Navigation Aids Part II

On Clarionet there is a switch marked Decca which nowadays ensures the bilge pump runs in reverse (a story for another day!). Long before I ever stepped foot in a yacht, Decca was as hightech a navigation aid as they come. Prior to that most leisure sailors including offshore racers, relied heavily on their navigator’s calculations of course to steer and if the mark or destination was upwind, on the strategic decisions of when to tack. Always aim to be both upwind and uptide of your destination!

On approaching the French coast the crew would lookout for recognisable signs that they were where they thought they should be. Even as recently as a dozen years ago despite the advent of GPS I can recall peering through the fog at the wall off Cherbourg wondering whether we were at the easternmost section or the central part. The skipper decided not to risk it and rather than turn to port in search of the eastern entrance turned to starboard. There followed a long uncomfortable motor into wind and tide until we eventually located what turned out to be the western entrance but better that than pile into the rocks to the east of the other entrance.

All of my sailing has been done with a GPS to hand ensuring with a few exceptions like the infamous incident when Temptress alarmingly appeared to be flying above Dartmoor for an hour or so, we know exactly what our longitude and latitude are. Since we bought Temptress, a chart plotter through electronic wizardry displays the boat and its track through the water on an electronic version of Her Majesty’s Admiralty’s charts.

Temptress’ original green and black chart plotter gave up the ghost ages ago. So for the last few years we’ve pressed into service the boat laptop as a subsitute, using a variety of navigation software to plan routes and record our progress. Our faithful Toshiba almost reached its eleventh birthday despite a life spent entirely in a salt-filled, damp environment, a testament to Japanese manufacturing both in terms of longevity and in terms of ability to survive such an environment. This summer it was time to source replacement technology. The laptop part was fairly straightforward – low energy consumption dictated by long periods on 12 volt batteries means no unecessary peripherals so a netbook is ideal and easily fits the space above the chart table. Kevin sourced a little Inspiron Duo at cost from his colleagues at Dell whilst I as Chief Navigator and software “guru” was tasked with finding our next navigation program, a task I approached with relish as its ages since I’ve had to review any software market and even better not to be doing it in a professional capacity! So what was I looking for:

What chart formats are supported and how much of the world do they cover?
There are almost as many chart formats as there are navigation software publishers. There are pros and cons of each which I won’t bore you with here. My main concern is coverage for our potential sailing area with plans for a future including sailing around Scotland then onwards towards The Falklands and South Africa before turning east (or even west) towards New Zealand. And the cost of future purchases must be sustainable on a limited income. In some countries like the USA charts are virtually free, in others the authority concerned keeps their production, sale and updates on a commercial footing (HM’s Hydrographer being the chief example). A program that suppports as wide a range of formats as possible is to therefore be preferred to ensure best coverage at least cost.

Does it contain a tidal database and what source is this?
This point is related to the next so I’ll just mention that using a US tidal database to calculate predicted tidal heights and times for UK ports can lead to some differences due to diffiering input data and algorithms used. In turn this can catch out the unwary sailor expecting it to be highwater with 3m above chart datum on their arrival at a port. Knowing the underlying source and its potential accuracy of predictions for a region can help avoid running aground or worse.
Will it perform Course To Steer (CTS) calculations?
GPS navigation is point to point ie the GPS determines the angle and distance in a straight line from your starting position to your next waypoint. This though fails to take into account the impact of six hours of east going springtide off Cherbourg which may help or seriously hinder your voyage across the Channel. If you can work out when to leave and what course to steer to ensure that the tide helps the boat along rather than fight it then the voyage will be faster and you’ll potentially cover less ground. It’s all a matter of vectors for those of you mathematically inclined but rather than use the Admiralty Tidal Atlas plus simple sums thrown in with a bit of trigonometry, it’s faster to use a computer to calculate all the possibilities and provide you with the best time to leave and the CTS. This all assumes too that the wind is in your favour (see below).

Does it display info from the cockpit instruments?
Nothing is more irritating than to have to heave yourself out of the navigators seat to check the trip or the wind in order to record it in the log especially if as cook/navigator you have yet to put your oilies on! On Clarionet too, the helmsman usually will complain that you are either in the way or the red light coming up the companionway is destroying their night vision. So having everything at hand at the chart table makes it much faster to record the necessary in the log. BTW on boats over 14m in length SOLA requires that a log be kept except when in waters like the Solent so on Temptress this means we have to record even short hops to Brighton.

Can it overlay weather data? 
Wind forecasts form an essential part of the navigators toolkit ensuring that the boat stays safe as well as sails efficiently. To see the wind overlaid on the chart and see what you can expect some many miles down the track is useful especially in conjunction with tidal data when deciding when to tack or whether to seek shelter in a closer port.
Ditto AIS
AIS stands for Automatic Identification System which in this case means ships not aircraft (it’s not a hugely intuitive term). Info from transmitting boats, ie all commercial shipping and some leisure boats, includes useful items such as course and speed as well as interesting stuff like last port, next port and cargo. The real interest to the average sailor in the middle of an ocean is will it hit me? By overlaying the AIS data on the chart with our track, the closest point of approach can be calculated by the software and not some addled navigator. Useful especially when the vessel is somewhere over the horizon or lost in fog and making 25 or more knots (nautical miles per hour) in your general direction. The horizon is usually about 20 nautical miles from the deck so a boat doing this sort of speed can be on you in less than an hour giving little room for manouevering by a yacht doing 6 knots or less.

