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.
Injection
Type
A diesel’s injection can be direct, where fuel is sprayed into the combustion chamber, or indirect, where fuel enters a small pre-combustion chamber and is mixed with air before entering the main chamber. Indirect injection is notably quieter, whereas direct injection uses somewhat less fuel.A diesel’s injection can also be mechanical, where a timed pulse of fuel goes through a separate line to each cylinder, or common rail, where an electronic controller opens each cylinder in turn to a shared high pressure fuel line: the rail.
Common rail diesels make less noise because small pre-injections of fuel soften the abrupt pressure rise that causes engine knock. They run smoother and are somewhat more fuel efficient, and they make less exhaust smoke. Engine makers are turning to common rail so they can meet increasingly stricter emission standards under Tier 3 of the Clean Air Act (40 CFR 1042). Westerbeke, for example, no longer sells diesels in the US because they cannot meet those standards.
Two key drawbacks of common rail engines are the complex electronics—notably different in each model—that control injection and also the need for exceptionally clean fuel. The electronics make special equipment needed for problem diagnosis and also make dockside repairs more difficult.
Among marine diesels available in the US today, the most common are:
Yanmar 4JH57: Japanese, 57 HP, common rail injection. Yanmar block.
Volvo Penta D2-60: Swedish, 60 HP, direct injection. Perkins block.
Beta Marine Beta-50 and Beta-60: British, 49 and 56 HP, direct injection. Kubota block.
Vetus M4.56: Dutch, 52 HP, indirect injection. Mitsubishi block.
Nanni N4.50: French, 47 HP, indirect injection. Kubota block.
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 valve 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.
Running
at Idle
Most diesel engines prefer to run at or near their rated RPM except when cold. After starting, the engine should run at fast idle of 1,000 to 1,500 RPM for a few minutes until the coolant temperature rises into the operating range. Some engines also benefit from a few minutes of fast idle before being shut down to prevent vapor lock. Between these times, it is best to avoid running at idle, when possible, particularly if the engine is not under load. Cold
Stacking
Running a diesel engine at low RPM without load causes a phenomenon called cold stacking where the vaporized fuel condenses on the cylinder walls and piston faces. The condensed fuel causes soot, which can damage the valves and pushrods, and it also washes fuel down the cylinder walls into the crankcase, diluting the oil. Overload
How heavily an engine is loaded at its rated RPM depends on the size and pitch of the prop. Unlike gas engines, where a throttle controls speed by changing the amount of air supplied, in diesel engines the fuel pump controls speed—by changing the amount of fuel—while the air supply stays relatively constant (except in a turbo-diesel).At low speed, when there is too much air, the excess goes out as harmless exhaust. At higher speed, adding more fuel can use up all the air and the excess fuel then goes out as black smoke. The speed control keeps on adding more fuel until the governor cuts in at max RPM, which might never occur if the overloaded engine runs out of air. An overloaded engine will wear out sooner and be quick to overheat.