…and a phone to steer her by

Mobiles have had a bad press as navigational tools, but if I were forced to choose one single piece of electronics to take to sea it would be my phone. That’s not a popular view among professionals.

Instructors and rescue services learn of many cases where boat owners, especially of powerful motor yachts and RIBs, set off for the open sea with nothing beyond a chart app on a mobile phone, and no knowledge of the underlying skills needed to navigate safely. For the Royal Yachting Association, mobiles are well down the list of recommended priorities, because of the risk that they will be used badly.

This view is reflected in the Royal Institute of Navigation’s book on electronic navigation for small craft#, which was written jointly with the RYA and the coastguard and published in December 2020. Using GNSS* as the new generic term for satellite systems, the book says:

“Increasingly mobile devices have built in GNSS receivers. In addition, many use a combination of GNSS with mobile phone base stations, Wi-Fi, Bluetooth and other sensors to generate a ‘blended’ position. Such devices are programmed to prioritise continuous position availability over accuracy. If GNSS is lost or degraded, the position calculation is derived from the other, less accurate, sensors.

At sea, mobile phone positioning uncertainty will typically be several hundred meters or more, which may be enough to put us into danger.” 

I was worried and puzzled when I read that final statement, which I’ve put in bold type, but I am now sure it is simply wrong. Even I, a complete amateur in this field, have been aware for years that my mobile tracks my Ordnance Survey maps accurately over long upland walks well outside any mobile and wifi signal, relying entirely on satellites. So why wouldn’t it be just as accurate at sea, where there are no obstructions to signals from above and no mountains nearby? I’ve often consulted the phone for position information when on our boat.

So the new book prompted me to check the accuracy of my mobiles on land and sea more rigorously, in case I was taking unnecessary risks. I ended up confirming my original impression, which was that the satellite navigation function in my 6 month old and my five year old Samsung mobile phones is impressively accurate and reliable, and comparable with a dedicated chartplotter. So I think the statement in the 2020 electronic navigation book must be many years out of date.

Accurate and cheap satellite navigation chips for all kinds of consumer electronics have become vital commercially, and big investments have been made to improve them in recent years. The great long-term incentive is the self-drive vehicle, but short term it has a lot to do with advertising. There is money to be made by big companies in knowing exactly where you are.

Confusion about accuracy is generated by the phones themselves. My phone is always nagging me to switch to the high accuracy setting to allow wifi, bluetooth and phone mast tracking, and it says I won’t get a good service without them. The language implies you only get an accurate position if these other aids to triangulation are helping your satellite chip.

In fact, that’s highly misleading except in certain well defined circumstances, such as indoors and among tall buildings or other sources of interference and satellite signal reflection. Research is under way to correct even those inaccuracies –  there’s a lecture on the RIN website about new satnav signal processing software which is claimed to achieve good accuracy even in cities and which its creators expect to be available on mobiles in the next few years. 

Behind this pressure to switch on the high accuracy setting there seems to be a money-making motive. Wi-fi location tells Google, everyone else in similar information harvesting businesses and their vast armies of advertisers which shop, restaurant or other facility you are in. And how else does Google get the data on the occupancy of restaurants at different times, other than by persuading mobile phone users to keep their “high accuracy” navigation function switched on, so they can be tracked indoors by the location of the nearest wifi hub?

What I confirmed with my own checks was that, away from tall buildings, the two mobiles I have owned recently both show a radius of accuracy on satellite navigation alone of less than 10 metres and most of the time 3 to 6 metres. That accuracy level is reliable over long periods. Except among tall buildings or indoors, using the high accuracy setting does not improve the fix at all, even where I know wifi hubs and phone masts are nearby. At sea, the accuracy levels and reliability of fixes are excellent, just as they are on upland walks. For how I checked the satellite accuracy of my two mobiles, one 5 years old and one bought in April 2021, see ‘how to check satellite accuracy on phones.

My tests are not worldwide or professionally rigorous. I do not know how my phones would perform in the Himalayas or among mountainous waves. But I do know that my phone’s satellite navigation is good in the places I frequent.

