Lightest form of construction

[GlacierJohn]

My hunting buddy and I just finished a Devlin Designs stitch and glue duck boat "Snow Goose". The boat came out great and the stitch and glue method of construction was really easy, the boat is ready for paint after three weeks of evenings and weekends plus five days after Christmas. We won't be able to launch the boat until spring but I'm confident it will float nice and high.

That said, the boat approx 6' beam by 16' length by reletively high freeboard is quite heavy. Now I want to build another lower freeboard, slightly smaller duck boat for shallow ponds and marshes. I used to build surfboards, and worked on fiberglass and cold molded boats in Hawaii and am interested in the lightest for same strength method of construction. The options I am considering are:

1) Devlin style stitch and glue.
2) Stitch and glue with 1/4" plywood for shape of boat covered with heavier fiberglass.
3) Foam or balsa core fiberglass.
4) Cold molded, cedar over partial bulheads and frame.

Any suggestions? Thanks in advance for your input.

John

[gonzo]

Cold molded is lighter than strip plankig. However it is more labor intensive and difficult. If you use plywood, 3/8" is adequate without fiberglass. It would be possible to go thinner if you have a small motor.

[tspeer]

These aren't fiberglass, but if you really want light weight, you might check out http://www.geodesicairoliteboats.com/boats/. I think it would be interesting to consider replacing the wood frame with pultruded fiberglass stock. That would increase the weight somewhat, but there would be nothing that could rot.

[GlacierJohn]

Thanks guys,
I was out of town for a few days so wasn't able to view your replys until today. Tspeer those geodesicairlite boats look very light and I might want to build a canoe or small skiff some time, but I think that method of constructing my not be strong enough for a duck boat which will have to carry 2 hunters, dog and gear plus stand up to a fair amount of abuse.

Gonzo thank you as well for the reply. After researching this site some more, it appears that cold molded wood or foam-core fiberglass would be the way to go for complex curved sailboathull shapes but the hard chine flatbotton duck boat shapes I'm thinking about are probably best done with stitch and glue plywood construction.

Originally Posted by GlacierJohn

Thanks guys,
After researching this site some more, it appears that cold molded wood or foam-core fiberglass would be the way to go for complex curved sailboathull shapes but the hard chine flatbotton duck boat shapes I'm thinking about are probably best done with stitch and glue plywood construction.

Lightest is always going to be a sandwich. And with the foam core coming in flat sheets it means that building a hard chine flatbottom will be dead easy.

On the other hand if you want it to be real light and bashproof then you need to use exotic fibres (kevlar for bulletproof [grin] ) and epoxy, and you could end up getting a whole lot more expensive than stitch and glue, depending on local ply prices of course, but probably save something like 10 to 20% weight. So you need to balance which you can stand being heavy better, the boat or the price tag:-)

[gonzo]

Sandwich construction is heavier than plywood in smaller sizes. There is a minimum skin thickness possible. This makes a small boat overbuilt. Also, because of the need to be puncture resistant, the minimum skin thickness in not enough. As to Kevlar being bulletproof, it only works in blankets. Once it is laminated with resin into a rigid panel, it is brittle.

[yipster]

.
http://www.geodesicairoliteboats.com/boats/ impressed me, first time i think to see airplane frame tech in boats, hasnt that taken flight? skinstrenght maybe? size? guess i better dive deeper in the FAQ's.

[gonzo]

Skin on frame boats have a long history. From Eskimo Kayaks and Irish curraks to Kepler folding boats. New materials make them lighter. Imagine hauling a boat covered in narwhal skins