Re: Materials/parts...

[Phil Nuytten <72020.572@compuserve.com>]

 Subbers:
        Just a quick jump in on the sub hull subject: Typically, commercial
subs (cylindrical) are made from pipe sections up to about 24" dia - after
that, the pipe is too heavy for its potential pressure rating.  Any boiler
shop, shipyard, or water tank/gas tank fabricator can roll up a cylindrical
hull with very little cost and effort. Mild steel  runs at about  500 lbs
per cu. ft and has a tensile of about 50 to 70 depending on grade, . A
rolled plate of the 'Kitteridge' size should'nt cost more than a few
hundred dollars. Propane tanks are excellent starting points and  they are
very cheap because of high volume. Since the thickness vs the dia  is 
typically such that the tank will have to be ring stiffened ( the internal
pressure inflates the tank so that the failure mode is material yield .
.whereas external pressure causes failure at a much lower pressure through
assymetric buckling) you can get in through the hatch cut- out and weld the
rings inside in two or more pieces. You should use a doubler plate over the
hatch to hull area 'cause the stress is unacceptably high in the right
angle joint - a way around that is to use a T stiffener externally,
perpendicular to the weld - this isn't too often done because not many know
that it can be! Hope this helps!
Regards 
Phil Nuytten