the boat's polar as a half circle: the wind comes from the top, the angles off the wind are marked at 30°, 60°, 90°, 120° and 150°, and the distance from the centre is the boat speed, with rings every knot (every 2 kn for fast boats). There is a curve for each of the true wind speeds 6, 10, 14, 20 and 25 kn, in the colours of the legend below the chart.

The chart shows the polar as it is in the file, without the boat's efficiency. Use it to check an imported polar at a glance: the curves should grow with the wind and be smooth, with the best speeds on a reach. A dent or a curve that falls to zero points at a mistake in the file.

Between the values in the table the router interpolates. Below the lowest wind speed of the table the speed goes down to zero at no wind; above the highest wind speed it stays at the highest column — the router does not reef or slow down in a gale by itself.

4.4 The polar library and importing polars

The polar library lists every polar you imported, with the number of boats that use it. Tap a polar to preview its chart below the list. A polar no boat uses has a ✕ to delete it; a polar in use says in use and cannot be deleted.

To import a polar:

1. Tap Import polar and choose the file.
2. If the file holds several polars (a Weather4D file can), choose one under Polar in this file.
3. Read the warnings, if any, check the preview and tap Import “…” with the polar's name. Cancel closes the import.

The app reads two kinds of polar file:

• Weather4D polars (.wpol). When such a file carries an efficiency, a new boat made with the polar starts with that efficiency.
• Polar tables as qtVlm and OpenCPN use them (.pol, .csv, .txt): the first line holds the true wind speeds, each further line a true wind angle followed by the boat speeds. The values may be separated by tabs, semicolons, commas or spaces; with tabs or semicolons a decimal comma is fine too. Lines starting with # or ! are skipped. The polar is named after its file.

A polar needs at least two angles and two wind speeds, both increasing, with angles between 0° and 180°. A file that breaks these rules is refused with the reason. Empty cells are read as 0 and give a warning, as do angles or wind speeds where every speed is 0.

4.5 Several boats

You can keep as many boats as you like: your own boat with different polars (say, with and without the gennaker), a friend's boat, or the same boat with a careful and a lazy efficiency. In the Calculate card you tick one or more of them; every boat gets its own calculation with the same wind, current, departure and options (see 5.3). In the Results tab each boat has its own line, so you can compare them on the map and in the panel under it (see 6.5).

5.1 The Routes tab

The list shows the routes of the area you selected in the Areas tab (Routes in …): those whose waypoints all lie inside the area. Routes elsewhere are folded away under Other routes, with their number. Each route shows its number of waypoints (wp) and its length along the straight lines.

• Tap a route's name to open it: its Calculate card appears right under the name (see 5.3), and the map shows the route as a dashed purple line with numbered waypoints and zooms to it. One route is open at a time; tap the name again to close it — the route stays on the map.
• + New route starts a new route in the editor, at the top of the list (see 5.2).
• Edit opens a route in the editor, in place of its Calculate card.
• ✕ deletes a route after you answer Yes to Delete?. Its calculations stay in the Results tab.

While you edit a route, the list is greyed out; save or close the route first. While you draw a zone of your own (see chapter 3), + New route and Edit wait until the zone is finished or cancelled.

5.2 Drawing and editing a route

Tap + New route, or Edit on a route. The editor opens in the route's row (a new route's at the top of the list), with the route's name, and on the map:

• Click the map to add a waypoint at the end of the route.
• Drag a waypoint to move it.
• Click the line between two waypoints to insert a new waypoint there.
• Right-click a waypoint (on a touch screen: press and hold it) to delete it.

In the panel, each waypoint has its position, a field to give it a name (for example the harbour or the buoy), and a ✕ to delete it. Below the list you see the number of waypoints and the route's length. Reverse turns the route around, for the passage home.

Type the route's name in Name and tap Save. Close leaves the editor without saving: a route you were changing goes back to how it was saved, a new route is dropped.

Put the waypoints where the boat must pass: the start in the harbour entrance or just outside, the finish at the destination, and points in between only where you want the route to go — around a headland, through a channel, to a gate in a traffic separation scheme. The router passes every waypoint in order and finds its own way in between, so there is no need to draw tacks or follow the coast. A route needs at least two waypoints to be calculated. Where the destination lies up a sound, a river or behind a headland, add a few waypoints for the way in (see 5.8).

5.3 The Calculate card

Open a route and its Calculate card appears under its name. It has four fields; the … next to each field opens its menu.

Boats

Tick one or more boats in the menu. Every boat gets its own calculation, with the same wind, current, departure and options; the card then says one calculation per boat next to Calculate. The card starts with the boats of your last calculation (see 4.5).

Wind

The weather model and its forecast run, for example GFS · run 06Z. The menu lists, per model of the area, the downloaded runs with their run time in your local time, the newest marked (newest) and the chosen one with ●. The card starts with the newest run of the model you chose last in this area; choosing a run in the menu also makes its model the one remembered for the area. Models and runs are downloaded in the Areas tab (see chapter 2).

Current

Which tidal stream the router uses:

• Forecast + tidal atlas — the downloaded current forecast, and the tidal atlas where and when the forecast has no data (for example after its last hour);
• Forecast — the current forecast only;
• Tidal atlas — the area's tidal atlas only, which reaches any date (see chapter 9);
• None — no current at all.

The menu offers only what the area has: the forecast modes need a downloaded current run, the atlas modes an atlas. The card starts with your last choice, or else the first mode of this list that is possible.

Departure

Now, or a date and time you set in the menu, in your local time. The card remembers your choice: Now stays now for the next calculation, a time you set stays that time.

Under the departure, an amber note warns you when the departure needs a second look:

• departure is in the past — more than ten minutes ago;
• departure is outside GFS 06Z (…) — the chosen wind run does not cover the departure time; the note gives the first and last time of the run. The router cannot start outside the forecast, so pick another run or another departure.

Calculate stays greyed out, with the reason next to it, until everything is there: a route with at least two waypoints, an area chosen in the Areas tab, a boat, and a wind run in the area.

5.4 The readiness labels

A row of small labels sums up what the calculation will use, so you see at a glance whether everything is fresh:

wind recent

The chosen wind run is the newest one published.

wind 3 runs behind

Newer runs have been published but not downloaded; refresh the area in the Areas tab first. · estimated means the app could not ask the provider and counted from the model's usual schedule.

wind older run picked

You chose an older run in the Wind menu, while a newer one is downloaded.

wind imported

The run is a file you imported yourself, so the app cannot tell whether it is the newest.

current recent

The same for the current forecast, when a forecast mode is chosen; + atlas is added for Forecast + tidal atlas. With Tidal atlas the label reads tidal atlas, with None no current.

zones on · TSS 15°

The area's zones and traffic separation rules are applied, with the TSS tolerance from the options (see chapter 3).

zones not downloaded

The area has no zones yet. Tap Download next to it to fetch the traffic separation schemes, wind farms, restricted and protected areas from OpenStreetMap; it then says downloading zones…. Without zones the route is calculated without exclusions and TSS rules, and the result says so.

zones off

You switched Zones and TSS rules off in the options.

coast 0.5 nm

The distance the route keeps from the coast (see the options below).

motor 5.5 kn

Shown when the options change the boats' own values for this calculation: sail only, motor … kn or min. sailing … kn.

