Re: [PSUBS-MAILIST] Which Through-Hull?

[Phil Nuytten <72020.572@compuserve.com>]

Hi, Shin:
        What are you going to screw your proposed penetrators into? That
is, will you weld in a threaded boss or weldelet (a short piece of
cylindrical, heavy-wall pipe, threaded internally, that is pushed into a
hole in the hull until it protrudes equally,and then welded inside and out
- or a threaded, contoured coupling that is welded on the outside only) or
will you weld in a smooth bore cylinder so you can use threaded fittings
with 'o' ring collars and a retaining nut inside? If you decide on a
threaded boss ( as most garage subs do) make sure that it is stainless
steel ( welds easily to mild steel) and has a very thick wall so that you
can drill it and tap it to the next largest thread size if you ever have to
. .for example, if you want to have a threaded hole that actually measures
1/2" in diameter ( like 1/4" NPT ) then the boss should not be less than 1"
in diameter - while 11/4" is better - an so on for larger sizes. The cost
of these, even custom made, is small compared to having to deal with a
rusted out or stripped penetrator down the road.
        For electrical thru' - hulls, take a double male pipe fitting  -
with a center hex wrench flat - either brass or stainless, and of a size so
that the male screws into your hull penetrator boss. Take an appropriate
tap and cut some threads on the inside smoth bore of the double male
connector ( doesn't have to be full depth threads - nothing will be screwed
in here)Get two or three long - at least 2" or 3" - thin - say 6/32 or
smaller - brass machine bolts and cut the heads off and dress the cut ends.
Get or make a female reducer coupling whose minor diameter will screw onto
the other end or your male connector ( the end that will not be screwed
into the hull boss.) and whose large bore is sufficient to take your cable
jacket with a 1/8th to 3/16th gap all round. Poke the bolts thru until they
protrude sufficiently to be able to solder onto( this will be the hull
interior), then space them equi-distant in the coupling bore ( use a thin
plexi or other plastic pre-drilled disc as a template/spacer)  cover the
spacer disk and the bolt ends with a ball of plasticine, being careful that
the disc doesn't shift. On the other end you have soldered  the two or
three wires of a length of cabtire (neoprene jacketted multi-conductor wire
- like heavy-duty extension cord) Clean the jacket after lightly sanding -
acetone or toluene) make sure at least 11/2" of jacket is inside the female
connector - pour the connectors full of two component, general purpose
rigid epoxy that has been heated to make it pour easily  . .you can use two
component polyurethane such as 3M 'Scotchcast' - it will bond to the
neoprene jacket well, but that flexible bond is not a requirement since the
portion of the cabtire in the connector sleeve cant flex, Properly done,
these are good to several thousand feet and are fully water-blocked if you
should damage the cable ( the water cant wick thru the solid bolts as it
would thru the multi-strand wires of a compression fitting) . Sounds like
lot of work - but pretty easy once you have it down pat and are making up a
bunch at a time. Be sure to pressure test each on by threading it into a
suitable 'T' - pressure gauge in one of the two remaining females, air
fitting in other - point it away when you first pressure up.  
Beats paying a hundred bucks+ a pop for tested thru-hulls. These should be
around ten bucks apiece.
        Sorry to be so long- winded - but with no napkin to draw on . . . 
Phil Nuytten