Ultralight Boat Building
Advantages of Ultralight Boatbuilding
Anyone who has tried to move and store a heavy boat, or tried to wrangle a tender onto a yacht deck single handed, appreciates the benefits of ultra light boatbuilding.
Besides the on-land qualities, a light boat offers many advantages. It's easier to move on the water whether she is being rowed or sailed. Less wind or oar power is needed making a sailboat faster in light air, and a rowboat less tiresome. An ultralight motor boat takes less energy to move, this could be useful when the power comes from solar cells or limited batteries. This would allow a light boat to go further on a charge than a heavier boat
A significant advantage of ultralight boatbuilding is the extra carrying capacity. More cargo can be carried in the same shape but lighter boat.
Reducing scantlings can make the boat less expensive to build. It can also reduce the time to build since sometimes, there is simply less structure.
There are some disadvantages to ultralight boat building.
In any situation where having some momentum in the boat motion is useful, an ultralight will be at a disadvantage. Thus an ultralight rowboat will not glide on as well as a heavier boat during recovery stage, or a sailboat might not have enough momentum to tack easily when the winds are higher. My Skerry behaves better in high wind when another person or a sandbag is sitting in the bow.
When modifying a boat to be ultralight often the builder does not take into consideration the fact that the boat hull was designed to have a specific waterline. Modifying the boat's waterline changes the way the craft handles and can compromise stability. An obvious case it old fashioned bank dories which need to sit lower in the water and did not stabilize until the fisherman had fish on board.
A lighter craft sits on top of the waves instead of slicing through, this can increase pounding and bouncing. My Skerry is a good example of this. When going into the wind it will be much quieter and smoother if it has some weight in the front end. At about 100 pounds the hull is very buoyant and can slap into waves unless some ballast is added.
Many boats use their weight to provide stability, Keelboats are a prime example. Reducing weight sometimes reduces stability.
Reducing structure can also weaken the ultralight boat. Certainly any skin on frame construction is vulnerable in its frames.
Workmanship and maintenance become more important in an ultralight construction because there is usually not so much redundancy in the structure and any damage can be significant.
Ultralight Boat Building Methods
Ultralight boatbuilding is a GOAL rather than a METHOD. To produce a light craft designers recommend light materials, including fittings, minimum required structure and the most efficient bracing systems.
Some methods of boatbuilding are lighter than others. I've already mentioned skin on frame such as Kayaks as being traditionally lighter and more economical of material. (It is certainly possible to make a heavy kayak but harder.) Lapstrake is lighter than Carvel usually. Plywood is often, though not always, lighter than solid planks. Many strip planked boats are exceptionally light.
Using ultra strong and stiff material, with exceptional weight to strength ratios, improves the chances that a boat will be lighter. Substituting carbon fibre for regular fiberglass can result in extremely stiff light craft.
Most designs and particularly those designed to be built by relatively inexperienced boat builders often have redundant strength and bracing to allow for mistakes and lack of skill. Increasing the quality of boatbuilding and reducing or eliminating extra bracing can significantly reduce weight. This means there is less margin for error though.
Ultralight boats often have little or no built in flotation. Because they are light they usually float anyway. This should be carefully considered when using an ultra light boat and extra strap in floats might make the boat significantly safer.
Several boatbuilders and tinkerers have been experimenting with corrugated plastic sheets such as coroplast. The boats are turning out to be ultra light and easy to handle. Here is my page on Coroplast boats.
Ultralight boatbuilding is not a new idea.
Some extremely light crafts have been made in the past using traditional materials such as cedar, birch bark or skin and frame. There are some admirable strip planked boats that are as light as any of the modern ultralights. It boils down to attention to details and construction, careful choice of design and materials and resisting adding extra, heavy stuff and finishes onto the boat.
Geodesic Airolite has a line of Skin on Frame Ultralights
Geodesic Airolite has designed a whole line of Ultra-light crafts. They are made by putting together a strong frame and covering it with Dacron Polyester which is heat shrunk on the frame. There is Kevlar roving in the frame to improve stability of the frame.
The result are strong beautiful Ultra light boats.
The resulting boats weight between 10 and 75 pounds with most of their boats sitting in the 20-35 pounds range.
Time to build is estimated between 30 for a simple solo canoe, to 250 hours for the more complex sailing dinghies.
Michael Storer built a 12 pound Balsa Canoe
Feather Canoe builds Ultralight Strip Boats
Wee Lassie style canoe is only about 20 pounds and gorgeous. They have plans for many others
Chesapeake Light Craft
Chesapeake Light Craft company has many stitch and glue boats that can be very light. Here the Sassafras canoe weight in at only 26 pounds and has floatation front and back.
The CLC Annapolis Wherry is only 65 pounds and is a full wood with fiberglass performance rowboat. No need to baby this boat.
It's a rowing boat that is 17 and a half feet long.
Many stitch and glue boats particularly kayaks can be built very lightly.
Check out the top and side bar for more links to PLANS, Builders, and interesting articles.
Building and using boats can be dangerous if you are not careful, so be careful already. Some plans and ideas are quite experimental and untested. By reducing weight, strength is often reduced so be warned. Since I have not built or tested them I can't recommend them.
email me if you find mistakes, I'll fix them and we'll all benefit: Christine