5.5 Options

Tap Options to open them:

Time step (min)

How often the router reconsiders the course: 10, 15, 20, 30 or 60 minutes. A shorter step follows wind shifts and tidal gates more closely and takes longer to calculate; for a long passage 30 or 60 minutes is enough.

Corridor (× leg length)

How far the route may stray from the straight line between two waypoints, as a part of that leg's length (at least 2 nm). With 0.5, a 40 nm leg may wander 20 nm to either side. Widen it when the wind forces a big detour; narrow it to keep the route near your plan.

TSS tolerance (°)

How far the boat's heading may be off perpendicular when crossing a traffic separation scheme, or off the lane direction when following a lane: 5–30°. See chapter 3.

Coast distance (nm)

The distance the route keeps from the coastline, 0–5 nm. Close to the start, the finish and each waypoint it shrinks to zero, so the route can leave and enter a harbour. With 0 the route only may not cross land. This needs the coastline data of Settings (see 10.6).

Minimum sailing speed (kn) and Motoring speed (kn)

The boats' own values from the Boats tab (see 4.2); when the ticked boats differ, the field says per boat. Type a value to use it for this calculation, for all ticked boats — for example a lower motoring speed into a head sea. Empty the field to go back to the boats' own values.

Sail only

Never motor. In very light wind the boat then goes as slowly as the polar says, so the route may not reach the finish within the forecast.

Zones and TSS rules

Avoid no-go zones and follow the traffic separation rules of the area's zones. Switch it off only to see what the route would be without them.

Below the options, Method has three switches that change how the router works; see 5.7. A changed method shows as a badge on the card.

The options are remembered from your last calculation, including changed speeds and Sail only. Where you changed a routing default in Settings since, the new default is used (see 10.1). Reset to defaults goes back to the routing defaults from Settings and each boat's own speeds.

5.6 Calculate and what happens next

1. Tap Calculate. The app switches to the Results tab.
2. At the top, under Calculating, each calculation has a line with the route's name and its progress. Cancel stops it.
3. When a calculation is done, its line in the list is ticked and its route appears on the map; the first one to finish is put in focus, with the instruments and the graph under the map. If the map already shows eight calculations, the oldest one not in focus is taken off to make room, and the app says which.
4. A calculation that fails gives a red line with the reason.

The calculations go on when you switch tabs. From here on, chapter 6 explains the results and how to compare them.

5.7 How the router works

The router uses the isochrone method: it lets the boat sail in every direction for one time step, keeps the points that got furthest, lets those sail on for another step, and so on until one of them can reach the next waypoint. Each leg between two waypoints is calculated this way, one after the other; the arrival at a waypoint is the start of the next leg, with the time, and whether the boat was sailing or motoring and on which side the wind was, carried over. A calculation runs on the computer that runs WeatherRouting, in the background, with only the forecast, current, tide, coastline and zone data it needs: the box round the waypoints, widened by the corridor, from the departure to the maximum duration.

Before it starts

The router first checks the route. It refuses to calculate, with the reason, when the departure lies outside the forecast's time, when the start or a waypoint lies outside the forecast's area, on land, or in a no-go zone. A start or waypoint inside a traffic separation scheme is allowed, with a warning. Without coastline data for the whole route it calculates anyway and warns that the route may cross land (see 10.6).

One step

From every point it keeps, the router tries a heading every Heading step degrees: 72 headings at the default of 5°. For each heading:

1. It takes the wind at that point and time from the forecast: interpolated between the four surrounding grid points, and between the two forecast hours around the time.
2. From the heading and the wind direction it gets the true wind angle, and from the polar the boat speed for that angle and wind speed, again interpolated between the polar's rows and columns, times the boat's Polar efficiency.
3. When that speed is below the boat's Minimum sailing speed, the boat motors on that heading at its Motoring speed instead (never with Sail only).
4. Time lost is subtracted from the step: the Tack penalty when the wind comes onto the other side upwind, the Gybe penalty downwind, and the Sail ↔ motor penalty when it switches between sailing and motoring. A tack counts against the last time the boat sailed, so motoring one step through the wind does not avoid it.
5. The current at the point (see 9.4) is added to the boat's speed through the water, which gives the course and speed over the ground.
6. The boat moves in a straight line over the ground for the rest of the step. Wind and current stay as they were at the start of the step; the next step looks them up again.

Which moves are allowed

A move is dropped when its straight line:

• crosses land;
• ends outside the corridor: further from the straight line between the leg's two waypoints than the Corridor times the leg's length, at least 2 nm;
• comes closer to the coastline than the Coast distance. Within Relaxed near waypoints of any waypoint that distance shrinks evenly to zero, and a move uses the smaller value of its two ends, so it can leave and enter a harbour;
• enters a no-go zone or breaks a traffic separation rule (see 3.3). The router tests the boat's heading, not its track over the ground. A move that follows or crosses a lane passes this on to the next move, so one passage through a lane stays a following or a crossing.

Which points are kept

Each step makes many thousands of moves, and the router keeps only a few of the points they end at:

• per sector of Sector degrees seen from the leg's start (1° by default), the point furthest from the start. In open water this is the edge of the area the boat can reach, the isochrone;
• within 1 nm of land, with Coast squares (see below), besides, the first point to reach each square of a tenth of a mile (of several in the same step, the one closest to the next waypoint). A sector widens with the distance from the start: 1° is 9 nm wide at 500 nm, wider than a sound or a harbour entrance, and a sector only ever keeps the point furthest from the start. The squares keep a route that has to go into narrow water, round a headland or up a river that bends back towards the start. A point in a traffic lane counts separately per lane rule it carries.

The method switches

The Calculate card's Method changes how the router works, so you can compare the results and see what each part does. Each calculation shows its method in the Results tab. With all three off the router is the plain isochrone method.

Coast squares (on by default)

Near land, also keep the first point to reach each square, as described above. Without it a route into a sound or a harbour behind a headland can get stuck outside.

Short steps at the ends (on by default)

Within two time steps' sailing of the start and of the end of each leg, step every 5 minutes. A harbour entrance needs turns shorter than a half-hour stretch, and the finish is more exact: with half-hour steps the boat must lie on a straight line to the waypoint at the start of the last step, and can lose up to a step getting there. A waypoint at the start of a narrow, bending traffic lane needs it too: a half-hour step out of it does not fit in the lane.

Per tack

Keep the furthest point per sector for each tack, wind on port and wind on starboard, instead of one per sector. Two points in the same place on different tacks are not equally good, as the next step may cost one of them a tack. Without it, short time steps can make the route tack at almost every step.

Reference router (slow)

No sectors at all. The sea is divided into squares, and per square the router keeps only the first point to reach it, separately for wind on port, wind on starboard, and sailing or motoring. A point that reaches a square later, in the same state, can never do better than the one that was there first, so nothing is thrown away on a guess; the only error is the size of the squares. Coast squares and Per tack do not apply; Short steps at the ends does. A boat too slow to cross a square in one step keeps its best move inside its square, so it still gets somewhere.

