Hi Marinos,
On Sun, 2010-07-18 at 11:59 +0300, Marinos Koutsomichalis wrote:
> I want to make extension cables for my hydrophones, so I can dip them
> further down,
To what depth do you want to have the joints? And do you really need
something you can unplug, or would just having longer cables permanently
be OK?
Underwater connectors definitely do exist, I used to use them when I was
working with underwater cameras in the North Sea. However the ones I am
thinking about were generally smeared with silicone grease to get a good
sliding fit, so I don't know what the contact resistance would be.
I have not yet been able to find any truly submersible connectors (i.e.
good for more than a few metres deep) on a quick web search. There are
lots of waterproof connectors available, but most of these are intended
for dousing with water at low pressure - deck fittings, that sort of
thing. A good place to start would be a supplier of underwater
photography equipment, as connecting cables between camera housings and
flash gun housings is a regular requirement.
However you will still need to be able to connect your hydrophone cables
to the waterproof connectors in a waterproof way. Are your cables
completely round in section? What diameter are they, and what is the
outer covering material?
If you don't need to be able to plug and unplug the connection then
things become much simpler. There are commercially available joint
potting kits (a couple of plastic shells that wrap around the joint, and
some potting compound to fill them up). You can do much the same thing
by making up the connection in the usual way - something like soldered
joints covered with heat-shrink tubing - then sliding a short length of
PVC tubing over the whole connection and filling the tube with something
that will set, but not go completely hard, like RTV silicone sealant
(marine grade is available).
In an emergency it is also possible to use electrician's
self-amalgamating tape (lots of it, applied carefully), to make a
waterproof cable connection. It's a bit of a bodge, but I have made
cable joints that proved good for 50 metres of depth this way
(completely surprised me that this actually worked!).
Richard
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