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Porposing at 60mph

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Porposing at 60mph

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Old 01-23-2003 | 08:56 PM
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powerboat
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Default Porposing at 60mph

I have a 22 degree V hull 28'. It tends to porpise a little when I trim it up. Is this a Center of Gravity issue. Should I move weight forward to lessen this or move weight back.
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Old 01-23-2003 | 09:54 PM
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The CG doesn't change as a result of trim, the Center of Pressure does. By trimming up you're moving the CP rearwards, which in turn is causing the boat to rock over on the bow. As it does, this moves the CP (Center of pressure) forward until the leverage of the drive trim regains advantage, and then you rock back, moving the CP back again, in a continuous rocker motion. You might try a bit of down trim tab when trimming the drive out and see what happens. Also, a prop with more bow lift might obviate the need for a higher trim setting, such as a Mirage plus (unless you're already using one and then we're back to issue #1).

Hope that helps.
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Old 01-23-2003 | 10:40 PM
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There are a couple of things that could be happening. Is the drive tight? Grab it and give it a good tug upwards. There should be no play at all. Also, what is your prop selection. A different prop my help carry the bow.
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Old 01-23-2003 | 11:34 PM
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powerboat
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The prop wasa bravo 1 26, now changing to a 24p.
 
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Old 01-24-2003 | 12:44 AM
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Too much trim
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Old 01-24-2003 | 08:09 AM
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Can you get on plane with a mirage+?
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Old 01-24-2003 | 10:08 AM
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check the steering play too
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Old 01-24-2003 | 02:42 PM
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Powerboat,
I think your'e going to want trim tabs if you don't have them now. I've got the same problem with my Baja Force 235 and have been told by other owners of same that tabs are the only sure fire cure for this boat. They say just a tad down with the tabs stops porposing with little or no loss in top end. I think my deadrise is also 22¡Æ which is probably part of the problem. Ran a 23P last summer and will add tabs this spring. Food for thought.
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Old 01-24-2003 | 08:12 PM
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I have Bennet tabs. I need to get indicators this winter. Looks like that might be the right answer.
Thanks everyone.
 
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