Engine Stringers - Design and Compostion

Discussion in 'Fiberglass and Composite Boat Building' started by ChrisN67, Dec 27, 2009.

  1. ChrisN67
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    ChrisN67 Senior Member

    Hi Folks, I have a modified Intrepid 337 in which the outboard engine bracket was removed and retrofitted with Yanmar 6LY2's 440BHP. The original mods were sub standard. SO I gutted the engine bay and started from scratch.
    I basically took the last 2 meters of the boat and took it down to the skin. I set the boat up on a jig holding it only by the chines and proceeded to place 4 layers 1708 biax then vacuum bagged 20mm of Airtex linear foam, then 4 more layers of biax. No time for the stringers.

    Anyone have a lamination schedule for stringers? I was thinking 10 layers of alternating 0/90 and +-45 biax then a 30mm thick by 60 mm thick aluminum tapping plate then a cap of 8 layers of alternating biax fibers. All work with MAS epoxy. Each layer tabbing out 1" from prior

    Thanks
     
  2. Herman
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    Herman Senior Member

    If you can, use uni on top, and biax +/-45 on the sides of the stringers. Depending on laminate of the boat, it can be a good idea to also place some uni on the bottom of the stringer. (packed in +/-45 to keep the uni together.)

    Place the unis alternating between the +/-45, also on top, to keep them together.

    Some place SS strips in the stack, to be able to drill and tap for engine bearers.
     
  3. gonzo
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    gonzo Senior Member

    The lamination schedule is the least of your problems. If you had done a structural redesign, the lamination would be already solved.
     
  4. pescaloco
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    pescaloco Senior Member

    I would recommend you consult Dave Gerr's book Elements of Boat Stregenth
    Your Laminate schedule sounds like a whole lot of extra work. Have you considered a cored stringer instead of solid glass ?
    The book discusses type / shape / core / laminate schedules all based on enginering calculations
     
  5. missinginaction
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    missinginaction Senior Member

    Yep, persaloco's given you the right advise. There is a formula in Gerr's book that will give you exactly the lamination schedule that you need. For Gods sakes though, don't think of making them out of solid fiberglass. Stringers can be cored using foam or ply or whatever you'd like. Study Gerr's book and you'll learn the engineering behind a proper load bearing member. The core is simply a material that you use to hold the skin in place until it's cured.

    Now get reading:) !

    MIA
     
  6. ChrisN67
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    ChrisN67 Senior Member

    I don't have time to read a book

    Hey guys,

    Just looking for advice on a lamination schedule. Over design is not an issue. Gonzo, this is not the Queen Mary. I am an individual repairing personal boat.
    Please read my remarks.

    If I had retained a naval architect and done a full engineering study I would have a lamination schedule.... but I am not willing to pay for that level of engineering. I only wanted input from people on a recommended lamination schedule

    In the end I am going with 12 layers of alternating 1708 +-45 and 0/90 with an embedded 30m by 60mm aluminum bar

    I think its probably going to hold. :)
     
  7. gonzo
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    gonzo Senior Member

    Jezz Louise, that laminate is probably what the Queen Mary had.
     
  8. pescaloco
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    pescaloco Senior Member

    What he said
     
  9. GG
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    GG offshore artie

    I agree and the funny thing about it is he wants to use 1708 with epoxy which is a very poor idea because of the binder or chop back which is not designed for epoxy and the fabric that should be used with epoxy is S or E - glass , which is made for epoxy .
     
  10. marshmat
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    marshmat Senior Member

    Chris,

    We understand that you're an individual repairing a personal boat, and don't want a full engineering study. And if it were an 18' bowrider, people probably wouldn't be questioning the "No time to read, just build it" attitude.

    What you've described here, though, is a 33-foot boat with, if I read correctly, a pair of 440-horse diesels. You're spending thousands of dollars on materials, and putting in thousands of dollars worth of your time.

    In this context, spending perhaps three hours with a comfy chair, a $35 book and a pocket calculator is the absolute minimum of due diligence that one ought to do.