It is not just the chips and the software that are improving, but also the number of usable satellites. Modern mobiles have access to the Russian, Chinese and EU satellite systems, so there are far more satellites in view at any one time than when phones, and indeed older chartplotters, had to rely on the American GPS.

Why would I choose to have my mobile on board in the unlikely event that it was my only instrument? The one fundamental fact I want to know above all else is where I am. I’m old enough to remember the days when you were never quite sure where you were until you got there. Crossing the English Channel in bad visibility in a boat doing 5 knots with a varying  cross tide of up to 3 knots could leave you uncertain of your landfall within five or even 7 miles if you were unlucky, or were thrown about too much to steer accurately. Radio beacons, the best electronic aid, were difficult to use in a bouncing small boat, and gave inaccurate fixes.

 So it is hard to exaggerate the enormous pleasure and relief that our first proper electronic instrument brought us in the 1980s – a Decca Navigator, which actually told us where we were to 50 metres. That accurate position seemed like a miracle. Everything else we now get from electronic navigation – way points, route planning, tracking, course over ground, electronic charts, overlaid displays  – is secondary to that magical fact of knowing a position. And that’s what a mobile phone can tell you accurately if you have no other electronics with you.

 It goes without saying that you’ll have to have paper charts to use the information in those circumstances, which is why heading out to sea in a powerboat with nothing but a phone loaded with a Navionics chart is a very bad idea indeed, as the RYA and coastguard are absolutely right to insist. Carrying some paper charts, if only as backup to electronic charts, remains important. And off course, I’m not really suggesting I’d go to sea with only a mobile when other electronics are available, because there is so much that is useful in many different ways.

However, I do think that, rather than dismiss mobiles as too inaccurate for navigation, it would be better to advise people positively on how and when to use them safely at sea, and that means setting out their pluses and minuses in a constructive way instead of condemning them as inaccurate. Here is my list:

Pluses

  • Accurate position finding anywhere in the world, giving a last ditch backup if all else fails.
  • Easily rechargeable for days on end with a few small, cheap booster batteries on board, useful if boat electrics fail.
  • During ordinary navigation, when you are away from the main chart plotter you can quickly consult a phone for position, course and speed over ground (particularly good for saving the energy of a skipper resting on a bunk!)
  • Many modern mobiles are water resistant, typically for half an hour submerged to 1.5 metres, so can be kept in an oilskin pocket in wet weather and would not be ruined by a scramble into a liferaft.
  • Close inshore: easy access to weather and other information through the phone network.
  • Offshore: much useful data can be downloaded to the phone and taken with you, including the weather forecast at the time you leave. Tide and current apps can be downloaded with several years worth of data.
  • On shore away from the boat, and in harbour: mobiles with electronic chart apps are useful for route planning – you can switch quickly between charts, weather and tide information to get an overview.
  • Charts on mobiles can be updated whenever you are connected to a phone network.
  • Mobiles can be protected easily – there are plenty of impact resistant cases designed for eg building site work which can make it probably the most physically robust instrument on board.
  • When near shore you can talk directly to home and to the emergency services.

And the minuses:

  • Small screen.
  • Not readable in sunlight.
  • The touch screen needs to be dry to operate.
  • Charts on mobiles do not have many of the useful extra functions available on software for tablets, laptops and dedicated plotters.
  • Unreliability if exposed in cold weather
  • Mobiles sometimes fail unexpectedly (though that applies to much other electronics, and on a yacht all the crew are likely to bring their own mobiles).

There are other factors that can cause reliability problems for electronic navigation (see Pass Your Yachtmaster, which has a brief summary) but as far as I know these apply equally to a chartplotter or tablet.

For a detailed account of how I checked my mobile’s accuracy readings, see ‘how to check satellite accuracy on phones’.

#‘Electronic Navigations Systems, guidance for safe use on pleasure vessels,’ available as an online book on the Royal Institute of Navigation website: rin.org.uk.

* GNSS means Global Navigation Satellite System, which embraces all four worldwide systems now available.

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