Use foam core and plywood in a catamaran hull

Discussion in 'Multihulls' started by Tchamo, Apr 7, 2019.

?

is it possible to combine foam core and plywood in a catamaran hull. using foam core on the bottom

  1. yes is possible

    6 vote(s)
    85.7%
  2. it is not possible

    1 vote(s)
    14.3%
Multiple votes are allowed.
  1. Tchamo
    Joined: Apr 2019
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    Location: mozambique

    Tchamo New Member

    Hi... i live in a country(Mozambique) were marine wood is hard to find...although we have a variety of good quality wood... at the beginning i was thinking of using one of the local wood and encapsulate with fiberglass and epoxy.
    my other idea was to build a hull using foam core in to bottom and use marine plywood for the hull's wall... for a 43ft sailing catamaran is it possible?
     
  2. Dejay
    Joined: Mar 2018
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    Location: Europe

    Dejay Senior Newbie

    What local wood species do you have?
     
  3. Tchamo
    Joined: Apr 2019
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    Location: mozambique

    Tchamo New Member

    pine, jambire, umbila, chafuta, chanate,african padauk...
     
  4. Dejay
    Joined: Mar 2018
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    Location: Europe

    Dejay Senior Newbie

    I can't give you any advice on the local woods but probably someone else can.

    What you are asking is possible, almost everything is but has trade offs so the question is if it makes sense. Wood is stronger and provides much better point loads for the bottom, so you'd need less fiberglass. Foam doesn't rot (but can still be destroyed by hydraulic erosion) so can take neglect much easier. Also depends how important weight and where and how you are going to use the boat.

    Ideally you'd buy boat building plans and ask the designer on how to build. Local woods would certainly be cheaper than marine plywood or foam but more work. Also depends on size. A smaller catamaran could be build in stitch and glue.

    Only thing I've found is this, I'm sure you can find more.
    Boat building lumber and plywood https://www.glen-l.com/wood-plywood/bb-chap5.html
    African Padauk | The Wood Database - Lumber Identification (Hardwood) https://www.wood-database.com/african-padauk/
     
  5. trip the light fandango
    Joined: Apr 2018
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    Location: Rhyll Phillip Island Victoria Australia

    trip the light fandango Senior Member

    The main issue is water absorption/ingress into the timber, if you seal each piece , especially the end grain it will last. If a timber has an organism in it that naturally breaks the timber down, eats cellulose, then it will turn into dust whatever you do[except*], but rot/fungus spores are the more likely problem. So a timber that is naturally very tough will have a sap that is insect and rot resistant. It is normally quite dense,/heavy and a hardwood but there are exceptions. Carpenters /woodworkers/bridge builders/ boat builders in your area will know which is the best and available timber to use. The West system impregnates wood with epoxy absorbing the resin and effectively using the grain as the structure like matt in fibreglass, [*]it turns wood into plastic sort of. When you put two materials against each other they have different absorption expansion/ shrink rates, flex and stiffness, foam is pretty predictable with stated characteristics, as is epoxy. If you get the combination and thickness of the combination right and treat the suitable timber correctly[cut it thin enough to absorb completely] you can definitely use it, if you don't it will fail with various consequences including of course potentially catastrophic failure. The west system concept is the answer. The west system is thinned epoxy specifically designed to cope with the thinning then reinstate as solid . Look into it carefully if you choose to use a non generic brand, ie a reputable chemist in the industry. Linseed/ lead/ chalk was the early alternative.
     
  6. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    The primary consideration for an amateur is ease of build and completion success.

    If you have the means for an indoor build; that is a first concern.

    Building outside takes longer. A vessel that size is a multi-year project. Epoxies cannot handle years of exposure without damage.

    Typically, foam builds are done using infusion or wet bagging. I do not consider either method amateur and both rather difficult for amateurs. Wet bagging such a large boat would be daunting. Infusion errors would be costly, but infusion would be the only way I would go if I could start again. (The materials are not the same)

    The easiest method would be plywood monocoque. The vessel at that size would probably be built upside down. An alternative would be strip planking, but you'd need carefully controlled wood moisture and careful selection of timbers.

    I am building a foam boat using wet bagging/dev panel and we are at what I consider the end of rational limits for size at 10 meter. Our table is 34 feet long. We glass 33' 6" panels with 3 people and our best time in the bag was 63 minutes with a 120 minute gel time. Our worst at the beginning was 110, so 50 minutes of learning in 8 panels. Our last large panel was bagged in 70 minutes. The tropical epoxy requires post curing the entire hull in an oven, although you could post cure each piece I suppose.
     