Fine squares, Open-water squares and Fine within

The size of the squares where it matters and where it does not. Within Fine within of land and of every waypoint the squares are Fine squares; further out they double in size every such distance, up to Open-water squares. With the defaults (0.25 nm within 2 nm, at most 1 nm) that is 0.25 nm up to 2 nm off, 0.5 nm up to 4 nm and 1 nm beyond. Smaller squares are more exact and slower: halving them takes about four times as long. Set both sizes the same for one size everywhere. The open-water size decides most of the accuracy of a long passage, because a little is lost at every step: Roompot to Lerwick took 81.7 h with the defaults (calculated in 1.5 minutes) against 80.6 h with 0.25 nm everywhere (12 minutes). The fine squares matter for getting into narrow water.

Reach test

Without it, a point that reaches a square already reached earlier is dropped, even when it lies further on in the square than the earlier one. With it, the earlier point only wins if it could have sailed to the later one in the time between, on the polar, wind and current where it was, without land, the coast distance or a no-go zone in the way. That removes part of the error of large squares: Roompot to Lerwick came down from 81.8 to 81.1 h with 1 nm squares. From 0.5 nm squares down it changes nothing, because most of the error left is points that reach a square in the same step, of which only one is kept (the one closest to the waypoint). It takes about twice as long and needs several times the memory.

How close is a route to the true fastest one? For a steady wind straight from the waypoint the answer is known: at 6 kn and 45° off the wind the boat makes 4.24 kn towards it, so 18 nm takes 4 h 15 min with one tack. With half-hour steps the router finds about 4 h 41 min, with Short steps at the ends 4 h 18 min. On a real passage there is no such answer, but the reference router gets close to one. Roompot to Lerwick (570 nm) came out at 81.8 h with 1 nm squares, 81.1 h with 0.5 nm and 80.6 h with 0.25 nm, and with 0.25 nm the same within 3 minutes at time steps of 10, 15 and 30 minutes. The faster methods found between 81.8 and 85.2 h depending on the switches and the time step: 1.5 to 6 % slower than needed. Keeping only the point furthest from the start is a rule of thumb, not an exact choice: a point that is less far can still lead to a faster route, and every step throws some of those away.

Arriving

Before each step the router checks, for every point it keeps, whether the boat can sail from there straight to the next waypoint within the step: on that heading, with that step's wind, current and penalties, without crossing land, coming too close to the coast, or breaking a zone rule. Of all points that can, it takes the one that arrives earliest. That arrival is usually somewhere within the step, so the last piece of a leg is usually shorter than a time step.

When it does not arrive

A calculation ends without arriving in one of these ways; the reason is shown in the Results tab (see 6.3):

timeout

No arrival within the Maximum duration after the departure.

partial

The forecast ends (the weather data ends at …), or the boat would have to leave the forecast's area (the route leaves the area covered by the weather data).

unreachable

Every direction is blocked (every direction is blocked by …, naming land, the coast distance, the corridor, a no-go zone or a traffic rule), or the router has come no closer to the waypoint for 24 hours (no progress for 24 h, with how close it came and where).

In all three the route is drawn up to the point that came closest to the waypoint. When the coast distance stopped moves on the way, the reason says so: a smaller coast distance, a wider corridor, or a waypoint at the entrance of a narrow passage often helps.

What you get

From the arrival the router follows each point back to the one it came from, down to the start: that is the route. For every step it records the time, position, heading, course and speed over the ground, speed through the water, the true wind and the apparent wind (worked out from the true wind and the boat's motion over the ground), sailing or motoring, tacks and gybes, and the current used and where it came from. The calculation adds the distance, the time sailing and motoring, the number of tacks and gybes, the traffic separation schemes passed and the warn zones crossed. The isochrones are recorded every hour: per sector, the point furthest from the leg's start, joined in order of bearing; a line breaks where it would cross land.

Limits

• The boat sails straight pieces of one time step. Where the route has to turn more often than that, in a river or among islands, add waypoints (see 5.8) or choose a shorter time step.
• Wind and current are constant within a step. A front or a turn of the tide in the middle of a step is felt from the next step on.
• The router knows no water depth: not sandbanks, not the tide's height, not your draught. It only knows the coastline, the coast distance and the zones. Check the route against a chart.
• It knows no waves and no gusts: the polar's speed in flat water at the forecast's mean wind, times the efficiency.
• Zones and coastlines come from OpenStreetMap and are not official chart data (see 3.1).
• The route is close to, not exactly the fastest: expect a spread of one or two percent between time steps and methods (see the method switches).
• The route is the fastest for the forecast, not for the weather you will meet. Compare models and runs (see 6.5) to see how much it depends on them.

5.8 Harbours, sounds and rivers

The router is made for open water. In narrow water it does less well: it keeps the points that got furthest from the start of the leg (see 5.7), and at the end of a long leg a harbour entrance, a sound or a river that bends is far too narrow for that to choose well. The route may then arrive late, with a messy last part, or wander along the coast before it finds the way in.

The remedy is the one you would use with a chart: plan the way in yourself, and let the router do the passage.

1. Put a waypoint in open water off the entrance, a mile or two out, where the approach begins.
2. Add a waypoint at each turn that matters on the way in: the mouth of the sound, a bend in the river, the harbour entrance.
3. End at the destination itself.

Each waypoint starts a new leg, so the router judges the last miles from close by instead of from the far start. Near every waypoint the coast distance shrinks to zero (see 5.5), so the route can pass close to the shore where it must, and the corridor round a short leg is narrow, so the route cannot wander off.

The price is that the router follows your way in. It cannot find out that another entrance would have been quicker with that wind and tide, for example the north entrance of Bressay Sound. When in doubt, calculate both ways in, or calculate once without the inner waypoints using the Reference router (see the method switches), which does find narrow water by itself, and compare the routes in the Results tab.

Short steps at the ends (on by default) helps as well: it lets the boat turn every 5 minutes near each waypoint instead of every time step.

6.1 The list of calculations

The list is a tree with three levels, the way you think about a passage:

• A route — for example Oostende2Harwich, with the number of weather models it was calculated with.
• A weather model and boat inside the route — for example Météo-France AROME · Palarran, with the number of its calculations.
• The calculations of that model and boat, for example after recalculating with a newer forecast or with other options. Each row shows the forecast run, the arrival time (ETA), the duration and the distance, and under it, smaller, when it was calculated, the departure, the currents used and the traffic separation scheme passes.

Tap a route or a model to open or close it (▸ / ▾). Routes start open, models closed. A closed route or model shows a colour square for each of its calculations on the map, and when its calculation was made, its distance and its duration: of the one on the map, or of the newest when none or several are.

At the top, This area shows the calculations made in the area you selected in the Areas tab; All shows every calculation. The next menu narrows the list to one departure day. Sort orders the calculations, and the models and routes by their best calculation: Time calculated (newest first, the default), Start time, ETA, Shortest duration or Shortest distance. Calculations that did not arrive come last.

