Chainplates and how to attach them to the hull

Discussion in 'Sailboats' started by BobbingAboutBob, Mar 12, 2019.

  1. BobbingAboutBob
    Joined: Feb 2019
    Posts: 2
    Likes: 0, Points: 1
    Location: Scotland

    BobbingAboutBob New Member

    I am investigating the feasibility of creating a pair of new chainplates on a 39ft sloop. The idea is to change the rig from a babystay to forward lowers, for a number of reasons that I won't go into just now.

    I understand that there are four different ways of attaching a chainplate to the hull
    - An external strap bolted through the topsides
    - A strap passing through the side-deck and glassed to the side of the hull
    - A strap passing through the side-deck and bolted to a bulkhead
    - A fitting on the side-deck with a tie-bar transferring the load down to a hull fixing (glassed directly to the hull, or bolted to a bulkhead)

    I'm curious about the pros and cons of each of these methods, and which would be most suitable. I don't think I have a bulkhead in a suitable location so that one is probably ruled out.
     
  2. Ad Hoc
    Joined: Oct 2008
    Posts: 5,854
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    Location: Japan

    Ad Hoc Naval Architect

    Hi BaBob

    welcome to the forum.

    It is all about load transfer. As you can attach it however you want, but you need adequate shear paths for the load transfer, and to make sure there is no bending.
    That's all.

    Thus do the calculations to justify the method.
     
  3. Blueknarr
    Joined: Aug 2017
    Posts: 410
    Likes: 48, Points: 28
    Location: Colorado

    Blueknarr Senior Member

    Absolutely do the engineering calculations.

    From a maintenance perspective:
    • I have repaired many leaky chainplate deck penetrations
    • Encasing a chainplate in glasswork starves it of O2 and makes it impossible to inspect
     
  4. BobbingAboutBob
    Joined: Feb 2019
    Posts: 2
    Likes: 0, Points: 1
    Location: Scotland

    BobbingAboutBob New Member

    Thanks for the replies.
    My feeling is that an external strap running down the outside of the hull would be the simplest solution.
    The main downsides of this approach would be that the strap must have a bend where it passes over the gunwhale, and also it may limit sheeting angle.
     

  5. Blueknarr
    Joined: Aug 2017
    Posts: 410
    Likes: 48, Points: 28
    Location: Colorado

    Blueknarr Senior Member

    Build a ramp of high density filler just below gunwhale.

    All stays interfere with sheeting and/or chaff. Its part of their job description. Your small jibs will sheet inside, while the jennies go around the outside.
     
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