Skin-on-frame canoe/kayak plan help

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

  1. Ruming Jiang
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    Ruming Jiang Junior Member

    Not SOF boats but I've built and seen many model airplanes in SOF structure
     
  2. Ruming Jiang
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    Ruming Jiang Junior Member


    Thank you for the long comment. That article on kayak length is something I have been looking for as well.

    My target is flatwater first. whitewater and open water will be something in the future. Certainly, the design should be different. I'm not there yet.

    Cutting boats into pieces solves the length problem, but they still take spaces in storage and transport.

    Weight matters on the water when load is right. A 20lb makes a difference from 80lb easily going solo, however, if loaded up to 500lb probably hard to tell. That being said, my purpose of lightweight is for easier handling, without trick, cart or assistance.
     
  3. Ruming Jiang
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    Ruming Jiang Junior Member

    Thank you for all the links. I did some study on origami designs and realize solving two problems (rigidity, flotation) with one material will hardly be optimal. The price and specs tell.
     
  4. Tiny Turnip
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    Tiny Turnip Senior Member

    As with any boat, with the possible near exception of inflatables, you don't solve all the issues with one material. Clearly, SOF is usually at least two materials, although to suggest that solving two problems with one material is not optimal is hardly logical. If you can achieve that, surely it's a win win?

    As with all canoes, flotation is achieved with flotation bags.

    Prices? 4mm coroplast - $21 for an 8x4 at home depot.

    (weight 9lb a sheet)

    But hey, you've clearly other plans, so I'll be interested to see what you end up with. - do share when you've completed it. Good luck!
     
  5. mitchgrunes
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    mitchgrunes Junior Member

    It would be nice if one of you with more boat design experience would correct what I say:

    Would the rest of you agree that the left hand design (assuming you complete it with the other half) would be very inefficient and require a lot of effort to paddle? Possibly more so than his 80 pound open canoe, though AFAIK, he hasn't shown his current boat. It would, however, be very stable in flat water, or near-flat water, because of the wide nearly flat bottom. Of course, If it did tip, you might not be able to right it while in the water, because most of that same stability would apply while upside down, and a swimmer might be unable to turn it upright!

    And that the right hand design would be very tippy, especially when standing still. Much, much tippier than he is probably used to.

    Also, the full length of both designs is very high over the water. They are going to blow around in the wind a lot. You will also have to place your center of gravity just right, or you won't be able to keep them straight in the wind. (You could go straight by sitting far forwards, but then your bow would dive into the water, and slow you way down.) That's one of the benefits of closed-deck boats - then ends can be pretty low to the water. Surf-skis (which you sit on top of) can be very low to the water, because the buoyancy chambers are completely enclosed, though the price is that you get wet if the middle is low to the water too. In saltwater, you may also get a lot of jellyfish stings as well, unless you wear something like a dive skin.

    What I think most people want is a reasonable compromise between long thin half-cylinder rounded hull cross-sections (which are theoretically very fast, but tip easily, because they are not stabilized by buoyancy at all, because the surface that touches the water is always the same shape, and provide no feedback), and a very thin V-hull cross-sections, which are also tippy, but for a different reason - because the sides of the boat mostly don't touch the water, until it is too late, and the boat is flooded.

    You might prefer something close to a half-ellipsoidal cross section, but with "chines" maybe a few inches above the waterline (though people disagree on exact chine placement), where the sides of the boat start to go straight, so as you lean the boat, those big flat chines touch the water and stop the lean before it goes too far. Does that make any sense? (All origami and SOF designs sort of have chines, because they can't really curve, but I am talking about a stronger transition than some.)

    Neither of your models really has chine, other than the sides of the boat, which extend all the way up. In both cases, the lean won't stop the lean until the sides of the boat touch - though the first design is stable enough (it might well require 50-100 pounds force or more to tip) without chine that that probably won't matter. The second is unworkable for most paddlers. Because you probably won't be able to successfully get into the boat without tipping it, nor keep it upright unless you have extremely fast reflexes. Some fast race boats look somewhat like that. The ones I have seen that come close are all surf skis, that you can enter by putting your legs around the back of the boat, and scooting yourself forwards. You could NOT do that with an open canoe, because the top of the ends are too high - though I'm not sure about the Oru designs - they are closed deck at the ends - maybe that would work.

