[PSUBS-MAILIST] Drop Wieght

[Phil Nuytten <72020.572@compuserve.com>]

Hi, Adam:
        May I suggest that you stay away from ordnance cutters for drop
weight release. You can rig to test the conductivity of the circuit each
time, but that's no guarantee that the bolt will fire when you need it.
There is no practical way to test each individual seperator without
destroying it. Our experience with explosive cutters on subs, particularly
those subs that are worked almost daily,  has been uneven. If you replace
the cutter at the end of season or at the end or a specified number of
dives, and then test fire the removed one - well, most often they fire . .
.but sometimes they don't.  When they do fire, and come apart beautifully,
you're left thinking "Damn! that was a good one! - I wonder if the one I
just put on will . . .etc" Gets kinda frustrating. 
        Do you have provision for a thru'-hull (penetrator) anywhere?
Doesn't have to be at the bottom of the pressure hull, altho' it's cool if
it is . .one large enough to take a 1/4" or 3/8" 0r 1/2" stainless shaft
would be good for direct physical activation, but any size opening can be
used if you use as an activation port - can be as simple as a length of
synflex tubing with a small piston at the end, operated by an 'or' ring
sealed, threaded rod in the cabin, with a handle to wind the rod/bolt into
the fluid-filled tube - to move the piston - to get out of the way of the
over-center swing hook - that's attached to the weight- that drops off the
sub that Jack built! - or one of many, many, variations on mechanical
releases. We have used a clever design that divides a 100 lb drop weight
into 10 stacked plates - each rotation of the thru'-shaft drops 10 lbs -
nice if it's not an emergency, but you you need a little extra upness if
you have over-filled the speciman basket or whatever.
        Magnets are OK - you can sandwich a mild steel disk in solid
neoprene or cast polyurethane or silicon rubber or fibreglass ( so it
doesn't rust) and attach a nylon bag filled with lead-shot ( getting harder
to find these environmental days) - usually about 20 to 30 lbs - use a
samarium-cobalt or neodymium magnet in a nylon sock ( no scratch) on the
inside of the edge of your vision dome - then you pull it off  ( the
magnet!) when you want the weigh to release - bit of a pain if you're
diving in a harbor, tho' - you wind up with a big clump of rust needles
where the weight attaches - looks like a sea urchin!
        Sorry, I'm rambling . . . Explosive bolts sound very James Bondish,
NASA, etc., but don't give the same piece of mind that a  chunk of
stainless rod does, IMHO.
Phil Nuytten