Hi Alan. I bought these Firgelli actuators because of the simple design.
Basically it's a piece of extruded aluminum tube and two end caps. The
square tube is continuous without seams. It has ribs inside
that stiffen the tube, and are used to hold the motor in place. I've
taken one apart and it's very simple. To pressure compensate the unit I just
need to bore a small hole in the back end cap for the oil to move
through.
To seal the whole thing I'm covering the tube/body with fiberglass up to
the end where the rod pokes through.
As for the wires, I'm using a small PVC female threaded coupling that is
fiberglassed into the back end and the wires pass through this coupling. It
gets a hose barb fitting screwed into it, and clear vinyl tubing to the
thru-hull where there's another hose barb threaded into the welded thru-hull
nipple.
For general purpose sealing of all tubes, hoses, fittings and whatever,
after all the clamps and/or parts are threaded, I'll be using a liquid
urethane product call Vulchem as a secondary sealer. You paint it on over the
hose clamps and threaded fittings and it creates a flexible but tough
over-seal. I've used it for many years and it is tough stuff. The beauty is if
you need to dis-assemble a connection you use a knife and slice through the
Vulchem, then peel it off. It has the consistency of rubber, resists sunlight,
can take a beating, stays flexible for years, and comes in gallon cans.
I first saw it used as a pour-in rubber liquid around built-in swimming
pools where the pool "cap stones" meet the surrounding concrete patio. It
lasts for years in direct sunlight and will withstand foot traffic. I've used
it for sealing things like galvanized roof-top air conditioning ducts ( big
stuff on commercial buildings ) and gone back years later and it's still
looking good. You could think of it like the Rhino coatings used on pick-up
truck beds. Chemically similar.
As for the articulating arm.....well, I'm pretty busy trying to get my
sub in the water so the arm will have to wait. Besides, that thing Vance is
working on looks like a real possibility. I saw the one used on the old Delta
sub ( in a video ) and it was amazing how simple and quick it was. No
wires, tubes, hydraulics or anything. Just a grabber on a swivel joint that
could extend in and out. I think that video is still around. If I get a chance
I'll see if I can find the link to it. I think it was on Youtube. The old
Delta sub is still in use today. I visited with the guys who own it in Moss
Landing ( near Monterey ) and they were working under contract for
the Monterey Bay Aquarium folks, doing maintenance on under water
seismic sensors in the Monterey Canyon. Something about measuring land slides
etc.
Frank D.