    (If you do, you'll find that several of the things you've mentioned- new stringers being only in a two-metre section, motor mounts being installed into the tops of the stringers- are not ideal ways to do it. The first one leads to a hard spot at the end of the stringer, ie. a stress concentration in the hull skin, and can be alleviated by making the stringers much longer; the latter can let water into the stringer, motor mounts on L-angles through-bolted laterally to the stringers is better.)

    You mention that the hull is currently propped up by the chines- have you measured how much the bottom has warped as a result? A distortion of perhaps five millimetres from the original shape could significantly affect the boat's performance at high speed. Before you start installing new stringers, you're going to have to spend some quality time under the hull with a straightedge and measuring tools- if you install new stringers into a hull that has warped or distorted, you'll lock in the flawed shape and all your effort and expenditures will be for nothing.

    The repair you're undertaking is certainly doable, but you need to be honest with yourself about how much work it is going to be, how much it will cost, and when you need to put down the grinder and pick up a book.

    As an aside, I heard about a Mayday call a few years ago involving a boat not too unlike yours. Nobody knew exactly what happened, because the thing sank in under a minute- but the crew, upon being rescued, thought that the inboard engines had punched right through the hull when the boat came down hard off a wave at high speed. I've also seen reports of such boats from well-known builders whose hulls broke up after spinning out in turns. Uber-beefy in one spot is meaningless- it's the sharing of loads between appropriate structural members that makes a boat strong.
     
  11. Herman
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    Herman Senior Member

    -most NCF (non crimp fabric) manufacturers use stitch bound CSM, not powder bound or emulsion bound. Stitch bound CSM can be used with epoxy, without problems with binder.

    -By far the most glass used (in gun roving and other rovings for pultrusion, filament winding, etc, woven roving, fabrics, rovicores, but also NCF's, are E-glass.
    It is a tough job to find anything else. (C glass, ECR glass or R / S glass) These latter glass types are only used if there are very specific demands for them, being alkali-resistance, other chemical resistance, or in situations where carbon is out of place (mostly due to electric conductivity, or in areas where galvanic corrosion is a factor, or if certain governing bodies (sailing class associations) rule it out.

    You might be confused with the binders that are on the glass, which can be of several types, in the past certain silane and volane binders were used, with the silane being most suitable for polyester, and volane for epoxy. However, 30 years of development gave us binders (silane based) which are suitable for both polyester, epoxy and phenolics. Now starch based binders are gaining field (slowly)
     
  12. KWT
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    KWT New Member

    Hi ChrisN67,
    if you have pics of your boat please post them here. lets see where you have achieved so far. i am very interested in re-modifying boats and etc.
     
  13. GG
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    GG offshore artie

    Herman , nobody is confused with binder's because stitched back binders with a chop back are made for resins like Poly or Vinyl and like i stated in a previous post on another thread i have seen the binders tear away from the fabric even though they were ( stitched ) and these were on new boat's at two different Boat Co's when they were making there transition to Epoxy or call it a learning curve .........either way , nobody is confused and a no chop back fabric such as 1700 double Bia 45/45 would be a far better choice for just about anything when using Epoxy .
     
  14. Herman
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    Herman Senior Member

    I guess we are mixing things up, me as well:

    2 different things:

    The SIZING on the glass fiber can be volane or silane, with (in the past) volane for epoxy, and silane for polyester. This has seen a huge amount of development, and silane now being perfectly compatible with both epoxy and polyester.

    The BINDER keeping the glassmat together. This still only works for styrene resins, so polyester and VE. Using these mats with epoxy indeed is not a good idea.

    I have no idea of what multiaxials look like in your place, but the stuff I sell is free if binders. Even the CSM which can be applied on the multiaxial is free of binders, and held together with the stitching only. (makes for a slightly more "fluffy" appearance, but who cares?).

    Still, using CSM (powder bound, emulsion bound or stich bound) with epoxy does not really make sense to me, except for perhaps some specific reasons.
     

  15. ChrisN67
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    ChrisN67 Senior Member

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