Advice needed on trimaran

Discussion in 'Boat Design' started by laukejas, Aug 29, 2012.

  1. Petros
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    Petros Senior Member

    Nice plan, looks like a heavy hauler, lots of reserve carrying capacity. If that is what you want, it is not a bad design. I would advise against having "hollows" in the hull. Otherwise that hull could be done skin-on-frame except it would have "hard chine" hull. Many stringers close together would make approximate round shape best, but it means more parts, I would keep the hull forms simple. For amas: two gunwales, two chine stringers and keel stringer, 5 total (they can all be the same size to keep it simple), for the main hull you can get by with 7 total, gunwale and keel can be a bit heavier size, and two chine or bilge stringers, no hollows. Also, I would raise the beams to rest on top of the center hull gunwales (laminate them so they curve down to the amas) to make assembly easier and you will not risk leaks where it passes through the hull wall.

    Hollows can be done with skin-on-frame (you have to stitch the skin to a stringer), but for a folder just avoid it or assembly will be even more complicated.

    If you have no choice but for folder than this is what I would advise: keep the part count as low as possible (saves time, cost and weight, as well as assembly time), keep assembly details as simple as possible (use bungee cords, lashings, draw strings, etc), avoid having to remove screws, nuts, bolts etc as part of your break down process (okay if fixed assembly but too easy to loose when assembly/disassemble, and takes too much time).

    For example, if you can get by with only one break or connector on the stringers that are 10 ft long each for a 20 ft hull, that is far better (faster assembly) than to have them break down into 5 ft lengths even though it would make a more compact package after folded up.

    Always look for ways to simply each component, rudder can be laced on with cord through a row of holes as your rudder hinge rather than using hardware for example. Use lashings and knots rather than shackles and snap links, keep rig simple (few parts).

    the comment about your sailing rig, I have been in a lot of different sized boats with lots of different sail configurations. I like best a simple single junk rig, fastest to rig, easy to sail, and least likely to malfunction. If you like messing with lots of sails go ahead and make cutter rigged yawl or schooner rig, and spend all your time untangling the sheets and adjusting sails. For a folding boat, fewer parts are better; keep it simple stupid ("KISS"). and you will use it more, and have more fun with it.

    Good luck.
     
  2. Skyak
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    Skyak Senior Member

    Since yesterday the commentary has gotten much more realistic. Petros is showing designs that are actually in your price range, and you are looking at designs that are big enough to sail with the crew you described. I still question if it can all add up to your big performance/small budget target, but you have real pieces now to add up.

    Petros, I rarely see skin on frame hulls with a transom, never on any traditional designs, but I see you have done it. How well did it work? I was thinking that it would require extra structure to prevent racking deflection. Based on the build times and costs I presume that all your boats have plywood ribs/bulkheads?

    I think it is time to talk sailing rig cost, size, and performance. The design Laukejas showed would typically have a 200sqft or larger bermuda sloop rig with large roach main or flat top. This is way too expensive and would shred any inexpensive materials that I know of. Do you have any good low-cost ideas for sail material? Junk rig reduces stress a bit but gives up performance. Lug goes another step lower in cost/performance. I am thinking that a lanteen rig might be the highest performance he can get in his price range but when I consider them, none are worthy of that big trimaran design. If I had that boat and $200 or less to put a sail rig on it I would buy a big used polyester sail and cut mine out of it.

    Laukejas, now you have an idea what kind of boat it takes to sail your load you can get some idea of how much it will cost. You asked about a folding design taking less flawless wood, that is not what I said. It is easier to find smaller pieces of wood without flaws, the bigger the piece, the more likely there will be a flaw. To make long pieces without flaw you will need to scarf together the small pieces you have.

    About the requirements for the hull material, below the waterline, the stress on the material increases exponentially with the distance between stringers. More stringers, less distance, far less stress. This boat is much bigger than what I had in mind when I recommended 1000 denier material, 3000 or more should be your target.

    You now have a capable hull design, and I see you now talk of flying two hulls. This is multihull heaven. Let me introduce you to multihull hell so that you do not end up there. In designing a multihull you must consider pitch-poling. You are in heaven, four crew on the windward side, sailing at speed, flying two hulls, when the lee aka buries (hits a wave, wind shift...). At this point you have the weight of the crew and boat, the force of the sail rig, plus the force of deceleration, all on the forward half of the lee aka. If it is not stiff enough it will reach this condition immediately. If your boat is not strong enough for this condition it will break. If it does not break there is still the chance it will end upside down -a plan for self rescue is needed. If you think you can get to heaven without ending in hell, go to youtube and look up Russel Coutes pitch-poles, falls through wingsail. Russel is the most accomplished sailor there is...

