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Thread: Plywood Catamarans

  1. #21
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    Default Re: Plywood Catamarans

    Here is a Tiki 30 in ply. Potting of fasteners is critical for avoiding rot.
    If we stretch this boat 3' and double the sail area and reduce the beam by 2' it will probably fall over just as well as the Reynolds 33.

  2. #22
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    Default Re: Plywood Catamarans

    This thread started with a query about experience with plywood cats.

    The 36'plywood catamaran Sleipnir II just crossed her outgoing track in the Ionian, completing a circumnavigation, with a few days sail left to reach her home port.
    Evi & Wolfgang had previously cruised from the Adriatic to the Caribbean and back and circumnavigated via the Panama and Suez canals, marrying en route on the beach of a tropical Pacific island.
    Their story can be found at http://www.sleipnir2.at/ .
    The site is in German but there are lots of pics, and on-line translation works fairly well if you're a monoglot like me.
    The boat seems to have stood up well to the voyage, although meeting a floating tree trunk near the Marquesas resulted in a haul out in Papeete to repair a split bridgedeck joint, possibly demonstrating how easily plywood construction is repaired!

  3. #23
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    Default Re: Plywood Catamarans

    Bobcats were one of the earliest cats built to an O'Brian design (and were the forerunners of the Catalacs). These boats were plywood, and sailed very well for their day. Whilst not to many around now, I would guess at the newest being about late 60's build.

    5-7 years ago I was reading the exploits of an owner who sailed his on his own from UK to Australia via Panama. Havent heard anymore for a long time now, but believe he is still somewhere in Australia.


    Good plywood, well looked after does have an astonishing long life.
    Insanity is continuing to do the same thing and expecting different results

  4. #24

    Default Re: Plywood Catamarans

    Hello,

    I have a plywood cat that is coming to the end of its restoration. It is from the 1960s and has obviously had some work over the years. I think when you are talking about plywood boats and epoxy-plywood boats they are two different things. I had a Debutante monohull which was painted. The paint was always falling off. I am not sure it was because it was a monohull!

    On the other hand the one I have now is epoxy glassed and that appears to be very durable, probably more so and lower maintenance than polyester grp. My cat being an old design is not as light as a modern cat but a couple of tons lighter than the grp version of the design made later.

    I think one of the most striking elements in terms of longevity of wood and presumably good quality plywood is the number of stress cycles it can take and still have a big percentage of its initial strength. The GeugeonBrothers did a lot of testing on wood in their manufacture of wind turbine blades. Having read their books it has made me look at wood in a different way and given me second thoughts about how strong an older grp or aluminium boat really is. Wood is a lot more honest. If the moisture levels are controlled before sealing it in epoxy, it takes a long time for moisture to go through the epoxy. Without moisture and oxygen wood does not rot. I recommend reading the Geugeon Brothers book before you either go for or dismiss plywood.

    Once you get into scarfing, repairs are not as arduous as I had thought and certainly less hassle than grinding off the gelcoat blisters that seem to be the number one activity in the boatyard around me. Wood is an easy material to work with and very satisfying particularly compared to using polyester resins.

    C class cats were to my knowledge built out of wood in preference to glass and designs like the Unicorn were very light. There are a whole bunch of performance cats made in ply. It is only since aramids that wood has slipped into a lower performance category.

    I am designing a new boat now and looking at my options I am likely to build it out of carbon and nomex core because I have bought a load of it cheap. If I was not in this position wood and plywood would still represent a very light/cost option.

    In any case the material you chose is just one of the many variables you will have to battle with but you could do worse than epoxy ply in my humble opinion.

  5. #25
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    Default Re: Plywood Catamarans

    I am going to be slightly contraversial here.

    My Plywood tri is 45 years old, yes --I have now had to replace 70%of the plywood panels. most of that was due to some idiot using mild steel screws through the toe rails and punctured the outer polyester skin of glass and then left the boat for approx 10 years with NO maintanence..at least 4 years on its last mooring full of fresh water some one pumped her out 2 twice during that time.
    There is no epoxy in site. nothing but paint on the inside. so i know that ply and epoxy is the ultimate. I have to say though---- 30 years then 10 years of abuse is not bad.
    I sail on an old plywood monoslug a Yachting World Diamond class. built in 1960. (confirmed) and is in SUPERB condition. and all original. 50 years old and still taking many trophys being picked up and at High level.
    Oh yes, its only painted. no epoxy.
    so all the doom and gloom about plywood is not really that convincing.

