Principles of naval engineering - Historic Naval Ships Association

PRINCIPLES OF NAVAL ENGINEERINGTRANSVERSEWAVES(NOT VISIBLE)STERNDIVEPGENTSBOW DIVERGENTWAVES147.45Figure 5-1. — Bow, stern, and transverse waves.relationships of the units required for the developmentand transmission of propulsive power.The geared-turbine installation is chosen for thisexample because it is the propulsion plant mostcommonly used in naval service today. The samebasic principles apply to all types of propulsionplants.The units directly involved in the developmentand transmission of propulsive power are theprime mover, the shaft, the propelling device,and the thrust bearing. The various bearingsused to support the shaft and the reduction gears(in this installation) may be regarded as necessaryaccessories.The prime mover provides the mechanicalenergy required to turn the shaft and drive thepropelling device. The steam turbines shown infigure 5-2 constitute the prime mover of thisinstallation; in other installations the primemover may be a diesel engine, a gas turbineengine, or a turbine-driven generator.The propulsion shaft provides a means oftransmitting mechanical energy from the primemover to the propelling device and transmittingthrust from the propelling device to the thrustbearing.The propelling device imparts velocity to acolumn of water and moves it in the directionopposite to the direction in which it is desiredto move the ship. A reactive force (thrust) isthereby developed against the velocity-impartingdevice; and this thrust, when transmitted to theship's structure, causes the ship to move throughthe water. In essence, then, we may think ofpropelling devices as pumps which are designedto move a column of water in order to build upa reactive force sufficient to move the ship. Thescrew propeller is the propelling device usedon practically all naval ships.The thrust bearing absorbs the axial thrustthat is developed on the propeller and transmittedthrough the shaft. Since the thrust bearingis firmly fixed inrelationtothe ship's structure,any thrust developed on the propeller must betransmitted to the ship in such a way as to movethe ship through the water.WATERCOLUMNPROPELLERSTRUTBEARINGDIRECTION OFREACTIVE FORCE(THRUST)Figure 5-2.— Principles of ship propulsion,47.42A86