----- Original Message -----
Sent: Wednesday, August 08, 2001 3:44
AM
Subject: [PSUBS-MAILIST] question about
general design?
"Is it better to put as much stuff outside
the crew compartment so that the amount of ballast necessary to reach neutral
bouancy is minimized or to focus on putting as much stuff inside as possible
so that you minimize the number of holes in the crew
compartment?"
Depends on your design. I've seen 'em built
both ways. Keep in mind, placing stuff outside will add to the
displacement, and could add to the buoyancy of the boat, if the pods you put
things like, say, battery packs in displace a volume of water that weighs more
than the pods themselves do. These are factors you must consider
during the design phase. You can buld a sub with all the goodies inside
or outside the pressure hull; that's up to you. Generally, I think
keeping it all inside makes the design math simpler, if nothing else.
But it all depends on how much stuff you have, the size of the pressure hull
you intend to build, and so forth.
"Second question. Are off the
shelf air tanks that you would get at Home Depot that are rated up to
125PSI sufficient for storing pressurized air for blowing your
ballast?"
Nope. Stick with high pressure air
tanks. Lots of reasons why.
We'll talk later...
"My sub would be rated to perhaps 50ft
and operated at more than say 25ft."
Generally, I don't recommend that people try to
build a flimsy sub. Build it stronger than you think it needs to
be. After spending all the time and money to build anything, you'll be
glad you built a good one; from a standpoint of functionality,
especially if some unforseen circumstance takes you deeper than you
planned to go.
"And if not, what is recommended."
Standard high pressure air tanks. Many guys
use SCUBA tanks.
"What mechanizism or used to hold drop
weights in place. "
A simple mechanical linkage will work. A
stainless shaft penetrating the hull via a watertight coupler (machined sleeve
with O-rings); there's a lever on your end, and a cam-lug on the end that
connects to a key-way in the drop weight. Turning the lever rotates the
shaft, aligns the lug with the keyway and the weight freefalls
away.
"Solenoids or Pneumatic. I assume
they would have to be deadman type devices like air breaks ."
Yeah, you can do that kind of thing, but it's a
hassle. The bathyscaphe TRIESTE had a hopper filled with lead shot,
and a valve held shut electromagnetically. When the power was cut (or
failed), the valve automatically opened, the lead shot dropped out, and the
boat came up. But this is a high-dollar project intended for really deep
use. For the kind of boats guys like us build in our backyards or
garages, the mechanical linkage is good.
"As soon as I get a scanner, I'll send you some
diagrams. Thanks Ken."
For sure. Talk to ya later.
Pat