Routing at sea

In this article we will start by discussing the Routing form (DOWNLOAD) and then we will discuss Routing and navigation software, Apps and websites, because they allow us to make calculations much faster and more accurately .

Routing form

Global planning of a multi-day sea voyage

If we are going to sail for a few weeks, we will have to start weeks in advance with a global planning of the routes and the ports we want to visit. People who are going on a world trip often spend years preparing. In broad terms, we have to plan which trip we are going to sail during the entire period. In practice, things can turn out differently, because we are very dependent on the weather.

Ship and equipment

Of course we need to know what the dimensions of the ship are, such as draft and the height of the mast. This can be useful if you want to sail under a fixed bridge or over a threshold or tidal flats. You know this about your own ship, but if you are going to sail on a rental ship you need to find this out properly. In addition, everything needs to be on board. It is wise to make checklists for safety and maintenance , provisions, ship documents, personal luggage, etc.

Weather forecasts

We always make sure that we get the most recent weather report just before departure. This reduces the chance that we end up in dangerous situations, such as a storm. The wind force and direction will also determine whether we can even sail the route we had in mind. Note per route at what time and on which VHF or radio channel current weather reports can be received.

Sun and moon

We find out when the sun and moon rise and set. Then we can take that into account when planning the trip (arrival in daylight) and the watch schedule (at night the most experienced skipper must be on deck). The moon gives a lot of visibility in clear skies and it is a world of difference between sailing with a clear sky and a full moon or night sailing in the rain.

Tidal current

The tidal current is essential for the trip planning. We base our sailing tactics, departure time, ETA, etc. on this. It is therefore important to know what the current direction is per time period and how strong it is on average and at its maximum. So don’t go into too much detail, but try to get an overview.

Limited passage

You can of course calculate the most beautiful routes, but if you cannot leave the harbour at the time you want to, for example because there is a threshold in front of the harbour entrance, which you can only cross at high tide, then you will not get far. Fixed bridges that you can only pass under at low tide can also hinder your passage. Also do not forget the operating times of locks and movable bridges.

Route

We roughly set out the route from waypoint to waypoint, taking into account sailing tactics based on tide and wind and of course we have to take into account the legislation at sea. As a waypoint we prefer not to choose a buoy, but a point next to it, because there is a big chance that you will sail into it otherwise. Especially if your autopilot is linked to your GPS. You also prefer to choose a point well next to a buoy with a light on it, than a blind buoy. When setting out the route we take into account sandbanks, recommended crossings of traffic separation schemes, etc.

ETD and ETA

Then determine the departure time (ETD) and take into account the preference to arrive with daylight, threshold or wantij and the direction of the current. Then determine the courses and take into account obstacles and busy shipping routes. Also think of sailing tactics such as the development of coastal winds, bending effects, divergence/convergence, weather systems, land effects, cape effects, direction of the current, etc. We look at what we encounter along the way and what we can use for navigation such as buoys, RACONs, fires, landmarks, etc. Once the courses and distances are known, we can calculate the expected arrival time ETA. Choosing the best ETD (and therefore also ETA) is one of the most essential things when making a trip plan.

Alternative routes / (flight) ports

It is wise to determine in advance the places where a refuge or alternative port can be chosen. For example, if the wind is stronger than predicted and it is no longer comfortable.

Shift system

Night sailing can be tough. It is often cold at night and fatigue sets in. Seasickness also occurs much faster, because sometimes there is no horizon to be seen.

If the number of crew members is large (for example 6 men), it is possible to create a watch system, which keeps the number of people on deck as small as possible (for example 2 men), so that it is not necessary to stay on deck for long. You can achieve this by creating multiple groups, which alternate with each other. 3 groups of 2 men means for example 2 hours on, 4 hours off. There is absolutely no added value to sit still and shiver in the cockpit with 3 men if 2 men can do it just as well.

With a small crew of 2 people for example, it is important not to be alone on deck for too long in heavy conditions. But the time should be long enough for the other to get some sleep.

