Prop size?

[Das_Boot]

If I am changing from a 36hp to a 54hp engine will I need to change my prop. if so how do I go about buying the right one. Also can I leave my old gearbox in or will I need to upgrade that as well. Any help would be most welcome

 

[philip_stevens]

There is a propeller calculator downloadable program on this link -
http://www.castlemarine.co.uk/pitch.htm

 

[oldharry]

Yes almost certainly you will need a different and larger prop. Sizing depends on the speed of the boat through the water, power available to rotate the prop and the speed the prop will rotate at full throttle. The calculations are quite obscure, and it would be advisable to speak to specialists like Lancin Marine, or T Norris for advice; they could also sell you the right prop.

Whether or not you can use the old gearbox depends whether it is compatible with the new engine: the box input shaft must match the output shaft of the engine to start with. Boxes are attached to the engine via an adpator plate, usually 6 or more mm thick steel, cut drilled and threaded to fasten to the engine, and to allow the gearbox to be bolted on to the plate. If a suitable adaptor plate is available, and the shafts match, then the answer is probably yes. Again you need to speak to marine engine specialists, or the manufacturers.

 

[Das_Boot]

Thanks I need to measure my existing prop so I can check it against the calculators outcome. Once again tnks for the info

 

[Das_Boot]

I can see there are no cheap cuts I will have to replace both. The hole gets deaper, the bank gets shirtier, my life expectancy gets shorter I think I will start a cold feet thread myself
anyway tnks for the info.