Lat and Long Notation...................whats best

NormanS said:
Yes, a friend "found" an uncharted, and previously unknown rock, 0.5m below LAT, and sent me its position. If I'd known that the datum that he was using was WGB84, while I was on OSGB36, I would have known precisely where the rock was. The position given was halfway up the hillside.:D
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Get the datum right and then decide which part of the boat you are going to hit with.:) Distance from GPS antenna to front of keels on my boat is about 0.003 nautical miles Or about .005 minutes if I'm heading east or west.:o Makes positions to three decimal places a bit meaningless and those to two places somewhat suspect.
 
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DJE said:
And can anyone think of a situation where it might be appropriate to give a boat's position to more than one decimal place? (i.e. 1/10th of a minute or about 200 yards.) All too often you hear people giving three decimal places ove the vhf! Even MCA navigation warnings often give the location of a hazard to two decimal places and then ask for a wide berth.
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I've motored right into Cherbourg in very thick fog.
From the loudness of the horn, I think I was closer than 200 yds...
I checked very carefully that that chart datum was correct with that on the GPS.

I think there is a good principle of writing down exactly what the GPS tells you.
A common source of errors is from rounding up 55.999 for example. If somebody received that as 55minutes, that's a mile out.
 
DJE said:
Get the datum right and then decide which part of the boat you are going to hit with.:) Distance from GPS antenna to front of keels on my boat is about 0.003 nautical miles Or about .005 minutes if I'm heading north or south.:o Makes positions to three decimal places a bit meaningless and those to two places somewhat suspect.
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Quite right. I always thought that the worst possible place for siting a GPS antenna was on the taffrail/pushpit (delete as desired). At least now, most plotters etc have built in antennae.
In the previous case that I mentioned, with the "new" rock, my friend had a plotter, so his electronic chart was WSG84. I had a GPS, but was using paper charts, which for the area concerned, were all based on OSGB36.
 
nigelmercier said:
...

You say: " ... degrees, two-two minutes decimal fife-fife ..."

...
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I also think this is probably ok, but why is it better than " ... degrees, two-two decimal fife-fife minutes..."?

I care only that it be understood and imagine myself saying it to someone with very poor or non-existent English, used to only to the proword vocabulary.
 
>We are expected to use the same concept/standards when writing and speaking of Degrees of Bearing i.e. 'Zero Three Four Degrees' rather than 'Thirty Four'. Every now and then, it really matters.... Especially when those whose first language is not English are trying to write down the details of a crackly Emergency Message.

Agree. Zero or zero zero must be used.
 
NormanS said:
Quite right. I always thought that the worst possible place for siting a GPS antenna was on the taffrail/pushpit (delete as desired). At least now, most plotters etc have built in antennae.
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Sorry I'm baffled by that one. On the pushpit it has a clear view of the sky but is low enough not to be affected by reflected ground waves. Seems like the ideal spot to me. Are you suggesting that I put it nearer the keels and then rely on a single source of position information for an accuracy of a few yards?
 
Basically it is all down to protocol, if you have a foreign speaker whose first language is not English then using a standard method to give the position helps with any translation and helps avoid any misunderstanding. (Much the same with the fairly rigid Mayday message structure, although in a panic things get forgotten).

The 3 decimal figures for a position are basically a direct readout of a GPS set and in an emergency situation someone is quite likely to read out the lot. I remember a sort of mayday by one hysterical woman whose husband had gone off in the rubber dinghy and lost his oars or engine and was being swept into the Solent. She was very distressed and when CG asked for her position she gave them the 3 digit GPS reading. She got the reply "Ah yes madam, telling us you were just off Cowes jetty would have been fine." To be fair to CG they did sort her and her hubbie out pronto and soothed her down.
 
DJE said:
Sorry I'm baffled by that one. On the pushpit it has a clear view of the sky but is low enough not to be affected by reflected ground waves. Seems like the ideal spot to me. Are you suggesting that I put it nearer the keels and then rely on a single source of position information for an accuracy of a few yards?
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I'm certainly not suggesting that you fit the antenna anywhere "nearer the keels". Most plotters now seem to manage pretty well with the antenna built into the set.
Say you are trying to follow a tricky track, or approach an accurate Way Point, on your plotter, with the GPS antenna is mounted right aft. Suppose the plotter shows the track or way point slightly to starboard, so which way do you turn? If you turn to starboard, your stern, and the antenna actually moves to port, further away from the way point.[. Much better to have the antenna closer to amidships, IMHO.
 
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