drift boat floor thickness?

Discussion in 'Fiberglass and Composite Boat Building' started by Coltrain, Jul 19, 2007.

  1. Coltrain
    Joined: Jul 2007
    Posts: 2
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    Location: Oregon

    Coltrain New Member

    Myself and a couple other people I work with want to build a few all glass drift boats. We figure we’ll split the cost to build the mold, then each pay for materials to build the boats. We can get glass and resin pretty cheap through our employer - $1.17 / pound for resin - it is polyester, but we figure most (all?) production glass drift boats are mode with it and should serve us well for the cost. Our question is how thick do we need to make the bottom? Would it be better to use heavier weave glass cloth, or more layers of lighter cloth?
     
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    The thickness of the "floor" is subject to several variables, none of which you seem ready to comprehend or understand. I mean no offense with this. Designing small craft can be a demanding task for the well schooled among us, down right difficult for the amateur.

    I'd suggest reading Dave Geer's book, "Elements of Boat Strength" to get an idea of what you'll need, scantling wise. I would also strongly suggest you have a designer work up the plans for your drift boat, so no surprises will meet you on launch day. If you elect to use traditional drift boat lines, then the 'glass version, again should have it's laminate schedule worked through by a designer.

    The material and labor necessary to build a GRP drift boat mold are quite substantial, requiring many hundreds of man hours, to get it right, smooth and solid enough to take on the repeated abuse of molding hulls.

    Welcome to the BoatDesign forum and best of luck in your endeavors, building drift boats. The book store on this site has many titles on design, construction and technique, it would be a worth while investment for your venture. It's very possible you'll discover a "one off" method that will reduce the effort and mold needs, to get out your 'glass hulls, all the while being better suited to your abilities and budget.
     
  3. marshmat
    Joined: Apr 2005
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    Location: Ontario

    marshmat Senior Member

    Welcome aboard, Coltrain.
    Before you jump in head-first, some advice on moulds (I've built a few, and now know enough to avoid them where possible). Getting a good, useable mould that will turn out nice hulls requires a LOT of time, money and effort. And I do mean a lot- think hundreds of hours of labour, slaving away on cutting a plug, sanding and polishing it mirror-smooth, then taking a glass mould, sanding and polishing that mirror smooth (about a week of solid 8-hour days of prep work on the plug surface is not uncommon, before you can even think about a mould, let alone a boat). You can't cheap-out on the mould, or try to save on labour by figuring you can get by with less than perfect quality, because if you do, all you'll turn out is junk boats. Not to mention that the moulds are, in general, substantially more expensive than the boats themselves in your size range.
    If you want nice, practical and elegant drift boats that you and your friends can build without too much expense or time, there are a huge number of stock plans available in well-proven glass-over-plywood or pure wood techniques, from well known and popular designers. It sounds like you're more eager to get out and enjoy the water than to slave in the shop over a can of resin; if this is the case, you'll be better served by spending the $40 for a set of stock plans that have already been engineered to suit your needs with a construction method that is cheaper and easier than setting up your own temporary factory.
     
  4. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    What they say. A couple three people working together could turn out three sure to work boats from proven plans in less time and money than 1 good mold would take. Plus, having a mold around that's not being used is a nuisance with storage, taking up room, moving it etc.
     
  5. Coltrain
    Joined: Jul 2007
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    Location: Oregon

    Coltrain New Member

    Thanks guys. I've been trying to convince those guys it would be easier to build glass over ply drifters. That's what I really want anyway; they are supposedly lighter, float higher, and I think they look a lot better. The other guys are experienced in mold making - that's what they do here, although they are usually RTM molds - and think they can build a mold that will hold up to making 5 or so boats using leftover and scrap glass. I don't want wavy cheap looking glass boat, so hopefully I can convince them to go the glass of ply route...

    Thanks for your help.
     
  6. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    Well, I sort of lied to discourage people who don't know what they are getting into from getting in over their head, which might not be the case here.

    If the hull is a shape that can be developed from flat sheets of ply, you can make a mold fairly cheap, quick and easy that will last for at least 5 boats if you treat it nice and don't get a hull stuck in it.

    I made one for a 16' flatbottom jonboat using frames spaced every 24" and then attached 3/4 x1" longitudinal battens every 6". I lined the whole thing with 1/8" thick hardboard that has a smooth coating on one side. It's stuff they sometimes call 'tileboard' and sometimes fakes the look of tiles and is used in very cheap tub enclosures or to line cheap bathrooms. The stuff I used was white coated on one side and the whole 4x8' sheet was smooth, with no fake tiles on it. Home Depot has it in the paneling section for less than $15 a sheet.

    That stuff I glued to the battens with Liquid Nails, holding it in various ways to the battens until the glue set. The corners were filleted with Bondo (something that doesn't set up so fast would be a lot easier) squeezed out of a baggy with the corner cut off, sort of like the squeeze bag used to decorate cakes. The fillets were rounded and finished by dragging a socket wrench socket of the correct size along the fillets.

    After 4 coats of wax and 1 of PVA, the boat popped out easier than a lot of production molds I've worked with. As with all these kind of things, the product only looks as good as the mold, so the more carefull you are making the mold, the better.

    As for the way I constructed the boat, I did it the same way Carolina Skiff makes theirs. At the time, their way was patented and protected, but the patent expired a few years ago and the process is now in the public domain. It makes for a real strong, lightweight boat with no internal framework to trip on and collect dirt, etc.

    Here's their patent...(#4495884) All the numbers on the left under "Field of Search" are the older patents that led up to theirs and are interesting in showing other/similiar ways of building boats or making lightweight structures.

    http://patft.uspto.gov/netacgi/nph-...50&s1=4495884.PN.&OS=PN/4495884&RS=PN/4495884

     

  7. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    I have an idea of where you work from the type of production you normally do, but let me know what shop it is.

    I have a drift boat mold, or at least I had one, some guys at another boat shop borrowed it and I don't have it back yet, that was only 5 years ago. You can use it if it's still around.
    It's a narrow 48" hull design, the last one I made from it I widened the hull and raised the sides, it was a much better boat after that. Hull bottoms on drift boats are much thinner than the chins so they will flex, the flexing allows them to slide over rocks better.

    You can make your own mold for one fairly easily, but it will still cost some money.

    Don't do the glass over wood construction, stick with straight glass, glass over wood won't last all that long on the west coast unless you keep it indoors when not in use.
     
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