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Thread: Scaling up/down skin on frame canoe plans?

  1. #1
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    Default Scaling up/down skin on frame canoe plans?

    I've completed a couple SOF kayaks and am in love with the process. I'm still prepping a strip canoe, but that won't be full steam ahead for a while as I slowly collect nice wood for it (been getting lucky at the big box stores every 2-3 months, and it's saving a lot of money over buying select stock from the lumber yard). I type that as if I need to excuse my penchant for SOF building

    I'd like to build some SOF canoes. I'd like to build two, specifically - one smaller, perhaps solo perhaps a bit larger, but not meant for 3+ people or tripping. And I'd also like to challenge myself with a larger one that could be used for a weekend trip with two adults. I've been digging around plans online, and Platt Monforts larger Snowshoe canoes seem to fit the bill for latter, probably the 16' one. There are LOTS of options for smaller canoes: Monfort has some, Dave Gentry has the gorgeous Rushton IGO, and so on.

    How do these plans scale? Is it possible to scale them? If I buy the Snowshoe 16' plans, could I reasonably scale them down? I assume it's not as simple as taking the forms, shrinking them by a percentage and then moving them closer together on the strongback by a similar percentage.

    Perhaps another way to ask this: is there a recommended resource to learn about canoe design? I've seen some resources for sail boats, maybe I just need to consume those?

  2. #2
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    Default Re: Scaling up/down skin on frame canoe plans?

    You should be able to shrink (pun intended <grin> the length by 10% or less by simply reducing the frame/mold stations distance. You should not simply reduce the plas by a % because if you decrease the beam you will greatly affect the stability of the boat. As well, you shouldn't decrease the boat length more than 10% of the plans because of unpredictable changes in boat performance.

    As far as I know, there is no "Learn Canoe Design" sources. Maybe some of our other Forumites know a bit more about this, and maybe will be able to prove me wrong.
    Hope for the best, but plan for the worst.

  3. #3
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    Default Re: Scaling up/down skin on frame canoe plans?

    I think the 10% rule is a commonly accepted guideline, but i have seen boats stretched by 25%. You might find canoes/ Kayaks built out in the wilds might use some common widths due to stability, but i would imagine that length is decided on use and whos building it. I should start building Daves SOF Chautaqua, but its minus 16 in the shed.....

  4. #4
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    Default Re: Scaling up/down skin on frame canoe plans?

    Thanks for the input. It sounds like there isn't a scale, just a new canoe! I should get into learning about boat design and work with some software on it ...

    And now I'm curious if I can convert any of my existing strip canoe plans into SOF ...

  5. #5
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    Default Re: Scaling up/down skin on frame canoe plans?

    Randy Bond built a really nicely done 18' Hazen Micmac tandem canoe a few years ago using SOF construction. The book "The Stripper's Guide to Canoe Building" by David Hazen comes with full sized templates for the 16', 17' and 18' Micmac models in wood strip/fiberglass construction, which are some of the best handling canoes I have ever had the pleasure to own and paddle (and I've owned and sold as a dealer a lot of canoes over the years). The boat was built to plan without design/size/shape modifications. For a really good tandem for general use and tripping there really is no reason to set off trying to design your own when there are plenty of good stripper designs already available from a variety of sources that could be modified to SOF.



    http://www.woodenboat.com/sites/defa...ond_B_6_04.jpg

  6. #6
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    Default Re: Scaling up/down skin on frame canoe plans?

    I'd take heed of Todd's remarks. There are subtleties to boat design. Why do it wrong when it's so easy to do it right.

  7. #7
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    Default Re: Scaling up/down skin on frame canoe plans?

    All good advice, definitely taking heed. That is a lovely canoe in the picture. Time to go find some stories about converting stripper designs to SOF - there's gotta be some advice in this forum!

  8. #8
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    Default Re: Scaling up/down skin on frame canoe plans?

