Re: [PSUBS-MAILIST] Through Hulls

["Walter Starck" <wstarck@ozemail.com.au>]

Dan h wrote:
" A description of how you design your through hull electrical
 connectors, what type of cable is better and for what reasons would be
 vary helpful to many of us in here.  This would be of far more use to
us
 amateurs.   Please describe how you recommend building an electrical
 through hull."

The following is for a continous (i.e. non-disconnectable) thru hull
fitting.

Start with a male NPT to metal tube flare fitting for tubing of the same
size as the cable to be used. Remove the flare nut, face off the nipple
in a lathe and bevel the resulting face at 45° sloping inward.  The i.d.
of the fitting can be bored out slightly if required to accept the
cable.

Use cable in which the insulated conductors are embedded in a solid
outer casing.  The common type that uses a fiber filler inside a tubular
outer cover should be avoided.  To effect a seal, pass the cable through
the original flare nut, followed by two O-rings, then the modified
fitting.  When the nut is tightned the O-rings are compressed inward by
the beveled inner face of the nut and by the inward sloping face on the
modified fitting.  This compression squeezes the O-rings into the outer
cable covering creating an annular depression and locking the cable in
place with a very effective watertight seal.  For use in depths of a
thousand feet or less this type of fitting is cheap, robust, easy to
make and highly reliable.  The fitting is of course used by drilling and
tapping to install it where required.  Depending upon thickness and
curvature of the hull a flat boss may be required for attachment.

Disconnectable through hull fittings are somewhat more complicated but
can also be made using the same cable sealing method but more complex
machine work is required as both plug and receptacle fittings must be
fabricated from bar stock.  They are joined with a pipe coupling nut
with O-ring seal  and employ an internal electrical connector for that
connectivity.

Walter Starck
Golden Dolphin Video CD Magazine
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