Slow speed,medium and high speed engine
normal speed – [60 – 300 RPM ].
These are generally two stroke cycle.
cylinder bore [269 -980mm]
Ships have tyoically one Slow speed engine.Sometimes 2 (two) used for main propulsion,it can we directly coupled to propeller and shafting.
It provides highe torque,Can burn low grade fuel and has high thermal efficiency.
The cylinder and crackase are separated crooshead type which reduces contamination of system oil by (contamination ) combustion products.
cylinder oil separated from system oil. it is a direct reversing engine, so FPP ( fixed pitch propeller ) is used for propulsion purpose .
Generally,Larger bore engine have better fuel economy,at lower Revolution and speed.
These engine have large longer life cycle then small engine of medium or highest speed engine.
example :- MAN & BMW– SMC,LMC,ME
Nominal speed – [ 300 – 1200 RPM]
These are there in line or V-type model.
Generally, cylinder bore- [ 200 – 600mm]
In most case, marine medium speed engine are multi cylinder Engines,4- stroke cycle and Trump type.
It has better power to weight ratio, power size ratio and lower initial cost.
Medium speed engines used for prooulsion require gearbox for Speed reduction and reversing or C.P.P( control pitch propeller )
example :- MAN BMW –L58 etc.
SULZER — ZA40S etc.
highe speed engine
Nominal speed — above 1200 RPM
Generally V – model
cylinder bore -[122 -125mm]
Marine high speed diesel engine,speed range 1500 to 2200 RPM
Designated for high speed or light craft as light and compact units.
Operate on distillate fuel
V-type engines are constructed with 2 banks of cylinder at an angle,using a common crankcase and bed plate.
for propulsion, purpose same 4 -stroke engine, gear box is required and or C.P.P is used.