A small coloured label under a model tells you when it is no longer on the newest forecast:

newer run

A newer run of this weather model has been downloaded, or the same run again — for example longer, after you raised the model's length. Recalculate to use it (see 6.4).

refresh area first

A newer run has been published but not downloaded yet. Tap Refresh area to download it, then recalculate.

6.2 Showing calculations on the map

Only calculations have a colour. Tick a calculation to show it on the map: its colour square then matches its line on the map. The tick box of the newest calculation of a model does a little more: when you recalculate, the new calculation takes over the tick and the colour, so the map moves on by itself — “show me the AROME route”. An older calculation you tick stays on the map as it is, also when newer ones arrive; use it to compare, for example, this morning's route with yesterday's.

Routes and models have a tick box too, to switch all their calculations at once without opening them:

• Untick a route or a model to take all its calculations off the map. The app remembers which ones were on.
• Tick it to put those back, in the same colours. When nothing is remembered, it shows the newest calculation of each model (for a model: its newest), which then follows recalculations.
• A route's tick box shows a dash (—) when only some of its models have a calculation on the map.

Motoring parts of a route are dashed. At most eight calculations can be on the map at the same time; when you tick a ninth, the app says so at the top of the list and leaves the box unticked.

One calculation is in focus: its values fill the instruments, the graph and the table under the map, and the time slider follows it. Tap a calculation to put it in focus; it is shown on the map as well if it was not, with a colour square but no tick.

6.3 The details of a calculation

Tapping a calculation also opens its details, right under its row, marked by a line on the left. Tap the row again to close them. The details show:

• whether the calculation arrived, and why not if it did not;
• ETA and duration, in your local time with the UTC time next to it;
• distance, the coast distance kept, the routing method, and the time sailing and motoring;
• the number of tacks and gybes;
• the wind and current forecasts used, and how many traffic separation schemes were passed;
• the boat values changed for this calculation, if any — for example motor 5.5 kn or sail only;
• the legs between your waypoints, with arrival, distance, time and motoring time per leg.

show isochrones (hourly) draws the lines the router reached every hour; they show how much room there was around the fastest route. A line breaks where it would cross land, for instance round an island. Reroute from here calculates the rest of the route from the boat's present position, using the same boat, forecast and options; it needs a position from the NMEA source (Settings → Position).

6.4 Recalculating with newer forecasts

Forecasts are renewed several times a day. To see how a new run changes your route:

1. Make sure the newest runs are downloaded: lines marked refresh area first have a Refresh area link.
2. Tick the newest calculation of each model you want to update and tap Recalculate Selected at the top. Only models whose newest calculation is ticked and not on the newest downloaded run are recalculated; hold the pointer over the button to see how many are already up to date.
3. The new calculations appear under their models and the map moves on to them.

A recalculation keeps the departure time, the boat, the options and the currents of the calculation it updates; only the forecast runs change. The ⋯ menu of a model recalculates just that weather model; the ⋯ menu of a route recalculates all its models.

6.5 Comparing routes

As soon as two or more calculations are on the map, the panel under the map compares them. Choose a view at its top left:

Tap a row in Summary or Now to put that calculation in focus.

6.6 Two models side by side

Split screen in the ☰ map menu shows a second map next to the first, with its own weather model. Both maps follow the same time slider and move together. Each map shows the instruments of the routes calculated on its own model, and a wind dial with its model's wind for the others, so you see at a glance where two forecasts disagree.

Choose the second map's model with the run caption at its top. Untick Split screen to go back to one map.

6.7 Deleting calculations

Use the ⋯ menus: on a calculation to delete just that one, on a model to delete all its calculations, and on a route to delete all calculations of the route. The app asks you to confirm in the menu itself before anything is deleted. Deleted calculations disappear from the map as well.

7.1 The time bar

The time bar under the map sets the moment the whole app shows: the wind and current on the map, the boat on the route, the instruments, and the time line in the graph and table. From left to right:

• ▶ plays, ⏸ pauses (see 7.2).
• 10 min/step — how much route time each playback step covers; only there when a route is on the map.
• ◀ and ▶| — one step back or forward. A step is the time step of the forecast shown, usually one or three hours.
• The slider and its scale — drag it to any moment. The scale covers the forecast shown; with calculations on the map it covers their passages instead, from the earliest departure to the latest arrival. A tall mark with the day (for example Fri 16) stands at each midnight, short marks at the hours, with hour labels (06, 12, 18) as far as there is room; over a long period only every 3 or 6 hours gets a mark. All in your local time.
• The time — in bold your local time, in grey the same moment in UTC.
• The time from high water, for example HW Harwich −5 h 22: the moment shown is 5 hours 22 minutes before high water at Harwich. It is measured from the nearest high water, before or after, so it runs from about −6 h to +6 h like the hours in a tidal stream atlas. It is there when the area you work in has a tidal atlas (see chapter 9). The port is the area's Reference port, set in the area editor; when that is automatic, it is the standard port nearest to the middle of the area.

The time bar is shown as soon as there is a wind forecast to show. Split screen, the Stream tool and the map's looks are in the ☰ map menu at the top right of the map; see 8.8, 8.9 and 8.6.

7.2 Sailing the route

With one or more routes on the map, ▶ sails them: the boats move along their routes together, on the same clock, and everything on the screen follows. Playback starts at the time shown if that lies on a route, otherwise at the first departure, and stops by itself when the last boat has arrived.

Each step moves the clock by the minutes chosen in the step menu — 2, 5, 10, 15, 30 or 60 — about six times a second. With 10 min/step an hour of passage takes about a second; choose a small step to watch a tidal gate or a tack closely. You can drag the slider or change the step while it plays.

Without a route on the map, ▶ steps through the forecast instead, one forecast step at a time, so you can watch the weather develop.

7.3 The instrument panel

When a calculated route is on the map, the instrument panel at the top left shows its instruments at the time on the time bar. With several routes on the map it has a card for each, in the route's colour.

The title bar of the panel holds its controls:

• ⠿ — the handle: drag the title bar to move the panel anywhere on the map. The panel stays there, also after a restart. Double-click the title bar to put it back at its own place under the area chip.
• Instruments ▾ — folds the cards away, leaving only the title bar; Instruments ▸ opens them again.
• Analog / Digital — dials or plain numbers (see 7.4 and 7.5).
• ⇆ / ⇅ — the cards side by side (⇆) or stacked under each other (⇅); tap to switch.

The bottom-right corner of the panel is a grip: drag it to make the whole panel smaller or larger, from 50 % to 150 % of its normal size. Double-click the grip to go back to 100 %. Moving and sizing work with a finger as well as with a mouse, and taps and drags on the panel never move the map underneath.

Each card shows the route's number in a round label of its colour — the same number as on its boat on the map; the routes are numbered 1, 2, 3… in the order they were put on the map — and the weather model. On an analog card the number sits in the top left corner and the model in large letters at the top, between the two dials, without the maker (ARPEGE rather than Météo-France ARPEGE); when the routes on the map were calculated for different boats, the boat's name sits at the bottom between the dials. The names never cover the dials. A digital card has them on a title line at its top, for example ICON-EU · Palarran.

