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Author Topic:   Proper prop pitch
rbohn posted 06-25-2003 10:36 PM ET (US)   Profile for rbohn   Send Email to rbohn  
Which pitch prop should I buy?
1989 17' Montauk
1989 Yamaha 90 (Max RPM rated 4500-5500)
Currently running Stainless 13 X 19 Prop
Raised motor one hole (Bottom of motor bracket now 2" above transom. Anti-cavitation plate approx 1.5 to 2" above bottom of hull.
RPM's 4,900 trimmed out. Saw 5,100 running into the wind in a slight chop.
Should I try a 13 X 15? I hesitate to raise the motor any higher. Boat seems to be a little squirrely sp? already. A hard turn will cause cavitation unless I trim the motor down now.
Any suggestions for a prefered brand of stainless prop?
Thanks
rbohn posted 06-25-2003 10:40 PM ET (US)     Profile for rbohn  Send Email to rbohn     
I neglected to mention. Current top GPS speed 41-42 mph.
taildropper posted 06-25-2003 10:50 PM ET (US)     Profile for taildropper  Send Email to taildropper     
My mechanic just finished rebuilding my 90 Evinrude. To try it out, he used his SS 13 3/4 X 15 prop. It came with 13 1/4 X 15. He said it performed MUCH better.
Sal DiMercurio posted 06-26-2003 01:14 AM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Your over proped by 3 inches.
A 16 pitch will put you right at 5,500 rpms.
Not many companies make a 13 x 16 prop as they usually come with the pitch in odd numbers such as 13, 15, 17, 19, 21, 23.
You could buy a Merc prop [ fits Yamaha ], size 13 x 15 & have some cup put into it, thus equal to a 16p & 5,500 rpms.
A 13 x 15 will put your rpms close to 5,700 rpms, 200 over recomended max.
I would try a 3 blade 13 x 15 S/S Stiletto [ with a Merc hub ] with enough cup to equal an inch of pitch, the prop shop will know what your saying.
Sal
Bigshot posted 06-26-2003 01:06 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Wit the Yamaha 13x17 SST prop my same package hit 5400 with 1-2 people and bottom paint. DO NOT run smaller than a 17"
rbohn posted 07-01-2003 10:00 PM ET (US)     Profile for rbohn  Send Email to rbohn     
Thanks for all your input. I am ordering a 13 X 15 prop and will test it. If the RPM's exceed 5,500 I will have it cupped to bring them down a bit.
Thanks again.
Bigshot posted 07-02-2003 10:10 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I guess you missed my post.....TOO SMALL!
rbohn posted 07-02-2003 09:24 PM ET (US)     Profile for rbohn  Send Email to rbohn     
OK Bigshot. I agree. I was assuming a 2" change in pitch got me 200 RPM's. I see now that for each 1" change in pitch I get a 200 RPM change. The drop by 2" from a 19" to a 17" pitch should take me from 4,900 up to 5,300. I think that is close enough to the max RPM's.
Thanks for checking up on me!
I will let you know how I make out after I try it out.

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