According to application and ustage,  there are four types of marine generator sets.  

1.  Marine main generator,
     To supply power in the whole vessel.  Main generator is laid in engine room.  This generator is large power and size, and often use sea water exchanger cooling system,  open type. 
     

2.  Emergency generator 
     Generally speaking,  emergency generator use radiator cooling, and closed type. emergency generator with double starter,  electric starter and air starter or electric starter or hand starter.  when the main generator don't work or emergency matter, can open emergency generator.  emergency power is smaller than main generator. 

3.  Habour generator or habor generator 
   Habour generator works when the vessel will arrive at habour or closed to shore,  Habour generator can install on deck or engine room.  
  If it is installed on deck, can use radiator cooling system,  but without double starters,  if in the engine room, can use double cycle water cooling.
  Not at all of vessel install on habour generator,  some times emergency generator can be used habour generator.  large ocean vessel have independent   habour generator 

4.  Shaft generator  (PTO /PTI operation)
    The shaft generator is applied in marine diesel engine output to generating.  to save diesel fuel oil, reduce lubricating oil consumption, etc.  Deep sea vessel or cargo can be used Shaft generator system. 
    

Mairne gearbox is transfer output from marine main engine to propeller, and reduce the speed.  So the gearbox selection is to learn the marine engine and propeller information.  

1.  Marine engine power and speed,   it will be decided on large or small.  the engine power is large, the gearbox will be large.  Gearbox must be working on rated speed range.  

2.  Transfer capacity.   Power/Speed,   the unit is KW/RPM or HP/RPM,  the gearbox must meet the transfer capacity, other wise, it is not enough. 

3.   Ratio:  gearbox reduction ratio is input speed/ output speed. that means engine speed and propeller speed. each gearbox must be confirmed ratio.
 The ratio have nominal ratio and real ratio,  different factory use different.

4.   Flywheel and housing,  gearbox flywheel must be in the consistent with engine, otherwise, can not install.  if the engine cancel housing, the gearbox also cancel housing.  

5.  Flexiable coupling,  large gearbox should be install on flexiable coupling or tooth block connection,  small gearbox without coupling.  install the coupling can increase transfer capacity about 8%. 

6.  Propeller push thrust:  Propeller push is larger, the gearbox should be large

1. Continuous Duty (CON) or P1,    unrestricted Coutinuous with full load,  80%-100% load,  Running time from 5000 to7000 hours per year.
    Applied for Offshore anr river tug, Ro-Ro, Ferries, Barge, Cargo, Passenger vessel.including MCD

2. Heavy Duty (HD) or P2 , Continuous with load variations  8 hours out of 12 with full load, 30%-80% load, Running time from 3000-5000 hours per year.
   Applied for Harbour turboats, mid-water trawler.

3.  intermittent Duty (INT) or P3, intermittent use in variable load application.2 hours out of 12 with full load, 50% load, Running time from 1000-3000 hours         per year.
    Applied for Crew boat, police and Miliary vessel. charter motor yacht.

4.  High Output Duty (HO) or P4,   High performance with load variations,  1 hour out of 12 with full load, 30% load factor, less than 1000 hours per year.
   Applied for  Patrol boat, motoryacht, cruiser.

1.  Working cycle:  Two stoke marine diesel engine, and four stoke marine diesel engine
2.  Intake mode:   Natural intake engine, turbocharged or turbocharged aftercooled engine 
3. Speed:  Low speed engine (<500RPM)  medium speed engine (500-1500RPM) High speed engine (>1500RPM)
4.Arrangement:  In-line,  V type,
5. irreversible or reversible marine diesel engine 
6.  Rotationary,    Left engine and right engine. 
7. Fuel types,   light fuel oil,  Heavy fuel oil, LNG,  Doul fuel marine diesel engines.