The card's tint and the coloured band along its bottom are the colour of its route on the map. Before the departure a card says not started, after the arrival arrived, and its dials are greyed out; hold the pointer over it to see the departure or arrival time.

7.4 The analog instruments

Each card has two dials, drawn like the instruments at your helm.

The wind dial is drawn bow up, like a wind instrument: the boat is in the middle with her bow at the top, the mark at the top of the ring. The ring is red on the port side and green on the starboard side, with a wider, lighter band from 20° to 60° on each side. Two arrows run from the boat to the ring and point to where the wind comes from:

• the blue arrow is the true wind angle (TWA), with the true wind speed (TWS) in the lower box;
• the orange arrow is the apparent wind angle (AWA), with the apparent wind speed (AWS) in the upper box.

The speed dial is drawn north up, like a chart: N at the top, E on the right. Arrows from the middle show how the boat moves:

• the dark grey arrow is the boat's speed through the water along her heading, with STW in the upper box;
• the teal arrow is the current, pointing where it sets to;
• the purple arrow is the speed and course over the ground, with SOG in the lower box.

All arrows on the speed dial use the same scale, chosen so the longest fits; a weak current is drawn a little longer so you can still see it. Where the current runs with you the purple arrow is longer than the grey one; where it is on the beam the two arrows open up, and the angle between them is your drift.

Hold the pointer over a dial for the exact figures, for example AWA 56° P · AWS 10.7 kn · TWA 98° P · TWS 8.9 kn. Angles are written with the side the wind comes from: P for port, S for starboard.

7.5 The digital instruments

Digital shows only the numbers, each in the colour of its arrow on the dials:

• apparent wind speed, with the apparent wind angle;
• true wind speed, with the true wind angle;
• speed through the water, with the heading (HDG);
• the current's rate, with the direction it sets to — when the route was calculated with currents;
• speed over the ground, with the course over the ground (COG).

Under the numbers the card says whether the boat is ⛵ sailing or ⚙ motoring at that moment, with the time, and the forecasts the route was calculated with and its departure time.

7.6 The route panel: graph, table and zones

Under the map, the route panel shows the calculation in focus over its whole length. (With two or more calculations on the map it compares them instead, see 6.5.) Choose the view at its top left; the ▾ button at the right folds the panel to a single line for more map, ▴ opens it again.

Graph draws the passage against time:

• solid lines in knots: SOG (purple), TWS (dark blue), AWS (orange) and Current (teal; dashed where the current came from the tidal atlas);
• dashed lines in degrees: TWA (dark blue) and AWA (orange), from 0° (head to wind) to 180° (dead downwind);
• orange bands where the boat motors, and T and G along the bottom for each tack and gybe.
• The colours are those of the instruments: dark blue for the true wind, orange for the apparent wind, purple for the speed over ground.

Move the pointer over the graph to read the values at that moment in the line under it. Tap the graph to move the time bar there — the quickest way to jump to the moment the wind heads you or the engine goes on. Tap a name under the graph to hide or show that line.

Table lists the route row by row: time, Sail or Motor, COG, SOG, TWS, TWA, AWS, AWA, the current (rate and the direction it sets to, greyed and marked atlas when it came from the tidal atlas), the zone the boat is in, and T or G for a tack or gybe. The menu next to the views sets the rows: every step of the calculation, hourly or every 3 h. Hourly and 3-hourly tables still show every tack, gybe and switch between sailing and motoring, and the arrival. Tap a row to move the time bar there; while playing, the table scrolls along.

Zones — for a route calculated with zones; the number is how many entries it has. It lists the traffic separation schemes the route passes, for example … crossed at 88° · 14 min or …: followed NE lane 3.2 nm, and below them the warn zones it goes through. Tap a scheme to move the time bar to the moment the boat enters it; hold the pointer over it for the times in and out. The zones come from OpenStreetMap, not from official charts — see chapter 3.

barbs on route draws wind barbs along the route in focus: the wind the boat meets on her way, at the time she gets there — not the wind at the time on the time bar.

7.7 The route and the boat on the map

A route is drawn in its colour on a white edge; motoring parts are dashed. A small dot marks every calculation step: hold the pointer over it for the time, sailing or motoring, a tack or gybe, SOG and COG, and the true and apparent wind there. Traffic separation scheme passes are drawn thicker, with a small sign in the middle: ⟂ for a crossing, ⇢ for following a lane, ↺ for a roundabout. When show isochrones (hourly) is ticked in the details (see 6.3), grey lines show how far the router got each hour.

The boat sits on the route at the time on the time bar, turned to her heading, with the route's number beside her (as on its instrument card). With one route on the map she has a white hull and blue sails, and an orange hull without sails while motoring; with several routes each boat has the colour of her route and white sails.

While sailing she carries a mainsail and a genoa, set to leeward and eased out with the wind angle: almost along the boat close-hauled, about 40° out on a beam reach, about 60° on a broad reach and all the way out running. Dead downwind she sails goose-winged, the genoa out on the other side. So the picture shows at a glance the point of sail and the tack.

7.8 Underway: your position and rerouting

When the app gets the boat's position from the NMEA network (Settings → Position (NMEA), see chapter 10), your own boat appears on the map as a red triangle pointing along your course over the ground, with a line showing where you will be in 30 minutes. It turns grey, with a dashed line, when no position has come in for a while.

The details of the calculation in focus (Results tab, see 6.3) then compare your position with the plan: Off track 0.40 nm · behind 12 min. When you are further off track or further ahead or behind than the limits under Settings → Deviation warning (1 nm and 30 minutes unless you change them), the box turns amber and says You have deviated significantly from the planned route. Tap Reroute from here to calculate the rest of the passage from where you are now, with the same boat, forecast and options.

Without a position the box says so, and Reroute from here cannot be used.

8.1 Moving around

Drag the map to move it. Zoom with the mouse wheel (a notch is a small step), with the + and − buttons at the top left, by double-clicking, or by pinching on a tablet. The scale bar at the bottom left shows kilometres and nautical miles. The map remembers where you left it.

The chart is OpenStreetMap with the OpenSeaMap sea marks over it. Both come from the app's own store of map tiles, so the map also works offline — for the parts you have downloaded (see 8.10).

8.2 Which forecast the map shows

The area chip names the area you work in, with its light, and the model and run of the wind shown (for example GFS 06Z). The light is green when the area is up to date, amber when its models are runs behind or its zones are incomplete, red when a model has no run yet or the zones were never downloaded, and grey while the app is still checking. Hold the pointer over the chip for the reason; tap it to open the Areas tab.

The run caption next to it says exactly what the map shows: the wind forecast and its run, then after a + the current forecast and its run. It adds (no data at this time) when the time bar is outside that forecast, and → tidal atlas when the tidal atlas supplies the current at that time (see 8.4).