Furthermore, it is taken into account that the best skipper is on deck at critical moments. So he must be on deck when an unknown port is called, a busy traffic route is crossed, etc. If the crew is large enough, it is wise not to schedule the skipper himself, so that he can decide for himself when he has to be on deck and when he can take a rest. With a two-man crew, that is not possible and then it must be taken into account that the best skipper is on deck at difficult moments.

Maps

You check whether you have the paper charts ready in order. Check in particular whether you have recent charts with a sufficiently large scale (with sufficient detail) ready, also for the areas where you might have to seek refuge if the journey does not go as planned. Of course, the charts must be updated using the Notices to Mariners . You also check whether the digital charts are installed in your on-board computer or chart plotter and are up-to-date.

Pilot plan

For the departure port, destination and also for the alternative refuge ports it is a good idea to make a sketch, with only the most important elements on it such as approach route, light lines, VHF channels, buoys and beacons, dangers such as sand anchors and reefs, etc. For this we also use the Almanac such as the Reeds Nautical Almanac. You can put the paper on the detailed map and trace the coastlines, so that you have a cheat sheet that you can even keep at hand outside in the cockpit.

Log

A logbook is required by law. In the event of an accident, you will be asked to submit a logbook. It will also help you to switch to dead reckoning if the GPS or chart plotter suddenly fails. A logbook is also useful during handovers during watchkeeping. In addition, we can identify trends in air pressure, wind and course, which can be used to adjust our tactics. Finally, it is also instructive to take the logbook after each trip and think about what we could do better next time to sail even more effectively. Have the right tactical decisions been made? Could we have sailed even more safely or faster? By discussing this with each other after each trip, you learn a little from each trip, which means you sail more and more effectively.

Routing and navigation software, Apps, websites and chart plotters

More and more digital routing tools are becoming available. With these modern digital resources (chart plotters, apps, software and websites) we can make calculations for routing much faster and more accurately compared to the “old-fashioned” way. Paper maps, almanacs and a compass are still more resistant to seawater, lightning strikes, GPS interference and are not dependent on electricity at sea. In addition, a large paper sea chart still provides a much better overview and you miss shallows much less quickly as happens on digital screens because you do not see details when you are zoomed out too much . For digital routing these dangers are also important but still slightly less important than with navigation, because we mainly do routing in the safe harbor or at home. Nevertheless, my advice remains to initially apply the “old-fashioned” route planning with paper maps and almanacs and then use the digital resources as a check and to make the route planning extra accurate. Digital resources are namely error-prone without you noticing and can be read incorrectly. If the route planning you make with paper maps, almanac etc. matches what the digital resources predict, then that gives confidence and better insight. Moreover, even now in 2025 there is still not 1 program that can really make a complete trip planning and that will remain the case for a while.

Chart plotter, laptop, tablet or smartphone?

There is software that you can install on your laptop or on-board computer. Personally, I prefer to use my laptop for trip planning, so that I have a large screen, keyboard and mouse. There are all kinds of programs available, also (free) Open Source. By By means of NMEA it can be connected to chartplotters and other navigation instruments, such as GPS, log, wind meter, depth sounder, etc. or you can use a simple GPS dongle.

Secondly, there are Apps that you can download from Google Play Store or Apple Store and install on your tablet or smartphone and on some Chromebooks. Apps on tablets and smartphones also have their advantages, namely that tablets or smartphones can also be taken into the cockpit (in a waterproof protective cover), because they are usually reasonably water-resistant. In addition, smartphones always have a built-in GPS and the battery lasts a reasonably long time. On some Chromebooks it is possible to install Apps from the Google Play Store. These Chromebooks start up quickly, work for a long time without having to charge the battery and do not have an internal fan for cooling (fanless), so that less sea air blows through it, as is the case with many on-board PCs, which of course quickly causes corrosion. The disadvantage of Apps on smartphones and tablets is that nowadays the crew stares at their phone too much while sailing. In addition, the screen of a smartphone or tablet, especially if it is in a protective cover, is no longer visible when salt water or bright sunlight is coming in and the touch screen is no longer easy to operate.

Despite the convenience of Apps, in my opinion a solidly built, fixed mounted, waterproof chartplotter that is clearly visible from the helm is the most reliable solution for navigation. It is also possible to export the route planning made on the laptop to the chartplotters.

