Planing hull inclines to the left

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

  1. fallguy
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    fallguy Senior Member

    What happens with the craft when they trim up the engine in this listing condition underway or before the listing condition at start?

    Will the boat porpoise? Is it listing even when porpoising?

    What is the transom angle?
    Transom measured height?

    It seems a bit of trim testing is in order whether with simply trimming up the engine. If trimming her up does nothing to the list; I would be surprised.

    Alternatively, an inexpensive test would be wedging the motor to see if that has any effect. Although this is going against my intuition; you could get the stern lower this way and determine if the bow is affecting the list. Often wedging is undesirable, but would be inexpensive to test say a 3 degree temporary set.

    But trim effects ought to be known and measured.

    I think it would be a little heady to believe integrated tabs perfect if never tested on a prior hull, so if engine trim adjustments result in affecting this condition; you may need to say goodbye to those and put in some tabs that offer some flexibility.

    The boat I own that has nearly the same bottom shape porpoises badly on a straight up install. I wouldn't expect your design to porpoise per se, but if you can't, that would be odd.
     
  2. JSL
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    JSL Senior Member

    I suspect it might be an 'airfoil' effect for'd . A 'Lines" showing the buttock lines would be helpful.
    Had another look at the 'Plan' view: the angle of entry of the waterlines looks quite fine for a boat of these L/B proportions which further reinforces my suspicions.
     
    Last edited: Jul 25, 2018
  3. Akeswins
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    Akeswins Naval Architect

    here the buttocks every 100 mm
    entry is fine but less than other designs that not suffer at all.
    currently we have no data about changes of heel depending on engine trim regulation. We will have other elements in next trial.
    The boat does not porpoise.
    transom angle 13°, height 615 mm (XL)
    Of course we all know that removing current integrated tabs and replacing with electric trim tabs, the question should be solved, lowering the port flap . But I would like to suggest them a less expensive solution, working on the existing tabs and reducing them
     

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  4. JSL
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    JSL Senior Member

    Maybe I missed it but I will ask - who designed this boat? The designer/naval architect should have some input.
     
  5. Ike
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    Ike Senior Member

    Just curious. Is the CG you have shown, for the hull only, or does it include any super structure (consoles, cabins, etc)? All the parts that aren't shown. The actual CG could be higher if these aren't included which would certainly change the balance. The USCG had a boat that did this. A 3o foot motor surf boat. I have seen some production recreational boats that also have a tendency to heel one way or the other when on a plane. It happens more often than not with deep vee hulls that are too narrow. Not saying yours is too narrow. It doesn't appear to be.
     
  6. DCockey
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    DCockey Senior Member

    That boat and it's behavior is discussed in the articles I linked to in a post above.
     
  7. JSL
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    JSL Senior Member

    As mentioned several posts ago, more info & drawings on the boat ( GA, structure, tankage, etc) would reduce or eliminate a lot of mind reading, guess work, and time wasting.
     
  8. Ike
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    Ike Senior Member

    David: I am familiar with the issues the 30ft MSB had. (I even had the Master Chief that got thrown out of the first one, at my unit in San Francisco) However the hull lines for it are markedly different than the one posted here. Thus my question about the CG of the hull. CG, Center of Buoyancy, hydrodynamic lift, as well as negative and positive pressures on the hull, all play a part. I read Lou Codega's study when it first came out but I need to go back and read it again. There has been a lot of water pass under the boat since then.
     

  9. Mr Efficiency
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    Mr Efficiency Senior Member

    The OP says the next step is to lower the engine height, by my reckoning, if the engine is perched too high, the lean will be to the right, not the left.
     
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