Can longitudinal cracks in ribs be glued and clamped?

Discussion in 'Boat Design' started by Dom Elias, Aug 17, 2023.

  1. Dom Elias
    Joined: Aug 2023
    Posts: 3
    Likes: 1, Points: 3
    Location: Dalsbruk, Finland

    Dom Elias New Member

    We're restoring my South Coast One Design (SCOD) yacht (mahoganny on oak, 1956) here in Dalsbruk, Finland, and I had an idea for an alternative rib repair:

    I know that usually cracked ribs are repaired by laminating/sistering/steaming of replacement ribs. When the crack is across the rib, I see no other alternative. Yet, for a crack along the grain of the wood, could gluing and clamping be an alternative option?

    [​IMG]

    As you can see from the picture, there is plenty of material on both sides of the crack, the wood is solid on both sides. My plan of action would be to remove the rivets first (planks in question are going to be replaced anyway) plug the wholes with wooden bungs, epoxy and clamp, then redrill for the floor brackets when (re)fastening planks.

    Maybe it should be said too, that the rib in question is one of 12 ribs holding the 6 metal floor brackets.

    So my question here is: Is gluing longitudinal splits in ribs an option you have heard of? Done it? Have a good argument for/against doing it like that?
     
  2. Ad Hoc
    Joined: Oct 2008
    Posts: 7,807
    Likes: 1,703, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Hi Dom,…welcome to the forum.

    If what you are proposing was for non-major structure, by that I mean, non-load bearing, this would “seem” to be a possible solution.

    However, since this is major structure, I would not recommend this.

    If you were to fill the “holes” with epoxy, the epoxy has a very different strain rate and Young’s modulus, E. It is also adhered to the wood. Thus when the structure is subjected to a load, the wood will move independently of the filler, as the strain rates and E are different. Think of, as a crude example, having 2 layers of wood separated by a layer of rubber. The wood and rubber behave differently owing to their mechanical properties. Thus when subjected to a load, the composite will not behave as one. It is also dependent too, on the adhesion properties between the wood and the filler. This would most like be the first failure, in shear. It would effectively delaminate between the two materials.

    So, lets clamp them? Well, that doesn’t really address the above. Since you are now relying upon a clamping force to hold the composite, and coercing to work as one member. Again, once a load is applied, and repeated loads over time (and even a slight overload) will reduce the clamping force effect. And then any loss of adhesion, owing to strain in the member, between the filler and word fibres, will promote the above, over time. The clamps would only delay the issue.

    Sorry it is likely what you don’t want to hear.
     
  3. Rumars
    Joined: Mar 2013
    Posts: 1,818
    Likes: 1,132, Points: 113, Legacy Rep: 39
    Location: Germany

    Rumars Senior Member

    I doubt the mechanisms described by Ad Hoc will even have a chance to manifest, the problem is much simpler. This is a frame heel, all the splits are heavily contaminated. Even if you manage to squeeze enough epoxy in there all you will be glueing is dirt to dirt. The moment the first rivet starts to set it will split again.
    Do the right thing, either replace the whole rib with a steamed or laminated one, or replace just the heel with a lamination, scarfing it to the old frame above the turn of the bilge.
    Laminating can be done in place, screw or staple the veneers directly to the planks over a layer of plastic.
     
    bajansailor, fallguy and Ad Hoc like this.
  4. fallguy
    Joined: Dec 2016
    Posts: 7,688
    Likes: 1,706, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    I don't like to argue with Ad Hoc or Rumars as I have immense respect for both. Consider my comments augments, not arguments.

    The biggest problem is not whether you can make the repair, because you can. Ad Hoc is right; the repair will be poorer. The biggest issue with sistering, or filling, which we see all the time, is

    ROT don't STOP!

    Now, I've watched wooden boat repairs costing 80-100k in our marina on some lovely old Chris Crafts, and they use the rotten floors and template and sister, but they don't remove the old timber; they simply epoxy seal the new, hoping that the rot won't migrate into/through the epoxy barrier, but the rot does migrate into plank or even sole timbers. Usually all the new materials applied are sealed, but adjoining not.

    It all comes down to simple decision making. Can you remove and replace without the boat losing shape? Because if you can then you ought.

    If, on the other hand, you had a small area of rot on a corner, removing rot and a minor repair always beats doing nothing.

    Maybe someone will argue this ain't rot; that is fine..I'm referring to rot.

    The timber in the picture is really in terrible shape to consider epoxy repair. As Ad Hoc says, questionable integrity on the repair and as Rumars says, dirt bond.and me, I'd avoid laminating to the old timber for rot potential.

    I am fixing an old church building. We removed the ceiling materials and things looked good. Got a closer look and tons of dry rot in floor joists on bottom. You will be really much happier with new timber.
     
    bajansailor likes this.
  5. Dom Elias
    Joined: Aug 2023
    Posts: 3
    Likes: 1, Points: 3
    Location: Dalsbruk, Finland

    Dom Elias New Member

    Many thanks for the comments! I have a better idea now why I couldn't find any descriptions of such crack repairs anywhere for ribs.

    I am, by the way, not "shying away" from laminating new sections, I was just researching why the "obvious" way to repair cracks along the grain didn't appear as an option in forums/books, etc... Now I know. : )

    I have analysed the nature of the cracks in the meantime and realised that they have been caused, indeed, due to general "wear" of the wood. So the problem as I see it now, would mainly be that I'd end up sticking glue to gunk. I guess it would be different in a fresh break.

    Again, thanks for your input – I'll laminate! : )
     
  6. gonzo
    Joined: Aug 2002
    Posts: 16,831
    Likes: 1,733, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Laminating is a lot more work than steam bending. If you just sister a new frame, the rivets will leak. Replacing the frame is easier anyway since you don't have to drill new holes on the planks.
     

  7. Dom Elias
    Joined: Aug 2023
    Posts: 3
    Likes: 1, Points: 3
    Location: Dalsbruk, Finland

    Dom Elias New Member

    Thanks Gonzo – my question was not about how much work is involved in the different repair methods: My question was fairly academically about the feasibility of gluing longitudinal cracks in ribs, and I have got the answers to that now, thank you. ; ) Again, I was not interested in how long a particular repair takes (see original quesion).

    I will laminate approx. seven 3mm veneer strips per rib with a an approx. 20cm overlap onto the firm part of the rib above the cracks with epoxy. This has and advantage over steaming, as I do not weaken the wood by heating it. SoI build up a 7-ply rib with practically no inner tension, and the grain always points in the direction of the rib. I've done it like this before, and looking at the repairs after 15 years, I'm happy that it holds. Les jeux sont faites, rien ne vas plus! ; )
     
    fallguy likes this.
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.