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Ok, I finally was able to borrow a friend's place diverter and found that it wasn't as effective as I had hoped. My fundamental question is what should I do now to fix my top-end problem?
Before - (No Place Diverter)
0-50mph - porpoising
50-70+mph - extreme porpoising and chine walking
After (With Diverter)
0-50mph - No porpoising, major loss of efficiency because I had to force the bow down.
55mph - Trimmed with bow all the way down, still porpoising. Couldn't break 55mph at WOT because of forcing the bow into the water.
55+mph - Trimmed with bow all the way up.... Worse than what I experienced before! Chine walked all over the place and porpoised like mad. I swear I caught two feet of air in each porpoise cycle!
I found that only in the neutral trim position of the diverter could I achieve the speeds I was getting before I even put it on. Kind of depressing, but good to know I won't have to buy one now.
If anyone's got a good answer, please let me know. I just want it stable at 70mph. Thanks!
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Most boats benefit from a place diverter ,but in your case I would speculate the problem is your hull if your boat chine walks at 50+ minus place diverter .In your case a small trimtab setup like bennetts, would be another route.It would stop porpoising and chine walking more efficiently than the place.Just my 0.02 cdn :)
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If it's porpousing at all speeds like that I would check a couple of things.
Does the boat have any "rocker" in the hull? I.E. is the bottom of it flat or does it have a big bow in the center of it?
2ndly it might be the center of thrust is wrong on the boat. Did you try anything like a "droop snoot?" Perhaps lowering the thrust line will help you.
I know an I/O's X-Dimension can be one of the most important things in solving a porpousing problem.
RD
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my friend has an old Hondo day cruiser and he has the exact same problem. He's looking into installing trim tabs. I'll have to find out if they worked or not.
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RiverDave2:
If it's porpousing at all speeds like that I would check a couple of things.
Does the boat have any "rocker" in the hull? I.E. is the bottom of it flat or does it have a big bow in the center of it?
2ndly it might be the center of thrust is wrong on the boat. Did you try anything like a "droop snoot?" Perhaps lowering the thrust line will help you.
I know an I/O's X-Dimension can be one of the most important things in solving a porpousing problem.
RDHoly Shit Batman, Riverdave is bustin some knowledge on the jetboats! :D
Diggler,
Dave and Spectra's info is right on. I would next mess with a droop to see if that helps at all with the porpoising. I'm a little curious how you know its chine walking if it is porpoising as bad as you say it is. With that much up and down motion, you are going to "feel" all kinds of input from the boat and the water's surface.
If the droop will quell the porpoising but you then still have a chine walk situation, the tabs would be the next upgrade. But Dave hit upon something very important... Your hull profile. If there are major issues with your hull, the droop, diverter, and Tabs will just be bandaids on a bigger issue. For a jet, the bottom should be fairly flat towards the back of the boat. What kind of hull did you say you had again? Maybe there is past experience with this hull on the boards that can get you results without all the trial and error. Good luck with it, and let us know what happens.
Chris
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Trim Tabs are going to slow the boat down just like trimming down on the place diverter did.
To scrub a little less speed you could make a Cav Plate setup, but ultimately all of those options are going to slow you down as well.
Does weight distribution in the boat make any difference as far as the porpouse?
Still waiting to hear if the bottom is straight or not.
RD
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!
RD
[ December 03, 2002, 03:06 PM: Message edited by: RiverDave2 ]
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Hey, thanks for the input everyone. Here's the pictures of the hull...
[img]http://free.***boat.net/gallery/Forum_Graphic_Depot/PF_at_Lost_Isle_21.JPG[/img]
Now here's some specific pictures of the bottom of it.
[img]http://free.***boat.net/gallery/Forum_Graphic_Depot/MVC-156F1.JPG[/img]
[img]http://free.***boat.net/gallery/Forum_Graphic_Depot/MVC-152F1.JPG[/img]
I can't add a droop snoot because I have a 12JC pump. However, I could add a ride plate, but I don't know if that will help either. Trim tabs would probably work, but slow me down also. Should I just accept my fate that I exceeded the design of my hull?
Thanks to everyone again!
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Oh, RD, almost forgot.... The bow gas tank has been taken out. I have saddle gas tanks of 14 gallons that distribute the weight to the rear.
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Oh, one more answer for FlatBroke.... I know I've been chine walking because the boat will start to rock back and forth about 40-45 degrees as it balances on the rounded keel. In fact, I was stupid once and let off the gas and when the bow caught, it hit a wake weird and almost spun me out at high speed. whew!!!