It is of course to be expected that in the coming years all fixed mounted chart plotters from Raymarine, B&G and Garmin will also have weather and tidal routing functionality, so that route planning on the laptop is no longer necessary but can be done directly on the chart plotter. At the moment, many boats do not have a chart plotter on board with that possibility and that is why this article is still current. Developments are moving fast and with the arrival of AI a lot will happen in the field of routing and navigation in the coming years.

Navigation, routing, weather and tide software

There are programs, apps and websites that were originally developed for navigation, such as Navionics (taken over by Garmin), C-MAP and OpenCPN (Open Source), where CPN stands for Chart Plotter Navigation. In addition, there are programs, apps and websites that were developed for route planning. The big advantage of this type of routing software compared to popular navigation programs, for example, is that it takes into account the polar diagram of your ship and uses grib files for wind direction, strength and current. If you have to tack up or down, the program itself calculates the ideal tacks/courses taking into account the wind and current and calculates the ground speed at the predicted wind and current strength and direction that varies per hour. Finally, there are programs, apps and websites that were developed to calculate only the wind or the tide or with data about ports and anchor bays or GRIB readers to read GRIB files. These are still very useful for route planning, such as:
www.windy.com
www.predictwind.com
www.navily.com
NLTides

In recent years there has been a trend that developers are implementing all functions: navigation, routing, tides, GRIB files for weather, port information, etc.

Commercial Routing Software and Apps

SQUID is weather forecasting and routing software. Squid is used on board boats in The Ocean Race and Vendée Globe. A subscription is affordable, also for recreational sailors. More information can be found on www.squid-sailing.com
Expedition navigation and sailing software is used on board The Volvo Ocean Race, Americas Cup, etc. More information can be found on www.expeditionmarine.com
Adrena Navigation software is used on board Vendee Globe etc. More information can be found on www.adrena-software.com
Savvy Navvy is a commercial routing App, more information on www.savvy-navvy.com

Practical example Routing with qtVlm

qtVlm is one of the oldest routing programs available and is still being improved by means of version updates. Since commercial routing software has a considerable price tag and I cannot discuss all programs, I have chosen to discuss qtVlm in this article. qtVlm offers a lot of possibilities and the other routing programs work more or less the same, so if you can work with qtVlm you can quickly learn to work with the other programs. The principle is the same. qtVlm offers so many possibilities that the learning curve will be steep in the beginning. You really have to sit down and learn to work with it, but that also applies to other extensive programs with many functions. It is worth the investment of your time, because it is a perfect tool to plan your sailing trips.

You can download the program for free at www.meltemus.com . You can also download the App in the App store and Google play. It works best if you use a combination of an on-board computer with a tablet or smartphone. You can then make the preparations on your on-board computer with a large screen and then export the routes to your smartphone or even better, to your fixed chart plotters. The name qtVlm consists of two abbreviations, namely: Qt (pronounced: cute) the technology with which it was developed and Vlm which stands for Virtual Loup-De-Mer (sea bass).

Navigating with qtVlm

qtVlm can be connected to NMEA sources such as GPS and AIS, so you can read all that data in qtVlm, but in this article I will focus on the routing function of qtVlm, namely calculating the fastest route, based on grib data for wind and current and the polar diagram of the boat.

Import polar diagram

A Polar Diagram indicates how fast the boat can sail on a certain course in relation to the wind and wind speed. In order to calculate the fastest route as accurately as possible, qtVlm can use the specific polar diagram of your ship. Via the menu “boat > boat settings > Tab Polar > Polars server” you can select a polar diagram specific to your ship or a ship with a similar rating. Polar diagrams can also be found on, for example, these links:
http://jieter.github.io/orc-data/site/
https://www.seapilot.com/features/download-polar-files/
https://download.meltemus.com/polars/
You can also import your own polar diagram. The shipyard that built your ship may be able to send you a polar diagram or you can make one yourself. In the video below I show you how to set the polar diagram of a Breehorn 37.

