Skin-on-frame canoe/kayak plan help

Discussion in 'Boat Design' started by Ruming Jiang, Mar 8, 2021.

  1. Ruming Jiang
    Joined: Mar 2021
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    Ruming Jiang Junior Member

    Thanks.

    Tried our friend's once, not a second time. Wife and kids almost quit paddling with it.

    A hardshell would be an average 15-17ft fiberglass/Royalex/kevlar canoe.
     
  2. Squidly-Diddly
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    Squidly-Diddly Senior Member

    1)get FREE Student Edition of Autodesk Inventor (learning will take few hours but MANY videos and FREE online forums where experts try to show off and solve questions).
    2)design boat by copying hull sections of similar boat, then subtrack 1.5" for the PVC pipe stringers and draw frames with semi-circle "C" cutouts to hold pipes. Use 7/8" good (more layers better, better wood better) plywood for frames drill through plywood into pipes to make boat. Use plywood for bow and stern inserted into keel pipe. If you can't find good plywood or have more time than money, instead of screwing THROUGH plywood into pipes, span frames with little blocks of plywood and put two screws on each side of frame into pipe. This will prevent weakening of frame from screwing through plywood "sideways" which plywood doesn't like. Cut pipes at sharp angles at bow and stern stems and screw into plywood.
    3)Cut sheets of PVC and glue to pipes. The CAD should be able to map out the sheets pretty well if you start with a CAD chine design so the outside of the pipes are the chine lines, then use CAD feature to flat them out and take those dimensions.
     
  3. Ruming Jiang
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    Ruming Jiang Junior Member

    Thank you. I got a friend to help with AutoCAD drawings. Will keep Inventor as a plan B.
     
  4. upchurchmr
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    upchurchmr Senior Member

    PVC pipe is weak, not stiff, and heavy.

    I saw a how to video where the guy broke the kayak in half when he tried to enter it.
     
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  5. Squidly-Diddly
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    Squidly-Diddly Senior Member

    but its cheap and easy to work with. figure a min of five 1.5" pvc pipes is gonna be pretty hard to break in half, even schedule 40. I'd go schedule 200 for the keel just to help hold the frames in place firmly while the rest of boat comes together. I guess you could also attach 1/8" plywood to PVC pipes with lots of small screws and maybe Gorilla Glue to seal it.
     
  6. Squidly-Diddly
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    Squidly-Diddly Senior Member

    AutoCAD is drafting, which is what people tend to use once they are making changes on already sorted situation, like circuit boards or office floor plan. Inventor is 3-D "design". Not sure AutoCAD will be able to flatten out curved panels from a design to map out for cutting out of flat sheets. But should be able import from AutoCAD to Inventor since same company.
     
  7. mitchgrunes
    Joined: Jul 2020
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    mitchgrunes Junior Member

    BTW, somewhat stretchable skins are needed to conform to frames, unless you do a fancy sew job to make the skin fit without stretching. I guess you could wrap your material around the shape, fold it to make it fairly tight, use safety pins to hold the folds together, then sew it, and use seam-seal, aqua seal, or equivalent. But even a little flapping around of loose material would create a lot of drag, and leakage is always possible.

    I hope no one kicks me off the board for suggesting you buy one pre-made, but there are used "Folbots" and other pre-built folding boat kayaks available.
    From what I can tell, there are a few big problems with folding boats:

    1. They sometimes break or need repairs.
    2. A fair amount of strength is sometimes needed to assemble them. I gave up on a couple boats that I looked at like that cuz I wasn't strong enough.
    3. They cost more and weigh a little more than non-folding boats of similar type
    4. This may not be a big problem if you limit yourself to low speed class 1 whitewater, but they could wrap around a rock, and trap you inside, possibly underwater, because they don't have the strength of a full blown cross-linked polyethylene whitewater boat. Lethal. That actually applies to any lightly built boat.

    Folbot has made canvas-over-wood-frame boats for a very long time. The newest designs are made from somewhat different materials.

