How to build a skin-on-frame boat.

Specific instructions are important as an introduction to any building medium. In the last ten years plenty of resource material has surfaced to help you through your first skin-on-frame project. There are also several shops, each with it's own specialty where for a very reasonable fee you can build under the supervision of an accomplished instructor and leave with a tested skin-on-frame design in 6-9 days. These classes are a good value and as a teacher I wish that they were available when I began building. There is a danger in specifics though. Skin-on-frame boat building is not like conventional boatbuilding where there might be one best way to get out a plank or one strongest way to frame a hull. There is no plotting, forms, or lofting involved. When we examine historic kayaks and skin canoes one discovers that construction techniques varied widely both geographically and temporally. Frames were both pieced and bent. Fastenings were lashings, pegs, and even nails. Skins were often sea mammal but sometimes caribou hide. Split and hewn driftwood, sinew, baleen, ivory, bone, spruce root, and even salvaged iron and timbers from wrecked whaling ships were employed as early as the 1600's. The Inuit skin boat build was a master of improvisation. Construction details were adaptable to the circumstances of the individual and it's here that we'll begin our journey to construct a modern skin-on-frame boat.

We'll start with a set of gunwales about as long as the boat in question ( a kayak, canoe, or rowboat) and sprung into a pleasing deck shape. They can be pinched and kerfed for fine ends or spread with headboards for a fuller deck plan. Sheer can be added by steaming, laminating, building up wedges, sawing out of a wider plank, or just allowing the natural flare to raise the ends. For a large Umiak these gunwales might be the size of two-by-fours, for a kayak as small as a nominal one-by-two. The boat will need some structure to define the hull so we'll need to plan for ribs, these can be fastened between an inwale-outwale structure or mortised directly into a single gunwale. Rib mortises can be as small as a single 1/4 inch hole spaced at 4 inches, or perhaps 3/4 wide and 1-1/2 inches long spaced at 12-inch intervals for a truly massive boat. In pieced rib construction scantlings might be even heavier and more widely spaced. A pieced rib boat is generally built from the floor structure up while a bent rib boat is built upside down starting with the gunwales. The deck will need some structure to hold its shape. In a kayak this can be curved or flat deck beams mortised into the gunwales and fastened however seems solid. For an open boat temporary braces are left in until a riser can be fastened to the ribs where thwarts will eventually take the load. Steam bent white oak is the choice material for ribs although locust, ash, yellow cedar and a host of other woods bend well too and resist rot. The ribs can be installed by eye or a keel and hull stringers can be blocked into place to provide some guidance on the boats' shape. Next a keel should be laid on; if you intend to nail it then for right now a few temporary lashings will suffice. If intended to be lashed then go ahead and do that, wobbly lines can always be faired later (try that in a planked boat!). Next stems can be fashioned out of laminations, wide sawn boards, or natural sawn knees. The stems are attached to the keel however seems solid. They can be fitted and lashed to fine gunwales with a breastplate added for stability, or mortised into a wider headboard and lashed or bolted. Now stringers will be laid on and fastened to form the chines; these can be tall and widely spaced or smaller and numerous. The important thing is that the skin won't later contact the ribs; there should be a 1/2" spacing between a stick laid across the chines and any ribs below. At this point any seats, flooring, oarlocks, or miscellaneous bits can be added. Now we can go over the framework breaking any sharp edges that might cut into the skin and making sure that everything is firmly fastened together. Remember this is not a rigid structure and every fastening needs to have a bit of play in it, bolts and even screws will allow the boat to work a little, but glue joints, especially where members meet at right angles are likely to fail almost immediately. Lashings are prone to chafe but are the strongest fastenings.

Clean up the shop, oil the frame with commercial oil or your own boat sauce of oils and thinners. Wipe it dry. Avoid varnishes or lacquers. Now it's time to think about the skin, and there are many ways to install it. Appropriate coverings can include, heavy canvas, nylon, polyester, and vinyl. I've even seen a boat skinned with cowhide! For open boats I like to lay the skin on and stretch it up to the gunwales and staple it there, later hiding the staples with a rub rail. A more traditional approach is to wrap the skin over the gunwale and lace it down to a riser. For kayaks I sew a pocket in each end of the skin about 4 inches shy of the length overall and then stretch the skin longitudinally hooking the pockets. I'll then pin the keel and wrap the skin up to a 1/2 batten secured to the deck. Using a hot knife I slice on opposite sides of the batten to leave an overlap. Then I use seine twine to lace up the deck and tighten the skin, the same as would have been done with gut and seal skin. Finally I use a whipstitch to close the seam. All that remains is to sew on a steam bent coaming.

What coatings provide the best longevity and performance depends on the covering material. Oil based paint is a good match for cotton canvas, although neither is very strong. Synthetic covering such as nylon and polyester seem to do well when painted with polyurethane. Personally, I use a light nylon cloth and a super tough two part polyurethane that is carded on, wet on wet, and cures in a single day. The finish is elastic, durable, and beautifully translucent. Some people have used liquid hypalon or neoprene, but these finishes are overkill for strength, extremely toxic, and expensive. Others have experimented with opaque vinyl sheet material which is quite tough, but tricky to work.

However you decide to build your skin-on-frame boat remember that balance, not beefiness is the secret to strength. This is an intuitive medium and you can easily see if something is wrong, and usually easily fix it, even later in the process. Skin boat building should not require hours of squinting at plans or fussing over details. Your process should be fluid and fun and when you're done you'll end up with a boat that is incidentally beautiful, but designed for use. Even if the first boat isn't everything you hoped, don't worry; you can always build another next week. Good luck!

Resources for skin-on-frame builders,

Websites:
http://www.capefalconkayak.com (the authors website)
http://www.traditionalkayaks.com (website for Harvey Golden, kayak builder, researcher)

Books:
Building the Greenland Kayak by Christopher Cunningham - buy from our Amazon store
How to build Skin-on-Frame Boats by Robert Morris - buy from our Amazon store
Eastern Arctic Kayaks (historic information) by John Heath and Eugene Arima - buy from our Amazon store

Part one of this article, about skin-on-frame contruction

Brian Schulz teaches skin-on-frame boat building at his shop on the Oregon Coast and across the country. He can be contacted at capefalconkayak@yahoo.com
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