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. redreuben
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    redreuben redreuben

    I think the term composite should be kept for foam sandwich or other cores with fibreglass skins, cedar strip is stretching it.
    The trend of using composite as a term for ply epoxy has been started by brokers trying to flog plywood boats.
    I think it’s dishonest.
     
  2. fallguy
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    fallguy Senior Member

    I would like your comments on cpes.
     
  3. Doug Halsey
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    Doug Halsey Senior Member

    I'd love to see a photo of your 1955 Moth.

    Here's one I built 10 years later, using mahogany veneers & epoxy. I have no idea how long it survived though.
    USA2775_in1970.jpg
     
  4. W17 designer
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    W17 designer Senior Member

    Off thread ...but I will see what pics I can dig up later today
    mike/

    And for Fandango:
    'Can Peter East Sardines?" I've no idea! ... but perhaps you can 'Trip my Light' a little on your particular CPES. The old brain is foggy this morning ;)
     
    Last edited: May 17, 2019
  5. Doug Halsey
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    Doug Halsey Senior Member

    The digressions are often the best parts of the threads :)
     
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  6. fallguy
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    fallguy Senior Member

  7. Blueknarr
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    Blueknarr Senior Member

    Visited the link. Sounded like the "Smiths" I used along time ago. Turned out for a is the new name of Smith's penetrating epoxy.

    I stopped using it when I was tasked with saving a rotten architectural beam. After I stripped off the paint, it was evident that penetrating epoxy was used four previous times in the same spot. There where rings of hardened stuff surrounded by rot. The hard zones varied from 1/16 to 1/2 inch.

    I found that the slow to evaporate solvents actually caused problems with paint.

    Needless to say. I don't endorse it.
     
    Last edited: May 17, 2019
  8. W17 designer
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    W17 designer Senior Member

    Doug Halsey: "I'd love to see a photo of your 1955 Moth".

    OK Doug ..let me first 'try' to share something in line with the Thread title .. call it a crude 'cover-up' ;-) and then I can slip over to the Moth.

    First, from Tchamo "can foam and plywood be used together on a boat bottom?" Certainly.
    Back in 1970, as my daughter approached 12, she heard about my first boat at 12 and said she was up for trying to build one herself too. I already had some 9" x 40" offcuts of some dense polyurethane foam panels that had paper bonded to both sides and were 3/4" thick, so decided to try something that I nicknamed "Plifoam". The challenge was to create a nice little sailboat that was light and also simple enough to make that my daughter would be able to build most of it. The whole hull was first shaped (hydroconic) out of 1/8" birch plywood (sold for door panelling) using copper wire stitching with the joints (pre-epoxy) of polyester car filler and 3"wide matt tape just over the joints. With only two frames and a transom, it was very easy to twist everything. But we then bonded in strips of the PU foam using contact cement just to stiffen the interior, leaving the brown Kraft paper bonded to the inside. We then simply painted the whole thing, paper and all, and it came out pretty well.
    I did make the mast and boom for the boat and bought her a small gunter-rig sail to reward her effort.
    I called the design 'Mosquito' and she christened her boat 'The Sting' after the Paul Newman film.
    She learned to sail in that boat and had hours of fun, but just capsized it far too many times for it to last long (3 seasons) as water found its way between the foam blocks and could not dry out ...and as I said, there was no epoxy readily available then. The foam inside put the 3mm skin in tension when moving around the boat, and for 2 kids of 100lbs, it was fine. Even the thwarts were made of 3mm ply with foam bonded on top and they were strong enough, warm and comfortable as they soon shaped 'to suit'. See pic - yellow inside.
    7 years later my son also wanted to build a boat at 12. So I designed him a double chine MicMac canoe and he used the same construction, except that this time, we laid in one layer of glass cloth over the inside bottom foam, to seal it better. The upper sides stayed with only the 3mm ply but with an interior pine gunwale. The 15'6"canoe initially weighed barely 40 lbs and it lasted an astonishing 26 years with careful treatment. Even when I finally cut it up with a chainsaw, the joints of polyester and glass matt were still perfect. (Random glass-matt bonds to wood better than 90/90 boat cloth does but is heavier and requires more finishing).

    So now to the Moth. In 1953, I participated in a once-in-a-lifetime dinghy race (200 boats) around the Isle of Wight (about 70 miles) to celebrate the Coronation of the Queen ..a high risk affair for the organizers as 1/2 of it was effectively in the Channel - Atlantic Ocean ! One of the top boats to finish was Coronet designed by John Westell .. a design that eventually spawned the 5-0-5. But I was very taken by the extended gunwale and decided to create a hard-chine Moth-boat with such an extension - one of the first in fact.
    As I was concerned about the strength, I kept this extension to about 5" each side, though later boats added more. The boat was called Flying Moth and eventually 26 Mk ll's and 2 Mk lll's were built. I managed a 2nd & 4th in a 1957 British Moth Championship and later heard that one finished 4th in the European Moth Championship around 1960, with this comment from the skipper "I was too slow on the downwind leg as compared to the newer 65lb boats, the boat was just too heavy at 100 lbs, but no one could touch me upwind. I was always 1st to the upwind mark, but sadly the races all finished downwind".
    So here are some pics of the Flying Moth .... the early one that was rediscovered and refinished recently .. ... plus a deck photo of the last one #28 that I called "Crew Cut"and rigged like a Finn.
    I see that your own Moth a decade later also had an extended gunwale. Neat.
    (I hope the Thumbnail pics will enlarge if you click on them)
    Ian sailing 'Sting' Mosquito#1 '72-2.jpg FM22 in section - as found 2014.jpg
    Enjoy/
    mike/
     