    I have found many convincing arguments that its actually better to just paint ply and to make sure its well maintained. if the epoxy coating is breached, there is no where for the water to get out so rots the ply.
    paint will lift and peel off. dry during the winter, re-paint, off you go.
    as to the extra strength, it needs to be(according to data I have read somewhere) that there is no significant strength gain untill the glass sheathing is above 450gsm. if you then add the same weight for resin, (less if vacuum bagged) then thats just under 1kg per m2 for no real gain (10%) in strength. thats a lot of weight to keep a bit of ply dry.

    I say all this but if I was building from new then I probably would eppoxy, but as I have an old boat there is no way I can so I am not sure if I trying to convince myself or others.

    Right I'll now put on my raincoat, put up the umbrella and not stand directly under the fan

    DUCK


    Kim
    just a scared rabbit in the headlights of life

  6. #26
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    Default Re: Plywood Catamarans

    Who ever tells you that marine grade ply rots must have had experience only with outdoor grade or household grade, NOT marine grade. Also there are various grades of genuine marine grade, if that makes sense. They range from very expensive to exceedingly expensive.

    My boat has a doghouse roof of ply. It was put on in 1972. The ply was sheathed with fibreglass of some unknown type or quality. Fittings were added and removed but not sealed. There was water under the sheathing, the ply was soaked and had been for years when I took it off two years ago. The ply looked bad. Two weeks in the sun wind and rain and it looked perfect. It was tough and sound all over! Holes were plugged. It was resheathed and is now as good as new.

    I was amazed by it. A professional boatbuilder just laughed at me and said 'of course'!

    I have seen on various threads people saying that outside grade will do. I suspect that comments expressed here indicate that it won't do.

    All IMHO of course!

    Mike
    Nothing works on an old boat, except the skipper.

  7. #27

    Default Re: Plywood Catamarans

    The grades and types of ply are probably worthy of their own thread.

    I am not sure that marine ply is in any way rot proof, although the woods selected tend to be more durable in the marine environment. The ‘quality’ of the ply is the number and quality of the structural laminates. In terms of quality I mean the way the individual laminates are cut or peeled, the type of wood, and the integrity of the individual laminates. This translates into varying cost of manufacture and retail.


    Few plywoods now use water soluble resins. Marine ply is essentially some form of hardwood (usually mahogany style wood) that passes various ultrasonic tests to verify the structural nature of the whole panel. Therefore some are passed as marine ply with the relevant iso code and some are passed as exterior. Exterior grade pieces that fail the quality control tests may look the same but can have voids which means their structural properties are not all that clever even if the wood type is durable in the marine environment. If you were lucky and only used the good bits of the board that passed the ultrasonic test, you would stand to make a saving! General exterior grades that you buy in DIY super stores tend to use less plies and have pretty poor internal laminates with large pockets of filler, which has little structural strength or just voids, which obviously has no strength and compromises the whole laminate. If epoxy saturated they can be durable even if the wood isn’t (abrasion aside) but the structural nature can only be guessed at in terms of voids and filler.

    If strength and stiffness was your only concern, rather than durability, birch plies offer the best performance and can be made more weather resistant using epoxy saturation of some form, an option that would probably not be warranted by paint manufacturers.

    All woods will degrade with high moisture content and access to oxygen eventually. Below a certain moisture content wood cannot rot in a traditional sense. Also if the majority of the wood has intact epoxy but an area is chipped, Oxygen is still restricted, so fungal/microbial development is slowed even if a bit of wood gets saturated with water, although this is still not ideal in terms of strength and medium/long term problems.

    Obviously some woods like purple heart used for sea defences have natural oils and chemicals that slow microbial and fungal decay but with oxygen and moisture they all rot eventually even if this takes a very long time. The reason that some of these very durable woods are unsuitable for ply manufacture is because they don’t glue well, have calcium inclusions that make peeling or sawing laminates uneconomic on the machinery, irregular grain or high internal stresses that result in plies that are all over the place and can’t be arranged into a panel that remains flat. Some woods are unsuitable because they are relatively brittle in terms of shock loading.

    Not only is wood more likely to be broken down by fungus but wetter wood has a significantly lower stiffness and structural characteristic compared with very dry wood and obviously weighs more. Sometimes the weight of epoxy might offset the higher moisture content on its own (depending on the thickness of the ply).

