Stringer questions

Discussion in 'Fiberglass and Composite Boat Building' started by Roboj, Jan 16, 2007.

  1. Rusty Bucket
    Joined: Feb 2007
    Posts: 76
    Likes: 5, Points: 0, Legacy Rep: 26
    Location: florida

    Rusty Bucket Junior Member

    P.T. plywood and boat repair

    I use pt wood for a lot of projects related to boats with success. One of the most persistant myths that you'll ever hear in boat building is that you can't use pt products, the story is usually that frp laminate won't adhere to pt. Thats true...but laminates using polyester resin really don't stick to much of anything all that well anyway. The reason production boat builders don't use pt is more than likely due to time constraints, they don't have time to wait for drying, also most available is CD grade, but the biggest time issue relates to that fact that the boat will probably be on the third owner and past warranty when the transom rots out any way. The really high end builders use no wood and vynalester resins and they crow about it in their advertising. I believe that if you dry your pt well and use epoxy resins to do your repair work you'll do just fine. I suggest that you test a couple of small panels and see how they turn out, at least you won't be commiting the same mistake the first guy did and that's a step in the right direction. Let me know,Rusty
     
  2. trawler builder
    Joined: Mar 2007
    Posts: 28
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    Location: nova scotia

    trawler builder Junior Member

    polyester resin sticks well to one plywood only and that is fir select ,for anyone to say that pt plywood is fine is just not true ,niether can it be said of spruce ,or other plywoods .(eccept birch finish plywood )
    we sometimes use a product we call "talc " it is a powder that you mix with resin to embedd stringers or tanks etc, once in place there is no coming out unless it is in pieces .
    when mixed this is like a body fill and you can change it's consistancy by using more or less resin . it is an old product but i like it because it is so strong ,we use it underwater also to fill seams etc .
    tb
     
  3. Roboj
    Joined: Jan 2007
    Posts: 18
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    Location: Vancouver

    Roboj Junior Member

    Hello,

    Rusty Bucket and Trawler builder thanx for your reply. When installing stringers do you bed them to the hull with putty or raise then 1/4 inch from the hull, leaving a gap and then glass them in? Also how do you secure fuel tanks? However mine was secured, it was too rotten to tell and I am trying to figure out how best to secure it. Also, all of my research suggests that poly resin sticks the same to pt plywood as it does to untreated, which may not be all that great to beginwith, but the pt has no adverse effects. I also think that douglas fir ply is the best to use.

    Thanx for your input.

    Rob.
     
  4. Rusty Bucket
    Joined: Feb 2007
    Posts: 76
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    Location: florida

    Rusty Bucket Junior Member

    Bonding pt plwood

    Hi Rob, I suggest that you check out the American Plywood Assoc. web site and read the wealth of tech. info relating to the various grades of plywoods and their proper applications. You will see that marine grade plywood is fir or larch plywood that has been constructed using exterior glue with core plys that are defect free or have been repaired to fix defects such as knot holes or splits. Marine grade plywood generally has 2 "a" sides and comes sanded. Marine grade plywood does not have more rot resistance than other types of exterior plywood, i.e. the typical AC fir that you might find down at the local lumberyard. Marine plywood is designed to bend and take finishes, rot is not really a consideration. Any exterior grade plywood is suitable for rebuilding a glass boats transom and polyester resin has certainly been used before to do the glue up. You might ask yourself why you're having to fix the transom if doing it that way to begin with was such a good idea. I suppose it depends on how long the repair is expected to last. Trust your instincts. Rusty
     
  5. Roboj
    Joined: Jan 2007
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    Location: Vancouver

    Roboj Junior Member

    Thanx for your reply,

    I am not rebuilding the transom, it is still OK. My prpblem is with the stringers, they are all rotten. Based on all the research that I have done, I think pt exterior fir is the way to go. The stuff I am using has a moisture content of about 7 to 8%, which is really dry, so the poly resin should work just fine. The part where I am looking for feedback on, is some have suggested that the stringer should not touch the hull, to leave a 1/4 inch gap, while others suggest bedding it to the hull with a resin putty. I was just wondering you have done this type of repair.

    Thanx and have a great day,

    Rob.
     
  6. Rusty Bucket
    Joined: Feb 2007
    Posts: 76
    Likes: 5, Points: 0, Legacy Rep: 26
    Location: florida

    Rusty Bucket Junior Member

    stringer repair

    Hi Rob, Sorry about the transom sermon, yes I have done this kind of repair. By stringers I'm going to assume that we're talking about longitudinal (sp) stiffners running along the bottom of the boat. If I'm right then I also can't imagine how a stringer would provide the needed stiffness without having some sort of physical connection to the hull. I'm going to guess again and assume that the spacing is to avoid "hard spots" or stress due to the contact of the stringer with the inside hull surface. I've personally never had that problem with a glass boat but then again I'm still learning. Here's how I'd do it, remove the old stingers and clean up the area real good, grind the interior surface where the stingers will go so as to promote good adheasion, trim your stringers to fit the bottom contour of the hull, but first make sure the bottom dosen't have a "hook" or bulge in it, watch your weight inside cause when you cut out the old stringers you might loose whatever integrity the hull had left. Fit the new stringers and mark each side with a marker and take them back out. Now you need to make some kind of bedding putty to bed you new stringers in with, Gosh, Ive run out of room,352-625-1598 call
     

  7. Rusty Bucket
    Joined: Feb 2007
    Posts: 76
    Likes: 5, Points: 0, Legacy Rep: 26
    Location: florida

    Rusty Bucket Junior Member

    stringer repair

    . Bed your new stringer I'm not that good at computers so bear with me. to continue, I use epoxy thickened with silica for putty but plain old bondo will work just fine. Do one stringer at a time amd lay a nice fat bead of putty down between the lines you made where the new stringer will go and sqush the new stringer down so the putty squeezes out around the bottom, use an old soup spoon and form a nice radius along the bottom of the stringer with the excess putty. The whole thing needs to be as smooth as can be cause you're going to be laying up glass along the sides of the stringer and glass don't like sharp corners. Drink a cold beer. After the putty kicks wipe it down with acetone and remove any sharp edges or ridges. If you used 2x6 for stringers you should ease the top edges of the wood so that the glass won't have to take a sharp turn over the top. Glass in the stringers by cutting strips of glass about 12" wide and long enough to go over the top of the stringer, down the sides and out about 4" out out each side. Work your way down the length overlapping about 2" each piece. Do three layers of glass cutting each layer about 1" shorter so as to get a nice taper into the bottom
     
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