Tap the caption to open it and choose:

• Wind — three menus: the area, the weather model, and the run. Choosing an area or model takes its newest run.
• Current (when you have current forecasts) — Automatic, or an area, model and run of your own choice. Automatic shows the current used by the calculation in focus, otherwise the newest current forecast.

You rarely need the caption, because the map follows what you do:

• When the newest run is shown and a newer one is downloaded, the map moves on to it by itself. A run you chose on purpose stays.
• When you choose an area whose forecasts are not on the map, the map switches to the model you last looked at there.
• When you tap a model in the Areas tab, the map shows that model (see chapter 2).
• When you put a calculation in focus in the Results tab, the map shows the wind run it was calculated with — and, with Current on Automatic, its currents — so the map shows what the route used.

8.3 Wind on the map

Shading colours the sea by wind speed: blue and green for light airs, yellow and orange for a good breeze, red and purple for a gale. The colour scale at the top right gives the knots, from 0 to 50.

Wind symbols are spread evenly over the map and show the wind at that spot:

• Barbs, as on a weather chart: the shaft points to where the wind comes from; a half feather is 5 knots, a full feather 10 and a pennant 50. A small circle means less than about 2.5 knots.
• Arrows point the way the wind blows, with its speed in knots next to them.

Without shading, the symbols themselves are coloured by wind speed. Over shading they are drawn black with a white edge, so they stay readable on every colour.

8.4 Currents on the map

Current arrows point the way the water flows — the direction it sets to — with the rate in knots and one decimal. Without shading they are coloured by rate; over shading they are black.

Set Shading to Currents to colour the sea by the rate of the stream instead of the wind: pale blue for slack water, through teal and yellow, to red for 4 knots and more. Tidal gates and the strong streams off headlands stand out at a glance; move the time bar to see them turn.

The currents come from the current forecast in the run caption. When your area has a tidal atlas (see chapter 9), the map uses it as well: the atlas fills in where the forecast has no data, close inshore, and takes over completely when the time bar is beyond the end of the current forecast. The run caption then ends in → tidal atlas. When the calculation in focus was made with the tidal atlas only, the map shows the atlas only.

8.5 Animated flow

Animated flow lets thin streaks drift over the map with the wind or with the current. It gives a quick feel for the pattern — where the wind backs round a low, where the stream splits around a bank — that symbols alone do not. The streaks run faster where the wind or stream is stronger.

The animation uses more of the computer's power than anything else on the map, so it is off unless you switch it on. It pauses while you move the map and starts again when you stop.

8.6 The ☰ map menu

☰ in the top right corner of the map (in split screen: of the right-hand map, or of the top map when a narrow screen stacks them) opens the map menu. At the top, Split screen (see 8.8) and Stream (see 8.9); under Map display everything about how the map looks. Each change shows at once; tap ☰ again, or anywhere outside the menu, to close it.

• Wind symbols — Barbs, Arrows or None.
• Current arrows — Arrows or None.
• Shading — colour the sea by Wind or by Currents, or None.
• Opacity — how strongly the shading covers the chart: to the left the chart shows through more.
• Zones layer — the zones of your area on the map (see 8.7). This is the main switch for the six zone rows below.
• Animated flow — Wind, Currents or Off (see 8.5).

Under Layers, sliders fade the parts of the map:

• Base map — the chart itself. Fade it to make the forecast stand out.
• Sea marks — the buoys, lights and beacons; all the way left hides them.
• One row for each kind of zone: Traffic separation (TSS), Wind farms, Restricted areas, Protected areas, Precautionary and inshore traffic and Manual no-go / warn areas (the zones you added yourself). Untick a row to hide that kind; its slider fades it.

8.7 Zones and area outlines

The zones of the area you work in are on the main map whichever tab is open: traffic separation schemes hatched, the others outlined in the colour of their rule (see chapter 3). When you zoom in, arrows in the traffic lanes show the direction of traffic, and an arrow in each roundabout shows its counter-clockwise flow. Hold the pointer over a zone for its name, its kind and the rule the router applies. Dashed orange circles and outlines mark holes in a scheme's data: a gap between its parts, or lanes that end without a junction. Hold the pointer over one for what it is.

The zones come from OpenStreetMap: they are not official chart data. Always check your charts.

While the Areas tab is open the map also shows the outlines of all your areas, the selected one drawn thicker. Hold the pointer over an outline for the area's name; tap it to make that area the one you work in.

8.8 Two maps side by side

Split screen in the ☰ map menu puts a second map next to the first (on a narrow screen: under it). Both show the same moment and move and zoom together; each has its own run caption, so each can show its own weather model. The second map's caption also chooses its currents: when your area has a tidal atlas, Forecast only, Forecast + tidal atlas or Tidal atlas only.

The area chip, the zones, the Stream tool and route editing stay on the first map. What the instruments show on each map is described in 7.4; how to use split screen to compare models in 6.6. Untick Split screen to go back to one map.

8.9 The tidal stream at a point

The Stream tool shows how the stream at one spot changes over the coming tide — useful to time a headland, a tidal gate or a harbour entrance.

1. Tick Stream in the ☰ map menu. Taps on the map now belong to the tool.
2. Tap the spot on the map. A graph opens at the bottom left of the map.
3. Tap another spot to see the stream there, or untick Stream to go back to normal map taps.

The graph shows the rate of the stream in knots, starting at the time on the time bar when you tapped. Its title gives the position and the nearest tide gauge with its distance; the dashed vertical lines are that gauge's high (HW) and low waters (LW), labelled with time and height. The red line is the time on the time bar and moves with it. Along the bottom, small arrows every three hours show the direction the stream sets to, north up.

The line is solid where the rate comes from the current forecast and dashed where it comes from the tidal atlas; the key at the bottom right says which are in the graph. Move the pointer over the graph to read the exact rate, direction and source at that moment. The menu at the top right shows 12 h, 24 h, 48 h or 96 h.

The graph uses the same currents as the main map (see 8.4). On land, or where there is no current data, it says No current data here; without a tide gauge within 50 nm the high and low waters are left out. Close it with × or the Esc key. Stream cannot be used while you are editing a route or drawing a zone.

8.10 Offline map tiles

The chart is made of small square pictures, tiles, for every zoom level. The app keeps the tiles in its own store on the boat's computer. While you are online it fetches the tiles it does not have yet and keeps them (unless you untick download missing tiles when online in Settings), so a part of the chart you have looked at while online is there offline as well. Parts you have never loaded stay empty while you are offline.

To be sure the whole sailing area is on board, download it in advance under Settings → Offline map: select an area on the map and the zoom levels, and download. The OpenStreetMap tile servers allow only small downloads at close zoom levels: download the whole area up to zoom 12, and the closer levels only for harbours. See chapter 10.

9.1 What the tidal atlas is

The atlas is fitted once to the past 30 days of hourly Copernicus currents for the area's box. For every grid cell of about 1.5 km it works out the tidal constituents — the regular rhythms of the tide such as the twice-daily lunar and solar tides — and from those it predicts the tidal stream for any date and time, without an internet connection.

