OMC Saildrive 15 hp
Is water being expelled with the exhaust? If there isn''t very much you may have a clogged water intake or a worn impeller. These engines also have a thermostat that is accessed by removing the cylinder head, this could also be the problem. You can check to see if its clogged or stuck.
Just because an engine is overheating doesn''t mean "it''s in need of a complete overhaul". And no, its not simple to do yourself. And its a 30 or 35 horsepower OMC motor detuned to 15 hp for durability.
The Honda 280 looks like a great rig but is pricey. A good choice for a smaller (up to around 28 feet I would think) sailboat over a heavy diesel.