Ship & Marine Propulsion Performance Lab.
Dept. of Smart Ocean Mobility Engineering, Changwon National University
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Ship & Marine Propulsion System
Ship and Marine propulsion system refers to the core equipment and systems that generate thrust to achieve the required operating speed of the ocean mobility.
Propulsor + Shaft + Engine or Motor
Type of ship and marine propulsors
- Screw propeller (FPP, CPP)
- CRP, Duct propeller, Composite propeller
- Waterjet, Podded propeller, Voith-Schnelder propeller, etc.
When a propeller develops a thrust as it absorbs a torque at a given rpm, the vessel moves forward until the total drag equals to the thrust.
For a given propeller RPM, propeller diameter D and mean pitch ratio (P/D)m can be calculated, having max. efficiency.
Pitch: the distance that the propeller “drive forward” for each full rotation.
Angle of attack is decided by propeller diameter, pitch angle and axial velocity which is induced by hull.
As rotating speed goes up, cavitation occurs on suction side of the blade.
When a propeller develops a thrust as it absorbs a torque at a given rpm, the vessel moves forward until the total drag equals to the thrust.
Design of propeller means to find an optimum shape that minimize the torque (power) and reduce the cavitation at target speed.
Cavitation
When a marine propeller rotates at high speed underwater, local pressure on the blade decreases and “cavitation inevitably occurs” where the local pressure falls below the vapor pressure.
It causes:
- Noise generation that starts at the inception of cavitation and it generally increases with the amount of cavitation.
- Reduced performance due to the loss of thrust with increase extent of cavitation.
- Vibration transmitted to and through the surface where the cavitation acts.
- Damage from the erosion of surface where the cavitation acts.
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