Given that you want to use it in the Intercoastal, a jet drive would be ideal.
You should be able to couple a hosepipe to the cooling intake somehow to flush with fresh water, and even if you can't (though it'd be a poor design that you couldnt') it should be easy enough to add a couple of stopcocks to make it possible.
How big a boat are you looking at?
Need spares,consoles,consumables,hire,training or even a new boat?
Please click HERE
and support our Trade Members.
Join up as a Trade member
or Supporter HERE