Comments on Support Under Compression Post

Discussion in 'Boatbuilding' started by savagepoint, Sep 6, 2021.

  1. savagepoint
    Joined: Oct 2017
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    Location: Vermont

    savagepoint Junior Member

    I've been wondering what's under the compression "structure" on my S2 8.0B sailboat and what kind of shape it's in as there had been some water intrusion before I re-cored the cabin top. There's always been maybe 1/8-1/4 inch depression in the plywood around the base.

    I drilled a hole and put a camera down there today expecting to find some kind of rotting support. What it looks like to me instead is that the one stringer providing support there is in pretty good shape but has either moved or was never properly attached in the first place. Am I on the right track there and any suggestions on an appropriate repair?

    Thanks,
    -Zach.
     

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  2. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Here is some background info on your boat from Sailboat Data -
    https://sailboatdata.com/sailboat/s2-80-b

    Is that big lump of timber in the photos the bottom end of a vertical compression post under the mast, or a horizontal member (stringer?) in the bilge?

    Re how you had to drill a hole to have a look in the bilge in this area - does this mean that you would have to cut out the sole in the forward end of the saloon if you wanted to get better access?
     
  3. savagepoint
    Joined: Oct 2017
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    Location: Vermont

    savagepoint Junior Member

    Yes. I drilled a hole in the salon floor about 8" aft of the compression post, then put a camera down facing forward. The lump of timber is the horizontal stringer supporting the compression post area: 1st photo is center, then starboard, then port side. It's hard to see but I'd estimate that it's 12-18" long and attached at each end to stringers that run fore/aft and are tabbed to the hull. It appears to slant downward from port to starboard where it almost appears that it has moved pretty extensively.
     
  4. bajansailor
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    bajansailor Marine Surveyor

    Thanks for the explanation - I think I understand it now.
    So that timber beam should ideally be in contact with the underside of the sole above it?
    If this is the case, then it is not currently providing any support at all.
    Is the mast stepped on the cabin top, with a pillar coming down inside, and the base of the pillar resting on the cabin sole?
    If so, would it be feasible to leave the existing timber beam (as shown in your photos) in place, and bond (with epoxy) some timber inserts to fill the gaps at the top and bottom?
    However this would most probably require chopping the cabin sole out - and if you do this, you can then inspect the beam much more closely before making a final decision.
    Or have it got it all completely wrong?
     
  5. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Full on confusion here.

    you are going to need to draw it all out and a three view drawing would be best

    the part that creates the most confusion is how a stringer would move

    if it indeed has fallen over sideways, or was made too short to contact the sole, then it is no longer working as intended, or never did

    To repair it, you would need to cut out access by removing a section of sole. Then you would insert a piece of timber bedded into epoxy peanut butter. Or, if the floor timber has fallen over, remove it and bed in a new one which is more difficult to do right.

    If you cut the sole away, cut it an inch or two inside of the attachments so you can epoxy glue cleats back in for the sole access repair hole.

    Absent a drawing, it is really hard to advise more.
     
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  6. savagepoint
    Joined: Oct 2017
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    Location: Vermont

    savagepoint Junior Member

    Yup. That's my view of it - but this is my first time viewing anything under the cabin sole. It does not look like it's providing any support at all currently. Mast is desk stepped with a compression post made up of half a bulkhead and three pieces of hardwood that are screwed together around it to form a strong corner under the mast. To do any repairs, I was considering just opening up a permanent access panel in the cabin sole and just leave that part of the bilge accessible. My questions sort of fall around:

    - what would have held that thing in place originally? Seems like at most it was maybe some fasteners and maybe some glue but that looks debatable.
    - what would be the recommended repair for it assuming the wood itself proves to be solid. I was considering drilling two additional holes straight down through it and running some bolts through to at least pull it backup tight to the plywood. but re-fastening the ends to the longitudinal(?) stringers I'm not sure what would be recommended.
    - the boat is currently on a cradle resting mostly on it's keel - is that good in this case, or should the repair be done when the hull is more in it's more natural state?

    Thanks,
    -Zach.
     
  7. savagepoint
    Joined: Oct 2017
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    Location: Vermont

    savagepoint Junior Member

    fallguy - thanks for the reply. I'll try to work up some kind of drawing. I don't <think> it flopped over because there wouldn't be enough space for it to stand in the other dimension. it's actually a fairly wide timber. I guess the next step is to just open it up and determine that for sure. And yes - the idea that it moved at all just isn't seeming right although there's maybe some evidence of that on the starboard side of the stringer, where it almost looks like it slid down and a fastener started to show through the top. I'm just thinking it came unglued at some point or was never in contact to begin with.
    -Zach.
     
  8. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    If you can open up the access to this area, I think you just need to make sure that the whole space from top to bottom is filled with timber, bonded in properly.
    Then it will all be in pure compression, and it will have enormous strength, and nothing will be able to move or break.

    In addition, re the three pieces of hardwood that are screwed on (are they just facia / trim pieces, or are they structural?) in way of the aft inboard corner of the heads bulkhead, it might be prudent to unscrew them (if this can be easily done) to inspect the condition of the wood underneath.
     
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  9. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    I would drill a camera hole on the other side.

    I think it is construction error and the under sole support never happened. The beafed up bulkhead is transferring the whole compression load the the side hull.

    REMOVE the mast before any support is taken away. If those trim pieces are structural, then removing them with the mast in place could be BAD.

    Bolts thru the sole will hold the beam in place while FG tabs cure.

    Repairing on the hard will probably facilitate mast removal and replace. Otherwise no preference for in water or on land.

    Good luck
     
  10. savagepoint
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    savagepoint Junior Member

    Yeah I should have mentioned earlier that the mast is off and she's on a cradle on my lawn at the moment so probably the perfect time to address this. Seems like the bar is pretty low here to make it better than it currently is so I'm going to go ahead and open up an access panel following fallguy's advice and get my hands, tape measure, and a better camera on it and then I'll report back. One way or another I'll get photos from the forward side too. The keel is an encapsulated lead keel/bilge area. 1-2ft aft of the compression post area there is a plywood bulkhead under the cabin sole that is tabbed to the hull and cabin sole for support. Even if this timber stringer from the photo were properly glued in place, the compression load would be on it and the longitudinal stringers and side hull. I'll report back with better pictures, but I think this area is actually forward of the actual "lead/heavy" part of the keel so if I were going to add extra support under that timber, it would basically be going straight down and tabbing in to the hull/leading edge of the keel like another bulkhead.

    -Zach.
     
  11. fallguy
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    fallguy Senior Member

    Can you add pictures from above here?
     

  12. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    If you are going to cut a hole, might as well cut it over the affected area so there is access for repair.
     
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