Skip to main content

Controllable Pitch Propellor

    •
   Advantages
        o    Allow greater manoevrability
        o    Allow engines to operate at optimum revs
        o    Allow use of PTO alternators
        o    Removes need for reversing engines
        o    Reduced size of Air Start Compressors and receivers
        o    Improves propulsion efficiency at lower loads

     Disadvantages
        o    Greater initial cost
        o    Increased complexity and maintenance requirements
        o    Increase stern tube loading due to increase weight of assembly, the stern tube bearing diameter is larger to accept the larger diameter shaft required to allow room for OT tube
        o    Lower propulsive efficiency at maximum continuous rating
        o    Prop shaft must be removed outboard requiring rudder to be removed for all prop maintenance.
        o    Increased risk of pollution due to leak seals

The CPP consists of a flange mounted hub inside which a piston arrangement is moved fore and aft to rotate the blades by a crank arrangement.The piston is moved by hydraulic oil applied at high pressure (typically 140 bar) via an Oil transfer tube (OT tube) This tube has and inner and outer pipe through which Ahead and astern oil passes. The tube is ported at either end to allow oil flow and segregated by seals.
Oil is transfered to the tube via ports on the shaft circumference over which is mounted the OT box. This sits on the shaft on bearings and is prevented from rotation my a peg. The inner bore of the box is seperated into three sections. The ahead and astern and also an oil drain which is also attached to the hydraulic oil header to ensure that positive pressure exists in the hub and prevents oil or air ingress
The OT tube is rigidly attached to the piston, as the piston moves fore and aft so the entire length of the tube is moved in the same way. A feedback mechanism is attached to the tube, this also allows for checking of blade pitch position from within the engineroom.

Operation Modes
There are two main methods of operation of a veseel with a CPP.
Combinator-For varying demand signals both the engine revs and the pitch are adjusted to give optimum performance both in terms of manouevrability and response, and also economy and emissions.Constant speed- The engine operates at continuous revs ( normally design normal max working revs), demand signals vary CPP pitch only. This is particularly seen in engines operating PTO generator systems

Emergency running
In the event of CPP system hydraulic failure an arrangement is fitted to allow for mechanical locking of the CPP into a fixed ahead pitch position. This generally takes the form of a mechanical lock which secures the OT tube. Either hand or small auxiliary electric hydraulic pump is available for moving the pitch to the correct position

Labels:

Comments

Post a Comment

If you have any doubts.Please let me know

Popular posts from this blog

Differences between MC/MC-C and ME/ME-C engines

The electrohydraulic control mechanisms of the ME engine replace the following components of the conventional MC engine: Chain drive for camshaft Camshaft with fuel cams, exhaust cams and indicator cams Fuel pump actuating gear, including roller guides and reversing mechanism Conventional fuel pressure booster and VIT system Exhaust valve actuating gear and roller guides Engine driven starting air distributor Electronic governor with actuator Regulating shaft Engine side control console Mechanical cylinder lubricators. The Engine Control System of the ME engine comprises: Control units Hydraulic power supply unit Hydraulic cylinder units, including: Electronically controlled fuel injection, and Electronically controlled exhaust valve activation Electronically controlled starting air valves Electronically controlled auxiliary blowers Integrated electronic governor functions Tacho system Electronically controlled Alpha lubricators
9 comments
Read more

Main engine interlocks

Interlocks are provided so that the engine can be started or reversed only when certain conditions have been fulfilled. When there is a remote control of engines, it is essential to have interlocks. This reduces the possibility of engine damage and any hazards to the operating personnel. Turning gear Interlock . This device prevents the engine from being started if the Turning gear is engaged. Running Direction Interlock . This prevents the fuel from being supplied if the running direction of the engine does not match the Telegraph. Starting Air Distributor in end position . This prevents starting from taking place if the shifting of the Distributor has not been completed. Main Lube. oil pressure, Piston cooling pressure, Jacket water pressure, and important parameters must be above the required minimum. Auxiliary Blower Interlock . The Auxiliary Blower is provided in case of Constant pressure turbo charging. Air Spring pressure Interlock . In case of the present generation
7 comments
Read more

Why is a man hole door elliptical in shape?

Any opening in a pressure vessel is kept to a minimum and for a man entry an elliptical hole  is lesser in size than the corresponding circular hole. More over it is prime concern to have a  smoothed generous radius at the corners to eliminate stress concentration. Hence other  geometrical shapes like rectangle and square are ruled out.  To compensate for the loss of material in the shell due to opening, a doubler ring has to be  provided around the opening. The thickness of the ring depends on the axis length along the  dirrection in which the stresses are maximum and the thickness of the shell. It is important to  align the minor axis along the length of the vessel, as the stress in this direction is  maximum. Longitudinal stress: Pd/2t where P= pressure inside the vessel, d= diameter of the arc, t=  thickness of the shell plating  Circumferential stress: Pd/4t  More over a considerable material and weight saving is achieved as minor is along the  direction of maximum stress.
20 comments
Read more