Plywood Catamaran – Frames

Discussion in 'Multihulls' started by APP, Jun 13, 2012.

  1. APP
    Joined: Nov 2010
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    APP Junior Member

    Plywood Catamaran – Frames

    I am considering a Cat 8-9 m long to be made by plywood. I am searching a site with a construction description of such a Cat. Namely I would like to know:
    - Type of Plywood used
    - Thickness for underwater and above water plywood parts.
    - Kind of wood for the frames (Hull and Bridgedeck). Plywood or timber and
    what kind of timber.
    -Dimensions of the Frames in plywood or timber (spacing, thickness, web).
    -The total weight of the particular Cat.
    Am I asking too much? Thanks for any reply.

    APP
     
  2. Mick@itc
    Joined: Jan 2011
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    Mick@itc Junior Member

    Hi
    Try Dudley dix's site, he has designs and materials lists.
    Regards
    Mick
     
  3. gonzo
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    gonzo Senior Member

    You are asking for construction plans. You usually get partial information only for free. The plans are a small fraction of the total cost and the worst part to save money on.
     
  4. ImaginaryNumber
    Joined: May 2009
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    ImaginaryNumber Imaginary Member

    Here's a link to study plans for Bernd Kohler's 11.5m Pelican

    Also, Richard Woods has examples of his blueprints here, which may give you some of the information you want.
     
  5. upchurchmr
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    upchurchmr Senior Member

    Gonzo hit it on the head. Buy a set of plans. Everything you asked for is the design of the boat. Pay money to get the knowledge of an expert, or even someone whos boat has held up. You can't really afford to go forward with less than complete information - it costs too much to fix something later. You save in the end.

    Richard Woods is a good place to start.
    Go to http://www.duckworksbbs.com/plans.htm for another selection of designers and boats.
     
  6. yellowcat
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    yellowcat Junior Member

    i have ordered Kurt Hughes (google his name) vhs and now on dvd. although i suggest you copy the dvd on your hard drive before it shows defects ... i have to get my vhs out of the garage ... (i dont know if he can send it via email) .
    this will give you a good idea of the cylinder mold technique. Very informative, it will give you a feel for what you can and cant do. There are other videos on youtube. Erik Lerouge designs are also being praised by a boat builder who built a large cat in epoxy/ply.
    You may be suprised at the prices for okoume in china 3mm x1200 mm x 2400 mm BS stamped, but you need to buy a container, unless you find a cobuyer who is interest also.
    I am in the budgeting process for a 60 ft long catamaran (ply/epoxy) i will need aproximately 1000 sheets of ply , i would need to explain what i want to do but 3 x 3 mm is pretty much what i plan to do for the vertical walls (with bulkheads and stringers) and reinforcements at the in-water sections.
    Cyl Mold is a very fast way of bldg a multihull. For Motivation on wood boats , check multihull mag article (april/may no 152) on James Wharram. I have nearby access to Gurit products (check their web site) i would like to at least buy stuff from them as good neighbor friend, their epoxies , galls, carbons, corecell, etc products are well knowned.
    I am considering Awlgrip and Alexseal paint systems but the trendy vinyl wraps are getting my attention for outofwater surfaces. Kind of fun and easy to apply (check on youtube).
     
  7. yellowcat
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    yellowcat Junior Member

    Gurit sells eglass, not galls ... !!! fingers tired.
     
  8. APP
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    APP Junior Member

    Thanks for the replies. Well, I do not think that the thickness of the plywood used is a professional secret. In several cases, I have seen the most used plywood is okoume', For cats 8-14 m, the bottom thickness is usually 18 mm, hull sides 12 mm, walls deckhouse 9-12 mm, bridgedeck floors 12-18 mm. Frames (Hulls+Bridgedeck) either hardwood timber oak, beech, etc. up to 40-50 mm thick or plywood 18 mm using shorter spacings and depending on the structural strength study. In several circumstances plywwod thicknes is added, e.g. to get a 12 mm sheet you may add 2x6 mm sheets.

