Prop question

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NicAndI

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Aug 31, 2013
4
TBD TBD TBD
Need a little help pls.
I'm in the process of buying a 1989 First 285 and the 2 blade folding prop is pretty worn + since I won't be racing it I would rather have a fixed 3 blade on it.. The problem is I don't know how to figure out the pitch and diameter ?!

It has a model 2002 volvo penta, 18hp, a 25mm shaft + a gear ratio of 2.37.
 
RichH

RichH

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Feb 14, 2005
4,773
Tayana 37 cutter; I20/M20 SCOWS Worton Creek, MD
Go to http://www.miwheel.com/propellers/prop-it-right/ and fill in the 'calculator forms' to get your 'close' answer. Youll need to calculate the rpm of the current propeller vs. engine rpm (correction for transmission speed/gearing ratio ..... Plus, determine the pitch and diameter of your present prop (should be stamped on the hub of your current prop.) and compare the data of the Michigan Wheel site results.
Such comparison should include the *current* boat speed vs. engine rpm.
 
G

Grouperhound

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Sep 8, 2013
71
Beneteau Oceanis 45 Rock Hall, MD
Assuming a theoretical hull speed of about 6.5 knots, 3600rpm max, and prop efficiency of 65%, you are looking at about of 8" pitch. I didn't try the prop calculator but will give it a go.
 
Ron20324

Ron20324

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Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
Most prop companies will calculate for you. Either online or the phone.
 
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