Bass Boat Restoration

Discussion in 'Boat Design' started by Cadwelder, Jan 9, 2011.

  1. Cadwelder
    Joined: Dec 2010
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    Cadwelder Junior Member

    I'm replacing the stringers and deck in a 92 Astro bass boat, my question is about the strakes. They are hollow now (I'm sure the wood has just rotted away) and rather weak, I was going to just glass another layer over them, but just my wieght cracked two of them. Should I go ahead and take them out, reform them and replace, or just try to form up the cracked part and reglass?

    If I replace them what are your thought on what to use as forms? I thought of using schedule 20 (very thin) PVC conduit rippied in half??
     
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    If just a little pressure (you stepping on them) managed to crack them, then the core (probably wood) was a large portion of the longitudinal strength of the stringers/braces assembly. What this means is you'll need a lot more material then
    to make them as strong as they need to be. Personally, I'd cut the damn things off the hull and start over, using epoxy and wood, but you can just cover them with more fabric and not have to worry about the wood aspect anymore.

    PVC pipe does make a good form, though it's a heavy material and the 'glass doesn't stick to it very well (one reason it's a good mold material), so it shouldn't remain in the laminate. When needing a temporary rounded form, I use Christmas wrapping paper tubes (cut in half most of the time), which can be had in long lengths or I just make up my own from "chip board". This can be left in place, adds next to no weight and it it rots, so what, it's just needed there until the goo cures.

    Are you using epoxy or polyester? Can you post some pictures of your project?
     
  3. Cadwelder
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    Cadwelder Junior Member

    Here's is a picture of the strakes in question (I think my terms are correct) I went ahead and cut a section out and it is definetely just a cardboard tube that was used at the factory. Since we've gone this far done, I'll take your advice and just cut them out (makes for easier grinding with them gone anyway) and rip a cardboard shipping tube in half to form them. There only function is to stiffen the hull a bit right? I'm using polyester resin.
     

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  4. PAR
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    PAR Yacht Designer/Builder

    If you cut them out, you'll have to replace the laminate, plus any additional laminate you'd like to include.

    After seeing you boat, just grind the surfaces clean with a 24/36 grit pad and apply more material over the reinforcement tubes (stringers) and call it a day. Why replace what's already there, when you can just top it off.

    A layer or two of 1708 over the whole area will stiffen things up fairly well. Reinstall the cut out pieces before you apply the fabric (mat side down of course).
     
  5. Cadwelder
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    Cadwelder Junior Member

    Good to hear the 1708, I have enough of it to build the boat from scratch. I going to use it to attach the new stringers. I'll just use some cardboard tube to fill in the broken areas and glass over them and then over the patch and the remaining with the same cloth I tie in the stringers with.

    Do you think one layer of 1.5 oz matt is enough between the transom skin and the new plywood? The plywood is extremely flat, it has a layer of very wet out matt between the two layers of 3/4" MG plywood and was put in a press to cure. Had even pressure all over, for 24 hours. I'll clamp the wood to the transom with equally even pressure.
     
  6. PAR
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    PAR Yacht Designer/Builder

    You could skip all the pressure and just dill a bunch of holes, say on 2" centers to let air escape as it's clamped in position. Fill the holes after you pull the clamps, then tab the plywood to the hull shell with more 1708, at least 6" of overlap on the hull shell and transom and at least 2 layers thick. Much of this depends on how much power you intend to throw at this transom. Naturally, the more HP the outboard, the more tabbing. Since you have only two layers of 3/4" plywood I'll assume you're maximum engine size will be in the less then 75 HP range, as typically you'd have more then 1.5" of transom thickness for bigger engines. So yes, with good pressure 1.5 ounce mat will do fine between the skin and plywood.
     
  7. Cadwelder
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    Cadwelder Junior Member

    Well actually the boat is rated for a 200 HP, it has a 175 Merc that will be going back, ( pushes the boat in the high 60's mph). I just went back with what was there on the plywood, had two layers of 3/4" originally. My plan was to tab in 12" on the first layer of 1708, 16" on the second layer and all the way to the sides on the third and final layer. The stringers tie into the transom along with the transom cross members also for added support. Should I go heavier duty?
     
  8. PAR
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    PAR Yacht Designer/Builder

    Your tabbing overlap is great, though with these HP figures you should increase laminate thickness, doubling what you have. Also the transom should be a minimum of 2" thick, though most would be 2.25" to 2.75" thick at those HP figures. You can go too light on your tabbing, but not too heavy. The same is true of its thickness.
     