Sail crossover diagram

It is also possible to enter the optimal sail setting for different courses relative to the wind and different wind speeds. You should make such a sail crossover diagram yourself or together with your sailmaker. See for example an example on www.quantumsails.com Once this data has been entered qtVlm can predict in the Route Logbook which sail setting is optimal and therefore when, which sail changes will be necessary. This is not only important during regattas but also during cruising it is good to know that a sail change is coming, so that you can adjust the watch schedule accordingly. For example if you know that a genoa change is necessary within an hour and the foredeck is just about to go to sleep…

Engine on/off

In the Boat > Engine and tacks/gybes menu you can set the engine to start when the speed drops below x knots and you can enter the speed on the engine to calculate very precise route planning, even during periods of calm.

Waves

It is also possible to enter a polar diagram for waves, because higher waves will slow down the boat more when sailing upwind. It goes too far to go into this in this article. It is recommended to read the full qtVlm manual after this short introduction if you want to use these kinds of functions.

GRIB files for weather forecasting

In qtVlm you can open or download a number of types of GRIB files. There are 3 slots available for this. In GRIB 1 you can for example download a GRIB file for the wind and in GRIB 2 the tidal currents. If you download a second GRIB file with another weather model for wind in GRIB 3, qtVlm automatically chooses the GRIB file with the highest resolution.

To download the GRIB files you can select the sailing area with the button “selection” (blue / orange square) and after selecting click on the right mouse button. Then you can choose from different ways to download GRIB files, for example:

• • Iridium GO! to download GRIB files (Saildocs, ZyGRIB or XyGRIB).

• • Squid GRIBs subscriptions / Great Circle

• • Saildocs: a service that sends GRIBs via email

• • If you do not have any of the above accounts, you can choose XyGRIB in qtVlm to download the GRIB files from https://openGRIBs.org .

Weather models

You can choose from different global and local weather models. These global models often predict with a higher resolution and are better for long-term predictions. Global weather models are for example:

• • GFS Global Forecast System developed in the USA

• • ECMWF European Center for Medium-Range Weather Forecasts

• • ARPEGE the global model of the French weather service (Meteo France)

• • ICON13 of the DWD (Deutscher Wetterdienst)

For short term forecasting you can also download a local model. Those local weather forecast models:

• • have a higher resolution and therefore provide a more detailed weather forecast

• • often give more predictions per day

• • but predict fewer days in advance

Examples of local weather models are:

• • ICON7 for Europe from the DWD (Deutscher Wetterdienst)

• • HARMONIE for the Netherlands, Europe and the Caribbean used and co-developed by the KNMI

• • AROME was developed and maintained by Portugal

In the video below I show you how to download a GRIB file (with weather model ICON), how to make the wind barbs more visible via Grib configuration, how to activate the Grib time slider and how to see the wind on a specific day and time.

GRIB files for tidal current data

For example, with a Squid GRIBs subscription you can easily download tidal current data from the area you select in qtVlm. To download free current data without an account you can search the internet, because many countries publish their tidal data online.

On MyOcean ( http://grib.weather4d.com/MyOcean/ ) you will find the GRIB files such as Global.grb.gz (whole world) and IBI.grb.gz ( Western Europe ). Of course, these files have a relatively low resolution. So you are better off looking for a file of only the area you are sailing. That will be a smaller file with a higher resolution.

For the North Sea you can look at stromingsgribs.nl . Also the openwrf GRIB files at openskiron.org/en/openwrf contain tidal currents on the North Sea: Download for example the files Dunkirk_4km_WRF… and Hastings_4km_WRF…

download the GRIB files HYPERLINK “https://www.bsh.de/EN/DATA/Predictions/Currents/Surface_currents_for_sailors/surface_currents_for_sailors_node.html” t “_blank”for Germany for free on the website of the Federal Office for Seeking and Hydrography.

After importing the GRIB files with tidal current data you can see the tidal current by clicking on the GRIB configuration button (button with the Windsock). There you select at Background: “Current map” and at Main Arrow: “Currents” and at secondary Arrow: Wind map.

In the video below I show how to download GRIB files from openskiron.org/en/openwrf which also contain the North Sea tidal current and how to import them and how to make sure you see both the wind and the current.