    It's easy to convert many a small boat to SOF, if one builds it in the traditional fashion - i.e. using bent ribs, rather than plywood frames. It should be no problem at all to convert your stripper.
    Quite a few years ago now, I wrote a short article for Duckworks about how I converted Rushton's IGO (and thanks for the kudos). It has an overview of the process, and it should be enough to get you there. I am happy to answer questions, too.
    http://www.duckworksmagazine.com/10/...hton/index.htm

    Alternatively, one of my next boats will be a family/expediton sized canoe, about 17' long, based in part on the Micmac (Todd's continued recommendations over the years have sunk in). Not sure when the boat or plans will be done, as I'm on the road to do some coastal cruising in Florida.

    Dave

  9. #9
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    Default Re: Scaling up/down skin on frame canoe plans?

    When you get ready to do a Micmac, there is an error in the stern stem profile on the most recent plan. Not a big deal, but it was designed to have a bit more "bite" at the stern than the bow, which makes the boat track better with less paddler correction. It ends up being about 1/2" difference in the shape of the bottom of the stem, which is worth including. This would be the correct profile from the original version. I have sketched in what is supposed to be the bow stem profile's bottom in red ink. The stern stem profile should be as shown.

    micmac-bow.jpg

  10. #10
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    Default Re: Scaling up/down skin on frame canoe plans?

    It is a common practice to use one set of forms for canoes from 15-18 feet long by varying the space between the forms.

    Platt's designs are fine, but his light Dacron aircraft skin is too fragile. if you build one of those use the heavier fabric and PU coating used by most SOF builders. Very few fabric skin aircraft run into submerged logs.

    If you use another design, Platt's framework is strong enough, so you can make a very light boat. The fabric weighs several oz per yard more than the aircraft skin, and will need more coating, so a 15 ft boat with around 5 yards of skin might weigh 3-4 lb more. Considering the inconvenience of a punctured bottom, that is a small price to pay on a portage. The Kevlar roving looks cool. Functionally, I don't see much value. I have been Volunteering at Urban Batbuilders foe about 12 years, and much of that time they were building SOF canoes. We went maybe 1/8 inch thicker on the frames and stringers than Platt. As the skin shrinks, it tends to hog the bottom, so building the frame with a few inches more rocker than you want will flatten out. A good source of skin and PU is https://shop.skinboats.com/2-part-Ur...-System_c5.htm

    There is some debate about the relative merits of the heavier Dacron and ballistic Nylon skin. Both fabrics can be stretched and shrunk to produce a tight skin that doesn't get baggy after a few days on the water. The stretching and shrinking process is different, and some people have had problems switching between them or found one easier to work with than the other. Both are very strong and puncture resistant. If you go to town on a test panel with a screwdriver, the Nylon will be harder to puncture. Very few lakes and streams have aggressive screwdrivers hiding in the shallows though, so my preference for Nylon is based more on familiarity than any significant difference in performance.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  11. #11
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    Default Re: Scaling up/down skin on frame canoe plans?

    Quote Originally Posted by DGentry View Post
    It's easy to convert many a small boat to SOF, if one builds it in the traditional fashion - i.e. using bent ribs, rather than plywood frames. It should be no problem at all to convert your stripper.
    Quite a few years ago now, I wrote a short article for Duckworks about how I converted Rushton's IGO (and thanks for the kudos). It has an overview of the process, and it should be enough to get you there. I am happy to answer questions, too.
    http://www.duckworksmagazine.com/10/...hton/index.htm

    Alternatively, one of my next boats will be a family/expediton sized canoe, about 17' long, based in part on the Micmac (Todd's continued recommendations over the years have sunk in). Not sure when the boat or plans will be done, as I'm on the road to do some coastal cruising in Florida.

    Dave
    Dave - Was hoping you'd chime in! I just read that article a couple days back, found it in this old thread that looks to have some other good advice: http://forum.woodenboat.com/archive/.../t-214890.html

    I'll be doing more traditional construction with ribs and stations, as I don't have the experience to figure out all those frames. And I prefer the aesthetic of the ribs. In doing some further reading, it sounds like I really just need to "notch" the stations for the stringers, so the skin sits about where the outer edge of the hull would be if I built it with strips. Let me know if I'm horribly wrong there!

