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

    Hi all, I would like to discuss about an issue that i noticed in a boat that i recently tested.
    This boat is a custom aluminum hull , 7m, walkaround type, powered by an outboard Honda bf 225 .
    She achieves near 35 kn @5400 rpm with 14,5x15" 4 blades apollo prop and something less with 3x14.5x19 solas inox.
    For the weight tested (1700 kg + 150 kg liquids + 2persons) performances are not exceptional but this is not the problem.
    The problem is that she tends to incline to the left at all the planing speeds range, from 12-13 kn to wot.
    The propeller, with its rotational effect , naturally tends to incline the hull leftwards but not so much to justify this inclination, we are speaking of 15-18°, that are big numbers.
    The hull afloat has good stability and also at planing speed does not suffer for the movement of persons. This inclination is not even compensated by 2 persons sitting on the starboard side.
    Afloat the inclination is 1-2° to the starboard side, so the weights are correct.
    Hull is quite common,has an average deadrise (17 transom, 50 bow) , 1 longitudinal strike for each side, and a wide flat chine (about 20 cm wide)
    Boatyard says that hull is simmetric, with no deformations . And seeing the photos, all seems correct.

    My suppositions are:
    -keel that doesnt lie in the symmetry plane (to be checked, but i guess, if yes, no more than some mm in 7 meters)
    -deformations in the hull : it seems no
    -propeller too big: i would say no, the diameter is correct for the size/weight.
    -lack of stability at planing speed: no, the boat has good stability
    -small zync fin on the outboard to be regulated : maybe? but it seems too small to be responsible of this large angle of inclination

    have you ever experimented something alike? do you have other suggestions?

    Thanks and Best Regards
    Alessandro
     
  2. JSL
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    JSL Senior Member

    Sounds like 'chine walking' or 'chine running' which is usually a hull form issue. You try to get up on a plane and the boat lays over to port or stbd side. I have seen good boats do it if forced to run 'level', particularly in glassy smooth water. Some boats can be modified and somewhat 'cured' and others are literally incurable 'write-offs'. My 'scariest' was a 33' catamaran (asymetric hull form) crew boat that would suddenly lay over (heel)about 10 deg. once up on the plane. Does not sound like much but for a cat it is quite noticeable. Through extensive modifications we did eventually minimize the problem to make the boat useable (top speed 43 kn) without terrifying the skipper and passengers.
    Another case was a 20' (6m) aluminum center console.... despite all the cures (and even some novel ones) it was incurable.
    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 scared.... and possibly get hurt.
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    Inclination of 15-18 degrees seems extraordinary. Are you sure it is that much ?
     
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  4. fallguy
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    fallguy Senior Member

    Ouch.

    Is there a jack plate? Guessing not.

    It sounds like the motor is too low in the water. Often with conventional chine walk, the motor can be up too high, but this is not technically chine walk. This sounds like the motor is the only bit in the water until the boat lays over. If this is true, then any rotational or trim effects are magnified and realized.

    More like chine falling over.

    You must maintain more hull in the water with your hull design I'd say.

    Of course once you start to go up on the transom; you may experience chine walk, so adjust slowly. Chine walk is dangerous and you must throttle down slow out of it to avoid incident.

    Technical chine walk is a shifting from side to side.

    As jsl states, hull forms may be incurable.

    Also, what is the max hp rating per the manufacturer.
     
  5. fallguy
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    fallguy Senior Member

    Also, use caution raising up the motor to make sure you don't lose coing water.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    Hard to see how the depth of the engine setting, is implicated here. If it was porpoising, you might think so. I agree with fallguy, that it isn't chine walking, which is an oscillation similar to porpoising, but crosswise, not lengthwise. I would advise checking to see if the engine is pointing dead ahead, when the boat is running in a straight line, if it is pointing to say, the one o'clock position, for whatever reasons, that will tilt it to the left.
     
