Newbie here with newbie question. Marine plywood or plywood?

Discussion in 'Wooden Boat Building and Restoration' started by photojunky, Jul 16, 2007.

  1. photojunky
    Joined: Jul 2007
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    Location: Pacifica, Ca. Surrounded by water.

    photojunky New Member

    I am going to be building a wooden kayak or wooden rowboat in the near future. If I coat the wood with epoxy/cloth, is it acceptable to use regular ½ plywood, or do I need to use marine plywood? I also plan on painting the boat and will not be keeping her in the water full time.

    When I start building, I'll post images of my progress for cheap laughs at my expense.:D

    BTW, this is one cool forum.
     
  2. USCGRET/E8
    Joined: Jul 2007
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    USCGRET/E8 Senior Chief

    If you're going to glass it, regular Exterior plywood will work fine.
     
  3. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Marine plywood differs from construction grades in significant ways. The veneer count is higher, which makes a more stable product, that is stronger and more reliably bent to conform to boat shapes. The quality of the panel construction is also much better, typically having same thickness veneers, few voids, defects, repairs and rot resistant species used throughout. This can't be said of construction grade plywood. You'll have to seal the plywood which ever grade you elect to use anyway, so it seems to me, like false economy to skimp on the planking, when in the end the marine grades will perform better and last longer. Generally, the planking is some of the finest material used in small boat construction.
     
  4. PsiPhi
    Joined: May 2007
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    Location: Queensland

    PsiPhi Newbie

    Photojunky
    I'm a newbie too - and was thinking the exact same question.

    What PAR says is correct (of course) and you will get the same good advice everywhere,
    however (PAR) my problems is Construction ply is $30 a sheet, Marine is $150.
    $120 x 6? sheets (for a average type dinghy) - the difference between $180 or $900 on ply is the difference between a cheap boat and no boat!

    Maybe the question Photojunky (and I) need answered is - What are we going to loose by using cheaper ply?
    Will our boats "Crash & Burn", figuratively speaking, or just die quicker??
     
  5. photojunky
    Joined: Jul 2007
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    Location: Pacifica, Ca. Surrounded by water.

    photojunky New Member

    Holy Sh*%#! :eek: 150 for marine! I think you just answered my question. Besides, this is my first boat so there will probably be some screw-ups so why waste the money on the marine grade when this is just a practice project.
     
  6. PsiPhi
    Joined: May 2007
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    Location: Queensland

    PsiPhi Newbie

    I'm talking Aussie dollars of course (I'm in QLD) - but I would guess their is a similar difference where you are.
     
  7. waikikin
    Joined: Jan 2006
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    Location: Australia

    waikikin Senior Member

    Photojunky & Psi Psi, !/2" is pretty thick ply for a canoe maybe 6mm/ - !/4" is closer to your needs & price difference less, Psi Psi in Aussie some of the misterply franchises have 6mm hoop pine ext type A bond with 5 veneers that would suit dinghy/canoe for about $70A of very good quality, I've cut heaps for fitout etc & found very few voids, also takes epoxy or paint well. Regards from Jeff
     
  8. USCGRET/E8
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    USCGRET/E8 Senior Chief

    I assume anyone posting on here has a very small budget as I always do. I therefore base my answers on that. In that you are building a rowboat or kayak I don't see a need for that expensive marine ply, which I had in mind in my previous post. If you were building a fast speed boat, then the marine ply wood be a safer bet.
     
  9. USCGRET/E8
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    USCGRET/E8 Senior Chief

    A speed boat I built using 1/4" exterior plywood then glassed. It held up fine.

    [​IMG]
     
  10. timgoz
    Joined: Jul 2006
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    Location: SW PA USA

    timgoz Senior Member

    While respecting others experienced opinions, I myself would go for marine grade ply. When you tally up oars or paddle, vest, skirt (if Kayak), and all the construction materials other than the ply, the ply is not as great a part of the cost.

    You hopefully would not skimp on proper technique for a "pratice" boat. Why then should you skimp on the quality of the materials going into it. If done right and with good materials it may last many years. If done right with inferiour materials it may last significantly less years.

    To me a boat, any boat, deserves the best you can afford. I am to poor to be cheap.

