Jon, Jim, Hugh.......
I went through the same problem a while back after Cliff pointed out that
my hull penetrations weren't up to par. I had been using the "cubic inches"
idea rather than the "square inches" as Hugh mentioned.
The solution I have developed with help from Hugh ( thanks again, Hugh )
is to remove the entire window frame for the largest 24" main window
ring and replace it with a much thicker ring.
The calculations we worked out came up as needing about a 1-1/2 inch
thick ring ( by 6 inches long ) for the larger window with a 2 inch thick
plexi-base ring inside the thicker window frame.
The smaller 12 inch windows need the same thing but the "fix" will
include replacing the current assembly with larger windows ( 16 inch viewing
area ) and again much thicker window rings.
This is a big change so will be done sometime next year. In the meantime
my maximum depth will be limited to about 50 feet until the proper design has
been run through a comprehensive FEA to determine the exact dimensions. I too
was confused by the documents as it relates to how much material to replace
what was cut out for the penetrations.
This is still a bit of guess work because the documents are really
talking about penetrations in the tube section rather than the end caps, so an
FEA that relates specifically to eliptical head penetrations will be
required.
Basically.......I'm not WHACKING a new hole in there until all the facts
are in !
Frank D.