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What makes a boat porpose?

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Old 08-08-2005, 01:16 PM
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Default What makes a boat porpose?

I love my boat , 89 251 Checkmate Conviencer. Did all kinds of work to get it where it is now. But the boat just porposes so easliy. Its very fustrating. It stops at 4,000rpm and up but anything below that it sucks. I tried the drive down not much help. Kinda just makes it come up and down harder. If I give it more throttle it helps but then here I am at of 4,000 rpm again. I tried to zig zag alittle not much help. I just put Eddie Marine 23 inch Billet tabs on the boat But they do not seam to help the boat either. And wouldn't they be the same as drive trim anyway? I dont have Gauges on the tabs and that makes them hard to use. I hate to put any more money in the boat if they wont do the trick either. So what does make a boat porpose more so then others? Its a great boat, fast haul for a 89 and built very well. The boat runs and looks awsome! I hate to give up on it and sell it. But I refuse to bonce up and down the river all summer long!

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Old 08-08-2005, 01:18 PM
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Default Re: What makes a boat porpose?

sounds like you need to blueprint the bottom, I bet there is a hook in it that needs to be taken out
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Old 08-08-2005, 02:05 PM
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Default Re: What makes a boat porpose?

My boat, 1989 24' Chaparral Villian III, has a similar problem but not as bad as you've said. With my drive trimmed all the way in it runs pretty stable. My best compromise between stability and efficient cruising is to have the trims down a little with the drive up a little.

I've heard of adding weight to the nose helps certain models. I tried a 50lb bag of sand in the anchor locker in my cuddy and it made a noticable difference. I'd like to try some more weight to see how it affects the porpose. I'm sure it's costing me some top end, but have it cruise smoothly is well worth it!

Search the General Q&A under the Tech section for "porpose" and you'll find some threads. I got the sandbag idea from there.
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Old 08-08-2005, 02:12 PM
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Default Re: What makes a boat porpose?

I do know that Donzi 22 Classics (and Cig 20's....same basic hull), are very sensitive to what type of prop is being used. Seems there was a thread on this before and someone switched from a 3-blade Mirage to a 4-blade
hydromotive and it did wonders for his.
I'd try hitting the prop guru's and technicians and see if this rings true.
Good luck
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Old 08-08-2005, 02:12 PM
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Default Re: What makes a boat porpose?

Being off balance will cause that. I know my boat isnt balanced very well but i just run some tab and get over it. Balance or a hook would likely be the cause.
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Old 08-08-2005, 05:10 PM
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Default Re: What makes a boat porpose?

Sounds like you have a major ballance issue. Let's start with a different prop and see if that helps things. From there we can look at drive depth, balance, hull design etc.
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Old 08-08-2005, 06:24 PM
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Default Re: What makes a boat porpose?

I think magnum 27 is half right; you need to blueprint the bottom, but the opposite reason. I think you have rocker and thats why the boat is falling off so often. A long straight edge will solve the question very quickly and then go from there. Of course, we both could be correct.
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Old 08-08-2005, 06:50 PM
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Default Re: What makes a boat porpose?

Quote:
Originally Posted by Cord
Sounds like you have a major ballance issue. Let's start with a different prop and see if that helps things. From there we can look at drive depth, balance, hull design etc.
Agreed. What is the current prop?
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Old 08-08-2005, 06:52 PM
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Default Re: What makes a boat porpose?

Checkmate runs the inner set of chines all the way to the transom. Everyone else stops about 4 or 5 feet short of the transom. This gives you tons of stern lift, maybe too much.

Try more weight up front? You could probably use a balast tank.
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Old 08-08-2005, 06:53 PM
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Default Re: What makes a boat porpose?

A very good friend of mine had the same boat, with an HP500 pumped up to 565HP. It would run 80mph all day, straight, true, and solid, and no porpoise. He had a Hydro prop and a B1 prop that he switch back and forth. I would try a few props, and if that does not help, have the bottom blue-printed over the winter.
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