    Attached Files:

    Last edited: May 18, 2019
  9. W17 designer
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    W17 designer Senior Member

    And for those intrigued by the MicMac Canoe .. here's a pic ... and a section through the keel and the chine, when I cut the boat up due to rotten topsides, but after 26 years !
    The midship cross brace was just bolted-in for handling on to a car roof (it was once my sons favorite hockey stick;). The raised ends were original 'MicMac' style .... used for the canoe to rest on when tipped over on a beach for sleeping under. But they added too much windage for an open lake, so we lowered them after 2 seasons.
    I got a kick out of using birch ply for this boat, as the originals were of birch bark - all local wood in both cases ;)
    mike/

    MicMac 15 - 1979.jpg ply 08.jpg ply 02.jpg
     
    Last edited: May 18, 2019
  10. trip the light fandango
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    trip the light fandango Senior Member

    The problem with using foam core as the bottom is that it can absorb water[small drain holes perhaps, which I think I'll do to my hobie foam sandwich hulls]] so will need a bilge that doesn't have foam... at the lowest point is all glass mat and to help avoid delamination from impact,. hobie uses this approach early on. Just addressing the original question..but those moths are lovely things. Hard to believe that little book that I had as a kid with pictures of various small boats in it, and one of the builders is here..
     
  11. trip the light fandango
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    trip the light fandango Senior Member

    Yes well I had no idea what it stood for.
    It would be very difficult/impossible to know when all the moisture and voids had been filled from rot, injecting in slow hardening epoxy would be the approach I suppose, just keep drilling and checking the shavings? until it's all epoxy or solid wood, then checking later. I should have said in the earlier post , it turns the" surface" of the wood in to a type of plastic, I wasn't specific enough, I keep getting pinged for that, rushing answers, ha.
     
    Last edited: May 18, 2019
  12. W17 designer
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    W17 designer Senior Member

    Trip the Light: The problem with using foam core as the bottom is that it can absorb water[small drain holes perhaps, which I think I'll do to my hobie foam sandwich hulls]] so will need a bilge that doesn't have foam... at the lowest point is all glass mat

    There is foam and foam my friend. There are high quality marine foams (such as Corecell, Klegcell and others) that are effectively 100% closed cell and remain that way for decades. In fact, we don't yet accurately know how long they last. Sunlight will likely be worse for them than water. Even properly formulated and factory produced PU (polyurethane) foams can be closed cell and the PU panels used for my canoe that last 26 years, were still water-free when she was cut up. A common problem with most bulk 'foamed in place' PU is that it shrinks with time and then water can get in to fill the voids. If that water then freezes, it can blow off the skin and cause havoc. That happened to two of my Division 2 sailboards despite their epoxy skin. But I am presently working on a 32' design that will use quality foam between an outer and inner bottom, to make a rugged 100mm thick bottom, Kevlar reinforced to be highly 'rock-resistant'.
    'Drain holes' as such in foam would not work as you'd need one for every microscopic cell ;-) haha, .. but draining areas around polystyrene foam IS a good idea. But if you're using poor quality PU (as sold in cans etc) or polystyrene (styrofoam), then its best to keep it out of continuous water exposure as it will slowly soak up water. Only a small percentage by volume though but it will add noticeable weight. After all, large blocks of styrofoam are still used under some floating houseboats and rafts, and although they slowly lose buoyancy and eventually need replacing, they still last many years. Glass matt and polyester resin has also proven over time to not be 100% waterproof .. as observed in many early fiberglass boats from the 50's and 60's.
    (Moving forward, perhaps best to advise on what you really have experience with mon ami)
     
    Last edited: May 18, 2019
  13. W17 designer
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    W17 designer Senior Member

    Fandango: Hard to believe that little book that I had as a kid with pictures of various small boats in it, and one of the builders is here.

    Want to share what little book that is? Was there a pic of the Flying Moth by chance? I do remember seeing one in a library once but that was decades ago. ;-
     
  14. Doug Halsey
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    Doug Halsey Senior Member

    Here's another Moth photo that isn't entirely off-topic for this thread.
    #2176, shown from astern in this photo from the 1964 Nationals, was the predecessor to the one I showed earlier. It didn't have the gunwale extensions of that boat, but both had a lot of flare in the topsides inspired by the 5-0-5.

    The relevance to this thread is that its construction was foam/fiberglass sandwich. It had a relatively thick core of 1" Styrofoam, with a single layer of glass/epoxy inside & out. It was fairly light (hull < 65lbs.), very stiff, and quite fast. It never had any problems with delamination, but it was extremely fragile in terms of dents & punctures.
     
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  15. W17 designer
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    W17 designer Senior Member

    Thanks Doug.
    Yes, I can imagine with such a soft foam and a relatively stiff single glass layer, that would pierce VERY easily! Boat life must have been pretty short. No great problem for 'constantly developing Moths' as to win, you almost need a new one every season! But for that reason its a fun class and 'relatively' inexpensive. I certainly never expected someone would find one of mine in such good shape after 62 years! Shows the potential of good plywood .. even before the days of epoxy. The UK restorer said 'the secret was the use of top quality marine ply, good African mahogany for the keelson, CB case, transom etc and finally, good workmanship". I'll accept that little encouragement with a smile, especially as I was 20 at the time I built it ;-)
     
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