It is pure tide: it knows nothing of wind-driven currents or surge. When the weather pushes the water around, the Copernicus forecast is closer to the truth for as long as it lasts.

The atlas only works on the North-West European shelf, where the Copernicus currents come from. For an area that lies partly outside it, the atlas covers the part on the shelf.

9.2 Building and rebuilding

Each area has a Tidal atlas line, at the end of the Current group on its area card and in the Atlas tab.

1. Tap Build (or Rebuild when the area has one). The app first works out the download size, which takes a few seconds, for example up to about 2.86 GB to download once (file 324.5 MB). This is an upper bound; the real download is often much smaller.
2. Tap Download and build, or Close to leave it.
3. The line shows what it is doing — downloading the past currents, then fitting day by day — with a progress bar. Cancel stops it.

Build the atlas in harbour on a good connection. It needs the free Copernicus Marine tool installed and logged in on the computer that runs the app; if the tool is missing, the line shows the commands to install it.

The tide's constituents do not change, so there is no need to rebuild regularly. Rebuild when the line says covers part of the area — rebuild, after you made the box larger. The ✕ deletes the atlas after Delete? Yes / No; deleting the area deletes its atlas too.

9.3 The Atlas tab and the quality figure

The Atlas tab lists every area with its tidal atlas: a green light when it has one, grey when not, and the atlas line of 9.2. Tap ▸ Tidal atlas to open a line and see the download size of a (re)build.

A built atlas is described in one line, for example built from 30 days ending Mon 12 Oct · 11 constituents · 58,231 cells · tide explains 94 %:

• the period of past currents it was fitted to;
• the number of tidal constituents;
• the number of grid cells at sea it predicts for;
• tide explains: how much of the movement of the water over those 30 days the tide accounts for, in a typical cell. Above 90 % the stream is almost all tide and the atlas is a good guide. A lower figure means wind, surge or river water mattered more, and the atlas will miss more of it.

9.4 Currents when calculating

The Current line of the Calculate card in the Routes tab (see 5.3) chooses which currents the router uses:

Forecast + tidal atlas

The newest current forecast of the area wherever and whenever it has data, and the tidal atlas beyond it. The best choice in most cases, and the default when the area has both.

Forecast

Only the forecast. Beyond its end, or outside its box, the current counts as zero. Use it to see what the forecast alone says.

Tidal atlas

Only the tide, for the whole passage. Useful for planning days or weeks ahead, or to compare departure times against the tidal gates without the weather of the moment.

None

No current at all, for example to see how much the tide gains or costs you.

The atlas choices appear only when the area has an atlas, the forecast choices only when it has a current run. The card remembers your last choice. In the Results tab each calculation shows its currents (cur. fc+atlas, fc, atlas); the route graph draws current from the atlas dashed (see chapter 7). The map shows the atlas behind the current forecast in the same way when the selected area has one, and the Stream tool shows forecast and atlas side by side for one spot (see 8.4 and 8.9).

9.5 The reference port and high water times

Sailors think of the tide in hours before or after high water at a standard port. When the selected area has a tidal atlas, the time bar under the map shows the time from the nearest high water at the area's reference port, for example HW Harwich −2 h 56, next to the clock.

The reference port is set in the area editor (see 2.3). Automatic takes the standard port nearest to the box centre; choose another tide gauge within 150 nm when your tidal stream atlas or pilot book works from a different port, for example Dover for the Channel.

10.1 Routing defaults

These values steer the router. The first four are the starting values of the Calculate card's options (see 5.5), where you can change them per calculation; the others are only set here and apply to every calculation.

Time step (min)

How often the router reconsiders the course; default 30.

Heading step (°)

From each point, the router tries a heading every so many degrees; default 5. A smaller step finds a slightly better route and takes longer.

Sector (°)

After each step the router keeps, per sector of this many degrees seen from the leg's start, only the point that got furthest; default 1. A smaller sector keeps more points: finer and slower. Within a mile of land it also keeps the first point to reach each square of a tenth of a mile, so a narrow sound, a harbour behind a headland or a river that bends back towards the start is followed whatever the sector.

Corridor (× leg)

How far the route may stray from the straight line between two waypoints, as a part of the leg's length; default 0.5.

Maximum duration (h)

The router gives up when it has not arrived this many hours after the departure; default 240.

TSS tolerance (°)

How far the heading may be off perpendicular when crossing a traffic separation scheme, or off the lane direction when following one; default 15.

Coast distance (nm)

The minimum distance kept from the coastline; default 0.5.

Relaxed near waypoints (nm)

Within this distance of a waypoint the coast distance shrinks to 0, so routes can leave and enter harbours; default 3. Make it larger for a harbour at the end of a long, narrow approach.

The Calculate card remembers the options of your last calculation; when you change one of the first four defaults here, the card takes the new default for it.

10.2 Zone rules

The default rule for each kind of zone — Wind farm, Restricted area, entry prohibited, Restricted area, other, Nature reserve / protected area, Precautionary area, Inshore traffic zone and TSS crossing area — is one of:

• no-go — the route never enters it;
• warn — the route may pass, and the result lists the zone;
• allowed — the zone is ignored.

Out of the box wind farms and restricted areas where entry is prohibited are no-go; the rest is warn. A rule set on a single zone in the zone list wins over the default, and the traffic lanes and roundabouts of a scheme follow the area's TSS settings (see chapter 3).

Junction: against arriving traffic within (°) — in a junction, where several lanes meet, a heading within this angle of directly against a lane ending there is refused; default 45°.

10.3 Position (NMEA)

With your boat's position the app shows the boat on the map, measures how far you are off the planned route (see 10.4) and can Reroute from here (see 6.3). It reads the position from the NMEA 0183 data on board (RMC or GGA sentences), as a multiplexer or chartplotter sends it over the network. Choose the Source:

• none — no position;
• TCP (connect to a multiplexer) — the app connects to the Host (its IP address or name) and Port of the device that serves the data;
• UDP (listen for broadcasts) — the app listens on the Port for data the device broadcasts on the network.

Stale after (s) is how long a position counts as current without a new one; default 30. A stale position is not used for rerouting.

The status line below tells you how it goes: the source (for example TCP 192.168.1.10:10110), connected or not connected, the time of the last fix in UTC (with (stale) when it is too old), the number of bad lines received, and the last error. It is updated every few seconds.

10.4 Deviation warning

While you sail a calculated route with a position from NMEA, its details in the Results tab show how far you are off the planned track and how many minutes you are ahead or behind it. When you are further off than Off track more than (nm) (default 1), or more ahead or behind than Ahead/behind more than (min) (default 30), the app warns You have deviated significantly from the planned route and highlights Reroute from here (see 7.8).

10.5 Offline map

The map is made of OpenStreetMap tiles with the OpenSeaMap sea marks on top. The app keeps every tile it has shown, so what you have looked at once is there offline. The settings:

download missing tiles when online

When ticked, tiles that are not stored yet are fetched from the tile servers as you move the map. Untick it to use stored tiles only, for example on an expensive connection.