  9. Cadwelder
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    Cadwelder Junior Member

    Because of the way the top cap is made, I done some measuring, and by the time you figure in the thickness of the skin .250" + wood 1.50" + tabbing inside .250" + the matt inbetween the layers of wood and between the skin and wood you'll be pushing 2.125" - 2.250" any thicker and the top cap would need to be modified for it to set back in properly. I don't have a problem with modifying it if you think I should.
     
  10. PAR
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    PAR Yacht Designer/Builder

    2.25" will work, though I'm surprised (I shouldn't be) they only used two layers of 3/4" on a boat rated for 200 HP. I think they were pushing the limit with the scantlings on your boat to tweak a few extra knots of top speed out of her. A really dumb idea in terms of longevity, but seeing as how you're now rebuilding her less then a couple of decades later and the obviously thin stringers you previously noted, not such a big revelation.

    Most production built craft like this have been "skimped" on in most every category, with laminate thickness and tabbing as big areas to cheat. Make your tabbing heavier then they did and the stringer laminate thickness heavier too. It's clearly undersized as I feel the transom thickness is as well. The tight stringer spacing indicates they knew the area was under high load and it appears they also used a heavier laminate from the factory, but only enough to get them through the warranty period.

    Lastly, if you bulk up the transom and the deck cap doesn't want to slide back down over it, you can grind the top of the transom down a tad to get it to fix good. So long as the core to skin interface is solid and the tabbing wide and thick enough, you'll be stronger then it was previously, which is apparently good enough for a 18 or so years. If the bottom laminate (stringers included) at the base of the transom and surrounding areas (plane patch area) are good and stiff, the engine torque will transfer from the bracket mount to the hull bottom without distortion and the laminate will not twist itself to death, which is likely what did in the previous laminate.

    Keep stroking it, you're doing fine . . . .
     
  11. Cadwelder
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    Cadwelder Junior Member

    Cool, will do just that (on the transom) now when I set the stringers in should I bed them in thicken resin mix, industrial adhesive, or just lay them against the hull? Orginally the back section was right on the hul but as they went toward the front there was a 1/4" or so gap between the stringer and the hull.
     
  12. PAR
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    PAR Yacht Designer/Builder

    I'm not sure I follow. If it's a cardboard tube, then you don't need anything, just place it where it belongs. Are you talking about a wooden stringer, before you 'glass it over? If it's a wooden stringer core, you can lay them against the hull, though some will complain about hard spots and oil canning. If terribly concerned about this (the factory wasn't), then you can sit each core on a piece of closed cell foam or pick up a tube of "3M-5200 Fast Cure" and use a 1/4" bead of this goo as the isolator, between hull and stringer core. Don't try to mash the goo out from under the core, just let it sit on top. If using the goo in a tube approach, then wait a day or two to let the goo cure. Next build up a fillet on each side of the stringer so the 'glass doesn't have to make a hard, 90 degree turn.
     
  13. Cadwelder
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    Cadwelder Junior Member

    No no, not the cardboard, sorry I wasn't clear. Yes to the wooden stringers, I've never worried about "hard spots" but thought I'd ask and yes the factory obviously didn't worry about them either. I usually make a resin paste for fillets and use a round over bit on my router for outside corners. Will one layer of 1708 be good to attach the stringers (wooden ones) or should I double that? They are 5" tall (tapers toward the front of course) and run from the transom to within 38" of the bow.
     
  14. PAR
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    PAR Yacht Designer/Builder

    Okay, we're on the same page now. The bull nose bit is how I do it too. All of the laminate is going to "attach" the stringers to the hull shell. Ideally you'll want a chemical bond with this, as a mechanical bond isn't very strong with this resin system. I'm not sure how much 1708 it's going to take to bulk up to the thickness you need, but the goal is at least the same thickness as previously (which was probably a little too light). I mention this because I'm a mostly epoxy guy and I don't used "bulked" fabrics like 1708 very often, as epoxy doesn't need the bulk.

    To answer your question, yes a single layer of 1708 will "tack" them down, but you'll want to get the rest of the laminate on the stringers while the resin is still "green".
     

  15. Fanie
    Joined: Oct 2007
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    Fanie Fanie

    Someone give Par some points for his help here. The man sits on 2009 rep points and we're in 2011 already... :rolleyes:
     
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