Planing hull inclines to the left

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

  1. fallguy
    Joined: Dec 2016
    Posts: 3,842
    Likes: 576, Points: 123, Legacy Rep: 10
    Location: usa

    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
    Joined: Nov 2012
    Posts: 800
    Likes: 56, Points: 28, Legacy Rep: 41
    Location: Delta BC

    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
    Joined: Jun 2005
    Posts: 202
    Likes: 9, Points: 28, Legacy Rep: 10
    Location: Sardegna Italy

    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
     

    Attached Files:

    • p5.JPG
      p5.JPG
      File size:
      32.5 KB
      Views:
      98
  4. JSL
    Joined: Nov 2012
    Posts: 800
    Likes: 56, Points: 28, Legacy Rep: 41
    Location: Delta BC

    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
    Joined: Apr 2006
    Posts: 2,448
    Likes: 315, Points: 83, Legacy Rep: 1669
    Location: Washington

    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
    Joined: Oct 2009
    Posts: 4,826
    Likes: 374, Points: 83, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    That boat and it's behavior is discussed in the articles I linked to in a post above.
     
  7. JSL
    Joined: Nov 2012
    Posts: 800
    Likes: 56, Points: 28, Legacy Rep: 41
    Location: Delta BC

    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
    Joined: Apr 2006
    Posts: 2,448
    Likes: 315, Points: 83, Legacy Rep: 1669
    Location: Washington

    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
    Joined: Oct 2010
    Posts: 9,334
    Likes: 708, Points: 113, Legacy Rep: 702
    Location: Australia

    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.
     
  10. Akeswins
    Joined: Jun 2005
    Posts: 202
    Likes: 9, Points: 28, Legacy Rep: 10
    Location: Sardegna Italy

    Akeswins Naval Architect

    Hello, a lot of time has passed after opening this thread but i report the updates.
    The problems has been solved in the further (same) boats , just cutting the fixed "fishtail" integrated tabs protruding over the transom. Also the speed has increased and now the boat is correctly balanced with no heel. Modify has been applied also in first boat improving speed by 3 knots and fuel consumption, now about 25 liter per hour @ 23/24 knots. Maybe it can help if someone experienced this issue.
     
    hoytedow likes this.
  11. DCockey
    Joined: Oct 2009
    Posts: 4,826
    Likes: 374, Points: 83, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    Thanks for the update.
     
  12. fallguy
    Joined: Dec 2016
    Posts: 3,842
    Likes: 576, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    Yes.

    One of my hunches was overtrusting those tabs. I am glad the issue was relatively simple to resolve and thanks for the update. I wondered whatever happened.
     
  13. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,334
    Likes: 708, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    I'd be interested in knowing why those (unusual) fixed tabs were there is the first place, and how their removal fixed what seemed a drastic heel. At the angle of heel mentioned, surely the one on the high side was no longer in the water influencing matters. So how was the one on the low side dragging it down ? A mystery, especially if these tabs were just a continuation of the bottom.
     
    Barry likes this.
  14. fallguy
    Joined: Dec 2016
    Posts: 3,842
    Likes: 576, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    the reason I did not 'like' them was they had no variability, so if the helmsman was say on the port side, one would assume the port tab would have a greater likelihood of dragging, or rather, any deviation in the weights inside would be magnified in effect...they would be like driving a stick down on each side
     

  15. Kayakmarathon
    Joined: Sep 2014
    Posts: 7
    Likes: 1, Points: 3, Legacy Rep: 10
    Location: SeaSide

    Kayakmarathon Junior Member

    Was this a problem with other copies of the hull built?
    Could the hull twist ever so slightly while under way?
    Cars with rear wheel drive when accelerated hard from rest can generate so much torque the frame twists.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.