    An epoxy skin of glass on 12mm or 8mm ply probably does not beef it up much but on thinner ply like 9mm, 6mm and 4mm, I have found long strips break under their own weight without glass and are both stiffer and stronger to handle with a single additional layer of epoxy glass. My friend’s dad has just made a 24’ tri of his own design and the external layer of glass made a huge difference in stiffness and presumably short term strength. The inner skin (it is an open day boat and has glass epoxy inside too) didn’t seem to make much difference in terms of panel stiffness. When I say short term structural improvements, glass fibres lose their strength a lot more quickly than wood with stress cycles.

    If you take your boat out of the water a lot and cover it, paint does have advantages. Painting epoxy on the inside will not add strength only moisture resistance (3 coats are suggested) and that does tot up to a lot of weight over a whole boat.

    On balance I would probably go epoxy, just because it works well.

    One of the things that has not been explored about ply in this thread it that it enables relatively easy modification of a boat compared to some other construction techniques. On the cat I own, one of the options I have if it sails like a pig is to stretch it in length, bridge deck air gap and beam. This would be pretty much out of the question starting with a different construction. Although this is an extreme example it does illustrate what a user friendly material it is, particularly if translated into ad hoc repairs in out of the way places. Try that on a carbon-nomex sandwich.

  8. #28
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    Default Re: Plywood Catamarans

    I hope this will help you and secure you more in your project.
    i ordered and seen it 3 times ... Kurt Hughes dvd on ply "okoume" and epoxy multihulls construction. My project is bigger (60 ft cat) , but very different from what we see. I find that CM method is inspiring. Also, I don't have a huge budget for construction and maintenance / marinas will have to be meticulusly dealt with. The little risk for ordering the dvd, probably you can download it ? i find can save you alot of $ later. I have seen a KH design in the "iles aux noix" area in quebec canada (the cat is on the richelieu very near lake champlain in vermont usa). The owner was very honest (he works at a marine store) and he likes it . He mentionned a designer he would use for his next endeavor which would be more "racing" capable. I am considering okoume BS1088 from china, my friend imports alot from china and he helps me. Check it out on alibaba for an idea on pricing ! My neigbor's daughter works at Gurit (corecell) so i have all the catalogues etc, i may feel a bit motivated to buy some of it for replacing the "balsa" core on top of the amas. I am worried at the material differential behavior, was catastrophic in past experiences combining fiberglass and wood. Epoxy brings hope to better cope with that. I have used epoxy for projects, it worked well but the temperature factor is to be taken seriously, i found the west-system literature helpfull.
    For what i read, don't you ever cover stainless with epoxy ! Check out with insurers if they will insure if you do that. I searched and found fiberglass nuts and bolts i am checking the loads specs. There are also fiberglass rods for concrete , pricy but could be of use.
    Best of luck in your project.
    PS i am in the trampoline material search, so far pvc coated polyester webbing seems to be the way to go, but i am not done yet.

  9. #29
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    Default Re: Plywood Catamarans

    Quote Originally Posted by mikecat View Post
    PS i am in the trampoline material search, so far pvc coated polyester webbing seems to be the way to go, but i am not done yet.
    My tramp is made from double corded, double knotted fishing net. Not comfortable to lie on, but allows the waves through without a problem and will provide plenty of warning when it needs replacement due to its construction. I understand it was pretty cheap as well.
    Insanity is continuing to do the same thing and expecting different results

  10. #30
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    Talking Re: Plywood Catamarans

    Yes, tramps can be quite catchy ... in the wind and waves ! My first choice was fish nets like on the ORMA tris, but i have to deal with my other cat (catwoman) and she just wont compromise on 2 things: 1: not sleeping in a basement like cocoon, 2: walking on almost transparent uncomfortable fish nets where she can see the sharks. She tolerated bungy netting on a 85ft cat. On the other hand, the project i have makes room for fishnets in the traveling fast mode from A to B.
    The key to my construction will be the lightest possible on a budget cat.
    I find that okoume is the answer with epoxy. I looked at trash ... but ctw doesn't like the smell and she is running out of fabreeze ! Another glue might just show up on the market, pretty much making epoxy obsolete but I am not in the R&D mood for my cat yet. And i am comfy working with epoxy. Especially the less VOC coming up. But i will try it on a nonessential item, i got a 2 liters of it.
    Out of this topic ? If you can hold your breath a little for getting a watermaker, something is soon coming up on the market, i designed the bldg last week and the delivery of the shop is in the fall. In fact, in my cat design, the watermaking matter is a very part of the architecture of the cat.
    On the topic of plywoods in boat construction, especially in multis, lightness and $$$$ is my primary constraints. The loads assesments, displacements and multiple uses and "green" design are the key to success in my opinion. Wood is a step forward but with all that formaldehyde ... ??? good thing epoxy seals it.
    For example, every deck furniture (sofas, beds, etc) , shelf or cabinet door is a spare daggerboard or a rudder or part of them, extra plys are the structure of the beds. The anchors are the structure of the captain's seats, the anchor chains help reinforce the cross beams, the batteries weight pump water and distribute the loads according to the wind, and more ! Tramps can make a good strong wrapping material on a trailer flat bed truck. Alot of that happens in the amas, no weight on the tramp. , yes the roof is colapsable and the cat can shrink from 40ft wide x 60 ft long to 16 ft wide and 32 ft long.
    All that keeping it simple my KISS concept...my friends scratch their heads, me too at times.
    Back to the dwg board (CPU ... mouse) i wonder when they are going to remove the word drawingboard from the dictionnary ... not yet ! i am still using them for charts and maps and modeling ... they are made of plywood !

