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Posted: Tue Nov 16, 2010 2:13pm

Post Subject: propeller pitch.

Hello I have 55ft narrow boat, with 8kw electric engine [10.5 hp?] with rpm of 2800 [as per the manufacturer]. The propeller is fixed at 16 inch diameter [no more space]. The reduction is 2 1/2 to 1. What pitch is best?


Posted: Tue Nov 16, 2010 4:14pm

Post Subject: propeller pitch.

The problem I have is that for displacement craft the propeller is selected against maximum torque NOT maximum power and as an electric motor develops maximum torque at zero rpm I do not see how any conventional propeller calculations can help unless you can find the torque curve of the motor and then decide what revs you would like the motor to stop accelerating. I am not even sure a propeller supplier would be over happy with specifying a prop for an electric boat unless they had done one before. It might be a very good idea if you joined and sought the advice of the Electric Boat Association ( A well known web based prop calculator suggests (with a guessed boat weight) a pitch of about 15.5 inches and goes on to say, as it does with most modern canal boats that the blades do not have a large enough area. Companies like Crowthers specialise in making props with a larger than normal blade areas especially for canal boats. I once again point out that the calculator expects an internal combustion engine so I would not trust the result one little bit. Tony Brooks

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