2016年8月14日星期日

Marine Propeller



Propeller is usually composed of blade and hub.Ordinary propeller often 3 or 4 blades, 2 blades propeller is used only for boats. Large ships to avoid vibration normally use 5 or more blades propeller.

Ordinary transport ship has 1 ~ 2 propeller. Large propulsion power ships, can increase the number of propeller. Large fast passenger has 2-4 propellers. The propeller is generally 3 ~ 4 blades ,diameter according to HP and draft, the following end does not touch bottom; the upper end is not over load waterline shall prevail. Propeller speed should not be too high, the marine cargo ship about 100 rpm, small boat speed up to 400 ~ 500 rpm, but the efficiency will be affected.

Propeller is propulsion device with disk shaped helical surface for driving ship, consist of blade and hub. Propeller blades number normally 3 to 6. Including single propeller, ducted propeller, rotating propeller, tandem propeller, controllable pitch propeller, super cavitating propeller, large inclined propeller etc

Marine propeller generally speaking, in the same diameter and pitch ratio, the more number of propeller blades, the thrust better, the higher efficiency of propulsion.

Marine propeller material
Most use copper alloy, the reason mainly: (1) copper alloy corrosion resistance good, basically can meet the requirements of propeller in seawater; (2) copper alloy of low melting point, for melting and casting not need heat treatment but only need processing. Propeller materials are generally manganese bronze or corrosion resistant alloy, stainless steel, nickel aluminum bronze or cast iron.

Nickel aluminum bronze has excellent resistance to stress corrosion cracking, resistance to fatigue corrosion, cavitation erosion resistance, resistance to erosion and sea bio fouling Resistance. And with excellent thermal conductivity, electrical conductivity, good wear resistance, welding performance, and low price.



Marine propeller main technical paramaters
Propeller diameter: single propeller D= (0.7~0.8)Tw; Double propellers D= (0.6~0.7)Tw, Tw is the ship full loaded draft
Disk ratio: in the design propeller, are selected the smallest disk without bubble.
Blade outline shape: design close to ellipse
Propeller blade number: more is advance in reducing vibration, few is advance avoid cavitation favorable
Propeller speed: the speed related to host selection




Controllable Pitch propeller
According to the need adjust the pitch, fully use the host power, improve the efficiency of propulsion, when ship backward not need to change the direction of rotation. The pitch is by hub mechanical or hydraulic steering the rotating mechanism of each blade adjustment. CPP for propeller blade load change has good adaptability, widely used in fishing boats and tugs.

Controllable pitch propeller device, consist of hollow hub with radial uniform blades, blade connecting end is through the hub peripheral wall bearing hole and extends into hollow hub short shaft.The hollow propeller hub cavity set transmission structure which can simultaneously drive the short shaft of each blade rotating and adjust the working angle of propeller blade.


Controllable pitch propeller can not only regulate the working angle of propeller blades according to different working conditions, and improve the utilization output power ratio and service life of engine.

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