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Contra-Rotating propellor

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Whenever a propeller turns it exerts a thrust but it also rotates the water and this gives a loss of energy. If a second propeller os fitted immediately down stream but rotating in the opposite direction the second propeller exerts a rotating force on the water which opposes that of the upstream propeller.
water flow is axial and the drive more efficient the costs involved are high due to complicated shafting and gearing that is required to drive the two shafts from a single source. In order to minimise problems of vibration the downstream propeller usually has more blades than the upstream blade but the thrust from each is designed to be the same.


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