  7. DCockey
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    DCockey Senior Member

    Thread about a boat with similar behavior: Planing Instability https://www.boatdesign.net/threads/planing-instability.48481/

    Relevant articles about planning boats which heel to one side above a certain speed:

    "Dynamic Stability of Planing Boats" Blount and Codega, Marine Technology, January 1992

    "Planing Hull Stability", Lou Codega, Professional BoatBuilder, October/November 1994

    “Correcting Dynamic Roll Instability”, Donald L. Blount and Dean M. Schleicher, Professional BoatBuilder, August/September 2003
     
    Last edited: Jul 24, 2018
  8. fallguy
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    fallguy Senior Member

    Listing 15 degrees at speed would make the boat nearly undrivable one would think.

    I'm not certain they ever get to porpoising even.
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    I was talking to someone with a planing power cat recently, that was leaning disconcertingly to the left, underway at speed. It was level at rest. It had recently been fitted with full depth, alloy outboard pods. It seems the pods were not quite identical, and the starboard one had a touch more or less rake, and was acting like a trim tab, with a different ( positive) angle of attack to the hull ahead of it, Without putting a wedge against the old transom to level it up, the solution that worked well enough was to trim the port engine well in, and the other side well out. That is not the ideal solution, of course, as fore and aft trim is no longer available, though in this instance it was not a great problem, the trim angle was quite OK for normal running.
     
  10. JSL
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    JSL Senior Member

    Lots of quick responses here. It might be more productive to lessen the guesswork. More accurate information about the boat: Lines Plan, General Arrangement Plan, tanks arrangement, photos, amount of heel, conditions, etc would help.
     
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  11. Mr Efficiency
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    Mr Efficiency Senior Member

    Ideally, a video taken for a drone ! Certainly not a "normal" problem from what sounds a "normal" design, but the lines plan would help. I seem to recall a recent thread, from I think Western Australia, with a similar complaint, about an alloy boat that, like this one, had wide chine flats, but his leaning problem was in beam seas. In the case of this boat, I am tipping it has "no feedback" steering, which sometimes makes it harder to work out what is happening.
     
    Last edited: Jul 24, 2018
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  12. DCockey
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    DCockey Senior Member

    Static stability with the boat at rest and stability at speed can be different. The paper and articles referenced in my previous post describe situations with boats which were symmetric and had good stability at rest. However at speed they would heel to one side and remain at that heel angle. The cause is thought to be the pressure distribution of the water flowing around the curved forward portion of the hull. The Professional BoatBuilder issues are available at Professional BoatBuilder Magazine - Written for boatbuilders, repairers, designers, and surveyors https://www.proboat.com/
    The Marine Technology paper is available from SNAME: Home - SNAME http://www.sname.org/home

    The boat in the thread linked had similar behavior which was corrected by adding lifting strakes to the bottom.
     
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  13. Akeswins
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    Akeswins Naval Architect

    Thanks for all replies.
    I give other informations: first of all, the engine was mounted with cavitation plate at the same height of the keel. Then it has been rised 1 inch, and no differences.
    Then, this is not a chine walking that is a side-to-side movements: the boat lies on her left side and is very stable. Nothing to do with Planing Instability https://www.boatdesign.net/threads/planing-instability.48481/

    She doesnt porpoise, doesnt roll.. act as a good hull in the rough sea but keeps this inclination. CG is averagely at 0.4 LWL, the trim angle afloat is about 0 and also running is between 3-4° correctly.
    Another thing could be the mount of the engine, it needs to check if perfectly centered. Some time ago i saw a boat with the same problem but the shaft was not in the centerline. I am sure that engine installer hasnt' make this fail.

    As DCockey says, i agree that something goes wrong with pressure distribution withe curved forward portion of the hull . The question is "why". Lifting strakes are already present and extended to the transom . Probably their extension in the forward part is not enough? I search for a lines plan to go deeper
    @DCockey, have you a link for the related issue in sname or proboat site?
     
  14. fallguy
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    fallguy Senior Member

    Shape of the keel?
     

  15. fallguy
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    fallguy Senior Member

    Do you have a picture of the boat on the hard with a shot of the running gear and the keel from aft?
     
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