Skin on Frame Boatbuilding Method
Skin on frame refers to a method of boatbuilding that has been around for a very long time. Typically a light frame often made of wood is assembled. This is then covered by a waterproof membrane. The resulting boat is light and econonmical of material
National Film Board Documentary (Ford Foundation) of Canadian Arctic Netsilik Kayak being made circa 1965. Lots of scenes of fishing and just living.
Kayaks and Umiaks
The first type of skin on frame boat that comes to mind is the Northern Kayaks. These were carefully assembled using scarce driftwood frames or sometimes whalebone, and covered with animal skins. Typically the frame was lashed together using rawhide or sinew. Wetting the rawhide allows it to stretch and as it dries it shrinks pulling the joints tightly together. Before metal tools were available, joints such as mortise and tenon were difficult to cut, many joints were shallow depressions instead, and having a material that held the joined pieces together was a great advantage. Often bow drills were used to make holes for the lashing.
Photo by flickr user wili hybrid - flickr.com, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=986538
Because these boats were lashed and covered in flexible skin they were able to give and move somewhat under stress. Just as the Viking ship lashing allowed movement and prevented stress to build up in one spot causing failure, the kayak were flexible.
Bending the wood strips was done by wetting in hot water and gently tapping or chewing on the ribs to coax them to bend.
The covering was often fresh seal skin. The adhering hair was scraped off as was fat and flesh. Carefully stretched so that it would shrink evenly it would help keep the shape of the Kayak. Meticulous stitching produced a watertight joint between skins. Once the skin dried it was covered with fat to help keep it waterproof and stop it from stretching out.
Many Inuit communities developed their own style of kayak. There is not one unified pattern but many traditional ways of putting together the frame.
While the Kayak was a fast silent one man boat used for hunting and fishing, the umiak was a large boat (upwards of 20 feet) used to carry larger cargo and to go longer distances. The kayak was a hunter's boat, the umiak (or woman's boat) was for travel, transportation and longer expeditions with several people aboard.
The original dry suit was sealskin with wrists and hood tightly closed and the waist attached to the opening of the kayak.
A fun place to explore Greenland types and other Kayaks is Instructable website. The link is for a 7 part step by step instructions on making a greenland type Kayak.
David W.Zimmerley has a great website on Kayaks and how to build them including plans for several types of Kayaks and paddles. Worth wandering through. His plans seem to be free and he has a publication he has written that can be purchased online.
Traditionally Skin on frame boats were covered with animal skins and later when it became available with painted canvas.
Modern Skin on Frame Boats Can be Ultralight.
Modern skin on frame boats are being constructed from wood frames and covered with ultra strong light fabrics. Once the fabric is attached to the frame (often with heat actiated glue) it is gently heated to cause it to shrink and tighten. This results in remarkably light boats some less than 20 pounds.
The availability of ultra strong adhesives and fabrics make it possible to construct surprisingly strong crafts. Whereas the old style boats were lashed and moved as they were used, some modern builders construct rigid structures that gain in efficiency. Stiffer boats are usually faster and more efficient but need to be stronger since there is little give.
Skin on frame is a building method that has been used for years on airplanes and the methods and materials have transfered to boats quite well.
Geodesic Airolite Has designed several ultra light boats using wood frames glued with epoxy rather than lashed and skinned with heat shrink polyester. Extra strength and rigidity is provided with Kevlar roving threads. The resulting boats are extremely light and surprisingly resistant. They are also very pretty.
Kudzu Craft canoes are also skin on frame. This is a fun video where the demonstrator pounds and eventually makes a hole in a skin on frame boat. They use Nylon or Dacron (polyester) but sewn not glued as Geodesic Aerolite does. then heat shrunk. They also have good videos on skinning a boat with polyester.
There are advantages to both Nylon and Dacron. Polyester (Dacron) seems to be a favourite. Nylon although strong and resistant, stretches when wet. It is also resistant to most paints. Polyester is more stable and can be painted with many different finishes. Polyester can also be easily shrunk with moderate heat.
All builders discourage the use of heat guns in favour of an iron because it is easier to control. A very light hand is needed to use a heat gun and it is easy to melt the fabric.
Silliness or is it?
At the complete end of the skin on frame spectrum, here are instructions to build a tree branch and polytarp skin on frame kayak also from Instructables.
email me if you find mistakes, I'll fix them and we'll all benefit: Christine
I don't claim to be an expert in anything. If you want to build a boat do your homework first. Using high tech materials usually require that you do it right for them to work. Use safety equipment and wear a lifejacket when paddling.