MEOclassIIexamnotes

Effective Power: The Power available at the output side of the engine i.e. at crankshaft flange of the engine which connects it with the flywheel and rest of the intermediate shaft Rated Power: It is the continuous effective power provided by the manufacturer of the engine for a desired or rated RPM of the crankshaft. Rated power includes the loads which acts on the engine due to auxiliary system running from the engine power Indicated Horse Power: It is a theoretical power calculated with a formula                                           (PxLxAxN)  / 4500                                             Where    P- Mean indicated pressure of the cylinder ...

HYDRAULIC FLOATING OF PROPELLERS Used for keyless propellers, ensures the correct interference fit using measured oil pressures for expanding the boss and hydraulic jacks or a Pilgrim nut for pushing it up or down the tailshaft taper. No heavy slogging required and low shock loads are applied, quick and safe. A disadvantage is loss of bearing area due to oil grooves which means that propeller must be longer or greater in Dia to give sufficient area to transmit the torque. To remove, nut just slackened back. Oil injection applied to expand the boss which allows propeller to move off the taper. Another disadvantage of wet fitting over dry fitting is that wet boss expansion stress is 30% greater than dry fitted which means that boss must be thicker. SLEEVED PROPELLER   Usually fitted on large diameter shafting. Usually hydraulically floated and keyless. Difficult to bed large props to taper, easier to bed sleeve. Also each time a prop is refitted, prop bore becomes large...

are used to lower vibration

 Sometimes refered to as half kort One or two nozzles may be fitted just ford of the propeller. There purpose is to steer the flow of water to enter the propeller with minimum shock. Efficiemcy claims are up to 3%. The advantage of this system over the full duct or kort nozzle is that it does not suffer from the same cavitation damage on the inner surface. A simplified version of this is two fins welded to the hull at a slight angle to the shaft centre line

This is a modern design trend under heavy investigation adn yielding good results. They are screw propellers fitted with end plates at the blade tips. The plates are deigned to give minimum resitance to flow.

Fin s of opposite hand to the main blades are mounted on the prop coss cap. These correct the prop hub vortex and recover rotational energy that would otherwise be lost. Fuel savings up to 5% are claimed

The grim wheel is a free turning propeller mounted after the main propeller. It use the rotational energy of the main prop wash that would otherwise be lost to provide increased propulsive force. The inner section up to the diameter of the main propeller acts as the turbine section. The area outside this is the propulsive section, thus the grim wheel must be larger than the diameter of the main wheel Initial design had the grim wheel mounted on the main propeller boss. Severe problems including entire loss occurred. The more modern approach is to mount the wheel on the rudder horn. This having the added advantage of allowing a dedicated lube oil supply and reducing main prop shaft and stern tube bearing loading Alternate design Shown below is a design of unknown origin but has appeared for some time in this site so the source is lost. I am unsure as to its correctness. It is unsual that the propulsive section should be fitted in the vortex produced by the main prop hub. Th...