  11. #31
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    Default Re: Plywood Catamarans

    Plywood and /or epoxy/cedarstrip cats are very noisy-PS Catamarans do not have "amas"

  12. #32
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    Default Re: Plywood Catamarans

    Quote Originally Posted by georgetheleo View Post
    Plywood and /or epoxy/cedarstrip cats are very noisy"
    Huh??????/ why -------My tri is far quiter than a friends tri of similar length as the fiberglass hulls are more U-shaped so when the waves hit it. it thumps hard. my tri being ply so there is more of V shape that parts the water a lot quiter.

    I would like to see the reasons for your statement.

    a ceder strip is stiffer and thicker than a fiberglass so less vibration transmitted through the hull

    the wood absorbs the sound so less noise transmitted.

    the only reasons I can think of is the panels can be flat areas but then a ceder strip is all curves

    the only real down side of wood is the fact you cant make the ideal shape. so they tend to have a high water resistance and the maintanence side of things. they cant be left in exotic places round the world for months whilst the owners take a break from their busy cruising schedule

    Kim
    just a scared rabbit in the headlights of life

  13. #33
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    Default Re: Plywood Catamarans

    You are correct i have been using amas for the nonhabitable hulls. The cat i plan to build is somewhat a Proa and a cat. the ama being the outrigger , the vaka the main hull, and the akas the wings or beams.
    The common noises we had when we built wooden boats were romantic and ***y squeeks, reminding of the old gallions. On the last cruises we took, one was an aluminum hull (mono) and a motoryacht in strip planking combo with fiberglass. Guests could'nt hear the difference, they were above ,08 alcohol in their blood, i dont drink so i could here that the aluminum was more of a bong noise but neither were unpleasant.
    The bang under a low cat is quite anoying i plan to have at least 4 ft clearance at full payload and 6 inches more at quick cruise mode. With a net 34 ft span, that should be enough.
    I am considering stern and bow wave piercing and an almost flat little rocker hulls . I'll develop more on this later if you are interested why. Its windy got to go.
    cheers.

  14. #34
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    Default Re: Plywood Catamarans

    So Mikecat, you are aiming to make a 64ft proa/cat!

    That will surely be an amazing undertaking! Yes all possible information please. It sounds fascinating

    Mike (little old cat!)(the boat, not me!)
    Nothing works on an old boat, except the skipper.

  15. #35
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    Default Re: Plywood Catamarans

    where are you located, perhaps we can look at buying a whole container of okoume bs1088, first calculations about 2400 sheets of ply 1/8 x 4 x 8 , check the prices from china on alibaba ... my friend imports hockey equipments from china and saves a bundle he gave me his brokers name.
    i am in eastern canada, in sherbrooke quebec near lake memphremagog (that lake croses over to Vermont USA). I have a friend that wants in too, but he will use the thicker plys for constructions , balconies, overhangs , etc.
    I dont know about importing epoxie and pvcs, my neigbor daughter works for Gurit (corecell) and they also sell epoxies. I might just replace balsa with corecell .

