If you want a boating radio for safety purposes, get a proper VHF marine radio. Figure it this way - you didn't get the boat for diddly squat, so why get a radio on which your life may depend for the same amount?
Who's to say the boat owner doesn't already have a marine band radio? Besides, the Marine Band doesn't allow communications with, say, your family waiting for you at your home on the shoreline. Wouldn't it be wise to stay legal?