Cold-moulding vs. Fiberglass sheathing

Discussion in 'Wooden Boat Building and Restoration' started by Chris Merriam, May 19, 2006.

  1. Chris Merriam
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    Chris Merriam Junior Member

    Probably opening a big can of worms with this one, but after removing the crappy fiberglass job on my 1955 Paul Luke I was planning on cold-moulding the hull. Now it has been suggested to me to use Diaginal Glass from Brunswick Technologies because of the cost factor. I have not seen a lot of cold-moulding over old wood hulls info, but liked the original thought of useing wood over wood.

    Any thoughts out there on the different methods?? The hull would need too much replanking to keep original, and many of the sisters done have been epoxied to the planks.
     
  2. gonzo
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    gonzo Senior Member

    Cold molding is a lighter way to reinforce a hull. Also, you can fair the hull easier. The veneers will tend to follow a fair curve. Epoxy staples make the job fast because you just leave them in. A layer of 10 oz cloth outside is good for extra abrasion resistance. There are many ways of doing it. If you are looking for the fastest, strip plank over the hull. One layer and you are done.
     
  3. DGreenwood
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    DGreenwood Senior Member

    Be aware that cold molding over a compromised hull still only produces a compromised boat. All the structure has to be solid before you put glass or veneers over it.
    Which ever method you choose, do it with epoxy. Do not even consider the cheap route.
    There have been many successes with both methods if done well.
     
  4. casavecchia
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    casavecchia Senior Member

    Gonzo,
    can you give more details about epoxy staples?
    Thanks,
    Marco.
     
  5. DGreenwood
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    DGreenwood Senior Member

    The staples I use are a polymer. You can sand them, They won't hurt a chisel or a plane, you canleave them in and no worries about corrosion.
    Here is their site:
    http://www.raptornails.com/english/firstframe.html
    Be aware that the staples don't like to go thru a cheap staple gun very much. You can make it work but it is better to buy their insanely expensive especially adapted staple gun.
    The nails seem to work OK in gypo guns though.
     
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  6. Chris Merriam
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    Chris Merriam Junior Member

    Somebody was just telling me about a method of using a Kevlar cord imbedded in a groove S shape on the hull and then a thin coat of epoxy over that is all you need. Anyone heard of this and where I can get info on it??
     
  7. DGreenwood
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    DGreenwood Senior Member

    That would be the Cutts and Case method. I don't know if they have a web presence but Wooden boat Mag seems to carry their ad every month. Check them out.
    Frankly, it strikes me as a lot of work for little progress. Equal results achieved with simpler methods.
    You will never meet a saltier more engaging character but there are easier ways to achieve the same hull strength.
     
  8. gonzo
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    gonzo Senior Member

    The kevlar cord does little or nothing. A double planked hull works just fine.
     
  9. brian eiland
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    brian eiland Senior Member

  10. Chris Merriam
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    Chris Merriam Junior Member

    Thought about it, and I have seen that site. I am now looking at C-Flex, but am still undecided. I wanted to leave my boat wood, but after much discussion I will need to resheath her. I stripped off all the old fiberglass and have been fixing frames and refastening with Bronze. The boat has been under cover for three years now and when I do resheath her she should be very dry. I can give you my, or anyone, shutter fly album if you give me your e-mail. Still figuring out that site as imagestation is going away.
     
  11. Ike
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    Ike Senior Member

    I would go with the wood veneer sheathing. One, your boat being wood expands and contracts and moves about, If you put fiberglasss or c-flex or anything but wood on it, it becomes a rigid inflexible structure, with two different materials that have different incompatible structural properties.

    Second, if you sheath it in wood, that extra layer will actually make the boat float a little higher on it's lines.

    Last, you just took the glass off. Why put it back on? I had a wood sailboat that had been glassed and it took me months to replace all the rotted wood after removing the glass. The glass does not allow the wood to breath and traps the moisture in the wood. Result? Rot!

