Richard Casady wrote:
On Wed, 5 Dec 2007 07:41:59 -0500, "Sal's Dad"
wrote:


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.

Casady


plywood floats.

Aluminum don't.

What am I missing here?

On Thu, 06 Dec 2007 18:32:10 -0600, cavelamb himself
wrote:

Richard Casady wrote:
On Wed, 5 Dec 2007 07:41:59 -0500, "Sal's Dad"
wrote:


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.

Casady


plywood floats.

Aluminum don't.

What am I missing here?

A clue.

Casady

Richard Casady wrote:

On Thu, 06 Dec 2007 18:32:10 -0600, cavelamb himself
wrote:


Richard Casady wrote:

On Wed, 5 Dec 2007 07:41:59 -0500, "Sal's Dad"
wrote:



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.

Casady


plywood floats.

Aluminum don't.

What am I missing here?


A clue.

Casady


I thought most aluminum alloys weighed in at .1 pound per cubic inch.
Except 6061 which is only .09 lbs/cu.in.

Ply was .025 to .033 lbs/cu.in.

So clue me in.

On Thu, 06 Dec 2007 23:22:23 GMT, (Richard
Casady) wrote:

On Wed, 5 Dec 2007 07:41:59 -0500, "Sal's Dad"
wrote:

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.

Casady

It may be.
Black ash 0.54
Birch 0.67
red cedar 0.38 (!!)
see the table here...
http://woodsgood.ca/woodDensity.htm

Regards

Brian W

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

"Sal's Dad" wrote in message
...

I'm not sure what you mean by "semi tunnel" but I built an Atkin Rescue
Minor with fully protected prop and rudder. Or you can modify the transom
of any skiff to give you a bit of a tunnel effect with an outboard - at
the loss of some "lift".

There are some "tunnel" designs for running an outboard a few inches higher
that just have a small tunnel at the rear of the boat. When I was really
reading a lot about boat building a few years ago I recall reading about
some of them.


--
Bob La Londe
Fishing Arizona & The Colorado River
Fishing Forums & Contests
http://www.YumaBassMan.com



--
Posted via a free Usenet account from http://www.teranews.com

I modified my Bolger Diablo along those lines - It had a 20" transom, and I
wanted to run a "short shaft" outboard. It worked ok 90% of the time, but
ventilated like h3!! when accelerating. So I cut a notch out of the
bottom - maybe 2 or 3" high into the transom, 16 " forward into the bottom
panel, and 8" wide. Sort of a mini-tunnel. I'm sure this causes a small
degradation in performance, but gains me a few inches of draft.

I'm sure you could take any skiff design, with a flat bottom, and play
around with this. I would start with a really deep tunnel, and high
transom. If that seems too much, just cut down the transom (and glue foam
into the top of the tunnel) until you get the desired performance. You
might be surprised.

But, if you are going to cut a big notch in the bottom, make sure there is
enough bottom left at the transom to provide lift. Maybe extend the panels
out beyond the transom, on either side of the tunnel - you can always cut
them off. If there is a good high-speed tunnel design for home-builders, I
haven't seen it. Atkin had a bunch of low-speed tunnels, you might take a
look at the Atkinboatplans.com website for ideas.

Sal's Dad

I'm not sure what you mean by "semi tunnel" but I built an Atkin Rescue
Minor with fully protected prop and rudder. Or you can modify the
transom of any skiff to give you a bit of a tunnel effect with an
outboard - at the loss of some "lift".

There are some "tunnel" designs for running an outboard a few inches
higher that just have a small tunnel at the rear of the boat. When I was
really reading a lot about boat building a few years ago I recall reading
about some of them.

"Sal's Dad" wrote in message
...
I modified my Bolger Diablo along those lines - It had a 20" transom, and I
wanted to run a "short shaft" outboard. It worked ok 90% of the time, but
ventilated like h3!! when accelerating. So I cut a notch out of the
bottom - maybe 2 or 3" high into the transom, 16 " forward into the bottom
panel, and 8" wide. Sort of a mini-tunnel. I'm sure this causes a
small degradation in performance, but gains me a few inches of draft.

I'm sure you could take any skiff design, with a flat bottom, and play
around with this. I would start with a really deep tunnel, and high
transom. If that seems too much, just cut down the transom (and glue foam
into the top of the tunnel) until you get the desired performance. You
might be surprised.

But, if you are going to cut a big notch in the bottom, make sure there is
enough bottom left at the transom to provide lift. Maybe extend the
panels out beyond the transom, on either side of the tunnel - you can
always cut them off. If there is a good high-speed tunnel design for
home-builders, I haven't seen it. Atkin had a bunch of low-speed tunnels,
you might take a look at the Atkinboatplans.com website for ideas.

Sal's Dad

That's basically what I figured. What I am really looking for is a shallow
water runner for an outboard. I suppose I could go with an air cooled mud
motor, but I already have a couple regular outboards. I looked at
converting one to jet, but there is no jet available for one, and the jet
available for the other is pitched for a smaller motor. My motor over-revs
with it.

I'll look at the Atkin designs. I'm figuring if I get this the way I want a
28-35mph top speed is all I can expect. That's about what I get out of my
current shallow water boat (16' flat bottom jon). 28 with one motor and
35-37 with the other. (gps speeds)

I'm not sure what you mean by "semi tunnel" but I built an Atkin Rescue
Minor with fully protected prop and rudder. Or you can modify the
transom of any skiff to give you a bit of a tunnel effect with an
outboard - at the loss of some "lift".

There are some "tunnel" designs for running an outboard a few inches
higher that just have a small tunnel at the rear of the boat. When I was
really reading a lot about boat building a few years ago I recall reading
about some of them.



--
Posted via a free Usenet account from http://www.teranews.com