    When you consider how much strength/stiffness it takes to stay out of hell you may want to change you aspirations. You also need to consider the cost of the sail rig it takes to drive the boat you are planning. Petro suggested light simple rigs. Tiny Turnip has a professionaly produced wooden 2man tri with such a rig and is offering to tell you about it -you should listen. I have some ideas how to make a folding tri strong enough, but you need to consider how much it takes first.

    Petros advice about using lashings and traditional methods is the best way to attach wood. Warram has been doing this for years and is the most experienced practitioner.

    http://wharram.com/site/
     
  3. Stephen Ditmore
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    Stephen Ditmore Senior Member

    I'm working on a 15'-6" kit canoe which will become a kit trimaran. Would that interest you? I'll say more about where I'm at with it if you private message me.

    I agree with Skyak that Yost is a top notch kayak designer. I like the other stuff I see in this thread, too.
     
  4. laukejas
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    laukejas Senior Member

    Once again, sorry for the time it took me to reply, I was out of contact.

    You all said a lot of very helpful things and provided useful information, it's a lot for me to consider.

    Since before I might have overestimated what I can do with my budget, my current idea is to build 17-21 foot folding trimaran for 2-3 people, cat or sloop rig (haven't decided yet, will have to look at final budget), wooden carcass with PVC fabric. 400$ for hulls, crossbeams, rudder, and cargo net. Sail, mast, rigging has separate budget. That is possible, right?

    Petros, I guessed that hollows will require attaching, so I think I'll make hard chine hull, just like you suggest. I'll try to make everything as simple as possible, it's just a lot to plan and consider. But planning doesn't cost.

    Skyak, talking of sails, I guess I'll go with Tyvek - next best thing to Dacron in terms of quality/price ratio, as far as I heard. Or maybe, if I save up some money, I might go with professional Dacron sails (I know a sailmaker who can make me a mainsail for about 100$ (depends on size of course). Still a bit much, but they will last many years, while Tyvek might need replacement after few seasons).
    For mast, I think I'll go with folding metal tubes (the end of one tube is a bit larger, so that a bit of another tube can fit in). My friend made a mast like that (about 12ft tall, breaks down into pieces of about 4 feet). The only way I know for foldable mast. I don't know any wooden mast design that is possible to break - down. Except for gunter rig... But it's complex.

    Talking of flying hulls, you mean that spectacular capsize of Russel Coutes in ACWS, Plymouth? If so, I saw it, not more than a month ago, as well as some other capsizes and dives through wingsail. I'm aware of dangers of burying nose into wave.
    But then again, these are like Formula-1 of sailing, they're light, fragile, meant more for speed than safety, and they are designed to ride on boundaries of their limits. And skippers do that, they risk, they push. I, on the other hand, am not making a racing ship, just something between racing and cruising, so I'll leave much bigger safety margin. And trimarans are quite harder to capsize or pitch-pole than catamarans, right?

    And this summer, with the ship I made (the one of which I posted photos in Facebook) I had flew a hull quite a few times. Speed wasn't great, comparing to any... well, "normal" sailboat, but nothing broke, and that ship, as you can see from photos, wasn't made well.
    But I understand that there is a need for more reinforcements, stiffness and so on. Thank you for the warning.

    I have just a few more questions, and I'll go plotting, since I guess my noobish questions might have already gotten a bit irritating.

    1. These wooden stringers, how strong are they? If, for example, we have 1/2 inch thick, 2 inches wide and 5 foot long stringer, how hard would it be to break with bare hands? I'm asking because I need to consider how thick I should make them. Is there any way of estimating what kind of force will these stringers have to endure, and how exactly thickness is proportional to stiffness?
    2. What about wood drying and shrinking? How to deal with that? I went into detail about this few posts before.
    3. If not with screws, how can I join 2 stringers end-to-end? If lashing, I would have to overlap stringers, but that would ruin hull shape at that place. So how would I do that?
    4. If I need to laminate few wooden strips for crossbeams/something else, what goes best for glue? Most boatbuilding guides I red suggest epoxy, but is there a cheaper alternative?
    5. How to join PVC fabric together? What kind of glue/stitching/heating or something that produces waterproof and durable joint?
    6. How exactly foldable skin-on-frame is assembled/disassembled? Old Russian canoe my parents had worked this way: (attached photo, too difficult for me to explain with just words):
    [​IMG]

    Would this work?

