One of the first questions the prospective home canoe or kayak builder asks is, "How much will my boat weigh"? It isn¹t an easy question to answer because weight depends upon the builder's skills, the materials he uses, and his objectives.
For instance, if you were building free style canoe that would never be used for anything more than a gentle paddle on a quite lake then the boat could be built quite lightly. If you were going to paddle a far northern river (and I have done so many times in my own strippers) you must be built more ruggedly). Also, a skilled builder will always produce a lighter boat simply because he knows how and to best use the materials. Finally, some woods and resins are lighter than others and you may not have easy access to the best materials.
Before digging into all the intricacies we must deal with the basics - what is the boat's surface area. These are the areas of the boats offered by NorthWest Canoe:
To calculate the skin weight we need to know what wood you are using and how much it weighs. Dry western red cedar usually weighs 28 pounds per cubic foot so one square foot of planking will weigh 0.58 pounds. You will sand or plane some of this off so the finished weight will be closer to 0.48. Typical laminating glass is six ounce boat cloth that weighs 6 oz. Per yard or 0.67 ounces per sq. ft. A good laminating job will use the same weight in resin so the weight per sq. ft of the glass on both sides will be 0.157 pounds. The hot coat weight varies depending upon how many you put on and how much you sand off. After weighing several of my boats I found that the finished hot coat ends up weighing approximately 0.08 on the outside. If you want a smooth coat on the inside it will weigh a lot more because it is so hard to sand and more will be left on.
So, our finished weight per sq. ft. will be 0.717 per sq. ft.
Would you like it lighter? Reducing the wood thickness works and I have used as thin as 1/8" with success. Also I have used 2 oz. Cloth on the inside. (Not recommended on the outside though. For every 1/16" of reduced wood thickness you save 0.145 pounds per sq. ft. For every ounce of glass reduced you save 0.026 pounds per sq. ft.)
If you intend to use your boat for serious tripping, I suggest you stick not reduce the thickness of the wood or the glass unless you are a careful paddler.
Of course, the skin is only a part of the boat. Rails, thwarts and seats add to the weight. Ash is the most commonly used material for these and it weighs about 48 pounds per cubic foot. Typical rails in ash will weigh about 0.30 pounds per lineal foot. The average thwart weighs about 0.40 pounds per lineal foot. Carved yokes vary so much that I hesitate to give a weight but three pounds is a good average.
Typical bow nylon web or cane seat will weigh 1.2 pounds, an stern seat will weigh about 1.3 pounds and a solo seat will probably weigh 1.8 pounds.
All of these weights can be reduced by about 40% if you use sitka spruce instead of ash and even further if you are careful in your sizing of parts. Now add about 1.0 pound for fastenings and two pounds for paint or varnish and 0.03 pounds per square foot for paint or varnish and you can calculate what your boat might weigh.
Now, keep in mind that all this is based on what I have observed over the years for amateur builders. My own strip built Winisk that endured a lot of abusive white water and tripping weighed 54 pounds. Your boat may weigh a lot more or even less. What I have provided here is just a guide. The finished weight is up to you.
Another question the boat builder asks is what are suitable materials?
For planking you can use western red cedar, redwood, basswood, white cedar, Spanish cedar, sugar pine, white pine or sitka spruce. I have used all successfully. Weights vary depending upon where the wood came from and how dry it is. Depending upon where you live these woods can be either cheap or unbelievably expensive. I have built boats using balsa wood and it worked quite nicely so you can use your imagination to some extent. Keep in mind that what ever you use must be dry, dry, dry.
I use System Three clear coat for laminating and then fill with regular resin. Using these materials and western red cedar I build 26' North Canoes that weigh 180 pounds and are durable enough for serious racing and camp use. You can use polyester but it will not be as durable or strong and polyesters vary in quality significantly between suppliers.
Rails, thwarts and seats can be made of ash, any of the mahoganies, basswood, sitka spruce, white cedar, Spanish cedar or even western red cedar. I do not recommend any of the pines or redwood because they are so brittle.
Do not use brass or steel fasteners. Use either bronze or stainless steel.
You can use most any good grade of enamel or varnish. I prefer the two part marine polyurethane paints and Z-Spar varnish.
Hope this helps you.
Happy Boat Building.