CHAPTER Power units


All those in charge of small craft at sea must have at least a working knowledge of a typical power unit. Whether the boat is a motor vessel or an auxiliary sailing yacht, this essential understanding makes the difference between a mishap rectified from within the boat’s own resources and a lifeboat call-out. A ‘can-do’ attitude to fixing engines is as important to the twenty-first century seaman as the ability to turn in an eye splice was to his historical predecessors. Since this manual is a general one, it will concentrate on the commonly used inboard diesel engine. Petrol (gasoline) engines, excepting outboards, are now rarely found at sea.


The inboard engine drive chain Primary (or Pre-)filter


An inboard diesel can be thought of as a device for converting the contents of a fuel tank into propulsive force. The interdependent chain of systems involves a number of universal elements which must be understood if typical operational faults are to be rectified:


Most installations feature a filter between the tank and the engine that takes dirt and water out of the fuel. This needs to be maintained in a clean condition and checked regularly for water. Spare elements should be carried.


Fuel and tanks


The first essential is a plentiful supply of pure, water-free diesel. Tanks must be cleaned internally whenever the opportunity arises, and kept well topped up in operation. If a tank is run near-empty in a seaway, there is a chance that the lift pump may suck air as the fuel surges, even though this tendency should be reduced by internal baffles. Furthermore, any sludge collecting at the bottom of a tank will concentrate as the fuel level declines.


Tap


All tanks should have a tap which can be turned off remotely from the engine in the event of fire. Find out where this is and make sure it works.


4


Injectors Shaft coupling


Stern gland


Fine filter


Injection pump


Fuel tank


Prop shaft Shaft bearing


Lift pump Pre-filter


Stop cock Tank drain


MANUAL OF SEAMANSHIP | 29


Power units


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