    If you find different thickness dimensions or disagree with the above, please post them here. It is good to collect a variety of opinions.
    Thanks
    Regards
    APP
     
  9. yellowcat
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    yellowcat Junior Member

    Thanks for the inputs, depending on the scarph or not. If all edges are scarphed, it will behave like a one piece ply. Holes and openings will also dictate the reinforcements.
    Those thickenesses are also what i hear and heard sailing on ply cats.
    I would prefer 4 x 3 mm for a total 12 mm with stagered joints or even better some spiral depending on the shape of the hulls. Glass and carbon hybrid reinforcements can be a cost / strength ratio better deal. Elongation factors are to be considered in longer units. I find that if it is not for racing, but still give a good ride, light wood like okoume is interesting at 8 pounds per sheet ... i am inclined to build up a multiply beam rather than adding hard wood (another type of wood and wood behavior) , i have teak and ply on my sailboat but not for the same purpose. Okoume has a poor rot performance check on Noah's boat supplies , they have comparisons if i recall correctly. Noah's is in Canada but plys come from all over, you can consider Greece ply manufacturers heard good comments. Chinese plys are cheap but you may have to buy more for rejects and research for a better manufacturer.
    My design will be very different from the usual, i lean toward the lighter structures and use 32ft twin masts and kites which are in my opinion a good compromise power/weight/fun/cost/felxibility .
    Have you checked out Kurt Hughes web site ? It is a must in my opinion.
    I will build my cat in modules, it will fit in container(s) and can be stored in a 3mx12mx2,4 m garage, the demasting will not require a crane and furnitures will be built with okoume as spare parts for repairs. Most everything will have to have double use, the least amounts of sit and be heavy stuff onboard.
     
  10. Samnz
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    Samnz Senior Member

    18mm! you gotta be joking

    there are plenty of 8.5m cats over here built of 4mm tortured ply. still going strong after a decade or two of hard racing.

    its critical to keep the boat light or it will be a pig

    google Tim Clissold yacht design. he designed a nice 8m cat out of 4mm ply. very fast and about 800kg all up (called Hard Drive)
     
  11. PAR
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    PAR Yacht Designer/Builder

    APP, you've jumped to several assumptions and we all know what this usually turns out like. You can assume you observations are correct and have a pig or you can do the calculations and have a nice preforming craft that falls within the scope of your SOR.

    Judging by your questions, you haven't the foggiest idea about scantlings (hence the inquiries), nor the engineering and calculations necessary to extrapolate them, again within the realm of your SOR. Given this, you have three choices, guess and hope for the best (good luck with that) or buy a set of plans where the calculations have already been preformed or lastly, spend a few years studying structural engineering and hydrodynamics.

    If you elect to just "go for it" you'd be wise to fine tune you scantlings "observations" in regard to the craft you've looked at. Your remarks about "typical" multi hull scantlings aren't even close frankly, so it would be best to stay very closely to known build schedules. Buying plans would be the logical route.
     
  12. sabahcat
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    sabahcat Senior Member

    Thanks mate, I need to clean my screen as I sprayed it with my lunch from laughing so hard.
     
  13. guzzis3
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    guzzis3 Senior Member

    http://sailingcatamarans.com/satmatlist.htm

    Mr Woods Saturn materials list. Freely available online. There you go. Several others in the same size range on his site.

    Those are typical for that size boat. Mr Hughes probably goes thinner because he uses cylinder moulding or tortured ply, unsheathed boats might go up a size.

    If your trying to design your own boat please be careful. Sailing is dangerous and it'd be a pity to kill yourself or people you care for. Mr Woods, Mr Waller and others offer good plans at good prices and excellant backup service while you build.

    Have fun.
     
  14. APP
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    APP Junior Member

    Thanks. I am not trying to design or reinvent the wheel. I just want to know the specifications/dimensions etc. using plywood for small boats.
    Regards
    APP
     
    redreuben likes this.

  15. gonzo
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    gonzo Senior Member

    The problem you have is that you don't have enough knowledge of boat design to understand the answers we are giving you. The dimensions of the construction materials are called scantlings. They vary enormously depending on the structural design and the type of material. A pine frame needs to be larger than an oak one. However, it doesn't scale directly, but depends on the application. For example, holding power for fasteners may be important. If it is a local stiffener, like in a large deck panel, a soft wood may be more appropriate. Plywood planking will depend on the framing. A hull with light or no framing will need a thicker skin.
     
    Last edited: Jun 15, 2012
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