Calculating lateral weight mis-distribution

Discussion in 'Boat Design' started by IronPrice, Dec 11, 2017.

  1. IronPrice
    Joined: Jul 2017
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    Location: NZ

    IronPrice Senior Member

    I have an issue with my trailer boat. It leans to one side at rest and at idle - confirmed with spirit level. It feels level on the plane but its hard to tell.

    I have a multi-roller trailer and the lean causes the boat to go onto the trailer at an angle which causes problems.

    The helm, house dc main, winch supply cables, control cables are all on the stbd side along with the anchor winch.

    So I plan to go out with a bunch of buckets, put them on the port side and fill buckets until I find out how much water is required to get her level. 1L = 1 kg

    Is it that simple? Or does the height of the buckets above the COG and their longitudinal distribution make a difference?

    The other option is just to move things around until she's level with me at the helm?
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Is it a tippy, tender boat ? Do you have an auxiliary motor off to one side ? It tilts to starboard ?
     
  3. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    This is common on small outboards equipped craft. The typical solution is to move some of the weights to port, to counter balance equipment and skipper weights, located to starboard. How long is this puppy?
     
  4. IronPrice
    Joined: Jul 2017
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    IronPrice Senior Member

    Answering both replies.

    It's a medium vee (about 18 degrees) 6m long.

    Not inherently tender but is designed to have an underfloor tank and currently running totes on the deck (1 x 40L each side). She has 2 x 70HP 2S outboards (no aux or aux-bracket).

    Tilts to stbd which is the side the helm and other asymmetrical weight is on.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    Obviously all you can do is shift weights that can be shifted, as far to port as possible. May be easier said than done, though. The idea of ballasting should be the last resort. Take a fat bloke fishing, with a seat to port. Solved !
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    Check for the possibility that water is trapped somewhere, that might be contributing. I vaguely remember having a boat with an inner liner where rain water had somehow pooled in a cavity on one side. Pumped a few gallons out of there, but sounds improbable in your case..
     
    Last edited: Dec 12, 2017
  7. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    This what I like about power cats (amongst other advantages), you can have 3 or 4 big bozos along one side of a boat this size, and not notice much lean, though it has to be said the fore and aft distribution is much more sensitive than many monos.
     
  8. IronPrice
    Joined: Jul 2017
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    Location: NZ

    IronPrice Senior Member

    No water below decks, there is nowhere for it to accumulate. The sub-floor structure is a grid with numerous limber holes. This is only an issue for trailering, no problem when using the boat. If the boat doesn't trailer properly, I have issues with the tie downs.
     
  9. IronPrice
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    Location: NZ

    IronPrice Senior Member

    Would re-installing a sub-floor fuel deck make the boat less sensitive to lateral weight distribution?
     
  10. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Only a trailering problem ? You mean while getting it on to the trailer, or after it is fully on ? What are your tie-downs ?ratchet straps ?
     

  11. IronPrice
    Joined: Jul 2017
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    Location: NZ

    IronPrice Senior Member

    It's complicated but ... if the boat isn't laterally level on the water it won't sit flat on the trailer (wobble rollers). It ends up leaning to one side, with the keel cranked off-centre, the outer-chine (hard) on one side slightly elevated and overhanging the trailer more than it should.

    I use ratchet tie down straps from the aft gunwale cleats (very, very solid) down the sides of the boat to OEM tie down points on the trailer chassis.

    If the boat isn't sitting flat across the trailer then .... on the side where the outer-chine is elevated, the tie down strop has to bend around the chine which causes it to rub. I use some lay flat rubber hose as a sacrificial sheath on the tie down to protect the boat and strop but it would be better if the boat was sitting flat.

    ( I also have a bow tie down which takes load off the trailer-winch during towing but that isn't affected).
     
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