My boats are built with 4 mm plywood. Thats just a bit thicker than 1/8". Only 26% thicker.
Years ago, I studied the buyers' guide in the Canoeing and Kayaking magazine. Canoes and kayaks varied in weight from 40lbs up to 65 - and even 80lbs! I was astounded at the wide variation. Studying further, I discovered that there were at least three ways to get a 40 pound boat.
(1) Steal one. That didn't seem feasible.
(2) Spend $3,000-5,000 to buy one. That didn't seem either feasible OR intelligent.
(3) Spend $600-800 and build one. Interesting!
Note: costs of store-bought boats have dropped, say, $1,000, while the cost of kits has risen by, say, a few hundred dollars. Market forces at work there.
When I built my first kit boat, the directions said it would take something like 106 hours. "Yeah, right!" So, I doubled that. Dividing the cost difference by the the doubled hours yielded a result of (as best I can recall) $16-17/ hour. Not the path to becoming a millionaire, but still decent wages for 20-25 years ago.
I've built 3 kayaks and a canoe. None weighed over 42 pounds. Most of the excess weight is from excess epoxy. All of these were and are used as a tool to get a job done. None has ever had a problem with structural integrity. The kayaks are of a full monocoque construction. All of their strength comes from the skin, like an egg, having no internal framing.
Some builders have built cheaper, and or lighter. Each builder builds to satisfy himself.
