Hey Gasman,
I was using the Uniden uh039P. These are small hand held UHF radios (twin Pack) with rechargeables about $140 with chargers etc
There is also a cheaper and smaller set available from Dick Smith and Tandy which is a 4 pack which uses AAA's for $100. You can run everyone on the same channel or use seperate channels if you prefer. 3+km range and 40 channels to choose from. Pretty good and quite cheap. I would put the Aquapac leash around your neck and place the radio down your wettie. This is any easy way to keep in contact with your buddies on the water. I think there are waterproof UHF radios, but they are REEEAAALLLYY Expensive!
We placed the Unidens into Aquapacks and then attached the Aquapac to the side of a Gath helmet with a bungee and cable tie setup. Although it worked reasonably well and made teaching heaps more efficient, we have opted to upgrade to the more expensive and very professional Headzone Coaching system this year in line with our total school upgrade.
The Headzone system uses proper impact resistant helmets with built in water proof battery and receivers with stereo speakers. This results in clearer communication and better head protection whilst providing greater comfort levels for our students.
Hope this helps. Good winds,