"Bruce In Bangkok" wrote in message
...
On Thu, 10 Dec 2009 19:03:00 +0000, Justin C
wrote:

In article
, Bob
La Londe wrote:
On Nov 29, 6:28 pm, "Bob La Londe" wrote:
I find it interesting that a lot of the small boat aluminum designs
seem to
say the main hull should be 3/16 and yet .100 is used in a heck of a
lot of
commercially available small boats. .125 is considered heavy duty. Is
it
just CYA?

Anyway, getting back to my original point. A lot of commercially
available boats seem to be made out of a lot light sheet than the
designers are reccomending in the boat plans they are selling.

http://www.seaarkboats.com/boat.php?...&boat=Big+Easy

For example: The link above is to a medium V design 24 footer. The
specs says .125 thick sheet. I can't buy a plan to build a boat that
size designed for .125 sheet. Most of the ones I have seen want to
spec .1875 which basically means .190. Now why is that? Is it just
the typical over building to cover your dearie aere, or are all those
commercial boat builders building inadequate boats and damn the
liability?

Could it be something to do with the ability of a professional to make a
good weld in that thickness, where an amateur might just be left with a
big hole? Maybe the plans are expected to be completed by self-builders
without the skill of the pro, and a margin for error is built in.

That is a good point. I'm not a great aluminum welder and thin aluminum is
a trick for me. The thinnest I have done with a MIG welder is about .043,
and the thinnest I have been able to do a fair job on is about .075.


Justin.

I don't think it is the welding as much as the warping. If you assume
at least minimal skills and reasonably suitable equipment a welder
should be able to weld thinner then 1/8". Perhaps not with stick but
using TIG it is not a difficult feat.

The difference, I believe, is the warping. Thin Aluminum would be all
over the place as soon as you struck an arc and without a really fancy
set of jigs and fixtures I doubt that anyone could get it flat. My own
thoughts are that the thinner thickness' are specified at thickness
that you might get away with without extensive fixtures.

1/8" is actually pretty easy. Fixturing is certainly the way to go.
Warping is certainly a big issue, which in part led me to the idea for the
other thread I started.