Need prop selection help...

[cordell]

OK here is the current situation. My boat is a 18 foot Bayliner Capri 1990 in year. My motor is a 85 horse power Force outboard 1987 in year. I am currently running 29-30 MPH with GPS @ 4850 RPM's. My motor shout WOT @ 5500 RPM not 4850. The prop I currently have on the boat is stamped 13 RP> 17. Though on this prop a bit over and also smaller 19 is stamped on it too. The load was NO gear, my wife and myself, and 1/4 tank gas (5 gallons). To bring up my RPM I need maybe a 19 pitch? I am also using a hydrofoil, I call it a whale tail, if a pic is needed I can post. Thanks for reading and any advice offered.

Oh the prop that gave me these numbers is not in the best of shape either...


cordell

 

[john from md]

Re: Need prop selection help...

If the prop has three numbers and a dash and then two numbers, the numbers after the dash is the pitch.

A 19 pitch prop will not help you as your RPM is already low. A 19 would slow it down more. Check the prop again, you may already have a 19 and so you should be going to a 17.

How is your compression? Have you cleaned your carbs lately?

John

 

[cordell]

Re: Need prop selection help...

Yes compression is fine and carbs are clean. The motor runs great, holds idle for as long as I keep it there (600 rpm). I have a good hole shot, not as quick as the prop that is marked 15 but I am happy with it. I have not rpm tested the 15 prop yet I intend to do so this Thursday. I know I am under powering my boat a bit too. 18 foot boat deep V hull and only 85 horse. The boat says 90 max HP on a sticker, but many websites rate the boat for 120 HP (including iboats). So if I go by the pitch being 17, maybe a 16 might get my rpm up a bit? I was thinking the other way higher number higher rpm...The prop is kind of beat up, I guess that is my main reason for trying to prop my rig is I need to buy a new one. I would hate to buy the wrong size and have to purchase another one.


cordell

 

[john from md]

Re: Need prop selection help...

I believe that Iboats has a prop "try it" program where you can try difference pitches and send the props back for exchange if they are not damaged.

Maybe another member might have more info on this.

John

 

[cordell]

Re: Need prop selection help...

That would be great..but given my numbers what one should I try?


cordell

 

[john from md]

Re: Need prop selection help...

I suggest a 13-17pitch as it is possible that your existing prop is a 13-19.

John