    I have two of your plans (Whitehall and Kidyak) sitting in a PayPal shopping cart I need to pull the trigger on soon! Looking forward to seeing what you come up with the "Gentry Micmac"!


    Quote Originally Posted by Todd Bradshaw View Post
    When you get ready to do a Micmac, there is an error in the stern stem profile on the most recent plan. Not a big deal, but it was designed to have a bit more "bite" at the stern than the bow, which makes the boat track better with less paddler correction. It ends up being about 1/2" difference in the shape of the bottom of the stem, which is worth including. This would be the correct profile from the original version. I have sketched in what is supposed to be the bow stem profile's bottom in red ink. The stern stem profile should be as shown.
    Todd - I admit, I'm a bit confused based on what you've said here, but I know I've seen you mention this in other spots on the forum. I'll keep it mind! Thanks for sharing!


    Quote Originally Posted by MN Dave View Post
    It is a common practice to use one set of forms for canoes from 15-18 feet long by varying the space between the forms.

    Platt's designs are fine, but his light Dacron aircraft skin is too fragile. if you build one of those use the heavier fabric and PU coating used by most SOF builders. Very few fabric skin aircraft run into submerged logs.

    If you use another design, Platt's framework is strong enough, so you can make a very light boat. The fabric weighs several oz per yard more than the aircraft skin, and will need more coating, so a 15 ft boat with around 5 yards of skin might weigh 3-4 lb more. Considering the inconvenience of a punctured bottom, that is a small price to pay on a portage. The Kevlar roving looks cool. Functionally, I don't see much value. I have been Volunteering at Urban Batbuilders foe about 12 years, and much of that time they were building SOF canoes. We went maybe 1/8 inch thicker on the frames and stringers than Platt. As the skin shrinks, it tends to hog the bottom, so building the frame with a few inches more rocker than you want will flatten out. A good source of skin and PU is https://shop.skinboats.com/2-part-Ur...-System_c5.htm

    There is some debate about the relative merits of the heavier Dacron and ballistic Nylon skin. Both fabrics can be stretched and shrunk to produce a tight skin that doesn't get baggy after a few days on the water. The stretching and shrinking process is different, and some people have had problems switching between them or found one easier to work with than the other. Both are very strong and puncture resistant. If you go to town on a test panel with a screwdriver, the Nylon will be harder to puncture. Very few lakes and streams have aggressive screwdrivers hiding in the shallows though, so my preference for Nylon is based more on familiarity than any significant difference in performance.
    Thanks for the details. Even with the added couple pounds, it's still far lighter than an all wood, metal, or wood/canvas canoe! And I do like the SOF aesthetic either way!

    I'm probably going to go with some form of polyester for these boats. I've used ballistic nylon and Corey's 2-part urethane for a couple kayaks, and it's nice ... but I dislike that I just cannot find ballistic nylon *anywhere* else, and I don't like being tied so tightly to a single material source. Perhaps that's silly and maybe selfish, but I do feel weirdly about Corey being the only person I can order ballistic nylon from! If you know of another source for the nylon or urethane, I think I'd be totally sold on ballistic nylon!

  12. #12
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    Default Re: Scaling up/down skin on frame canoe plans?

    Todd - I admit, I'm a bit confused based on what you've said here, but I know I've seen you mention this in other spots on the forum. I'll keep it mind! Thanks for sharing!
    On the latest printing of the plans which come with the book, a small section of the line representing the bow's stem profile was omitted. The profile shown is that of the stern stem only. The red line I drew onto the plan is the missing portion and is how that area of the bow stem profile is supposed to be shaped.

  13. #13
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    Default Re: Scaling up/down skin on frame canoe plans?

    Quote Originally Posted by Todd Bradshaw View Post
    On the latest printing of the plans which come with the book, a small section of the line representing the bow's stem profile was omitted. The profile shown is that of the stern stem only. The red line I drew onto the plan is the missing portion and is how that area of the bow stem profile is supposed to be shaped.
    Ah, that clicked for me. Thanks!!

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