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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