Planing hull inclines to the left

Discussion in 'Boat Design' started by Akeswins, Jul 23, 2018.

  1. Akeswins
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    Akeswins Naval Architect

    here some images
     

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  2. DCockey
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    DCockey Senior Member

    "Planing Hull Stability", Lou Codega, Professional BoatBuilder, October/November 1994 Professional BoatBuilder - 31 - Oct-Nov 1994 https://pbbackissues.advanced-pub.com/?issueID=31&pageID=1

    “Correcting Dynamic Roll Instability”, Donald L. Blount and Dean M. Schleicher, Professional BoatBuilder, August/September 2003 Professional BoatBuilder - 84 - Aug-Sep 2003 https://pbbackissues.advanced-pub.com/?issueID=84&pageID=1
     
  3. Akeswins
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    Akeswins Naval Architect

    @MrEfficiency
    yes, I am sure that the inclination is about 15-18°.
    @fallguy
    no jackplate, but this hull has incorporated flaps.
    @David thanks
     
  4. Akeswins
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    Akeswins Naval Architect

    after reading the interesting articles related to the link, questions increase . It seems that boat does not fall in anyone of the examples . Not a heavy boat, not fore CG, W^2/3 / Awp < 2.9 . But there are maybe some indicators.
    First of all, the integrated flaps surely tend to put the bow down. Not so much, but like 0° flaps. Second, is probably that forward sections with no lifting strakes cutting the flow, increase the common bow suction effect. This, in combination with the rotational effect of the propeller, could do the job.
    So my thinkings to solve the problems are: 1)mount the engine lower. With more possibility to trim (more grip), bow section can rise and the suction friend maybe can be reduced
    2)cut the starboard integrated flap , not all but almost 30%
    3)extend the lifting strakes more forward, only if previous 2 solutions dont run
    what do you think?
     
  5. DCockey
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    DCockey Senior Member

    I would not cut the starboard flap. Boat might then might heel the other way.
     
  6. DCockey
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    DCockey Senior Member

    The area of the planing bottom may be more rearward than the boats in the articles, which means CG may be relatively forward.
     
  7. Akeswins
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    Akeswins Naval Architect

    yes, so cutting a little the flap could show some direction of improving. Of course i don't want to cut all the stb flap, only a small piece, at least to counteract the propeller rotation. I guess that it will not eliminate at all the heel , but at least could decrease it
     
  8. DCockey
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    DCockey Senior Member

    The "flaps" are really just extensions of the bottom. To counteract prop rotation try putting a small wedge or vertical dam on one side.
     
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  9. fallguy
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    fallguy Senior Member

    As a casual lover of boats, I have no credential, but I am telling you so you can disconsider if you like.

    This boat is similar hull shape to one I own that is smaller. The great difference are the strakes. My boat has strakes only on the sides for lifting to get on plane and the keel is sort of a bulb type strake.

    I am curious about whether the strakes were added to fix the problem and did not or whether they were in the original design.

    In my rather simple minded view, the hull is seeking out the most stability and is finding it.

    I would consider removing or modeling stability sans strakes, or leaving the two strakes nearer the keel and shortening perhaps and moving the side strakes forward or away completely.

    One more annoying question. Did you ever sight the keel and or measure the strake to keel distances well?

    I also think I'd try to run a video camera on each side as near to the WL as well to gather details about what is really happening versus guessing.

    Ideally a hydraulic jack plate would get involved as well to see if motor height helps. I don't think it will alleviate.
     
  10. JSL
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    JSL Senior Member

    your problem may?? originate from the forward hull region .... about where the strakes stop. As a first step, I would consider extending the strakes to the stem. These should have sharp edges (use 'L' bar) and not be formed plate with rounded edges which are essentially useless.
    One odd feature I notice on your "Lines Plan' profile is the chine is not really a 'fair' curve: it appears to have an abrupt change about amidships. It would be useful if the 'Lines Plan' showed the buttock lines.
    Finally, earlier I called it chine walking etc. but a more accurate term might be "progressive heeling". Correcting this 'problem' can sometimes be a long process and may not always be successful.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    This falling to the left is not changed with alterations to engine trim ? If it still does it with the engine trimmed right out, when you should basically be just running on a monohedron, if I interpret the pics correctly, then the curved forward portions of the hull can be ruled out as the cause.
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    It looks like there is an abrupt turn in the shape where you mention, one assumes a conical development generating line can be drawn from the point where the forefoot begins to turn, to the chine just touching the forward end of those two strakes. Hence why I ask whether trimming the engine right out, putting that forward part clear of the water, eliminates the issue. If it does, suspicion then falls upon the forward shaping.
     
  13. JSL
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    JSL Senior Member

    So...., if someone asks me about testing a boat I suggest they load it up, get to cruising speed in calm water, and then trim the bow down (tabs, engine, weight shift/move people for'd ) to see what happens. Sometimes the 'heel' can be gradual ( about 3 seconds) or sometime sudden and without warning. Either way, people can be scared.... and possibly get hurt.

    This was the reason I mentioned the 'above' yesterday.
     
  14. Mr Efficiency
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    Mr Efficiency Senior Member

    I have been in boats that have a sudden change from the monohedron, though, and they showed no such vices. But it was a straight vee section throughout.
     

  15. Akeswins
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    Akeswins Naval Architect

    @DCockey
    yes they are extension of the hull. We could consider them as a neutral plaps, that act as smaller wedges or even smaller dam (interceptors). So decreasing their surface, center of wetted surface will shift forward, and stern lift decreases too.

    @MrEfficiency
    Extending/modifyng the strakes is not possible now. I can only suggest to the boatyard some small changes now that not require weldings/repainting. So I have to move step by step.
    As for the trim, they say now there is no difference using it. But the first modify, lowering the engine, will go in that direction.

    @fallguy
    no, i havent' measured strikes simmetry, i did not see the hull personally. Only photos but the boatyard measured the distances of the strakes from the keel and they are simmetric.

    @JSL
    chine has not abrupt changes and volumes seem fair. Otherwise the developable surface would have turned on some alarm.

    Now they will make another test (more accurate) by the end of the month with another engine. I let you know .
     
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