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Propeller Sizing and Drivetrain Consulting

Old 06-21-2019, 11:10 PM
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Lightbulb Propeller Sizing and Drivetrain Consulting

Utilizing the latest software we can analyze your propeller application and determine the correct size, type and material for your vessel.

Shaft sizing calculations to recommend the proper diameter and material for your application.

Contact us today or post any question you have - Get Back On The Water!


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Old 11-05-2019, 04:17 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.
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Old 11-05-2019, 11:10 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!
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Old 11-05-2019, 11:53 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
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Old 11-05-2019, 11:57 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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