stainless prop slowing down the boat

[minocqa]

hi<br />i have a 1976 70hp johnson<br />i put on a new stainless steel prop on my boat and the darn thing goes slower than it did before <br />i put the aluminum back on and the speed returned <br />they are both the same pitch i want to say <br />13 1/4 x 17, but they was both the same size.<br />its got me confused<br />thanks<br />Don

 

[Reel Appeal]

Re: stainless prop slowing down the boat

One prop may be a "cupped" prop,the other may not.<br />Thickness of the blades can also affect speed/drag.The aluminum prop may have thinner blades.There are also design variations that can have negative(or positive) performance on your boat.

 

[Bob in Calif.]

Re: stainless prop slowing down the boat

What was the RPM reading using each prop, with the throttle wide open? ...Bob in Calif...

 

[Cricket Too]

Re: stainless prop slowing down the boat

Is the prop brand new or just new for you? If it is used check the hub.

 

[minocqa]

Re: stainless prop slowing down the boat

hi<br />the SS prop is brand new and it is a cupped prop.<br />the boat acted like it was draging a weight <br />Don

 

[chilifriedpork]

Re: stainless prop slowing down the boat

I can recognize a cupped prop pretty easy, but what does it do compared to a non cupped prop? <br /><br />Perhaps the prop wasn't suited to your boats performance abilities, but that doesn't make sense?<br /><br />Good luck, I thought a SS prop would reduce drag and be thinner than aluminium.

 

[Bob in Calif.]

Re: stainless prop slowing down the boat

As I recall, when you replace a non-cupped prop with a cupped prop, you should reduce the pitch by 2 inches. So your non-cupped prop of 13 1/4 X 17 should have been replaced by a 13 1/4 X 15 cupped prop. Does your engine have tilt and trim? If not, I believe the rule of a 2 inch drop would apply. ...Bob in Calif...

 

[walleyehed]

Re: stainless prop slowing down the boat

Bob in CA. has been doing his homework and is 100% correct- ya gotta drop 2" with a cupper. The best thing is, all flat, non-cupped props, have for the most part been discontinued.

 

[wikelam]

Re: stainless prop slowing down the boat

B in C, I am new to props. I have had boats and just put stock props on the motors. This info will help me in the future. thanx