Lapstrake ?

[seedtick]

don't know lapstrake - sorry

[shikeswithcanoe]

Those overlaps are going to add significantly to the rigidity of the hull. If I recall correctly rigidity is a function of thickness cubed. So those overlapped parts are going to be 2 cubed or 8 times as rigid as the non overlapped sections. Lets say 10 percent of the "planks" consist of overlap. So, that overlapped section is 8 times as rigid but only has 10 percent of the surface area, (8 times 0.1) so it contributes a value of 0.8. The non overlapped section contributes a rigidity of 0.9 (1.0 times 0.9). The total rigidity is 0.8 plus 0.9 or 1.7. So, for a twenty percent increase in weight you've gained a increase of rigidity of 70 percent.

Thats a back of envelope simple calculation that may well be a bunch of baloney. But if you think of the overlapped sections as stringers, I think it is apparent they do add significantly to hull rigidity.

Also, in a lapstrake construction your hull can have curvature in 2 dimensions and the joints do not rely at all on fillets for strength. Both these are positives in terms of hull rigidty and/or lightness in comparison to a pirogue.

I would suggest a lapstrake construction is something between a pirouge and a strip construction in terms of its generally characteristics. I suspect a well engineered lapstrake build could compete with a strip build or pirogue build in the rigidity/strength per weight category. And each build type has different advantages, disadvanges, and ways to do it wrong so it is neither particularly light or strong.

[JEM]

I've always like the lapstrake look. But it takes a lot of TLC if the exterior gets banged around because it's almost impossible to apply any fiberglass to the hull for protection. So wood quality becomes even more critical.

[Kayak Jack]

Lets accept your back of he envelope calculations as OK. The fasteners then become the weak point. I'd think that glue-nail construction would be a very good thing. I'd want epoxy soaked well into each of those overlapping joints.

BTW, lapstrake was the method of construction used on Viking boats - the last boats to ever successfully invade England's coast. Can't be too shabby.

[tx river rat]

length: 11' 6"
beam 27"
weight: 27 lbs.
These are the specs for the lapstrake,

Sparkys canoe is a 14 ft by 30 inches wide ,that means it is 2 1/2 ft longer and 3 inches wider and also has some small decks and it weighs 30 lbs.
Makin Mends built a thirteen ft Laker that weighed in the low 20s.
I have to agree with Jack here ,I am plenty skeptical of a lot of the stated claims. Longevity is another thing I would worry about.
Ron

[shikeswithcanoe]

Oh, KayakJack.

I am definitely referring to epoxied overlapping joints with THIN plywood since I was addressing the issue of lightweight boats. That whole fasterner thing would be almost a nonstarter. Of course the same could be said of pirouges and strip construction when you are talking about strong and lightweight boats. If you rule out epoxy useage the winner probably becomes skin on frame boats where you can lash it all together.

Note, I post as a person interested in boat building that understands a bit about engineering, not as any sort of expert boat builder.

[JEM]

Lapstrake is sort of like skin-on-frame, skeletal construction. Sort of....

[shikeswithcanoe]

A pirouge is sorta like a lapstrake with just 3 planks.

A strip boat is sorta like a lapstrake with lots and lots of planks

A skin on frame is sorta like a lapstrake thats very thick at the overlaps and very thin everywhere else.

Since a pirough, a strip boat, and a skin on frame can all be built pretty light if done just right I'd say the same applies to a lapstrake. Each just has slightly different challenges in construction, skill, design, materials and overall execution to get there.

[Kayak Jack]

A plywood stitch and glue kayak hull is a full monocoque construction. Exact opposite of a skin on stick kayak, where the strength is in the frame, and skin just covers it.

Lapstrake, it seems to me, is a semi-monocoque construction with most of the strength in the skin?

In general, I wouldn't see an advantage in any of the ways, only interesting and pertinent to applications in certain situations. In my eye, they are all beautiful (boats, planes, and women are elegantly shaped - not necessarily in that order of priority). Lapstrake always reminds me of Vikings' dragon ships - and that means adventure - even if it is setting on the front lawn.

[shikeswithcanoe]

If lapstrake was good enough for these vikings its goog enough for me!

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