cored hulls

Discussion in 'Boatbuilding' started by aguest, Dec 6, 2003.

  1. aguest
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    aguest Junior Member

    I have my theory just wondering somebody elses. Anyone have a high tech lamination schedule for a go fast type boat? What do you use to bond the cored material down? Just getting different ideas - Ricki
     
  2. Guest

    Guest Guest

    Share your layup and some information about boat size and power with us so we have some idea of what you want.

    Carbon and Kevlar /carbon is great layup if you have a real small (100# hull + 150# payload) boat with high speed (jet power & 100mph) requirements.
     
  3. aguest
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    aguest Junior Member

    I'm wanting to buy some 25 ft go fast hull / V- bottom. I have been doing research. Lam schedule I am looking at - gelcoat - skin coat (2) - Biaxial - coring and biaxial again. After the 1st biaxial what holds the coring down? Resin or core bond? Do you have a light / strong lam schedule you reccomend? Ricki

    Carbon - kevlar not in budget

    Balsa or foam coring?

    Wood or composite transom?
     
  4. Guest

    Guest Guest

    I just do high tech (carbon and kevlar / carbon).

    Dave Gerr's book covers most of your "low tech" options. He has an adjustment for high speeds
     
  5. aguest
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    aguest Junior Member

    Can anybody else help me here? Just learning and have some questions -Ricki
     
  6. mmd
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    mmd Senior Member

    Not to put too fine a point on it, but you are asking someone else to do your work for you. If you have decided to become a speedboat designer - even for only one boat - you sorta have to accept the responsibility to do the whole thing, or be willing to pay for the hard-earned knowledge of someone who has taken the time to get the education and experience required for the job. Basing structural design decisions that may impact the success of your boat (and in a fast speedboat, possibly your life) on the anecdotal information gleaned from internet conversations with people who do not know the specifics of your intended boats' structural arrangement is tatamount to folly.

    In regards to my statement above, I have good news, and I have bad news: The bad news is that I'm not about to do several hours of engineering calculations for you without being paid my professional fee (should you wish to hire me, I think you will find that my fees are quite reasonable, and you can contact me at the e-mail address in my profile). The good news is that I can speed you on your way to learning this stuff for yourself. To whit, acquire & read any or all of:

    "Fibre Reinforced Resin Systems" - Weatherby (Applied Science Press)
    "Marine Design Manual for Fiberglass Reinforced Plastics" - Gibbs & Cox (McGraw-Hill)
    "The Elements of Boat Strength" - Gerr (McGraw-Hill)
    "Rules for Construction and Certification of Vessels Less Than 15 Metres (1983)" - Det Norske Veritas
    Back issues of "Professional Boatbuilder" (WoodenBoat Publications)

    What you need to determine is the maximum slamming loads expected, and the panel strength of the hull skin. The latter is a function of the unsupported panel size and ratio, the former a function of vessel mass and velocity. Neither are too difficult to calculate for a "normal" vee-shaped monohull planing boat. Bear in mind that small changes in any of the parameters can have a large effect on the hull strength, so what works on "similar" boat might be wholly insufficient on yours.

    Finally, so as to not be a total PITA, in my experience the best core/laminate bond is created by applying a proper core-bonding putty (preferably supplied by the same manufacturer as the resin so there are no chemical incompatibility issues) to the core and laying it on a wet, resin-rich intermediary laminate and then vacuum-bagging it. Sounds complex and expensive, but for a smallish one-off it can be done pretty inexpensively.
     
  7. aguest
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    aguest Junior Member

    mmd:

    Hey it wasn't me that clogged up your wet out system - haha. Thanks for the help - Ricki
     
  8. aguest
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    aguest Junior Member

    mmd:

    If you don't mind me asking , so I apply resin to the last lam in the hull and then core bond to the coring (face down)? Ricki
     
  9. mmd
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    mmd Senior Member

    That's right. Here is the general schedule that we would go through on "hull lay-up week" at the boatyard I managed, where we built 60-foot sailing catamarans for the Caribbean day-charter trade. Please keep in mind that this was a few years ago and far, far away from where I am now.

    On the first day the crew would be split into two groups; one would prep our moulds and apply mould release and gelcoat, the second group would prepare all the cut laminate materials and coring from patterns so that we could lay them in without any fussing. The next morning we would lay in the outer laminates, finishing with a resin-rich layer of light CSM. As the laminators were rolling out this last layer, the other workers would trowel on core-bond putty to the faying (mating) surface of the core, making sure to bend the core over special benches we had constructed to open up the cuts in the core that allowed it to bend easily, and filling the cracks with putty. They would come behind the rollers and lay down the core, closely followed by the bagging crew who laid down the vacuum hoses and plastic film. The pumps would be turned on, the bag checked for leaks, and it was time to go home. On the third day the bag was removed, the core checked for adhesion and repaired if faults were found. Then a couple of guys with angle-sanders would jump in the mould and clean off any exterraneous resin that came through the seams and breathing holes of the core and round off all the core edges. A couple of workers then jumped in and vacuumed the dust out and inspected the grinders' work for "holidays". When the big cheese of the place (me) was satisfied with the prep work and core repairs, the laminators descended upon the mould and laid in and hand-rolled the inner laminates of the shell.

    It was a rather stressful dance requiring pretty tight orchestration of the various tasks, but the crew was experienced and carried it off with remarkably few screw-ups given the somewhat primitive facilities we worked with. Each hull consisted of two halves, and each vessel had two hulls, so it took a crew of twelve two working weeks to create the hulls for a 60' x 27' x 8' (depth, not draft) catamaran. Hull thickness was about 1-1/8". Note that this was done in the tropics, so we tried to do all major laminating as early in the morning as possible, before the heat got too nuts and shortened the gel time of the resin.
     
  10. aguest
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    aguest Junior Member

    You the man for the help! That was very nice of you to go into detail. I also went to Baltek's site and got the skinny on the core bond. I got it now and you helped with the bending of the core to fill in the cracks. Much appreciated. Now I have to figure out the vaccum bagging out. Can I buy a complete system somewhere to vaccum bag? Ricki
     

  11. mmd
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    mmd Senior Member

    Yes, you can, but if you are doing a "one-off" boat I wouldn't go to the expense. A couple of "big box store" shop-vacs with garden hose and duct tape will be a lot cheaper. I think that there is a thread on vacuum bagging around here somewhere; if not there is one in the "Build & Repair" forum at www.woodenboat.com
     
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