    Tiny Turnip, if you could share some experience from your trimaran with regard to what I plan to do, I would appreciate it! I just don't really know what to ask now except for what I already asked in 6 above questions.
     

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  5. Stephen Ditmore
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    Stephen Ditmore Senior Member

    On the subject of sails, have a quick look at
    http://www.baloghsaildesigns.com/
    This is a sailmaker in my area who specializes in sails and rigs for kayaks. They also make the inflatable floats.

    For more information on the folding kayaks you see on the website above, see
    http://www.longhaulfoldingkayaks.com/

    If you're looking for sailmaking expertise in your area at a lower price than the big commercial sailmakers, try talking to people involved in remote control sailboat racing.

    Note also that for unwrapping boat shapes to flat patters in fabric, plywood, or any sheet material, TouchCAD, a Swedish computer program, can be very helpful.
     
  6. Skyak
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    Skyak Senior Member

    In general I think you need to look at the cost of what you plan to build and what performance you expect from it.
     
  7. rwatson
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    rwatson Senior Member

    Yes - this is how the traditional FOLBOAT Kayaks went together, as one of my friends had many years ago. http://www.folbot.com/kayaks/

    Skyaks comments on the practicality are very spot on.

    Rather than have two halves exactly divided, the originals only had one-third of the boa and 1 third of the stern as a solid section to insert, and an expanding ladder centre bit inserted in the middle that provide the tension

     
  8. laukejas
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    laukejas Senior Member

    Yeah, I shall do that. A lot of things to consider, so it'll take time.

    This is the price of a finished sail. At least my information says so. It may be something around 6-8 square meters.

    I just said that for example, of course I'll make much taller mast :)

    Well, I'm not focusing on it, I'm just trying to learn from it - because it is proven it works. Of course, on that scale, on that budget, but it is very efficient design, so I believe I can grab a few general ideas.

    That is a very good link, but where can I find correct data to input for wood? For example, Modulus of Elasticity, Moment of Inertia, Deflection, and so on?

    Well, I suspect that much, but how exactly do you deal with it? Do you dry the wood before cutting pieces, or cut bigger pieces from dry wood to compensate for shrinking, or something else? If former, how to calculate how to compensate for shrinking?

    Yeah, I see that's way better.
    I watched that video, rwatson, thank you! I'll definitely go for this construction.
     
  9. Stephen Ditmore
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    Stephen Ditmore Senior Member

    In addition to the information on folding kayaks at:
    http://www.longhaulfoldingkayaks.com/
    See:
    http://www.yostwerks.com/
    http://robroy.dyndns.info/pakyak/
    http://robroy.dyndns.info/baidarka/
    http://robroy.dyndns.info/baidarka/slideshow/node-i22.html

    I'm collaborating with someone who is roto-molding floats in individually watertight sections. Each section is about 1.5 meters long, the center section being a near cylindrical parallel midbody, for a total bow/midbody/stern length of about 4.5 meters and a total submerged displacement in the 120-140 kg range. I'll have more information in a few weeks. We'll be able to offer these at a very attractive price along with cross-tubes and connecting hardware. They're already being manufactured; we can begin taking orders very shortly.

    Please private message me if interested.
     
  10. Skyak
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    Skyak Senior Member

    See the eBook about wood properties at;

    http://www.gutenberg.org/files/12299/12299-h/12299-h.htm#I_05

    I am not an expert on woodworking, I am an engineer so this book caries more authority than I do.

    The one point I would add is that cross grain shear strength is my favorite indicator -it generally indicates the wood will not be sensitive to flaws and easy to work.

    As I said, in the US we only do final cuts in dry wood. You can rough cut to a larger size, dry, then final cut. The one exception is steam bending which works best on wet green wood. Finishes on the final frame minimize expansion/contraction -take special care to seal the end grain.

    $100 for an 8 sqM sail is a great deal. This is the best resource you have mentioned. And in addition to making sails, this friend has the heavy duty sewing capability you want for your hull. I wish I could get new sails at that price.
     
