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Old 06-21-2019, 10:10 PM
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Old 11-05-2019, 03:17 AM
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Default Need prop choice help...

I have an Ď86 Pennyan 21í fishing boat engine is a 4.3 omc cobra sterndrive. It currently has a 15x17 3 blade prop. I can only achieve 4,000 rpm and 33 mph at WOT. Iíd like to get my rpm in the 4500 range and squeeze 35-38 mph if possible. By changing to a different prop but I can get any info to suggest which direction to go to get both a few more rpmís and a few more mph. Thanks in advance for your help.
Old 11-05-2019, 10:10 AM
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Hello Oxbow 26

You could go to a Powertech OFS 3 blade 15 1/4 x 15.As you increase rpm there is room to get speed since I believe you have not achieve maximum hp at 4000 rpm on this set up.

Please forward any questions!
Old 11-05-2019, 10:53 AM
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Thank you! Thatís the most complete answer Iíve gotten. Iím certain Iím not obtaining peak rpm and several have mentioned a 15 pitch prop but none have said how itíll effect my speed since Iím losing pitch. Thatís where Iím lost... I need RPMs (dropping pitch) but need a few more mph too so itís a catch 22
Old 11-05-2019, 10:57 AM
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Oxbow 26

There are certain times when going to a lower pitch will reduce speed.
Sometimes we have to opt going to a lesser pitch to increase longevity of the engine and not so much expecting a result of speed increase.
I believe in this particular case you should see a speed gain.
Again, it depends on whether the engine has already hit the maximum horsepower curve or not.

Please forward any questions!

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