Re: Good for sea water?
You still won't say what kind of boat you have, so we can't address this completely. I know your motor and your intended waters. Now that you mention "lakes" I assume you are coming from the west shore and not the Eastern. I am relieved that you find it "unwise" but you are still tempted.
I grew up in this Navy town and can tell you, being in the Navy does not make you a boater. I know brass who can't cleat a line, run an outboard, or swim. My uncle was in the Navy; he learned to swim for the first time when his ship was sunk.
Kayaks can be more seaworthy and stable than motor boats their size and larger, and even canoes. Don't use them as your standard.
A friend of mine when he was about 13 crossed the 20 mile mouth of the Chesapeake Bay (and returned) in a 13' whaler with a 25 or so. The fact that "it can be done" does not make it a good idea. He also got in big trouble when his parents found out!! (busted by sand dollars he found on the other side).
So if you want to keep "asking around", ask here, but tell us what boat you have!!!