One that floats :-)
I would assume the transmit ability would be important and perhaps the ability to set the range (i.e. crank it up when you really need it). Also the type and ability of the battery..
Basics:
http://www.marineelectronicsjournal.com/how_to_buy.cgi?article_id=133Ratings:
http://www.powerboat-reports.com/sample/vhf.htmlWater "proofness"
* JIS-0 -- no special degree of water protection
* JIS-1 -- resistant to vertically dropping water
* JIS-2 -- resistant to dripping water at an angle of up to 15 degrees from vertical
* JIS-3 -- resistant to falling rain at an angle of up to 60 degrees
* JIS-4 -- resistant to splashing water from any direction ("splash resistant")
* JIS-5 -- resistant to direct jetting water ("jet resistant")
* JIS-6 -- sealed against direct jetting water ("watertight")
* JIS-7 -- sealed against water incursion in one meter (three feet, three inches) of water for 30 minutes ("immersion resistant" or "submersible")
* JIS-8 -- sealed against continuous submersion under pressure specified by the manufacturer ("submersible" or "submersible plus")
Read more at Suite101: Submersible VHF Radio: Understanding Waterproof Ratings
http://boats.suite101.com/article.cfm/su...s#ixzz0v8e8iGjO