Yes, it is a sailboat, and yes, it moves before the wind. The most useful sail in your inventory is nonetheless likely to be your iron jib. An engine is of course handy when the wind dies. It is even more useful when entering or leaving port, when anchoring, when hoisting or lowering sails, and when heading upwind. It is almost essential for rescuing a man overboard.
Almost all sailboat engines are diesels because these avoid the danger posed by gasoline and its fumes. A marinized diesel engine is basically an automotive engine or electrical generator engine fitted with a marine cooling system and perhaps other accessories, such as the alternator, that were modified for a marine environment.
Optimal
size
Modern marine diesels run at lower RPM and produce more torque than their earlier counterparts. An auxiliary engine made recently should therefore be of a size that offers about 3 HP for every ton of displacement. More is not necessarily better, as fuel economy will suffer. Less is bad because the boat might not move to windward in a gale.Life
expectancy
Diesel engines like to run long, hard, and often (but not too often). A marine diesel that is started only once daily and run at 90% of full throttle all day might last for many thousands of hours. Running the engine less often, or at low RPM, or for only short periods of time will greatly reduce this life expectancy.The main enemy of marine diesels is not wear, but rather, corrosion, particularly in the cooling system where it leads to overheating. Running the engine long and hard will counteract the effects of corrosion. A 10-year old engine with 5,000 hours on it is therefore often in better condition than the same 10-year old engine with only 500 hours.
Exhaust
smoke
Exhaust can diagnose some diesel engine problems. Black smoke contains carbon soot from partial combustion caused by lack of air (check filter, air intake or exhaust restriction, engine room ventilation), too heavy a load (fouled prop or bottom, engine slipped out of alignment), or too much fuel from a bad injector.Blue-tinged smoke signals that oil is being burned as a consequence of worn parts in the engine or overfilling with oil.
White smoke that rises and quickly dissipates is harmless water vapor (ie, steam). White smoke that hangs low near the water and fails to dissipate is unburned fuel (bad injector or else worn value seals or guides, rings, or cylinders). White smoke is normal, for some engines, until they warm up and also on cold, humid days when you can see your own breath.
An engine that has idled for a long time will be smoky under load until the cold stacking fuel deposits burn off. Water in the fuel makes steam or white smoke. Low quality fuel burns inefficiently and makes black smoke.