Need some ideas on porposing
10-02-2010, 10:58 AM
#11
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Location: EASTON MA.
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I'll try switching the rotation first and some trim up. It did seem to get worse as I trimmed up but not having enough prop to power thru is holding me back. I have more throttle left but I know I'd be up on the limiters. Do you think I should re gear the lowers and then start over? I'm pretty confident that the boat has 115-120 in it if I can get it to settle down a bit. far as I know it was always a Bravo hull. Ran out of Kurts Marine in Brick NJ, Danny built the engines I have now and they still do the heavy work on it. Wish the season was gonna hold out a little longer so I could do more changes.
10-03-2010, 09:30 AM
#12
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I have found porpoising to be a function of the center of gravity of the boat and the condition of the bottom running surface. It's telling me the CG is alittle forward of the lifting point of the tunnel. If you can imagine the air pressure in the tunnel all results in lift at a specific point, your CG is slightly forward of that point. Be sure everything of weight is out of the nose. I would do all testing at neutral trim, limiting your up or down to less than 10% from neutral (propshaft in line with the bottom). Next check the bottom carefully for hooks, they will drive the boat back to the water while the tunnel is trying to lift it. I buy 80# bags of quickcrete because they are cheap, add weight as far back by the transom as possible and compare the handling. Yes the boat will be slower, I'm more interested in removing the poroising or seeing the effect. Finally I would sand the bottom to reduce water surface tension. A shinny smooth surface may look good but it sticks to the water. Whatever you choose to do make one change then run the boat, you will never learn anything making multiple changes, but you may get lucky.
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02-13-2011, 09:39 AM
#15
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I have found porpoising to be a function of the center of gravity of the boat and the condition of the bottom running surface. It's telling me the CG is alittle forward of the lifting point of the tunnel. If you can imagine the air pressure in the tunnel all results in lift at a specific point, your CG is slightly forward of that point. Be sure everything of weight is out of the nose. I would do all testing at neutral trim, limiting your up or down to less than 10% from neutral (propshaft in line with the bottom). Next check the bottom carefully for hooks, they will drive the boat back to the water while the tunnel is trying to lift it. I buy 80# bags of quickcrete because they are cheap, add weight as far back by the transom as possible and compare the handling. Yes the boat will be slower, I'm more interested in removing the poroising or seeing the effect. Finally I would sand the bottom to reduce water surface tension. A shinny smooth surface may look good but it sticks to the water. Whatever you choose to do make one change then run the boat, you will never learn anything making multiple changes, but you may get lucky.
