The article by Mark Thome that Sim mentioned is worth the read. It tells you everything you ever wanted to know (and then some) about using your GPS while diving. I have used the technique outlined quite effectively many times and it works great.
However, I think where some folks are confused (especially us geeks who all KNOW that you can't use GPS underwater, right??) is that it really covers a specific type of diving. That is, we use it when beach diving or drifting long distances is relatively shallow water. Here in FL (like most places) you have to drag a dive float and flag, I keep my Garmin eTrex clipped on me (on a finger spool) in a simple clear Pelican model 1010 box that floats (never hand an issue with flooding BTW, even though the manufacturer does not recommend submerging the box). When I want to mark a new feature (like a lobster hole?) I usually modify the outlined procedure by using a finger spool to simply "shoot the GPS" just like shooting a bag. Give it a minute to settle in and get a signal... then reel it back down (in 20 feet of water or so, unless there is a ridiculous current the unit stays "close enough" overhead that I get a "close enough" reading). Remember, the unit does not get a signal underwater but will show that last know good spot from the surface when you reel it back in. Write the numbers on your slate and get back to bagging lobster. It's that simple.
This also works great when we are kayaking. I leave the auto-tracking feature on and take the unit with me in the water - "shoot" the unit every now and then. When I get back to the computer on land and download the track I get an outline of exactly where we went, the underwater portion of the trip is just a dotted line instead of a solid line. Throw that into Google Earth and you are in "Map Geek Heaven"!
Understand that this would not be practical on a 70fsw wreck dive, but since all the wrecks we dive are well known anyway there is no real need to bring the GPS along.
Are you tracking me? If all this sounds complicated, let me know and I'll be happy throw together a "GPS Diver" Specialty Course for you and go over everything from start to finish.
However, I think where some folks are confused (especially us geeks who all KNOW that you can't use GPS underwater, right??) is that it really covers a specific type of diving. That is, we use it when beach diving or drifting long distances is relatively shallow water. Here in FL (like most places) you have to drag a dive float and flag, I keep my Garmin eTrex clipped on me (on a finger spool) in a simple clear Pelican model 1010 box that floats (never hand an issue with flooding BTW, even though the manufacturer does not recommend submerging the box). When I want to mark a new feature (like a lobster hole?) I usually modify the outlined procedure by using a finger spool to simply "shoot the GPS" just like shooting a bag. Give it a minute to settle in and get a signal... then reel it back down (in 20 feet of water or so, unless there is a ridiculous current the unit stays "close enough" overhead that I get a "close enough" reading). Remember, the unit does not get a signal underwater but will show that last know good spot from the surface when you reel it back in. Write the numbers on your slate and get back to bagging lobster. It's that simple.
This also works great when we are kayaking. I leave the auto-tracking feature on and take the unit with me in the water - "shoot" the unit every now and then. When I get back to the computer on land and download the track I get an outline of exactly where we went, the underwater portion of the trip is just a dotted line instead of a solid line. Throw that into Google Earth and you are in "Map Geek Heaven"!
Understand that this would not be practical on a 70fsw wreck dive, but since all the wrecks we dive are well known anyway there is no real need to bring the GPS along.
Are you tracking me? If all this sounds complicated, let me know and I'll be happy throw together a "GPS Diver" Specialty Course for you and go over everything from start to finish.
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