Prop Advice

[Lundman99]

I have a 99 Lund Mr. Pike 17 with 90 hp Merc. Am currently running a 13 5/8 x 21 ss Michigan prop. Looking to buy a backup prop or possibly main one and put the current one as backup if it performs better. Don't quite get the speed I want. I only get about 5000 rpm wide open. Manuals say I should get 5500. Didn't know if maybe a 19 pitch would help boost rpm maybe in aluminum? Not really that knowledgeable about props. Any ideas? Thanks

 

[steelespike]

Re: Prop Advice

Welcome,If you answer the questions in "read this first" at the top of props main page we can tell better if your set up is working and what might work better.

 

[Lundman99]

Re: Prop Advice

Don't know what my boat weight is. But get about 35 mph at 5000 rpm under normal load. Think everything else is in my original post.

 

[Silvertip]

Re: Prop Advice

The 21p is apparently a bit much for your combination. That said, decreasing pitch to raise rpm does not mean the boat goes faster. Rpm increases because the prop takes less bite on the water so the engine needs to run faster to achieve the same speed as before. Speed does increase if, and only if the engine was severely overpropped. In your case the prop calculator shows a theoretical speed of 38.2 mph with the 21p. At 5500 the 19p shows 38.1 using 10% slip. Sliop might be a bit less with the 19p.

 

[Lundman99]

Re: Prop Advice

Thanks for the advice. I think I might try the 19p. I read that if your motor is running lower than your max rpm it could damage the motor cause it is too much for the motor to keep turning the too big of a prop.

 

[steelespike]

Re: Prop Advice

Thanks for the advice. I think I might try the 19p. I read that if your motor is running lower than your max rpm it could damage the motor cause it is too much for the motor to keep turning the too big of a prop.

I believe your motor is within its correct rpm range; but dropping to a 19 will improve your overall performance.
And as Silvertip pointed out it may maintain speed.Sometimes that doesn't happen.