G.P.S. FAILURES

[mystymike]

Hello.
I have read several articles and passage accounts over the past year in which the G.P.S. unit has failed. I was reading PBO issue No.441 this morning on "Our First Atlantic Crossing", where the G.P.S. failed after fifty miles due to active antenna failure and this is on a new yacht.
How reliable are G.P.S. instruments and how many should a cruiser carry?

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[gjgm]

brings back the whole reason for the requirement to carry charts and the necessity to keep a log. I doubt Garmin et al are going to publish gps failure rates, but judging how much gps has invaded different walks of life recently, i'd imagine that they are exceptionally reliable. For any liferaft, I d assume people have a handheld. That gives two gps....but remember not long ago sailors managed with none....funny what becomes essential

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[Skyva_2]

In 8 years our fixed unit failed once and the aerial once. In both cases the manufacturer (Garmin) replaced for free. My handheld has never failed (now watch it collapse tomorrow!)

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[Capt_Marlinspike]

About 8 years ago I did some research for a UK police force on the availability, reliability and maintainability of GPS. They were looking at fitting it in their patrol vehicles. Even at that time the reliability of the equipment was impressive. I looked at 3 units Trimble, Garmin and one supplied by MoD (do not rememeber who made it). For the report we did testing at a specialist lab and also had data supplied by the manufacturers. All the units exceeded the requirements and in most respects were better than the very expensive custom radios that they were going to use to transmit location data back to control.
I do not have the report any more but from memory the best unit was the Trimble, second Garmin and third the MoD unit. Even the MoD unit was only expected to have 1 failure in 3 years.
I have a fixed GPS and a handheld. If they both fail then then gods of chance are having a game with me that there is no way to win!

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[Stork_III]

You need one or three. If two, and they give different positions, which is correct. with three chances are two will correspond.

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[bob_tyler]

Different positions? I doubt it. One is probably set to one standard, WGS84 or whatever, and the other to a different one.

Alternatively one shows degrees, minutes and seconds and the other degrees, minutes and hundredths of a minute. It just looks different!

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[Oldhand]

GPS receivers rarely give the same position, for a start you can't have 2 antennas in the same position and as a result on a practical installation, the unobstructed view of the constellation is likely to be different. Add to that differences in hardware and software etc...

Anyway, I carry 3. A fixed mount unit with its own antenna, which can also use the input from a second active antenna "sensor" in "repeater" mode. That covers an antenna failure. I then have a handheld as a totally independant unit which can also be kept in the liferaft grab-bag along with a portable VHF.

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[roger]

For the long distance sailor the advice I like is to keep one GPS in a steel box with extra batteries in case of lightning strike

<hr width=100% size=1>Roger

 

[Evadne]

gps in liferaft?

I've often wondered why people would buy a gps especially to put into a liferaft. Unless you have an iridium phone as well, you can't tell anyone out of line of sight or more than 5 miles away (hand-held vhf range) your position, and unless you have some sails (in which case it is a lifeboat) you don't need it to navigate, because you are going slowly downwind whether you like it or not.

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[chriscallender]

Re: gps in liferaft?

S'pose it depends where you are - out in the deep blue yonder what you say is probably true - but for example in the raft in fog in the English Channel, a mayday on a handheld would probably be answered pretty quickly and a GPS position would certainly help them find you rather quicker than they would otherwise.

However even without a position as you say, you would be found in fog once the lifeboat arrived with radar and direction finding on your VHF transmission.... as long as your raft wasn't run down by any of the shipping in the meantime.


Chris

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[dickh]

I have two - a very old Magellan Nav6 with 6 satellites(an early v large portable) which is wired up and is the main boat unit and a new Garmin map76. I had them on the table last night and compared them, and they were remarkably consistent, certainly the difference you wouldn't be able to plot on a normal chart.

<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[Haddock]

It's the old chestnut - "use all available means" when navigating. Never rely on one method of fixing position. Sure GPS has made it all too easy. But you are only fooling yourself if you do not learn and routinely practice the older non-electronic methods.



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[Birdseye]

Giving a probability answer is meaningless, since there is no decision you can take based on it. The only answer to your question is "way more reliable than the alternatives". So to my mind, it makes more sense to have a second GPS than it does to mess around with old technology like the sextant. And for the price of a decent sextant and reference books, you can buy maybe 5 spare handheld GPS sets.

A sextant depends on visibility of heavenly bodies, a decent timepiece and your correct workings out even to get you as close as a mile or so. The weather's less reliable than the GPS, so are my workings out and the timepiece is probably similar in reliability. Multiply all those probabilities together and you get a much worse figure than a gps.

<hr width=100% size=1>this post is a personal opinion, and you should not base your actions on it.