Transom Material

Discussion in 'Materials' started by Fred707, Nov 25, 2011.

  1. Fred707
    Joined: Nov 2011
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    Location: California

    Fred707 Junior Member

    To make a long story short I hire this fiberglass guy to work on my re-power which involves a moderate amount of fiberglass work in the rear of the boat. Upon arrival at the work site, a month after he starts the project, I see CDX plywood scraps sitting next to the boat (the transom wood is being replaced & glassed over). I also see one bolt going thru the middle of the transom holding the whole thing together as the resin cures. when I make the new cutout for the new stern drive there is a 3/16" gap around 1/5 of the opening. Now keep in mind that I initially instructed him that I wanted this thing done right & built strong as I'm installing a 350hp VP D6 in a boat I take 50+ mile offshore (its not grandpa's 14' aluminum lake boat). I also gave him plenty of money to buy marine grade materials. Then he goes over the transom wood inside the boat with a few layers of what appears to be 2oz chopped mat.The transom wood is not tabbed into the sides of the boat or the bottom. Now this really don't look right to me & is only one item out of many that appears to done incorrectly. So what I'm looking for is an opinion from you guys choice of materials & techniques.
     
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    If you brought this boat to me, I'd tear out the whole thing and do it again, right this time. CDX is about the worst material you can use. It has a minimum of veneers, is full of defects and frankly isn't something I'd ever use on a boat. Considering the power you're going to toss at this transom, it needs to be stout, well assembled and especially well tabbed to the hull shell. You're right to be concerned and this (repair) guy shouldn't be let near your boat again. I'm sure he can fix someone's Bayliner well enough to pull a 15 year old skier on a local lake, but if you want the insurance necessary for an offshore ride, you need to know it's right.

    You already know what needs to be, by the sound of your post. I'd use a minimum of BS-6566 grade plywood, though the best is BS-1088, it's not really necessary in a transom. I'd use epoxy, not polyester, just because it's easier and much stronger. The core would be well tabbed with biax fabrics, then the whole shooting match skinned with cloth. It can be done with polyester, but you'll use twice as much resin and fabrics, which will make up the difference in price between epoxy and polyester.
     
  3. pasty63
    Joined: Oct 2007
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    pasty63 Junior Member

    I have a 32ft bayliner with inboard diesels. I replaced a small part of the transom (lower port) 4 years ago when replacing the stringers and tank bunks, but most of the plywood in in the transom looked and sounded OK at the time. There must have been some rot lurking on the outboard side of the plywood however, as it is all beauty barkish now. I've started digging the plywood out, and am thinking that I'd like to lay up a half inch thickness of 2oz mat to replace the 1/2 inch layer of plywood. Since there isn't any drives or engines hanging off the back - would this be a suitable approach. I'm tired of digging out the "fillers" when I could just replace them with a glass sandwich.

    Thanks -.b
     
  4. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    A half inch layer of mat is a huge amount of resin and fabric. The exotherm alone would make a one shot deal prohibitive, than there's the weight issue.

    When doing a transom core, you can't leave any old core in it and expect good durability. Invariably, you'll have spores remaining in the old wood, which will affect any new you put in it. Simply put, it's not the wood's fault, but the installer's (no offense intended).

    After a few decades of repairs, I've never had a transom returned, after I've replaced the core, unless it's been bashed in by something. In fact, I've had to repair my own work and I cussed about how stout it was the whole time. I've also never "pieced" in a transom repair. It's an all or nothing deal. The way I figure it is; if you're going to the trouble of opening up the transom and working on the core, you might as well just replace the whole shooting match and forget about it.

    Secondly, I wouldn't use mat only. If using polyester or vinylester resin, then a stitch mat product is what you want, such as 1708. This is part mat and part directional fabric, stitched together (hence the name). The mat helps the bond issue and the biax fabric the strength. If using epoxy (my strong recommendation) then I'd not use any mat at all, just biax fabrics.

    For what it's worth, if you went with all 2 ounce mat, you'd need in the area of 75 layers to make up a 1/2" laminate. If you used 10 ounce mat, you'd need in the neighborhood of 15 layers! The logical thing to do is replace the core, but this time do it right, regardless of resin system (both work). If proper procedures and techniques are employed, you'll get decades of hard service out of the new core/laminate. If you piece meal it, well, you already know what happens.

    BTW, if you do make this 1/2" thick mat laminate, it will not be particularity strong and it will weigh about twice as much as a plywood core. You can make a strong all 'glass laminate, but you'll want to use alternating roving and mat, until you bulk out to the thickness you want (assumes polyester or vinylester). Naturally, this will cost a lot more then a plywood core, but it will be rot resistant.
     
  5. groper
    Joined: Jun 2011
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    groper Senior Member

    Or you can use high density foams or coosa board type materials, zero rot and lightweight cores... stiched fabrics with epoxy, well tabbed, you cant go wrong...
     
  6. pasty63
    Joined: Oct 2007
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    Location: Lake Stevens, WA

    pasty63 Junior Member

    Thanks for the replies. I happen to have an abundance of mat, so I thought I would suggest it. I can look around and work a trade for heavier cloth or maybe even some 1708. I've seen the suggestions on epoxy coated plywood here so I may still go that route.

    -.b
     
  7. groper
    Joined: Jun 2011
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    Location: australia

    groper Senior Member

    If you want to go the solid glass route, consider using some coremat in the layup. It bulks up thickness quickly without using as much resin and achieves a similar density/weight to plywood once its wetted out. Use it in the center of the layup with strength fibres on both sides...
     

  8. mydauphin
    Joined: Apr 2007
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    Location: Florida

    mydauphin Senior Member

    I would use layers of Marine Plywood with epoxy. Last time I did this was 3 layers of 1 inch Marine Plywood. Each layer glued together with roving all the way to the sides of the boat. Hard to explain but about 7 layers of roving and 3 plywoods in a large sandwich, all from one side of boat to other, and connected to stringer too. Glass only is heavier and not as strong.
     
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