Requests per second

How fast a tile download asks the servers; default 2, at most 10. Keep it low, as the tile servers' usage policies ask.

Max tiles per download

The largest download the app accepts; default 50000.

User agent

The name the app gives itself to the tile servers. If OpenStreetMap refuses the tiles, the app tells you to change it.

Before a passage, download the tiles of your cruising area in one go:

1. The box shows what is stored now (Cached: OpenStreetMap … tiles, sea marks … tiles).
2. Tick OpenStreetMap and/or sea marks, and choose the zoom levels (zoom 6 to 12 to start with).
3. Tap Select area on map and click two opposite corners of the area on the map (Cancel or Escape stops).
4. The box shows the number of tiles and about how many MB, and any problem — for example more tiles than allowed. Tap Download tiles.

10.6 Coastlines for routing

To keep routes off the land, and the coast distance of the options, the router needs coastline data for your area. Without it the box says No land data installed: routes may cross land., and every calculation warns no land data for this area – the route may cross land. Install it once, on a good internet connection:

1. Download the OpenStreetMap land polygons, land-polygons-split-4326.zip from osmdata.openstreetmap.de (about 800 MB), and unzip it on the computer that runs WeatherRouting.
2. Under Install a region, type the path of land_polygons.shp in Shapefile path.
3. Give the region a name (Region name, letters, digits, - and _), and leave Simplify (m) at 20 unless you need more or less detail.
4. Tap Select area on map and click two opposite corners: a bit larger than where you sail.
5. Tap Install. When it is done, the region is listed with its area, its size and the date.

The ✕ next to a region deletes it after you answer Yes. The coastline data also lets the app drop zones that lie on land.

10.7 Download log

Open Download log to see the last 200 lines of today's download log: every request for forecasts, currents and tidal atlas data, and what the server answered. It follows along while a download runs; Reload reads it again. When a download fails, this is the place to see why.

10.8 About

About shows the version of WeatherRouting and the source of the tide gauge data. It also warns when a tool the app needs is missing on the computer; the Settings tab then has a small dot:

• ecCodes is not installed, so GRIB files cannot be imported. — install it with sudo apt install libeccodes-tools. Most weather models arrive as GRIB files.
• nccopy is not installed, so NetCDF-4 current files cannot be imported. — install it with sudo apt install netcdf-bin.

10.9 Settings only in config.json

Some settings are not in the Settings tab, because they hold keys or choose what the server runs. They are in the file config.json, normally config/config.json in the WeatherRouting folder; edit it on that computer with a text editor. The app reads a saved change within a few seconds; a file with a mistake is ignored and the old settings stay.

Météo-France keys

Under sources.meteofrance: aromeApiKey (also used for AROME HD), arpegeApiKey, and apiKey, a shared key for a model without a key of its own. The endpoints aromeWcs, aromeHdWcs and arpegeWcs are there too; leave them as they are. See the appendix for where to get the keys.

Copernicus currents

Under currents.copernicus: datasetId (the current forecast), atlasDatasetId, atlasDays and atlasThin (what the tidal atlas is built from, see chapter 9), and extraArgs for the Copernicus Marine tool. The Copernicus login itself is not in the file: it belongs to the tool.

Download relay

Under relay: enabled, host, user and keyFile (an SSH key used for the relay only). With the relay on, a refresh asks it first and the model's status says via relay; when it cannot help, the app downloads directly and says why. Setting up the relay itself is described in docs/relay.md. Settings → About shows whether the relay answers, its version and the models it offers (checked when the app is opened).

For example, with your two Météo-France keys:

"sources": { "meteofrance": { "aromeApiKey": "<AROME key>", "arpegeApiKey": "<ARPEGE key>" } }

A.1 Weather models

These are the weather models an area can download (see chapter 2), with the names the app uses. Forecast length is the length a new model starts with in the area, and the longest you can choose; Steps are the time steps you can choose between the forecast hours.

Notes:

• The app takes the newest run that reaches the forecast length you chose. Where a maker runs some of its daily runs shorter, those runs are left out for a long forecast length.
• Every model except the Met Office UKV arrives as GRIB files, which need ecCodes on the computer (sudo apt install libeccodes-tools; see 10.8).
• The Met Office UKV runs on its own map projection; the app turns it into a latitude/longitude grid of 0.02° by 0.03° (about 2 km) for the area.
• Météo-France keys. Register for free at portail-api.meteofrance.fr (with a plain user name, not your e-mail address), subscribe to the AROME and ARPEGE APIs and make an API key (not OAuth2) for each; the validity is given in seconds (31536000 is one year). Put the keys in config.json as sources.meteofrance.aromeApiKey and arpegeApiKey (see 10.9). Météo-France allows 50 requests a minute, so these models download slowly.

A.2 Currents

The same Copernicus data, over a month of past days, is what the tidal atlas is built from (see chapter 9).

The app downloads Copernicus data with Copernicus's own tool, which you install once on the computer that runs WeatherRouting, as the same user:

1. Create a free account at Copernicus Marine.
2. Install the tool: sudo apt install pipx, then pipx install copernicusmarine and pipx inject copernicusmarine netCDF4.
3. Log in once with copernicusmarine login; the tool keeps the login.

When the tool or the login is missing, the download fails with a message that names the command to run.

A.3 Other data

Map

The map tiles come from OpenStreetMap, the sea marks on top from OpenSeaMap (see 10.5).

Zones

Traffic separation schemes, wind farms, restricted and protected areas come from OpenStreetMap, fetched through the Overpass API (see chapter 3).

Coastlines

The land the router keeps off comes from the OpenStreetMap land polygons of osmdata.openstreetmap.de (see 10.6).

Tide gauges

The harmonic constants of the tide gauges come from TICON-4. The app states (Settings › About):

Tide gauge constants: TICON-4 (CC BY 4.0), Hart-Davis, M., Dettmering, D., Seitz, F. (2025), TICON-4: TIdal CONstants based on GESLA-4 sea-level records, SEANOE, doi:10.17882/109129; method: Piccioni et al. (2019), doi:10.1002/gdj3.72. TICON-4 derives from GESLA-4 records, of which the CMEMS, University of Zagreb and City of Venice sources are research use only; use this data for research and personal use.

A.4 Licences and attribution

• Map data and zones: © OpenStreetMap contributors, available under the Open Database License (ODbL), openstreetmap.org/copyright. The map shows this in its corner.
• Sea marks: © OpenSeaMap.
• Tide gauge constants: TICON-4, CC BY 4.0, for research and personal use (see A.3).
• Weather and current forecasts are the open data of their makers above, each under its own terms; read them at the maker's site before you pass the data on.
• The fonts of the app and this manual, IBM Plex Sans and Barlow Semi Condensed, are under the SIL Open Font License.

A.5 Routing advice only

WeatherRouting gives advice, not a passage plan you can follow blindly. Forecasts can be wrong, and more so near the coast and in showers; the polar is an estimate of your boat; the zones and coastlines come from OpenStreetMap, not from official charts. Always check the route against your official charts, the notices to mariners and the latest official forecasts and warnings, and keep a proper lookout.