    If these are not major concerns, you might look at
    thea.com/Kayaks-Kayak-Folbot
    Maybe you can find a used one in your area through craigslist, etc.

    They are also available new at pdf.nauticexpo.com/pdf/folbot/folbot-catalog/20914-95825.html

    (There are also hybrid folding/inflatable boats, in which a bladder is inflated to stiffen the boat.)

    There is a completely different style of folding boat, in which there are creases in otherwise stiff material that fold like origami: www.orukayak.com. That company calls them kayaks, but many don't need or spray skirts, and have fairly large cockpits. They aren't super-light or super-high-performance, but I saw a couple at REI, and they looked simple to assemble and serviceable. To make something like that yourself, search online for "DIY folding boat" or something like that. Maybe a smart handy guy could build something a little heavier out of (coated)plywood and door hinges, but you would need a skin to keep it waterproof.

    Of course, like almost any small craft like that, you need flotation - I suggest strong airbags, such as the ones that have folding closures so you can store gear inside to keep it dry.

    I once worked for an outdoor equipment store. In the trade, two-person kayaks and canoes are called "divorce boats". That's because the two people have to cooperate to steer well and control the boat, which often means that one person needs to be in charge, which isn't always ideal for interpersonal relationships. A similar phenomena often occurs on "bicycles built for two". But a few couples make them work, in both cases.

    I wonder if anyone has made raft-like boats out of cheap pool noodles and bungie cord. If you have enough flotation, you don't need a skin, because you don't need to seal out the water - in fact you want holes, to let the water drain, just like a sit-on-top boat. Probably very low performance.

    I know people have made boats entirely out of cut foam, including the cheap foam you buy to insulate houses. The obvious problem is that little pieces of foam peel off and pollute the water. Little pieces of foam are one of the most environmentally harmful forms of pollution at sea.
     
    Last edited: Mar 9, 2021
  8. Rumars
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    Rumars Senior Member

    Now that you actually have defined some criteria I'll try to explain the problem you are facing:
    For lightness you have to sacrifice either durability, shape, or size. Shape comes from an internal frame or inflatable elements, or a combination. The more frame or higher pressure, the better the boat handles, but it also means more weight. The frame is usually Al, but could be carbon fiber if you sacrifice durability and price. High pressure means material able to take it, wich means weight. When you increase the boats size (2-4 people), it means more material for frame and skin, wich leads to more weight.
    At the moment on the market there are several 20lbs boats, canoes or kayaks, all in the solo, 12.5ft class. (For example here Pakboats Kayaks - Pakboats Pakboats Kayaks - Pakboats https://www.pakboats.com/folding-kayaks/ )
    I know of several special one offs in the same class that are well under this weight, but durability is severely impacted, they have to be extremely pampered (no abrasion or impacts allowed). You could possibly get a 15ft, 2 person boat, to 20lbs that way, but that is the lower limit with today's materials (I am talking about something that still paddles reasonably, not "rafts"). Building something like that for under 300$ is only possible if you don't have to buy the materials yourself. Heat weldable TPU (or other more exotic materials like cuben), carbon, epoxy and varnish (plus auxiliary supplies) don't come cheap.

    I don't really know why you want the whole boat under 20lbs if it's going to be transported by car. For portage (rapids, etc.) you divide the weight between several people (those 2-4 users), and you can also use trolleys. For anything else the boat is disassembled anyway, you handle only the individual components. The single most heavy component that can not be subdivided is the skin, and 20lbs allows for a reasonably durable 17ft boat skin without breaking the bank.

    To build the boat under 300$ retail, you have to use PVC for the skin, plywood frames and wood or Al stringers.

    Yost's methods and materials can be used to build any shape and size boat you want. There are other ways, for all wood builds, more rigidity, no sponsoons, etc. but the underlying principle is the same, you need a way to make stringers from separate pieces, a way to hold them to the frames, and a way to tension the skin. If you are actually interested I can detail further, but it only makes sense if it brings you some advantage over Yost's methods.

