[PSUBS-MAILIST] Through hull penetrator

[Alan James via Personal_Submersibles]

Jon,
I sent this email out last year as an idea for using castable rubber in a electrical penetrator.
Hank is already doing something similar minus the castable rubber.
The idea is to buy a bronze reducer fitting of appropriate size from a marine supplier & machine
an o-ring grove in it. The bronze fitting Preferably has a conical reduction shape ( not shown in diagram ). The reducer compresses the epoxy under pressure in to the narrow area & stops it extruding through. Doug was having all sorts of problems epoxying pins straight through a fitting without reduction.
In this iteration I epoxy the wires & sheath in to the reducer. You could use pins which would
be more in line with G. L. as if the wires are sheared water could run through the individual
wire sheaths, but bend the pins. I looked closely at how my subconn penetrators were made, & they mold a thin rubber sheath over the cable about an inch back from where it enters the penetrator. So as
the wiring sheath compresses under pressure this rubber sheath moves with it. The drawing isn't the greatest but I can elaborate if interested. I have a 3000 psi test cylinder to test these but haven't got round to it.

 As this has created a lot of interest, I thought I'd follow up with a
couple of drawings of my through hull idea :) (Attached at bottom.)
I am using a common reducer fitting to butt or key the epoxy.
There are standard reducer fittings with o-rings.
I am going to silicone over the outer part of the fitting & along the
cable jacket. Then mold over this with the castable rubber to 
tidy it up. 
The theory is the silicone will compress under pressure on to
the jacket (which should itself compress), & seal the jacket better
than just epoxy.
I looked at a long video of Doug Jackson making through hulls
for his rov by epoxying in brass pins. They were failing badly in most cases.
I will never trust epoxy again.
https://www.youtube.com/watch?v=UDZQIDkWs4w
Regards Alan


From: Alan James via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
Sent: Friday, November 13, 2015 10:52 PM
Subject: [PSUBS-MAILIST] Castable Rubber

Was thinking about home made electrical through hulls & came
across this castable silicone rubber.
How to make a moldable castable rubber (homemade Sugru, Oogroo)
 
 

 
 
 
 
 
How to make a moldable castable rubber (homemade Sugr...
View on www.youtube.com
Preview by Yahoo
 
Basically it's builders silicone mixed with corn flour about 50/50.
There are other recipes with builders silicone & baby powder.
My thought was to pot wires inside a suitable bronze or SS threaded fitting 
& encase the electrical sheathing where it enters the fitting with straight silicone.
Then when hardened, cast the silicone / corn flour mix over the top to tidy it up.
The simple recipe may have a lot of other applications.
Cheers Alan

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