  7. redreuben
    Joined: Jan 2009
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    Location: Beaconsfield Western Australia

    redreuben redreuben

    Why do you want to build ?
     
  8. jamez
    Joined: Feb 2007
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    Location: Auckland, New Zealand

    jamez Senior Member

  9. redreuben
    Joined: Jan 2009
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    Location: Beaconsfield Western Australia

    redreuben redreuben

    My guess is your local Woods are heavy hardwood not suitable for a multihull. If your going to use foam do it all in foam, hulls, decks, bulkheads and furniture. Make melamine moulds for glossy finishes etc. Resale will be worth it and you can tool up for one build method and use one resin system. For foam use Vinyl Ester.
     
  10. W17 designer
    Joined: Oct 2010
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    Location: Vermont, VT

    W17 designer Senior Member

    Trip the Light: Quote: “The West system impregnates wood with epoxy absorbing the resin and effectively using the grain as the structure like matt in fibreglass, [*] it turns wood into plastic sort of”

    The author meant well I’m sure, but I need to correct this far too common assumption.

    I have worked with epoxy since its inception (post Adagio~1970) and used it since for numerous boats and other items too.

    While epoxy is a wonderful product and can last many years and is ideal for bonding and creating joints etc., is does NOT impregnate wood to any worthwhile degree and most certainly cannot turn wood into any sort of plastic! In fact, after the first coat is applied, the wood is now mostly sealed against any absorption, so IF there’s any penetration, the first coat is critical.

    So can the first coat of epoxy be thinned for this purpose? Well, some 20 years ago, WEST System published a detailed article about the effects of thinning epoxy in their seasonal magazine EpoxyWorks. I will try to summarize what I remember of that, for readers who may have missed it. As it came from WEST System themselves, I think it’s worth noting.

    Epoxy can be thinned with acetone (or lacquer thinner) but its strength properties are affected. (I’d recommend to never use more than 3% thinner - which will already lower initial viscosity by about half and cut strength by 20%). But if used in a concentrated area, such as to repair rotten wood, solvent can become trapped in, causing the epoxy to shrink over time … leading to cracks that will then allow water in!

    If one insists, a better way to thin is to keep the resin at least at room temperature and then warm the surface to be coated …. say up to about 110 deg F .., that’s warm to the touch, but certainly not hot. After the resin is applied, the material then cools and the resin is drawn in ‘a little’. (As’ drawing-in’ takes time, you’ll need to use the slowest hardener for this). But as will be noted, this is really only justified to get a little extra strength for joints made with very hard woods.

    Epoxy will never impregnate as one might wish it to. I have over-coated numerous material samples and once cured, sliced them to examine the penetration under a magnifying glass. It’s seldom visible. In fact, it’s only very hard woods like oak, maple, birch etc that will gain anything from first starting with a thinned epoxy, as the bond to just the surface of a softer, weaker wood (especially like cedar), will already be much stronger than the actual inter-fiber strength of the wood itself. And it’s worth remembering that the strength still comes from the wood fibers themselves, so if you’re repairing rotten wood, you are only making the repair hard, you’re not making it stronger, unless you also add on fiber like fiberglass, Kevlar or carbon.

    So plan on using epoxy as the manufacturer suggests … using several coats to build-up a waterproof membrane … but first make sure the surface is dry, free of oil & dust, and at least at room temperature.

    The less joints and sharp corners you have, the more continuous and effective that barrier will be. Solvents can cause more trouble than they are worth and will weaken the strength of the epoxy. Too much complex framing is also a problem, as any coating system struggles to protect corners ... see more below.

    Because of a rash of ‘penetrating epoxies’ that came on the market a few years ago, WEST System were forced to defend their case, so their chemist wrote a more recent article on “the penetrating epoxy myth”, that reiterated most of the facts from their earlier article of 20 years back.

