This is a common when you try to apply the wrong solution to a problem. The
application you describe requires a flanged portlight with a lip. The lip
sets into the welded tube and is sealed with polysulfide rubber caulking.
The flange is designed to bolt to the welded tube flange trapping the inside
hull liner between the portlight and tube. This is the traditional way
portlights are fastened to steel hulls. Additionally, these portlights use
armored glass and are also equipped with deadlights on the common hinges for
safety and they are usually bronze. Unfortunately, they are also expensive.
I use the same type. I had mine custom cast by Davies in London. No, they
don't have a Website. Depending on size, they will cost from $500 to $1,000
each. Normally, you pick the portlight, then weld up the matching tubes to
suit. If this has already been done, it was probably done to fit an
available portlight. I would ask the previous owner where to find it.
Steve

wrote in message
oups.com...
Hi there!
Does anybody know how to install a porthole that is designed for 1/4
inch (6 mm) thick fiberglass in a steel hull that consists of 1/8 inch
(3 mm) sheet metal on the outside, welded to 3 inch (75 mm) angle iron
and 5/8 inch (16 mm) wainscoating. Total thickness roughly 4 inches
(100 mm). Any advice (preferably with drawings or links to websites)
very welcome. Thanks in advance-Przem