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I've got a heavy(9000lbs) Boston Whaler with twin 250 2 strokes on it. Max RPM was 4900 trimmed all the way in. 3 blades on it now with 21 pitch. What pitch should I go too? Is there any difference between a 3 and 4 blade with a 19 pitch? Not much interested in speed.
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What is recommended RPM range of the motors (what motors)?
What is your max RPM trimmed out?
What are you interested in optimizing if not speed? -
I believe the max WOT should be 4500-5500. Should this be checked at max trim to get the highest RPM possible? It seemed a little sluggish to get on plane. I would like to get and stay on a good plane at medium RPM.Comment
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props
1 inch change is about 200 rpm change....stay with a three blade and don't "Run" trimmed in...find the "sweet spot"Comment
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"Max RPM" is found by running wide open, with the trim as high as it will go until you either ventilate or speed drops off, instead of climbing.
Prop the boat to get into your specified range with your typical/normal load and you should be just fine. I prefer to be on the higher side of the range so that when I'm running a heavier load, I'm still not bogging the engine. For those few times when I'm running light, I can control the Max RPM with throttle.2000 Yamaha OX66 250HP SX250TXRY 61AX103847T
1982 Grady Weekender/Offshore (removed stern drive & modded to be an OB)Comment
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Bajakeith, I'm interested to know why you suggest staying with 3 blade on such a heavy boat?Originally posted by bajakeith View PostComment
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props
Hi Zeno,, a three blade is a good choice of prop for such a app..a 4 blade is usally for more bow lift..Dennis's post is spot on...also when blindly trying to find the right pitch prop..it not a good thing to start changing number of blade's... going up one (1) inch of pitch will lower RPM 200...going down one (1) inch will raise 200 rpm.....in general...a 21 inch pitch prop in this app,, sounds WAY too much !!
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