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Old     (el1070)      Join Date: May 2007       06-05-2007, 8:49 PM Reply   
On our boat there is a 220 hp Merc. engine. we are running a 19 pitch prop. once you get around 5 people in, the boat takes forever! to get out of the whole. I am interested in putting a lower pitch prop on but I am worried that the engine will overrev. How low can I go?
Old     (05mobiuslsv)      Join Date: Apr 2006       06-05-2007, 9:06 PM Reply   
Call OJ or ACME, they are the only one's that will tell you exactly what you need.
Old     (rallyart)      Join Date: Nov 2006       06-06-2007, 6:59 AM Reply   
I assume you have a sterndrive. If you do there are a few things you can try in addition to the prop. First would be a hudrofoil attached to the leg.

As far as the prop goes you need to know the RPM that your boat is running when you are at top speed with a normal load. Then you need to know the maximum RPM that your engine could run at.
Old     (rallyart)      Join Date: Nov 2006       06-06-2007, 7:42 AM Reply   
earling that should say hydrofoil instead of hudrofoil on my earlier post.
Once you have that info you can use this formula to calculate how low the pitch can go:

Current pitch TIMES RPM at top speed DIVIDED BY RPM maxumum rated EQUALS your new pitch.
Eg. 19 X 4200 / 4600 = 17.3
So, IF you are running 4200 now and your engine can run 4600 you could get a 17 pitch without any risk of over revving the engine.

Once you know the Maximum RPM of the engine you could also just put a piece of red pinstriping or tape on the tachometer to remind you of the Redline for your engine and run whatever pitch you choose. Just throttle back a bit when you get to the redline so you don't over rev.
Old     (hal2814)      Join Date: Feb 2006       06-06-2007, 7:46 AM Reply   
For a 220HP Merc, I'm assuming you have the Alpha One outdrive. It's redline is 4500RPM. You can pitch it at whatever you want but if you pitch too low, you'll just have to keep the redline in mind. I marked it with tape on my boat to make it easy for other drivers to remember for days when i go with a lower pitch.
Old     (dkjbama92mariah)      Join Date: Dec 2005       06-06-2007, 11:19 PM Reply   
1" of pitch = 200rpm. General rule


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