    You’ll find it here:
    Penetrating epoxy: legend or myth? .... https://www.epoxyworks.com/index.php/penetrating-epoxy-legend-myth/

    Personally, my approach is to try and build structures with the lowest length of sharp corners, the least number of softwood parts, to presheath the interior side of plywood before it’s built in and finally, make sure that end grain will stay well sealed for the life of the project. To help achieve this, I came up with the cleaner, simpler way to build with flat panels (for my W17 trimaran) and anyone interested can search for this ‘ABC System’ on my website. (Just use the Google search panel). There’s nothing for sale .. it’s simply free advice if it interests you … as are the other 180+ articles posted there.
    Hope this helps someone.
    www.smalltridesign.com
     
    Last edited: May 15, 2019
  11. trip the light fandango
    Joined: Apr 2018
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    Location: Rhyll Phillip Island Victoria Australia

    trip the light fandango Senior Member

    I thought I was giving good advise but are happy to stand corrected. I suppose it is clutching at straws to say that the surface profile of a piece of plywood[not finely sanded but clean] will have a texture made up of the fibres of the timber. Epoxy is thinner[runnier] than any polyester resin I have used and as it settles into these albeit surface fibres, it plasticizes the texture.[like a mat...] I 'm surprised that it doesn't absorb more, it kind of makes a mockery of what I thought west systems innovation was, it's just a slow hardener, but then how could it replace resins already present ?... If you are saying that timber doesn't take up epoxy via the end grain to some extent , I don't actually believe you W17 ,again that may well be my ignorance , I best start reading.....
    After reading I can add that I have used slow hardening 4 to 1 epoxy, and rereading my original post should have stated clearly that epoxy doesn't replace the natural resins in timber or turn the whole thing in to plastic ,it plasticizes the surface making it impervious to water ,I did state how to.... A sore loser., rereading my post it does or could imply all the resin is absorbed .ha ,cheers and thanks W17, I've learnt something from you again.
     
    Last edited: May 16, 2019
  12. Dejay
    Joined: Mar 2018
    Posts: 350
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    Location: Europe

    Dejay Senior Newbie

    I think you can say that wood + epoxy becomes a composite.

    There is stabilized wood used for pens and the like that is vacuum infused in a bath of some kind of very thin and heat activated resin. Sometimes colored. That apparently soaks up resin depending on the density of the wood.

    Still curious if you could vacuum infuse layers of veneer to make your own plywood in a female mold and create a monocoque hull :)
     
  13. BlueBell
    Joined: May 2017
    Posts: 848
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    That's how they make rowing shells... well, in the old days!
     
    Last edited: May 16, 2019
  14. Blueknarr
    Joined: Aug 2017
    Posts: 703
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    Location: Colorado

    Blueknarr Senior Member

    Yes. Cold moulding is considered composite construction. So is glassed over stitch-n-glue plywood.
    The wood is dyed first then glued together. Dyes are much smaller particles than glues or epoxy. The smaller the particles, the greater the penetration.
    Like cold moulding? The veneers would have to be extremely thin for a vacuum to flex them. Compound curves require darting. Could be done but not easily. Traditional cold moulding over a male plug is far more efficient.
     
    Dejay likes this.

  15. W17 designer
    Joined: Oct 2010
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    Location: Vermont, VT

    W17 designer Senior Member

    I think most pro-builders and designers would say that a boat is 'composite build' when 2 or more materials are used to create the structural strength. Although it might be argued, sheathing over plywood when the plywood alone is actually strong enough and the sheathing is only for water or surface-abrasion protection, is not normally considered 'of composite built'. Traditionally, it was always a lightweight core (foam or balsa etc) with strong skins of a fiber with resin, but has morphed into other combinations over time.

    Moulding boats using thin veneers for boats is actually an old system that goes back at least 75 years. In the UK, it was started by Uffa Fox, first for a lightweight lifeboat he designed during the war (that could be dropped from an airplane to save shot-down aircrew) and then for the 12ft Firefly and a couple of others. It was first developed by De Haviland for making planes during WWll ... when nearly 8000 small bombers (the Mosquito) were built using wood (see old photo), as aluminum and steel were of very short supply being needed for guns, tanks, lorries etc. Saunders-Roe close to where I lived, also worked with wood veneers and special presses ....way before epoxy was available. Glues were generally casein or resorcinal, until a urea based glue was developed (with a liquid hardener) called Aerolite 300, that I personally used for the first dozen boats I built in the UK*.
    None of these 'moulded-veneer' boats were or could be considered of composite construction as the structure was all of wood.
    * readers might be interested to know that a Moth boat I built in 1955 using Aerolite 300, was rediscovered in 2017 and as all the plywood and the bonds were found to still be excellent (after 62 years!), she was fully renovated and is now back sailing in the Vintage Series for old racing classics ;) Note that none of those early glues were gap-filling, so all joints had to be of pretty high quality.
    www.smalltridesign.com
    Mosquito bombers being made at Fairey Aviation during WWll.jpg
     
    Last edited: May 16, 2019
    bajansailor and Dejay like this.
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