Repairing Rotten wood under mast step on 470 dinghy. What kind of wood to use?

Discussion in 'Sailboats' started by Philippe Thuillier, Jul 13, 2020.

  1. Philippe Thuillier
    Joined: Jul 2020
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    Philippe Thuillier Junior Member

    The small section under the mast step came off exposing rotten wood on the stringer. I suspect the section that broke off had been repaired before because it came off as a very clean and square 5x2 inch.
    So while the repair does not seem too complicated ( apparently I read on other forums I should be able to use a small piece of wood to replace the void, bond it to the wood below, and then use fiberglass to seal it).
    My question is what kind of wood should I use, does it matter for such a small section or should I go for the hardest wood. I read recommendations for Teak, but it seems many people use pine (Doug fir ) as well. And it seems there was a small darker section of wood (possibly teak) in the broken section that came off.
    Any recommendations on my approach and on the choice of wood?
     
  2. Philippe Thuillier
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    Philippe Thuillier Junior Member

    The section to repair is 1/2 inch deep
    99B9D547-88C2-4F97-9BA5-6B5017657363.jpeg DC9FF271-793C-4DBF-8C17-64C2FF57DE47.jpeg D1C055E1-6A9F-43B9-8981-BB47E04ED4B8.jpeg ACA324CB-6699-4285-BB64-FD8DD274EC7D.jpeg 4A4F6651-03CD-48F4-8BAC-BB34A2D5B476.jpeg
     
  3. wet feet
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    wet feet Senior Member

    I would use iroko,purpleheart or maybe locust.Bond it with thickened epoxy and it would probably be best to try for a scarf of sorts at each end to avoid a sharp transition.It looks as though the old step was encapsulated in glass beneath the step itself.
     
  4. Philippe Thuillier
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    Philippe Thuillier Junior Member

    Thanks wet feet
    By a scarf , do you mean fiberglass ?
     
  5. hoytedow
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    hoytedow Wood Butcher

  6. The Q
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    The Q Senior Member

    if it's allowed by the class rules I'd be tempted to replace it entirely with Fibreglass, the floor bearers in our class have the same problem so we just cast one in glass..and bond it in.
     
  7. gonzo
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    gonzo Senior Member

    That is in compression. Pine or fir will be fine. However, you should first remove all the deteriorated wood.
     
  8. wet feet
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    wet feet Senior Member

    I'd be uneasy about the resistance of pine to compressive loads across the grain which is why I recommended hardwoods.One other thought;there is an eye just aft of the damaged area and I hope the line running round it is for a centreboard control line and not a vang as its a bit far from the mast.
     
  9. hoytedow
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    hoytedow Wood Butcher

    Yellow pine is pretty tough.
     
  10. gonzo
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    gonzo Senior Member

    Pine has a compressive strength of approximately 4200 KPa or 610 psi. It is also laminated with fiberglass over it. How much force do you expect? There are at least 8 square inches of wood.
     
  11. hoytedow
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    hoytedow Wood Butcher

    If the base of the mast were as tiny as a heel tip of a high heel shoe I would worry.
     
  12. gonzo
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    gonzo Senior Member

    Let's advice the OP not to laminate a high heel shoe on his boat then.
     
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  13. wet feet
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    wet feet Senior Member

    The 470 tuning guides online recommend using a number of 39 on a Loos gauge.This image gives an idea of what that might be https://images-na.ssl-images-amazon.com/images/I/811QS3JYvpL._SY445_.jpg .I also asked whether the other eye was anchoring the vang as that would transfer the downward component of the vang load to the mast step.Add to this is the load of a crew on the trapeze and potential shock load of coming off a wave crest and crashing into a trough and the loads can be very considerable.
    Having spent several decades as a trapezing crew on slightly larger and faster boats on the North Sea,I would overbuild the mast step rather than use a softwood and hoping for the best.
     
  14. gonzo
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    gonzo Senior Member

    I am not hoping for the best. As an engineer, using an appropriate material and technique is considered good design. Overbuilding is bad practice.
     

  15. Eric Lundy
    Joined: May 2017
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    Eric Lundy Junior Member

    Black locust is a good choice. It is about as strong and hard as oak yet has better rot resistance. May be hard to find mb
     
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