Similar to AIS, this is data from the radar which enables collision avoidance, if the radar can be configured correctly, a problem we have yet to resolve on Temptress.

Can it calculate Great Circle routes?
When sailing across oceans the Mercator projection commonly used in local maps or charts becomes inaccurate because the sphere has been flattened to make the the map creators job easier. The great distances involved mean in turn that a straight line between two points on the chart is no longer the shortest distance, a circular route roughly following the Earth’s curvature is. Software that can automatically create this arc between two points on the Earths surface is useful though not essential as long as the navigator is aware of the issue.

All this at what price?
The average cruising sailor, and we will be no exception, has a very small budget. Savings are for retirement and our potential future income small just covering day to day expenses with a little bit to spare so we wouldn’t want to have to pay large sums to buy charts for new areas nor for chart, tidal or software updates. Some charting packages are aimed at the professional user, some at the local (mainly USA or UK ) sailor. I was looking for a program that is somewhere in the middle – affordable intially but easy on the purse later (even if we have to forego updates) whilst providing the features and chart coverage we might require. As with many things on a boat there are bound to be some compromises.
After looking at a round dozen of software products, some were discounted quickly on coverage being either too USA or too UK oriented, and some on price leaving a handful of contenders: Software on Board (SOB) from Digiboat, SeaPro from Euronav, and Maxsea. The first was discounted as it did not calculate a CTS and help is provided in .PDF format, not the easiest thing to have to look through when at sea in a tight spot plus the interface was hard to use. The latter Maxsea for not having CTS or Great Circle unless you purchase an expensive add on, and a user interface that is anything but intutitive especially at sea (I’ve used this one on other boats). That just left the reviewer with EuroNav’s Seapro, already tried and tested on board Temptress in rough and smooth conditions. I did objectively try to find another tool as I love new gadgets but this time it seems I failed! Sea Pro, even allowing for our familiarity with its slightly non-Windows standard mouse handling, installs and finds your instruments without too much configuring of com ports, it has a fairly affordable chart coverage of most of the world at the level of detail we’d require, has almost all the features we were looking for and the UI is easy to use at sea. All in all a close race but won on some key features and the price was right.

It does leave us with plotting great circle routes by hand but I’m sure it’ll be a useful skill to acquire. An honourable mention should also go to Navsim’s SailCruiser which had one of the best user interfaces I’ve come across in PC software (intuitive and easy to reach the things you need at sea) plus a unique tool for calculating time to go based on wind angle and tacks required. It was a just little too USA oriented for my liking.

Below is a summary of the findings (sourced from software publishers own websites, demo copies and reviews). It is as accurate as I could get at the time of publishing this survey but I bear no responsibility for an inaccuracies that might have crept in. In fact if any publisher of navigation software would like to provide their product a fuller trial I’d be happy to hear from them:

Product  Price  Chart Types Tidal Data CTS GPS Inst AIS ARPA GRIB Gt Circ
OpenCPN  £ FOC   1,2,7 N N Y Y Y N N N
Nuno  £120.00 NA N N Y N N N N N
Neptune Planner +  £195.00 NA Y Y Y N Y N Y N
Maptech  £256.00 4,2 Y N Y Y Y Y Y N
SOBv9 (Digiboat)  £302.00 1 Y N Y Y Y Y Y Y
SeaPro  £360.00 2,6,7 Y (£39.95) Y Y Y Y Y Y N*
Maxsea  £420.00 5 Y Y* Y Y Y ? Y Y*
Seatrack UK  £480.00 1,4,9 Y Y Y N Y N Y* N
Raymarine RNS 6.2  £512.00 1,2,9 Y Y* Y Y Y Y Y N
Nobletec Admiral  £850.00 1,10 Y Y Y Y Y Y Y Y*
Rosepoint  $399  2,3,4,6 Y N Y Y Y Y Y N
NavSim Sailcruiser  $549  1,2,3,4,7,8 Y N Y Y Y Y Y N

Happy to supply my spreadsheet summary to anyone who’d like it. It includes some extra notes on each product, indicated mostly by the asterisks above but left out here to avoid an even longer blog! I would also mention as a retired software product manager that many of the above listed websites leave a lot to be desired in terms of design and navigation, some will try the patience of any who venture there, you have been warned!

Chart Types Key:

1  Cmap  NT+, MAX or MAX Pro (CM93)
2  BSB  (Raster)

3  Softchart 

4  Maptech 

5  Mapmedia 


7  S57 vector 

8  Geotiff 

9  Navionics 

10  NV Charts  Mostly Caribbean