    Any kayak or canoe plan intended for rigid or normal SOF construction can be buildt as a folder, there is no need for you to learn how to design a boat from scratch. You can do that of course if you like, but it's not necessary.
     
  9. Ruming Jiang
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    Ruming Jiang Junior Member

    The problem with foldable/inflatable is they tend to get floatation and rigidity from one material, thus the solution is suboptimal.

    Thanks for the insights on two-person boats. I'll stay alert if wife talks me into one.
     
  10. Ruming Jiang
    Joined: Mar 2021
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    Location: Vancouver BC Canada

    Ruming Jiang Junior Member


    Thanks for the insights. There definitely will be a lot of trade-offs. Durability is less concerned as it is not intended for heavy use, although it will be tested against abuse. Skin can be patched with tapes or disposable when cheap enough. Now you see why I insisted flat film sheet.

    20lb is the ballpark number I think light enough to make handling a pleasure rather than a burden. I feel sad to see many older paddlers (like the gentleman I bought mine from and a few others along the search) giving up the pleasure due to reduced strength, health problems and downsize to smaller residences and vehicles (thus why takedown). I have no problem with my 80lb boat now but in 30 years or so I will be in a similar position. Solving their problem, by developing a technically and commercially sustainable product, solves my problem in "near" future and makes me satisfied.
     
  11. Rumars
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    Rumars Senior Member

    Ruming, you don't understand material properties. All SOF boats are skinned with "flat sheet" that's how the fabric comes, as a flat sheet on a roll. This fabric is flexible in the sense that you can fold it any way you like, but it is not elastic, meaning it will not strech in two directions, it's not rubber. Depending on the coating and its thickness, the fabric can have some strech, usually in one direction only, or none whatsoever. This determines how many shaping seams the skin has, beginning with stem and stern half seams (the boat gets thinner and you need to cut the excess away, but the fabric has some strech), up to multiple full panel seams (fabric has no strech whatsoever and each panel is cut to the chine outline).
    The used coating has to permit either glueing or welding in order to assure watertightness and repairability. Right now there are three used coatings, hypalon, PVC and (T)PU, over polyester woven fabrics. You can go to lighter, more exotic things like non woven laminates, but those exhibit poor abrasion resistance and are hard to glue, not to mention cost.
    Frame material has different problems, you don't see much carbon used because it has very little advantage. You can make very light and stiff tubes with it, but the walls are so thin that they crack with minor impact, plus the tubes have to be custom made because of the reinforcements where they sit on the frames. By the time you make them thick enough to allow normal handling, aluminium is not far away, especially if you use constant thickness walls.
    With the materials we have now, ~20lbs for a 12.5ft folding boat is the limit for normal use. Maybe it will change in 30 years, I don't know. You can get lower if you are willing to baby the boat and accept that any minor abrasion means that you may sink.
    It's also possible to get lower if the boat does not fold, and still have acceptable abrasion and impact resistance, that's because of the difference in construction technology.

    As I said, the big advantage of a folding boat is that the only time you have to handle the full weight is when launching and retrieving, and for that god gave us wheels and rollers, there is no need to lift the whole boat and carry it, you just have to drag the thing a few feet in and out of the water. With 40lbs weight allowance you can make a really nice boat that handles like any rigid one, and still be lighter than most. It just means you have two or three backpacks to haul from and to the car. There are even special trolleys available that can be used for launching and disassembled transport, they were invented a long time ago for use with public transportation.
     
  12. kerosene
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    kerosene Senior Member

    I appreciate your eagerness to find a a better solution.

    But if there would be easy solution that would beat your goals someone with more experience would probably have done it. it almost never makes sense to come up with very "new" solutions as an amateur.

    easy to build: plywood.
    tarnsportability: nesting design that can be split in half. (or 3 parts)
     
  13. kerosene
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    kerosene Senior Member

  14. kerosene
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    kerosene Senior Member


  15. Ruming Jiang
    Joined: Mar 2021
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    Ruming Jiang Junior Member


    Thank you for sharing. It's a nice boat.
     
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