Ideas needed to reinforce mast step

Discussion in 'Boat Design' started by srossfbt, Jul 4, 2019.

  1. srossfbt
    Joined: Jul 2019
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    Location: Mill Valley, CA

    srossfbt New Member

    I've taken on my dad's home built 30' custom sloop (cold molded hull) as a project and need some design ideas to strengthen the mast step. The mast is supported only by a stringer which can't handle the compression load. The stringer and mast is deforming the hull. I was thinking of installing a jock strap to relieve the load but I'm open to other ideas. I've never done this kind of work before and might be in over my head but I want to give this a go and try and save the boat. Here is a pic, can post more that would help.

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  2. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    A thicker stringer.
    Laminate another 50mm of timber over the existing one, and see if the solves it. Make it as long as practicable.
    fallguy likes this.
  3. TANSL
    Joined: Sep 2011
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    Location: Spain

    TANSL Senior Member

    The load of the mast must be distributed over a larger area. Not only increase the thickness of the existing area but increase the area that bears the load.
    fallguy likes this.
  4. jehardiman
    Joined: Aug 2004
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    Is this a MORA boat (i.e. a bay area quarter tonner?)? As a custom, who was the designer? Where are the shrouds landed? How tight are the shrouds? I know there have been issues before with small light cold molded boats with keel stepped masts having hull deformation due to over-tensioning the rig and leaving it that way. Typically, the light open floorless hull does not have enough stiffness to support a constant compressive load from the shroud tension and the wood/epoxy will creep. Though there appears to be a full bulkhead fairly close forward and a deep floor just aft, that won't help the hull if the shrouds are placed poorly. You may need jack stays or some other structure to carry the shroud loads lower into the hull skin.
  5. JSL
    Joined: Nov 2012
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    Location: Delta BC

    JSL Senior Member

    You need at least one floor ( rough guide: a depth about 1" per foot of span) and it should be worked in with a transverse frame and deck beam (or a transverse bulkhead) to take the rigging loads.

  6. Howlandwoodworks
    Joined: Sep 2018
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    Location: USA MO

    Howlandwoodworks Member

    I had a similarly problem with a smaller boat, a hot molded 1953 14' Jet One Design Class. There was nothing supporting the mast step froward of the swing keel trunk support, never had anything there. Things were coming apart at the seams. I replaced the mast step with one as long and wide as would fit and installed a galvanised piece of strap metal under the new step and up both sides of the mast to the deck at the mast opening above. You might want to use a aluminum strap. I adding a sister joist to the deck framing member forward of the mast opening. If the deck will handle the load it would allow for unimpeded traffic way. If you put a large piece of metal under the mast you would run the risk of creating a dew point temperature on the metal, it will sweet and rot out the surrounding wood.
    Last edited: Jul 13, 2019
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