My wife shaves her legs sitting on the side of the inflatable in salt water. Try using hair conditioner rather than shave cream.. works well and doesn't leave suds on the water.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)