    There are some things you can test with small scale origami designs, provided you use a material that doesn't absorb water:
    1. If you tried pulling the first shape through the water, it would generate big waves which would waste energy. Fluid dynamics doesn't really scale right (Think about it: a bumblebee wouldn't fly if it were much bigger, because it doesn't have big enough wings) - but you can certainly see that a wide short shape generates waves.
    2. If you put the second shape in the water, with a weight to simulate your weight, or two weights to simulate you and your partner, you could very easily see that even slight weight shifts, including when you step into the boat, make the boat tip.
    3. To see where the waterline falls, I think you want to scale the weights with the volume, which goes up roughly as the cube of the size. E.g., if you make a 1/10 scale model, it has about 1/(10*10*10)=1/1000 the volume, and you want the weight of the model (probably insignificant for thin origami materials) + the weights to be about 1/1000 that of the full scale model (whose weight you can calculate from by multiplying the weight/area of the coruplast material by the area) + the maximum weight of the people and their gear.

    The only length that matters much, as far as speed and performance is concerned, is the length of the waterline - i.e., the part of the boat under water. Any added length just adds to the weight of the boat, and is nearly useless. (That's not quite true. To some extent, it can push splash away from the paddlers. And rounded bottom ends do make it easier to pull the boat onto the land. But still, it's mostly wasted.) And the only width that matters much, is the width of the waterline. A 12/1 length/width waterline ratio is pretty fast, but maybe 7/1 or 8/1 might be a better compromise between speed and stability for someone used to wide heavy boats that are relatively stable. You can't really determine speeds and efforts from your scale models, because of scaling effects, I think you just have to use simple ratios, unless you want to get into computer modeling.

    And, as I said, you might want the chines to start somewhat above the waterline, probably with the weight of both people (and any weight of gear inside). If it is below the waterline, it can't really stop the lean the same way.

    Anything much more sophisticated requires computer modeling, and you won't get it from your little origami models.

    However, everything I just said is open to correction by more experienced designers.

    But I don't think you will gain an understanding for how boat designs interact with the water without actually trying boats with similar shapes and weights. Do you have friends with boats, belong to a club with such people, or a shop that lets you try or rent boats? The two designs you have proposed have such major issues, that I think this would be very helpful.
     
    Last edited: Mar 12, 2021
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  6. mitchgrunes
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    mitchgrunes Junior Member

    From what I've read online, the Oru boats do fairly well, if you don't want super-high performance specs, and much of the performance loss comes from being too wide for speed, rather than from loss of regidity alone. Sure, stretching a skin material with high tensile strength over a material with high compression resistance and strength can create a pretty stiff design, without much weight, and that is the whole point of SOF. But extreme rigidity only matters all that much when people want to go very fast or be super-efficient. Which I guess you don't. And if you cared, I guess you could use inflatable bladders (which need not take much space deflated nor be especially heavy) on the inside to stiffen such a boat somewhat. (Which would mean it would no longer be one material.) (Inflatable bags or bladders are highly recommended for safety in any lightweight boat, though I admit they don't need to be inflated tightly enough to make the boat rigid just for safety.) (Could you simulate inflatable bladders in origami designs by using long thin balloons??)

    The Oru boats are expensive because they can be. There isn't a lot of competition from similar designs, for now, except from home builders. And most competing commercial boats, made of plastics or composites, are either heavier and even more expensive, or both. Until there is more competition, they can stay expensive. That doesn't mean yours has to be.

    This discussion has convinced me that a corruplast + inflatable bladder design might be a fun easy build for me. It looks so easy. I wonder how durable it is...
     
    Last edited: Mar 12, 2021
  7. Ruming Jiang
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    Ruming Jiang Junior Member

    canoe1.JPG canoe2.JPG What would be the noticeable performance differences between these two? (flatwater, average paddling speed, 3mph maybe)
     
  8. bajansailor
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    bajansailor Marine Surveyor

    I don't think that the 'kink' in the hull amidships of the green deck version will do you any favours - if both boats are the same size and displacement, I would have thought that the brown one on the left would have slightly less resistance?
     
  9. Ruming Jiang
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    Ruming Jiang Junior Member

    Certainly it is optimal hydrodynamically but best fits the material I intended to use. Haven't learned much about boat design yet. Which properties are most relevant to the performances of a canoe? Thanks

    upload_2021-3-13_8-29-2.png
     
  10. portacruise
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    portacruise Senior Member

    Preferable to minimize water movement turbulence / eddies that might be created by hull shape disruption to the flow. For example, square back canoes have additional drag from turbulence off the stern, is my understanding. Does SOF construction introduce some significant turbulance because of material flexing or possible faceted surfaces at 3 knots? Just some humble thoughts from a tinkerer...
     
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  11. mitchgrunes
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    mitchgrunes Junior Member

    So cool that you have gone this quickly to real designs and modeling! And you are above my level on the latter.

    Looks like you have moved entirely to a flatwater design. I assume you know that on large lakes, as well as the ocean and bays, waves are not flatwater.

    The red one certainly looks a lot more like a traditional canoe, so would be the more conservative design.

