This question has been gnawing at me for the past week or so. Some recent posts have made estimates about weight gain when adding accents of heavier wood. I remeber a very informative post by Mike Loriz (I think I got the name right) from several years ago where he made a couple of kayaks out of a mixture of oak, walnut and cherry. I believe he used strips that were a "fat eighth" or 5/32 of an inch. His boats ended up weighing under 40lbs (if my memory is correct - I can't find the post).

I wanted to get an idea of how the numbers worked out for myself. First, I used the surface area I found for the Cape Ann Expedition (no reason, its the first one that had surface area listed). The hull was 33 ft^2 and the deck 25 ft^2. I skipped coaming, hatches and bulkheads.

Next I used the densities of 3 woods. Cedar at 23 lb/ft^3, Fir at 33 lb/ft^3, and Walnut (or maple) at 42 lb/ft^3. This covers a pretty good range of densities.

I also calculated the weights at a strip thickness of 1/4, 3/16, 5/32 and 1/8 of an inch. I figured about 10% loss from shaping and sanding. I'm also guessing that a boat made of thinner strips would likely use narrower strips as well to limit the loss of thickness when shaping to still around 10%.

A cedar boat had a wood weight of 25.0 lbs when built with 1/4 inch strips.

A 100% fir boat's wood weight was 35.9 lbs with 1/4 inch strips. 3/16 inch strips drops this to 26.9 lbs.

A 100% walnut (or maple) boat's wood weight was 45.7 lbs. 5/32 inch strips drop this to 28.5 lbs and 1/8 inch strips gets down to 22.8 lbs.

These last two cases are for a boat that is has its entire surface area (deck and hull) made from the same type of wood. If the heavier woods are used as accents, the weight gain would be less.

A boat from 90% cedar, 5% walnut and 5% fir has a wood weight of 26.6 lbs from 1/4 inch strips.

A few general observations.

1. The weight of a heavier wood can be offset by using thinner strips. Mike's post made a pretty good case that the heavier woods can use thinner strips for similar stiffness and strength. I'm not sure about building a cedar boat from 1/8 inch strips, but I know that Rob Macks uses 3/16 inch thick strips on his boats.

2. The wood weight of the surface area account for 25 lbs and these boats typically weigh 40 to 45 lbs. That means the rest of the boat (hatches, coaming, bulkheads, epoxy, fiberglass and rigging) weighs around 20 lbs. If one is to worry about the weight of the wood, equal care should be taken to limit of the extra 20 lbs as well. It won't do much good to save 2 or 3 lbs of wood weight and have 6 extra pounds of epoxy on your boat.

3. The surface area when formed out of 1/4 inch strips has about 1.1 cubic feet of wood in it. 3/16 inch strips drops this to 0.8 ft^3.

4. Building a boat from 3/16 inch cedar strips weighs 18.8 lbs - saving 6.2 lbs.

Here is a table of what I calculated. (sorry about the dots - trying to get a table to form! - only took 4 tries)

.........Strip thickness.......1/4.....3/16.....5/32......1/8.....inches
.............100% Cedar....25.0.....18.8.....15.6....12.5.....lbs
...................100% Fir....35.9.....26.9.....22.4....17.9.....lbs
............100% Walnut....45.7.....34.3.....28.5....22.8.....lbs
90%Cd 5%Wl 5%Fr....26.6.....19.9.....16.6....13.3.....lbs

I am pretty sure that none of this is new. I just felt like sharing.

Steve