    Tim
     
  11. ATCSchaefdog
    Joined: Jul 2007
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    ATCSchaefdog Junior Member

    marine or regular

    Regular plywodd would work great. But the question is...is the boat of your dreams, the boat to end all boats? If it is, then use marine grade, if not, go cheap.
    Steve
     
  12. catman021
    Joined: Jun 2007
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    catman021 Junior Member

    I've got to echo the popular sentiment here and go with the construction grade plywood myself. On my rebuild(sic), I've looked at both plywoods, fibergalss overlaid foam, composite materials, and being just a working joe, knowing that I'm going to coat/glass it in completely anyway.....for my money saving the money is the way to go. This is also driven by the not so small factor that I can get the cheaper stuff from HD or Lowes and not pay any outrageous shipping fees to boot.
     
  13. VKRUE
    Joined: Mar 2006
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    Location: Central Illinois

    VKRUE Just another boat lover

    IMHO...

    I'm with Timgoz.......... "I am too poor to be cheap".

    Are you serious about building this boat ? If so, then why not make it a point to build a real craft, with skill. You will develope the necessary skills as you go. Sure, you will make mistakes. But, if your like me... the fact that this piece of plywood cost me $100.00 for a 4' x 4' sheet will be a lot of encouragement to take care in everything you do.

    Below is a picture and caption from my blog regarding the making of two gussets and two patch boards for my boats hull... I removed a small section of the hull to replace a damaged section of the keel about 36" long:

    [​IMG]


    Here you see the hull patches. They are made of 3/8" okume plywood with 7 plies. I had purchased the wood thru Boulter Plywood
    http://www.boulterplywood.com .

    The wood was shipped directly to my house here in central Illinois.

    Each patch board was carefully shaped, dry fitted and clamped into place many times untill I was satisfied that the shape was precise. This was a real pain because at the time I hadn't figured out how to flip the boat over yet. The first half (patch) took an entire day. Then I pre-drilled each piece every 2" around the outer edges all the way around. I counter-sunk the outside holes to accomidate brass screws while the inside holes (directly over the keel) would recive silicon bronze ring-shank nails. Don't ask me why I used brass :( I don't know why I used these instead of silicon bronze like I should have. Brass, I have found out is very soft. Everything else on the boat is getting silicon bronze below the waterline and bronze or SS above.

    During the intire process of making each of the gussets and patchs I was lucky to have only wasted one small board due to a mistake. After making the first gusset, I got the brilliant idea that the peice on the opposite side would be identical ( a mirror image) to the first. Oooooooooops ! It doesn't work this way.



    You will develope the skills as you go if your serious about what your doing.
    However, many people might see using cheaper materials as "a way out" of trying as hard as they could. In the end it could be a total waste of time.

    Par has given a good explanation of the differences... and he knows what he's talking about too.

    Also, if you use the proper plywood to start, there shouldn't be any reason to have to glass over it (if you build the row boat).

    Like I said.... In My Humble Opinion
     
    1 person likes this.
  14. timgoz
    Joined: Jul 2006
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    Location: SW PA USA

    timgoz Senior Member

    Another thought. The thinner you go the more important it is to use the best ply available.

    If doing a kayak or other very light skinned craft, the voids "found" in inferiour ply are potentially much more problematic.

    Is the boat to be used an very small lakes and ponds or to be put to more dramatic tasks. If the later, where you are to far offshore to "swim for it", top quality translates to a proper outlook on safety.

    Tim
     

  15. charmc
    Joined: Jan 2007
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    Location: FL, USA

    charmc Senior Member

    Marine plywood not that costly

    Yes, marine ply is more costly than construction grade, but the prices mentioned above seem too high. Here is a place in FL that sells full and half sheets, as well as smaller pieces. Prices are 50 -60% of those mentioned earlier.

    http://www.buckwoodcraft.com/marine_plywood.htm#Okoume Marine Plywood - Quick Reference Price Sheet

    Another thought: For a kayak that will be glassed over, I can't see anything thicker than 1/8". Easier to bend into shape, and, with proper technique and internal supports, more than strong enough. The lightness will translate into better performance, and will be appreciated when you're taking it out of the water, as you mentioned.

    A bit of philosophy here: If you set out to build something as cheaply as possible, on the assumption that you're not skilled, you're probably going to make something that looks like an amateur built. If you set a higher goal of building something that will be as fine as possible for your budget, you'll look for ways to get the best for less, you'll take the time to learn the best techniques, practice on scrap so you'll do the real thing well, and you'll make something to be proud of.

    Here and in many other sites there is a wealth of information about building small boats from plywood, as well as good people ready to give support and specific help. This site describes building a plywood kayak; the planking is 1/8" to 1/4" max, with supports cut from heavier stock.

    http://www.glen-l.com/designs/canu-row/kayak.html#avail

    Good luck
     
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