[PSUBS-MAILIST] How thick to make the pressure hull? Some history.

["Michael B. Holt" <mholt@richmond.edu>]

I found an engineering text from 1934.  There's a chapter on
thin-wall cylinders.  The specific topic is boilers for steam.
Boilers in this chapeter are assumed to be riveted.  

First of all, the book demands a safety factor of five (5).

Pressure is assumed to be internal, of course.  To calcuate
the thickness of the wall, one must know the inside diameter
of the boiler AND the working pressure.  There is a formula
to find the thickness.  

But then the very next section says that one must know
the "Effeciency" of the joint.  This is the percentage
of reduction in strength of the cylinder as a result of
being riveted.  A "single lap joint" (the plates are
overlapping on the edge) is 50% to 60% of the strength
of the cylinder wall.  That's a low as it gets; the
highest efficiency ("Eff") is a "quadruple butt joint,"
which is 85-94% efficient.  (A quadruple butt joint
as two straps through which four lines of rivets are
driven.)

This is, of course, only a historical footnote at this
point.  It's of interest to me because I'd like to 
evaluate the design of a sub from 1864.  Even the builders
of those old subs acknowledge that they used boiler 
thinking to create hulls.

Offhand, I'd say "Don't do this at home."



Mike