help choosing pitch

[susan61]

90 HP four stroke<br /> fiberglass Sea Hunt 172 center console<br /> Installed Bennett trim tabs<br /> Aluminum prop is marked 12 5/8 X 21P<br /> RPM at WOT is correct at 5500 RPM<br /> Boat seems slow, top speed is 30 MPH trimed out<br /><br /> Engine specs call for a 14" diameter prop.<br /> I want to order a 14" stainless steel prop<br /> Any input as to what pitch to select ?

 

[walleyehed]

Re: help choosing pitch

Is the 12-5/8 the prop that came on it????<br />What make is the 90, and also, what year???

 

[susan61]

Re: help choosing pitch

WALLEYEHED<br /> The 90 HP is a '94 Johnson or a white Suzuki.<br /> Yes the 12 5/8 dia prop came on the motor.<br /> Although the WOT rpm is within range, I supect the 12 5/8 dia prop is not what the motor was designed to run.<br /> I'm thinking performance could be improved with a correct 14" prop.<br /> Question is how much will I have to reduce the 21" pitch if I go to a ss prop ?

 

[susan61]

Re: help choosing pitch

WALLEYEHED<br /> The 90 HP is a 2004 Johnson or a white Suzuki.<br /> Yes the 12 5/8 dia prop came on the motor.<br /> Although the WOT rpm is within range, I supect the 12 5/8 dia prop is not what the motor was designed to run.<br /> I'm thinking performance could be improved with a correct 14" prop.<br /> Question is how much will I have to reduce the 21" pitch if I go to a ss prop ?

 

[susan61]

Re: help choosing pitch

OPPS, "Senior moment"<br /> Sorry about the double post. 2004 is the correct year not a 94. What was I thinking ?

 

[walleyehed]

Re: help choosing pitch

susan61..you're right about the diameter on that engine...the closer you can get to 14 the better in this case...Are you sure the Max RPM (recommended) is 5500???<br />I thought it was 6000 on that engine...of course, follow the book, but I thought it was higher than 5500..???

 

[susan61]

Re: help choosing pitch

WALLEYEHED<br /> The red line on that 90HP Jon/zuki is 5500.<br /> The red line on the 115HP is 6000. Identical engines except for the ECM module. Overrev kicks in lower on the 90. Thats the difference.<br /> Question remains going from a 12 5/8 X 21 to a 14" prop how much will I need to reduce pitch ?

 

[walleyehed]

Re: help choosing pitch

This is where a loaner would be in order...<br />I'm not sure you'll need to change pitch...that depends on the design, but you may end-up with a 19-20, but I would test with the 21 first

 

[bradly2072000]

Re: help choosing pitch

im having a similar problem. I just bought a 1985 Sunrunner 165 (First boat). I has a Mercruiser 120, nut sure what kind of prop it has. It's a really nice boat, engine runs great, fires right up, never fails. The only problem is, Its really slow. Top speed is 24-25. If I change the prop. to a 24 or 25" pitch, would that fix the problem?