Part VIII. Reversing the engine. Controllable pitch propellers.

The slow speed Diesel engine is mostly a direct reversible - or direct acting - engine.

This means that the shaft is directly connected to the engine. In order to go from ahead to astern – or astern to ahead - we must stop the engine first and then reverse it. With a reversing gear the engine can be reversed without having to stop the engine first. It is used in small vessels. Vessels that require to be highly manoeuvrable, with variable rated capacities, are equipped with controllable pitch propellers.

By pitch is understood the distance travelled after one revolution of the propeller, but it also indicates the blade-angle of the propeller.

A Controllable Pitch Propeller, or C.P.P, is fitted with adjustable blades. These blades can be put in various positions, whereby the angle of the blades determines the speed at which the vessel will proceed.

In other words: the propeller-pitch can be controlled by adjusting the blades. The blades can even be put in such a position that the sailing direction can be altered from ahead to astern.

The advantage of the C.P.P. is that the number of revolutions per minute (RPM) will remain constant, in spite of an increase or reduction of sailing-speed.

The engine will have a longer life, because it does not suffer from extensive wear that is normally caused by a constantly changing RPM.

C.P.P. with adjustable blades

Дата добавления: 2015-07-25