Well, all engines are cooled by the water the boat is operated in.
The difference is if that water goes through the engine block or if it's antifreeze.
What you'd want to look for is 'closed loop cooling' if that is a concern where you boat.
Look for an antifreeze bottle on the engine block, or near it. Also there is usually a heat exchanger mounted top center front of the engine. Fairly hard to miss. (I also assumed you were talking about I/Os)
Keep in mind that the engine is just one thing that needs cooled. Often times the exhaust, oil coolers, steering coolers still end using 'raw water' cooling. Still better than the block being exposed to salt water, but still have parts exposed. just FYI.
