Different prop pitch for 15 hp Force OB ?

[pecheux]

Got a 15 hp Force (dont laught I love this OB ... lol) and I beleve the prop pitch is 9 X 6 original prop. I may be wrong on this since engine is stored and I cannot get near to read the prop specs. I am planning to buy a spare prop for safety reasons. Question is ... would there be any avantage in getting a different pitch ? I beleve 9 X 7 is available. The OB is mounted on a 14 footer fiberglass boat and it runs the boat on the step easely with 2 persons on board. tx

 

[Silvertip]

Re: Different prop pitch for 15 hp Force OB ?

Without any rpm data you don't know whether the prop you have is correct, or what effect more pitch will have. You need to make make wide open throttle runs with an average load and see what the engine rpm is. If its operating in its recommended wide open throttle rpm band the prop is correct. Adding pitch will pull rpm down and cause lugging which two strokes do not like. If the engine is over reving, then adding pitch is necessary. Since you don't have a tach we can't offer any recommendations either way. Add a "Tiny Tach" and do the testing.

 

[pecheux]

Re: Different prop pitch for 15 hp Force OB ?

Thanks for your feedback. On such a "Mickey Mouse" kit I realise it was probably a stupid question on my part ... LOL Is a tiny tach a portable unit ?

Regards

 

[Silvertip]

Re: Different prop pitch for 15 hp Force OB ?

They can be attached to the engine temporarily or mounted permanently. They have a battery inside and get the tach signal from a spark plug wire. They are a little smaller than a credit card. Google "Tiny Tach". They are readily available.

 

[javsam]

Re: Different prop pitch for 15 hp Force OB ?

I also have a 15 hp force(86) and can tell you that the owners manual lists an 8 pitch,8-1/4 dia,3 blade prop as standard equipment. Follow advise already given by silvertip.

 

[pecheux]

Re: Different prop pitch for 15 hp Force OB ?

Javsam: I will double check ... mine is a 1997, not that I think it would make any difference with prop size ... I am pretty sure I read the first number as a 9 X ? unsure of the second one. Will keep you posted. Tx

Silvertip: Tx for the tiny-tach info. At that size makes it more interesting to make the test.

Would anyone know what difference in performance would be expected comparing these 2 props : 9 dia X 6 pitch Vs the 8 1/4 Diam X 8 pitch ??

 

[pecheux]

Re: Different prop pitch for 15 hp Force OB ?

I also have a 15 hp force(86) and can tell you that the owners manual lists an 8 pitch,8-1/4 dia,3 blade prop as standard equipment. Follow advise already given by silvertip.

Hi, I managed to get close to the motor and the reading on the prop seemed to match the specs you wrote. Although paint is still like new around those numbers .. still hard to read.

I checked on Iboat and that size is nla ... closest available would be 9 X 7 that's 1 inche more in diam and 1 1/4 less on pitch. I would not know what to expect for that difference ??

Tx for your information ...

 

[javsam]

Re: Different prop pitch for 15 hp Force OB ?

As silvertip already stated ,you need to find out where your running at with a tach and go from there.The operating rpm range is 4500-5500 rpms with the latter being where you should be operating at wot. My 15 hp force was on a light 14 ft alumimun boat(Alumacraft ts-14) and pushed the boat well with two people.Yours being fiberglass would be a heavier load.That said I have found that larger diameter props push a heavier load better.And reducing pitch increases the rpms .I think mercury still sells props for force outboards under their quicksilver brand.

 

[pecheux]

Re: Different prop pitch for 15 hp Force OB ?

Thank you for your feedback Javsam, when you wrote better push with a larger diameter prop are you refering to the 9 dia X 7 pitch I mentioned ??

The boat runs ok with 2 people in it ... but it sounds like it's not running 5500 rpm. I ll see if I can get my hand on one of the tiny tach ...

Have a great day,

 

[Frank Acampora]

Re: Different prop pitch for 15 hp Force OB ?

Hate to recommend a competitor but since you already checked iboats and they don't seem to have what you need: Try West Marine. Their catalog lists several different props and average size boat and load it would be used for.

With an engine that small, you would probably be close enough without the added expense of buying a tach.

 

[javsam]

Re: Different prop pitch for 15 hp Force OB ?

Pheceux,I was speaking of what I have found to work with heavier loads.I dont think you have determined what size prop you have on your motor right now.Either,remove the paint covering up the numbers or take the prop to a prop shop have them tell you.Then use a tac to find out where your running at.If you cant find a prop here for your motor then propmd sells mercury quicksilver props for force 15 hp outboards in various sizes.

 

[pecheux]

Re: Different prop pitch for 15 hp Force OB ?

Pheceux,I was speaking of what I have found to work with heavier loads.I dont think you have determined what size prop you have on your motor right now.Either,remove the paint covering up the numbers or take the prop to a prop shop have them tell you.Then use a tac to find out where your running at.If you cant find a prop here for your motor then propmd sells mercury quicksilver props for force 15 hp outboards in various sizes.

Did answer that in previous post ... 8 pitch X 8 3/4 original prop. Got that after you informed me to the size prop there was you your 15 hp. tx