  16. #36
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    Default Re: Plywood Catamarans

    60 ft long , 40 ft wide ich. foldable to 32 ft long 16 ft wide and containerable.
    i'll describe later the program. Just came back from the water, spinakers are always nice to look at ! Easy sailing with 10 k south steady wind.
    later

  17. #37
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    Default Re: Plywood Catamarans

    are U familiar with Cylinder Mold and vacuum bagging ? My friends and i watched many times the dvd sold by Kurt Hughes. His thoughts reached my thoughts as the basis of the development of the concept. He has a nice web site to read, quite detailed.
    I started my design in year 1997 and the construction method evolved (confirmed by KH doing pretty much it also) in 2001. For health and $ set backs we had to postpone the construction untill soon. Now we are motivated. The aim time schedule for the construction is 3 months ! 4 people some part time and 2 full time. The idea is to use prefinished and easy to get materials.
    Many years ago, i helped build steel and cement monos. Up to 55 ft . I was a kid to become an architect so i remember why and whats. Heavy stuf then but perhaps today they could be much much lighter, could make some sence if you like monos.
    I did enough monohull sailing to know it is fun , but not my fun.
    In order to set your mind to my concept i have a few pointers or clues. (pardon my english i just dont have time to look at my dictionnary) i will use some french words at times.
    Constraint 1 - almost anything that embarks on the multihull must have multifunctions.
    (daggerboards, rudders, batteries, food, anchors, chaines, motors, tanks, nettings, etc your mind can run wild)
    Constraint 2 - My good friend is in a wheel chair since his Gylain Barré desease and my wife likes to fall in stairs (her extreme sport of sort ...) so no stairs except ramps.
    Constraint 3 - Obviously from C.2 no sleeping in a basement like cocoon (the mono main discomfort for them)
    Constraint 4 - Ease of repairs and maintenance and no hard to deal with huge mast and rigs. Demasting using the abyss !
    Constraint 5 - could be c.1 , budget ALAP and construction AFAP and for me ASAP. In a garage 40ft long, 10 ft wide and 8 ft h (2 end doors 7'-0"h x 8 ft w) plus one or 2 garages for temporary storage.
    Constraint 6 - hovercraft dingy, need to allow for it, but will use existing dingy for now.
    This hovercraft dingy is quite advanced in the design but not enough to share besides the hovercraft enthuthiastics. We are in the detailing and part of that is the insertion into the cat design.
    Constraint 7 - not the least, the cat has to fit into 1 or 2 containers and can be trucked on a std flatbed or even on my large trailers.(the wakeboard boats trailers good for heavy stuff ...)
    Constraint 8 - raft and half floating beach under the tramp and insertion of Nacra beach cat into the hulls.
    Constraint 9 - Leave and forget twin masts and large kite(s) steering near the wheel man ...
    Constraint 10 - it folds to 16 ft w x 32ft L for marinas .
    That's it for now.
    My wife and her friends take care of the food and luggage matters, but i gave them space constraints otherwise you guessed it ... AND this is a 1 master stateroom that can be split into 2 well soundproof cubicles, no need to elaborate ... 1 main guest room for my friend in WCh. and 2 mini staterooms for crew and kiters. The other party dudes can sleep on the tramp...
    OK Skype is ringing.

  18. #38
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    Default Re: Plywood Catamarans

    Thanks!

    As I said, fascinating. After reading more than once, I am still struggling to work it all out.

    Good luck. Please keep posting. It probably needs a new thread as it will be big.

    Mike
    Nothing works on an old boat, except the skipper.

  19. #39
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    Default Re: Plywood Catamarans

    like the Tour de France, one "étape" step at a time. Got to put gas in the boat, honestly, if it wasn't for wakesurfing and deep water (no more scuba) swimming, i would sell this noisy and smelly gizmo. Makes my other half happy . I am more and more considering the raft or rigid bimini roof (upside down) with wakesurfing ability, seen an all electric wakeboat at the boatshow this past march, we are getting there ! another good application for okoume ply.

  20. #40

    Default Re: Plywood Catamarans

    Nothing wrong with ply if built properly and fastened/sheathed with epoxy. We have been very happy with ours over the years and previously I owned a share in a ply light aircraft. The catamaran designer Bill O'Brien started on ply flying boats I believe. One of the best twin night fighter bombers during WWII, the 'Mosquito' was ply built.

    Why not renovate/refit or just get an old 'Bobcat' and see what you think - they are not expensive and projects can be very cheap. Ours is 48 yrs young and I believe the first 'Bobcat' and 'Oceanic', a lot older than ours, are still alive and well.

    Bill's designs were great - nothing like it available now for home build unfortunately but many get a new lease of life with a new owner. Huge cockpit for the friends and admirers!

    http://www.facebook.com/media/set/?s...1&l=4bb1db54ee

    A few photos of our much loved 'Bobcat' - where she prefers to be … whilst looking for a new home, skipper and crew!

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