    Have you attempted to assess stability with you and/or your partner and gear in the boat? Obviously, that depends a lot on what type and position of seating or kneeling arrangements you have planned. If the software you are using only takes into account the boat, and not what is inside, it won't give accurate results, especially since you want a lightweight boat. E.g., your bodies will effect the center of gravity, and the way wind interacts with your boat, and if it tips enough, your bodies and gear may shift to the low side of the boat.

    It is not uncommon for water to get inside a canoe, by a variety of means. E.g., if your boat tips, either of your designs will let in a lot of water. The movement of that water can affect stability too. One reason some people sometimes choose canoes over kayaks and surf skis is that they hold more stuff. The shifting around of that stuff also affects that stability, unless you tie everything down. Whitewater open canoeists often fill most the empty space with strong airbags, in effect creating a closed deck boat, but flatwater canoeists rarely go that far. Though if the boat fills completely with water, some airbags or foam are necessary to prevent sinking. In fact, I'm not sure it is legal in some jurisdictions to have a boat without some foam flotation.

    Also, if it tips, have you attempted to assess how easy it will be to tip back upright? If you are in deepwater, you can't rely on pushing off the bottom. You want to assess how many pounds (or newtons) of force you can exert, and determine whether that is sufficient - again with some gear and water inside. There are some obvious techniques that might help. E.g., if there is something at the sides of the boat to tie webbing to, you can place the webbing (or rope) over the boat, and use your body weight instead of your body buoyancy to pull it upright.

    Details for a later day:

    Why no thwarts? (Or maybe you just haven't drawn them yet.) Some people use them as seats, though that raises the center of gravity and bodily wind resistance a lot. In addition, if the boat fills with water, and you roll it over on the land to empty it, thwarts help prevent damage by strengthening the structure. And the sides of the thwarts, if they have places to tie into, could act as tie points for the webbing or rope I just mentioned. And if you do use large airbags, the thwarts can help prevent them from falling out of the boat, directly, or by tying ropes between them. And you should have a way to tie your paddle(s) back to your boat, so if you drop them, they don't blow away in the wind and waves.

    While you are at it, don't forget a way to tie painters, fore and aft on the boat, so you can tie it to a dock or tree, or if you car top it, to the front and back of your car. You may also have to tie red or orange cloth flags at the front or back - if you do put the boat on top of a small car, and the boat extends past the ends of the car, in many jurisdictions, such flags are legally required. Even where they are not, it is very important that other people can see your boat when parked on dark nights, especially in retirement communities, so they don't run into it.

    I assume your actual colors are TBD at this point. Hunters are taught to avoid shooting at orange things, but everything else sometimes gets shot at, though red is sometimes avoided too. Your green boat especially would be treated as a likely game animal, especially by hunters who have had a bit to drink, and don't look at shapes. :) In general, earth tones are a questionable decision in places where people hunt.
     
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  12. ImaginaryNumber
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    ImaginaryNumber Imaginary Member

    I haven't read clear through this thread so I apologize if it's already been mentioned. You might find Tom Yost's DIY designs of interest. Some are folders, some are rigid, some inflatable.

    Yostwerks - Kayak Building Manuals

    [​IMG]
     
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  13. portacruise
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    portacruise Senior Member

    If I had to use SOF, myself would probably start with a flatish bottom half sphere coracle shape and refine the shape by forming 2 points as much as needed to get max efficiency at 3 mph or so. That shape would appear to give the highest passenger capacity numbers, and best stability, for the same total weight of SOF craft. To get the weight down to 20#, explore use of strong and lightweight skin material plus maybe CF or bamboo for the frame. Inflatable construction will get you the weight and minimal storage volume, if that doesn't work. Neither is likely to be cheap.

    Here's some ideas on how to fold a coracle:

    Nautiraid Folding Coracle Dinghies - Nestaway Boats https://nestawayboats.com/shop/nautiraid-coracles/
     
  14. mitchgrunes
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    mitchgrunes Junior Member

    Hey guys, I know this is a bit off-topic, but, looking at that transparent SOF picture, I love the look of transparent boats.

    Am I correct in assuming people usually use vinyl when they want to be transparent?

    Does sufficiently thick vinyl stretch much, or must the skin and the frame fit each other very, very well? How does the strength and abrasion resistance of vinyl compare to that of coated nylon or polyester, and how well does transparency hold up against minor scratches?

    People also talk of transparent neoprene - is it transparent enough too look like that?
     
    Last edited: Mar 15, 2021

  15. Ruming Jiang
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    Ruming Jiang Junior Member

    Found (confirmed) the answer in Delftship manual!
    upload_2021-3-16_18-43-12.png
     
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