There are lots of sources of materials density out there.

http://www.rfcafe.com/references/gen..._materials.htm
shows:

Aluminum at 171 lb/cu ft. Divide by (12*8) to get approx. 1.78 lb/SF for
0.125 aluminum.
Plywood (5/8 thickness construction grade) is 1.77 lb/SF (or 34 lb/cu ft)

So I stand corrected. 1/8 aluminum weighs about the same as 5/8 construction
grade ply. Maybe, when I calculated this a few years ago, I used a
different grade or species of plywood, or alloy of aluminum - I honestly
don't recall. But either way, it gets you into the ballpark. There are
relatively few elegant small boat designs using material this heavy.

Sal's Dad

--

as 1/8 aluminum weighs about the same as 3/4
ply.

If you divide 2.7, the density of aluminum, by 6, you get .45. I
thought plywood was heavier than that.

On Fri, 7 Dec 2007 15:33:51 -0500, "Sal's Dad"
wrote:

Aluminum at 171 lb/cu ft. Divide by (12*8) to get approx. 1.78 lb/SF for
0.125 aluminum.
Plywood (5/8 thickness construction grade) is 1.77 lb/SF (or 34 lb/cu ft)

So I stand corrected. 1/8 aluminum weighs about the same as 5/8 construction
grade ply

I thought a figure was a bit high. It is, slightly, but had I known
the difference was a small as it is[I will take your figures] I don't
think I would have bother to post anything. It did smoke out some
interesting figures. Plywood tends to be about as dense as the wood it
is made from, it seems. The texts seem to give the density of woods in
pounds per cubic foot but with a modern calculator[HP48] any and all
units are convenient.

Casady