164 ELECTRIC AUXILIARIES ON MERCHANT SHIPS. 



of an oil Servo motor. All parts should be readily accessible. Even with the greatest care 

 there is always liability that the lubrication may be momentarily interrupted, and as the bear- 

 ings should be examined before the machinery is placed in service they should all be readily 

 removable for inspection. An overspeed or emergency governor of the simplest and most 

 reliable type should be fitted. Very specific and simple instructions should be issued to show 

 the operating engineer the necessity of testing the governing mechanism periodically and 

 assuring himself that it is in perfect operating condition. 



THE MOST SUITABLE ELECTRIC POWER. 



All references indicate that at the present time direct current is being generally adopted 

 for auxiliary power on merchant ships. Some time ago there was considerable discussion as 

 to the relative merits of alternating current and direct current. The following tabulation 

 will show why direct current is being used to the greater extent : 



Cargo Ships. 



direct current. 

 Arguments For Arguments Against 



1. Simple wiring. 1. Commutators require some at- 



2. Any speed control easily obtained. tention. 



3. Equally suitable for continuous and 

 intermittent duty. 



ALTERNATING CURRENT. 



1. Lower cost of motors and genera- 1. Wiring more expensive, 

 tors. 2. Unsuitable for variable speeds 



2. Absence of commutators. necessitating hydraulic or 



other gear for winches and 

 windlasses. 

 Tankers. 



direct current. 



1. Simple wiring. 1. Commutators require some at- 



2. Equally suitable for continuous and tention. 



intermittent duty. 2. Little necessity for variable 



3. Speed of cargo pump can be varied speed motors. Special cases 

 to suit pressures and most efficient could be fitted with hydraulic 

 rate. or direct-current power fur- 

 nished from small motor-gen- 

 erator set. 



3. Special precautions must be 

 taken to ventilate motors in 

 tarik room. 



ALTERNATING CURRENT. 



1. Lower cost of motors and gener- 1. Wiring more expensive, 

 ators. 2. Special motors necessary to 



2. Absence of commutators, particu- change speed, 

 larly desirable in pump room. 



3. Cargo handled by constant speed 

 ptmips. 



