Question about marine plywood

Discussion in 'Wooden Boat Building and Restoration' started by sab, Feb 7, 2014.

  1. ancient kayaker
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    ancient kayaker aka Terry Haines

    Water ballast is for boats that are dry docked, which makes it easy to remove when the boat comes out of the water. Otherwise you have to deal with pumps, fouling and ensuring the tank is either full or empty, and it will rapidly become a pain.
     
  2. rwatson
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    rwatson Senior Member

    Not as bad as it sounds - the Macgregor 26, the most popular WB larger boat is easy to manage - it requires no pumps as it is cleverly designed to empty under power or on retrieval. Filling and checking levels is also easy.

    Designing a system on smaller boats is where the complexity comes in, and often its easier to solve with custom weights.

    On a say - 16 footer, its easy to carry ~ 100 kilos of steel or concrete ballast to suit, whereas on the Mac, you are looking at over 500 kilos - not something you would want to throw in your boot.
     
  3. tinpin4544
    Joined: Dec 2013
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    tinpin4544 Junior Member

    Marine ply

    I know this is a late response, but Meranti is cheaper and way tougher (but heavier). I wouldn't use Okoume on a duck or jon boat that will be in the shallows. Just my opinion. I agree on using marine ply, as Home Depot stuff will check, but 6566 Meranti should do a great job at 1/2 the price of Okoume.
     
  4. tom kane
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    tom kane Senior Member

    I can not understand why some one has not made available sheets of resin + fiberglass or carbon + resin plus lumber of the same material for many building projects.
    Built under factory conditions it should be a great product.
     
  5. FMS
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    FMS Senior Member

    Coosa provides sheets of "high-density polyurethane foam reinforced with layers of fiberglass."
     
  6. rwatson
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    rwatson Senior Member

    Not only Coosa boards, but a whole variety of specialist products have been created throughout the years.

    Standard 'glass products like beams, tubes, etc are readily available

    But, glass constructions by their very nature take advantage of the strength in compound curves, and the very layup schedules are tweaked for individual designs.
     
  7. oldsailor7
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    oldsailor7 Senior Member

    Previous
    That designer was Lock Crowther.
    He considered, (and rightly too), that water ballast on a properly designed multihull was not a good idea.
    Water ballast is no better than adding lead to provide stability.
    Bouancy is the whole principle of multihull stability.
    If the boat is properly designed, and is being overpowered, it is better to reduce sail area. It may not seem logical to some, but apart from making the boat feel safer, it will actually allow the boat to go faster.
    Loading the boat up with extra ballast, water or not, increases inertial loadings on the structure as well as increasing induced and wetted surface drag.
    I speak from experience as I experimented with sealed water ballast compartments on my Buccaneer 28. When loaded up with water the usually lively boat became a DOG, the motion became unpleasant and pumping the water in and out on every tack became a chore and definitely not effective for racing. :(
     
  8. ancient kayaker
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    ancient kayaker aka Terry Haines

    Pre-preg may be what you're looking for, sheets of carbon fiber impregnated with epoxy that sets off with heat. Not really an amateur's material I suspect. Last time I saw it, it was being used for fighter jet wings . .
     
  9. ancient kayaker
    Joined: Aug 2006
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    Location: Alliston, Ontario, Canada

    ancient kayaker aka Terry Haines

    Previous
    The advantage of water ballast over lead is it can be moved around, added or dumped. I can see it being useful in multi racing to augment crew weight. Unlike lead it does its best work when it starts to rise out of the water which happens on a multi long before effective sail area is lost to heeling. Crew has to be pretty slick when tacking . . .
     
  10. PAR
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    PAR Yacht Designer/Builder

    I've long thought that water ballast was nothing more than a fad, that racing rules favored for a while, that happened to trickle down to the masses. Water sucks as ballast for a number of reasons. Mostly you need so much of it, to really do anything, you have to sacrifice huge hunks of accommodations, which isn't a problem for a racer, but anyone else . . .

    I class this with the wing keels seen after the 1983 America's Cup, that really served no useful purpose, but as a marketing tool for production builders. Next up will be humongous foils to hoist a Formosa 41 out of it's forever entrapping LWL governed speed limit, so it can keep up with it's dinghy.
     

  11. oldsailor7
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    oldsailor7 Senior Member

    The first three boats I built (one mono & two Trimarans), were built with "good one side" exterior grade Douglas Fir plywood. The "Bad" side had some knots and even knotholes in the outer layer of the ply, and this side was layed up on the inside of the boat. All these boats were coated on the outside with a layer of glasscloth set in polyester resin. The insides were painted with ordinary housepaint above the floorboards, and the bilges were saturated with green copper napthenate, (Cuprinol).
    Results were OK for a short time. Douglas Fir rots quickly in fresh water, and rainwater eventually accumulates in the bilges. As a result the bilges had to be treated with the Cuprinol every spring, and the whole business was pretty messy.
    Later boats were built with mahogany marine ply and were encapsulated with epoxy. Two coats on the inside and three coats on the outside----no f/glass.
    The epoxy had to be protected from UV by two coats of a good quality polyurethane paint, in colour of choice,---and that's all.
    This method proved perfectly effective and some boats still exist in good shape after 40+ years.


    ,
     
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