I have wondered just how deep a GPS receiver would work, if in a watertight case. My suspicion is, with as low as the signals from GPS satellites are (we use a GPS satellite simulator at work, and the signal level is far too low to measure with any of our standard test equipment), that it wouldn't take more than a few inches of water to attenuate/reflect too much signal for the receiver to work.
The next time I go diving, I might just have to pick up a clear, waterproof case and see how soon the receiver loses lock underwater.
One thing I decided to carry in my BC is a small parafoil kite with streamer tails, along with the SMB. If there is enough breeze to kick up some decent swells, there should be enough breeze to loft a kite up over the waves, and it would be visible much farther than an SMB would be. Parafoils use no spars, and being made out of sailcloth, aren't affected by submersion in water.
Just as an amusing aside, anyone else here think of all the Verizon "Dead Zone" commercials? I can picture a spoof of one of those commercials, with two divers surfacing far away from the boat. The one diver pulls his cell phone from the waterproof case, only to be told by the other, "Are you crazy? This is a dead zone! You can't make a call from here!"
The other diver says, "I've got Verizon." The camera view pulls back to show that whole huge crowd of Verizon workers floating behind them, and the waterlogged spokesman saying, "You're good."
Then the Jaws theme starts playing, and Verizon workers start disappearing one by one...
