Pressure hull calc's

[Dick Morrisson <rmorrisson@unidial.com>]

I have been playing around with a hull strength program and decided to
test it out with the numbers Vance said he was considering for his
boat.  In a formula attributed to Roark, "Formulas for stress and
strain", 1961, the crush depth for a 42" hull with .25" wall and ribs on
12" centers would be 1505'.  This goes to a working depth with safety
factor of 2.25 (Navy) of 669' or with safety factor of 1.5 (ABS) of
1003'.  According to Flugge, "Handbook of engineering mechanics", 1962,
the crush depth would be 1673', and the working depth would be 743'
(Navy) or 1115' (ABS).  One of these is nearly the 1200' Vance mentioned
(and he did say approximate).  So Vance, or anybody, which calculations
are recommended and why.  Have there been any correlation studies on
theoretical versus actual crush depths?  Also, what is the criteria for
the "T-rib" design.  I am closing in on this one too and would
appreciate the help.  I expect the design is based on column loading of
the rib using the transferred load from the hull and a characteristic
length equal to the circumference.  Quite technical I know (read "dry"
and boring) but if anyone cares to comment (to the group or directly) I
would enjoy hearing from you.  Also, the safety factors I have used I
took from previous postings assuming they were accurate.
Thanks,
Dick Morrisson