I don't think any bubble pack radios are going to give you that kind of
distance over water.

If price isn't an issue I'd get a couple of Yaesu VX-6s and mod 'em to xmit
on the GMRS bands. (flame shield: ON)

Otherwise you're going to have to rig an antenna on your mast or something.
A couple of watts from approx 8 feet above the water isn't going to get you
3-4 miles.