Sea charts

In qtVlm there are several chart types available: Online charts, Raster charts, Mbtiles charts, Vector charts and CM93 charts. You choose the chart with one of the buttons on the top left in qtVlm.

For example, to download the sea charts of Zeeland, Wadden Sea and Dutch inland waters, you can go to www.vaarweginformatie.nl and there you can download the most recent sea charts of the sailing areas in the Netherlands where you are going to sail. Unzip the file. In qtVlm go to menu > qtVlm – Configuration – tab Charts – tab Rasters and Vectors – button Folders – button Add and paste select the folder with the charts on your computer – click OK. Activate Vector Mode (button top left). See also the instruction video below.

There are of course many more nautical charts available, see for example the list on this link: https://opencpn.org/OpenCPN/info/chartsource.html Some countries provide free nautical charts made by their hydrographic service, such as the Netherlands for the inland waters (see the example above). There are also free or very cheap nautical charts in circulation, such as www.meltemus.com/index.php/en/meltemus-charts I recommend, especially if you are going to use qtVlm for navigation, to ensure up-to-date nautical charts that meet the standard of the International Hydrographic Organization. For this you can contact a good distributor, such as datema.nl

There are two types of digital nautical charts available:

• • RNC Raster Charts, which are “old fashioned” scanned images of original paper nautical charts

• • ENC Vector Maps are smart files that make it possible to show more details when zooming in and less when zooming out

Since you now have a fast internet connection and only want to use qtVlm to practice routing you can use the Online charts. Go to menu “qtVlm -> Configuration > tab Charts > tab Online and enable OpenSeaMap to see at least buoys, wind farms and traffic separation schemes. In the video below I show you how to activate OpenSeaMap.

Barriers

In qtVlm it is possible to create Barriers, to ensure for example that no route is calculated through a wind farm, traffic separation scheme or other dangerous zone. See the video below.

Routing with qtVlm

In the meantime we have done the most important preparations to have a route calculated. We have a polar diagram, set when the engine goes on and off, entered a GRIB file for the wind and a GRIB file for the current, OpenSeaMap active and entered a barrier to ensure that we do not sail straight through the wind farm.

Now we can calculate a route, for example from the Roompotsluis to Harwich. How simple that is, you can see in the video below. You can export this route as a .gpx file to your chartplotter or App on your tablet or smartphone.

Multi-routing

With qtVlm it is possible to generate multiple routings using multi-routing to determine the optimal departure date and time (ETD), based on wind and current. To do this, go to Routings > Options tab and select Multirouting. This is a very useful function because, for example, it can happen that leaving 2 hours later means that the journey will take 5 hours longer. You can see how this works in the video below. Incidentally, in this example there was probably too much wind to leave, but the principle is that the journey time differed considerably depending on the time of departure (approximately 10 hours 54 minutes or 6 hours and 59 minutes, so a difference of about 4 hours).

Pathways

Suppose you want to prepare a trip via a certain waypoint. For example a trip from Roompot, via the approach to Harwich to Dover. In that case you first have to create a Pathway. To do this, go to Create a pathway in the menu and then click on the Append POIs (=waypoints) button to add waypoints by clicking on the map with the mouse. While creating a pathway you can zoom in and out with the buttons at the top of the bar and with the arrow keys on your keyboard you can move the map up, down and from left to right. Then click in the menu create routing and then select Use a Pathway. Once the route has been created you can delete the Pathway. See the video below.

Preset Minimum/Maximum Wind speed/Waves/CAPE

We can also preset a minimum and maximum wind (also gusts). We can also set the maximum wave height and steepness and a maximum value for CAPE. The term CAPE stands for “Convective Available Potential Energy” and indicates the chance of developing thunderstorms. After setting, qtVlm will then try to avoid areas where, for example, the wind is too strong (or too little) or where the waves are too high or too steep or where the CAPE is too high.

