I am really going to show my ignorance here

[rlouns]

I am looking for a propeller for a 1991 90 HP Force. How do I determine the Dia. - and since some of you have told me to go to a 13" I have to assume - (here we go ;0)) - that means pitch. The problem is I have run across 13 1/4" and 13 1/2" and 13 3/4" Dia's and the lowest pitch was 15" then 17" & 19". Also single exhaust and dual exhaust. Now on a car I would look at the exhaust pipes under the car for sing vs dbl but (here we go again ;o)) what do I look for on the outboard??<br /><br />May I be safe in saying that since it is a 1991 that it is a single exhaust and 1995 to 1999 are dual?? <br /><br />

 

[kev_79]

Re: I am really going to show my ignorance here

Rob,<br /> What size boat is your motor on? I am not fimiliar with the previous post, but I would imagine that you would need at least a 15 on anything that would hold a 90 hp force. I have heard about some force's having dual exhaust, and I am guessing that it means through prop and over prop both. That thing that comes out at the end of the cavitation plate at the very back is the over the prop exhaust. If you wanna check, put some muffs on it an see if it is coming out of both the over the prop exhaust, and through the hub. I would think that if you use a prop with through the hub exhause capibility, you would be ok no matter what. I had a 90 model 90 hp, and I would think that a 13 1/4X15 would push up to about a 20-21 foot boat ok, but I am not sure. I was running a 13.5 X 17 on an 18 footer that weighed about 1700lbs. Good luck

 

[rlouns]

Re: I am really going to show my ignorance here

Thanks for the quick reply Kev,<br /><br /> I will bring you up to speed. I have a 21' Deck (like a pontoon but it has a trihull fiberglass body instead of aluminum tubes) boat. I was having a prob with WOT. It would only run at 3750 RPM's. It turned out to be a broken wire to the #2 coil. Thereby not allowing it to fire and loss of power. While running thru all of the possibilities I had asked what the top RPM's should be. I was told 5500. Well, I said, it only ran at 4250 tops and 23 MPH. That was when some one told me to drop 2" on my prop size. When I said that I had a prop that had a 17 on it, and nothing else, someone said go to a 13" and that would get me to 5500 rpm and max effeciency on the 90 HP FORCE.<br /><br /> Now hopefully that is everything I went thru in a nutshell.

 

[kev_79]

Re: I am really going to show my ignorance here

The only problem is that you are going to have a hard time finding a 13 pitch prop for a motor like that. You can find them though, I will look at some of my sources in a bit, to see what I can come up with. Also, you can have a prop shop repitch your old one, but I don't know how low they can take it. Good luck, and I will get back with you.

 

[sony2001]

Re: I am really going to show my ignorance here

Robert L the props you came across are for 15 tooth shafts. Yours is 13 tooth. Go to www.miwheel.com and look up your model to double check their years for dual and single exhaust. Get the model # for Michigan props. Understanding props is not easy.

 

[sony2001]

Re: I am really going to show my ignorance here

The dual exhaust model is the only one of the two on boats over 22 feet.<br />From 22' to 25' use 14X13 Mich#031055<br />From 25' use 14X11 Mich#031054

 

[rlouns]

Re: I am really going to show my ignorance here

Thanks for the info Sony,<br /><br /> I happen to have a 1994 21' Smokercraft Deck boat and the engine is a 1991 90 HP Force. I do not know who picked the power for it. I do not know if they picked it when the boat was new or as an after thought.<br /><br /> I also purchased a 1989 24' Pontoon boat with a 1997 90 HP Force (glutton for punishment I guess). It has (by the definition given to me earlier) a dual exhaust (or at least an open port through the piece above the prop). The 1991 does not have an opening - as a matter of fact someone has welded a flat peice of aluminum onto it so that it will stick out further in the water (it looks like a piece may have been broken off of it).<br /><br /> Maybe that info will shed some light. ;o)

 

[rlouns]

Re: I am really going to show my ignorance here

ckecking