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Old 05-07-2012, 11:00 PM   #1
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Ruby Red Lip
 
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Default Prop advice

Ok finally got the boat in the water but with the bigger engine it over revs. First off as much info as I know. It is a mercruiser 260, in a 20 foot formula thunder bird, the current prop is a three blade 15-3/4 x 17 as I aproach wide open throtle it jist barely pegs the tach at 6000. As I understand wot rpm shoul be like 4400 to 4800. Does anyone have input on a new prop for this boat?

Thank you
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Old 05-07-2012, 11:07 PM   #2
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I've got a 15x 19 you could try...
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Old 05-08-2012, 12:01 PM   #3
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That would probably be gelpfull at least kinda get a base line im pretty sure I am going to need to end up being around a 23 pitch.
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Old 05-11-2012, 10:04 AM   #4
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Ok so I went up to the prop shop and picked up a cupped 21 pitch prop. We picked up about five miles an hour but we still peg the tach out over 6000. Am I going to be able to get that down to around 4800 with prop or am I going to have to change the gear ratio.
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Old 09-07-2012, 08:39 PM   #5
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You should be able to get it down with the correct diameter and pitch. More pitch less rpm... I believe it is something like for every inch of pitch you go up, it drops rpm by 3-4 hundred. That's apprx but gives ya a starting point
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Old 09-08-2012, 12:55 AM   #6
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A lot of good info here: http://www.dansdiscountprops.com/propeller101.htm
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Old 09-08-2012, 05:55 AM   #7
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Contact the boat manufacturer and ask them.
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