  11. Stephen Ditmore
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    Stephen Ditmore Senior Member

    Some species not mentioned in the reference above:

    Black Locust (Robinia pseudoacacia) is an excellent North American boatbuilding wood with interlocked grain that makes it resistant to splitting.
    Different from Honey Locust (Gleditsia triacanthos).
    Some oaks are good, but don't glue as well as other woods.
    Southern Live Oak (Quercus virginiana) is not specifically mentioned, but perhaps should be. Joshua Humphreys went out of his way to use it in the construction of the American heavy frigates he designed.
    Tulip Poplar is not generally considered a durable Boat Building material, yet some knowledgable boatbuilders have advocated it. It has good cross-grain strength and can be compared to Okoume.
    I'm surprised there's not more discussion of Cedar, a wonderful and popular group of woods for boatbuilding. Spanish Cedar is not to be overlooked. Redwood is a sometimes less expensive relative of cedar. I suspect Siberian Cedar is a good boat building wood, but I don't know much about it.

    For strength numbers on some African woods, see http://www.shelman.gr/en/proionta_pages/plywood/shelmarine.htm
    The species mentioned at this website are sometimes referred to as "African Mahoganies". Sipo is also known as Utile. The strength numbers for this wood speak for themselves. Iroko and Afromosia are sometimes referred to as "African Teak". They are excellent boatbuilding woods, but sometimes contain hard deposites that are tough on saws. If building in North America I would favor Black Locust, but the African Teaks may be easier to obtain in Europe.
    True teak is great stuff, but the oils that make it rot resistant make it glue poorly, it's heavy and becomes gray in sunlight.

    Lauan, Meranti, Philippine Mahogany - quality tends toward inconsistent because these terms lump together a number of different SE Asian species.
     
  12. laukejas
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    laukejas Senior Member

    Well, thank you all for your answers. That pretty much covers all I need to know. I'll now get into planing and budget considerations.

    By the way, maybe someone made folding kayak/canoe with plywood crossbeams and aluminum stringers? If so, how that combination worked out? (in terms of cost, strength, building time and maintenance)
     
  13. Wavewacker
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    Wavewacker Senior Member

    Interesting thread building from scratch materials, I have a swimming pool cover that's pretty tuff stuff, you can walk on it when it's deployed over the pool. About 18' by 32' , bad part is that there is a small reinforced drain in the center. It's a PVC coated material, not sure what the fiber is or it's "thread count" but it's also reinforced for the attachments every five feet across.

    You might check a pool supply company and see if you can get a pool cover that has been replaced, mine is in excellant condition but pool covers are replaced if damaged along the eyes, the material should be fine. New ones are very expensived (this one was $900.00) so look for a used one. Might find material in the dumpster at a pool company. Same with awnings at awning fabricators.

    Depending on your design, you may have few seams and rather short runs on any seams. PVC materials can usually be welded, a plastic welding process used by material fabricators. If you are near anyone with a plastic welder process I'd suggest trying to see if they would do the seams for you, if you scronge the material the welding process could be well within your budget, probably a few dollars a running foot.
     
  14. Skyak
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    Skyak Senior Member

    Do share your plan when you have it.

    I have seen tube stringers (aluminum and steel) on plywood frames, but not on folding designs. The reason is that plastic (HDPE) allows for a snap fit with no added parts. I looked at adding a snap feature on plywood frames, but decided to go with HDPE partial frames in a 'C' shape. The cost of HDPE is not bad if you don't have much waste. With 'C' shapes I can cut smaller frames from the wasted middle of larger frames, so I can cut 3 frames from each of the large frames. The frame tops can be tubing or plywood.
     

  15. laukejas
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    laukejas Senior Member

    Thanks for the information, Wavewacker, I'll check that out.

    Skyak, we discussed that HDPE earlier, and I don't remember, but I think I thought that it costs too much, so I decided to go with plywood frames and wood stringers. However, I found a company in Lithuania which sells round aluminum tubes very cheap: for example, 8x6x1x5000mm round metal tubes are sold for 0.47 dollars per meter, buying more than 30 meters there is 15% discount. Or, 16x13x1,5x5000 costs 2.53 dollars per meter. Since I don't think anything more than 10mm is needed except for main hull bottom, I can get away very cheap. That 8mm tube weights 60 grams per meter, 16mm - 180g. Of course, there are many intermediate options, this is just for comparison. Also there are different shapes.
    I don't think that I can make wood stringers for such price and strength/weight ratio. Wood requires drying, cutting, painting, and re-painting after some time. Aluminum is cut-fit-go, no maintenance, just replace after some years, but that should be easy and not expensive. Am I right?
    HDPE, on the other hand... Well, I can't find prices in Lithuania, so I can't calculate if it will fit into my budget. But I know prices of marine plywood, so here I'm considering this plywood + aluminum combination.

    Am I right about the advantages of aluminum over wooden stringers?
     
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