    To me glassing a wood boat is only a last desperate solution for a boat that is going to die anyway and you want to prolong it's life a few years. If the boat is worth saving then do it right.
     
  12. brian eiland
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    brian eiland Senior Member

    Notice that another layer of wood is required in the Cutts method, not just 'a thin coating of epoxy':
    http://boatdesign.net/forums/attachment.php?attachmentid=16252&d=1190733867
     
  13. brian eiland
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    brian eiland Senior Member

    I agree with all you say!!
     
  14. PAR
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    PAR Yacht Designer/Builder

    I find it irresponsible to suggest putting glass on wooden structures is not a good thing. This makes one believe that all composite, most strip plank, Lord method and molded construction techniques have "incompatible structural properties". This is clearly ill informed and frankly insulting.

    Everyone should be well aware of my opinion on 'glassing traditional wooden construction methods. In this we're in complete agreement, the structure has to move and this isn't compatible with the vast majority of resins we employ in modern restoration, reconstruction or repair efforts. Encapsulation is the only way these materials can be compatible, but these blanket statements rub me wrong and do a disservice to those looking for unbiased information about products, techniques and material properties for their projects.

    I've never had a laminate fail if schedule, plan and material recommendations were adhered to. Maybe I should give the check back to the gentleman that just bought a set of my plans for a strip planked version of my RYD-26. It would be the upright thing for me to do in light of "anything but wood on it, it becomes a rigid inflexible structure, with two different materials that have different incompatible structural properties." hindsight you've just provided. Damn I've been mis-engineering structures for nearly 35 years now, glad you straightened me out . . .
     

  15. alan white
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    alan white Senior Member

    Planking generally opens between seams. When the boat was new, it was accepted that some minor leaks were normal, and managable, since a properly built hull would not be considered faulty if a dribble showed up. The most carefully built hulls leaked but a tiny bit, some so little that evaporation solved the problem.
    Back to the future. The leaking typically is through the seams, and through faying surfaces in the deadwood, stem and transom. Not in the middle of the planks, which, even after many tears, are still basically sound.
    The seam leaks are a matter of distance and surfaces. The seams take a lot of punishment. They have progressively been distorted and widened by recaulking and moisture cycling. The fibers of the plank edges have been crushed down a bit more with each passing year, taking up against greater and greater thicknesses of caulk. Over time, every time the caulk tightened as the planks grew, more crushing took place.
    Refastening is required at some point for the same reasons. Metal screws don't expand but wood does. Planking wood generally expands twice as much in thickness as it does in width. With each expansion cycle, the underside of each crew-head, like an incredibly slow hammer, crushes a bit deeper into the seat beneath it, resulting perhaps in a half-turn of tension loss in thirty years.
    Refastening is just as necessary if the hull is sheathed with wood or glass. What I'm suggesting is a renewal of the seams.
    This renewal process would involve refacing both edges of the seams, and epoxying a carefully fitted thin strip of wood to one face only, creating, in essence, a brand new seam exactly like the original.
    Of course, other seams like transom-to-sides and stem/deadwood would need to be dealt with too, but the main body of the hull, if also refastened, would be as good as new structurally (no matter what, frames must be replaced if cracked or broken).
    As good as new does mean as good as a carvel-planked hull will ever be---- and good planking stock will last a very long time---- fifty? Seventy-five years?
    The question is whether the average modern owner will be happy with a carvel hull that's doing what carvel hulls do---- leak a bit. Not much, but a little.
    i would look seriously into this common-sense measure, as the cost is barely more than labor, it can be done in stages, and it keeps the weight down.
    Covering planks, solid ones, in any other way is going to create potential problems. All methods cover up the original fasteners. Repairs and refastening become problematic. The appearance changes to that of a "rescued" boat in the eyes of the future buyer.
    Finally cost can be substantial. No matter what, thousands will be needed to pay for whatever method is used to cover the planking correctly.

    Alan
     
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