Imagine that we plan another trip from Roompot to Harwich after 08:00 on January 7, 2025 and we agree that the Max TWS must remain below 22 knots. If we plan (as above with standard parameters) 5 multi-routes from 08:00 with intervals of 2 hours, we see in the Routes Comparator that the Max TWS is slightly above 22 knots and we do not want that. That is why we are going to set in advance that the MAX TWS must remain below 22 knots. We do this as follows:

• • Create Routing > Disable the setting: Automatic Parameters on the General Settings tab

• • On the Options tab, select Multi-routing with 5 routes with a step of 2 hours again.

• • On the Advanced settings tab, we set 21 for both beating and reaching (then qtVlm uses max 21.99 knots, or a maximum of 22 knots as max TWS)

• • Click OK

You will then see that qtVlm proposes completely different routes than with the Automatic Parameters. For example, the more southern route that avoids areas where the wind blows above 22 knots. The travel time is also longer and the ETA later if you want to avoid the areas with wind above 22 knots. Note that the southern route in this video goes against the direction of traffic, straight through a VSS, which I have to advise against in practice 😉 If it is impossible to sail the route without wind above x number of knots, you will see that immediately, the route is then aborted or you only see zeros in the Routes Comparator. For example if we set max TWS to 15 knots we see this:

Case routing

To conclude this lesson we will create the following case.

Suppose it is Sunday evening 5th January 2025 and you want to prepare a sailing trip from Fowey, where your boat is currently moored, to Dartmouth (South UK). Your boat is a Breehorn 37 with a draft: 1.90m and air draft: 16.40m. The crew consists of yourself and your partner. Since you would rather not sail when the waves and swell are higher than 2.0 metres, the average wind is stronger than 25 knots and you also do not want to arrive in the dark, you do not yet know exactly on which day you will leave (Monday, Tuesday or Wednesday). It is January and around 6 degrees and it feels icy cold. To solve this case you can use the following:

Almanac

You do not yet have the latest version of the Reeds Nautical Almanac and will therefore have to make do with version 2024. If you do not have that Reeds , please see:
https://www.google.it/books/edition/Reeds_Nautical_Almanac_2023/6qKEEAAAQBAJ (Info Dartmouth)
https://www.google.it/books/edition/Reeds_Nautical_Almanac_2024/nTrUEAAAQBAJ (Info Fowey and tidal streams)

In the Netherlands, strangely enough, you don’t see all pages. So set your VPN to Italy, for example. I have also added the most important pages to the case material.

The following data is all in the following folder which you can download below:

DOWNLOAD FILES

Tidal Data

Since you have not yet purchased a new Reeds Almanac, you have downloaded the tide data for Dartmouth, Dover and Plymouth from the Internet.

Sea charts

You have on board the following paper charts, neatly updated with the latest Notices to Mariners:C10 Western English Channel Passage Chart2400 The West Country Chart PackIf you do not have these charts, you can use these links:
https://www.c-map.com/chartexplorer/
https://fishing-app.gpsnauticalcharts.com/i-boating-fishing-web-app/fishing-marine-charts-navigation.html#15.07/50.3326/-4.6327 (set the depth units to meters instead of feet)

GRIB Files

You downloaded these GRIB files on Sunday 5 January 2025 when you made the trip planning:Channel_12km_WRF_WAM_250105-12.grb
Atlantic_Coast_12km_WRF_WAM_250105-00.grb
Plymouth_4km_WRF_WAM_250105-12.grbFor the questions, let’s assume the GRIB file: Channel_12km_WRF_WAM_250105-12.grb.bz2, so that the answers do not differ due to the use of different GRIB files.
By the way, the GRIB files also contain the current.

You may receive a message that the last date of the grib file is earlier than today. The GRIB file cannot be loaded. In that case, you can set the date of your PC back to January 5, 2025. On a Windows PC, for example, you can go to:

• • Settings

• • Time & Language

• • Date & Time

• • Disable: “Set the date and time automatically”.

• • At “Set the date and time manually” click on the Change button

• • Set the time and date to: January 5, 2025 at 5:00 PM.

• • After the exercise, don’t forget to set it back to: “Set the time automatically”

Weather maps

In addition to the GRIB files, you have downloaded the weather maps, the MetOffice Extended Outlook and the weather forecast via Windy.com with various weather models on Sunday 5 January 2025.

If necessary, make the routing plan using the routing form.