what prop size and pitch.

[jurgenscraft]

I have a Jurgens craft marine cabin boat , which is 4.5 mt long and is of the deep vee and reverse chine hull configeration fitted with a Yamaha 55 el two cylinder two stroke motor .This motor boat was designed and maufactured in South africa and is designed for carrying persons to the max load of 300 kg.exc fuel and motor.<br />the motor is currently fitted with a 11 1/2x12 prop , I also have a 11 1/2 x 13 prop , I find that the boat gets onto the plane easily, but seems to be over reving at WOT. What is a good base line prop size and pitch for this motor, and what was the standard prop for this motor I have a feeling the prop is too small or requires more pitch (more bite ,less slip )

 

[WillyBWright]

Re: what prop size and pitch.

There is no such thing as a Standard propeller on anything much larger than a 25. There's no way for the factory to know if the motor is going on a speedboat or barge. The prop you want is the one that allows the motor to achieve maximum recommended RPMs with a normal load. However boats that are underpowered might have a problem with holeshot with the "appropriate" propeller. Say a boat is rated for 150Hp but only has a 50. It's common to need a low pitched propeller to get up on plane, but once it is it's too low to avoid overrevving. The prop that allows the proper WOT RPMs may be too steep to get this boat out of the hole. In most cases, educated guesses help get you close. But there's no way to avoid trial and error. You never know what it wil do until you try one. What is your boat rated for?