RE: [PSUBS-MAILIST] Through Hulls

["Alec Smyth" <Asmyth@changepoint.com>]

Dan,

I know far less about electrical through-hulls than some folks here. However one thing I can say I've discovered is that the commercially available ones are not uniformly expensive. I've bought commercial connectors off Subconn and Sea Con. In both cases I found helpful people who pointed me to their less expensive product lines when I explained I was a home builder.  You'd be amazed at the price differences between their first estimates and what I ended up getting. Try SeaCon's rubber molded series, for example. They've been around for decades and are in the sub-hundred-bucks price range. To me the peace of mind is certainly worth that much.

Subconn have one connector which is not one of the cheap ones, but which might be of interest to anyone using trolling motors. It's got 4 conductors rated for 50 amps each, which happens to be just about right for a pair of trolling motors. Of course it does violate ABS rules to have both polarities go through the same penetration. But if you can live with that (e.g. by protecting your circuit so as not to exceed the 50 amp limit), you get the 4 cables you need to the outside with a single failure point and for less than $400.

I think if I was making an unmanned vehicle, I'd shoot for making my own penetrators. But if its my skin, and the boat is being designed for significant depth, I'd consider commercial ones.

cheers,

Alec

-----Original Message-----
From:	Dan h [mailto:machine@epix.net]
Sent:	Thu 11/21/2002 10:03 PM
To:	personal_submersibles@psubs.org
Cc:	
Subject:	Re: [PSUBS-MAILIST] Through Hulls

Thanks a lot Walter

I didn't think capturing the jacket of a cable like that would be enough to
keep it secure at that kind of depth.  I was planning to epoxy each
conductor of my cable separately to ensure it wouldn't slide through and/or
leak.  My way is far more complicated and doesn't really keep water from
getting into the cable jacket.  I'll make a test piece with your method in a
few days.

Thanks again!
Dan H.

Walter Starck wrote:

> 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
> The premiere publication of diving and the ocean world.
> www.goldendolphin.com

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