I was just reading the ABS rules and it says that if you have a
cylinder of air or oxy inside that if it is totally released the internal
pressure should not be greater than 15 psi. Also if you had an air leak then
the internal pressure could rise so that when you hit the surface the hatch could
pop before you vent the MBTs. You also have to have a relief valve with an
isolating valve wired open. What do you set the relief valve at. Also the
name plate on the vessel must show maximum external pressure and maximum
internal pressure. This would also be required to determine the number of
bolts holding the viewports in. Hugh From:
owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of vbra676539@aol.com Minimum internal pressure? Hmm.
I'm not sure it matters as even a hard vacuum would be marginally less than
your 15 pounds. Maybe I'm missing the point. For the seal test, an inch of
vacuum would be more than enough. Half a pound or so, I think. -----Original Message----- Thanks Vance, that’s good to hear. Another
question. What is the minimum internal pressure allowable in a PVHO??
I have seen reference to 15 psi but the catches etc need to be
looked at. Regards, Hugh From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org]
On Behalf Of vbra676539@aol.com Hugh, No Perry that I ever heard of completely flooded a battery pod. My
two experiences had partial flooding, taking on water steadily while we
surfaced and managed the recovery. Typical to those events was that the pod
went heavy on the back upon surfacing due to the forward mount of the MBTs.
Complete flooding would shift your CG to the heavy side and move your CB. But
certainly not enough to drag the sub all the way onto its side. The metacentric
heigh would be rotated that way, but not overcome. Worst case, the wet pod
would become your keel, more or less. A 20"X120" pod takes on about half a ton of water in the
worst case scenario. This may be glaringly obvious, but don't forget the
battery volume displacement when you are doing the figures. Batteries aren't
quite as heavy underwater as they are in air, natually, and whatever volume
they take in seawater is subtracted from the flood quantity. Plus the acid is
lighter than seawater. It isn't a calculation for weight gain. It's
strictly a negative displacement puzzle. How big are your ballast tanks and how are they distributed (side
to side or fore and aft)? The Perrys are shoulder tanks, of course, and that
was done for a couple of reasons, mostly to clear the bow for viewing, but
secondarily to offset the heavy pod in case of flooding. You could vary the
lift if needed. One of the standard "hanging-in-the-paint-locker" items
was a pair of big teardrop floats with short pennants and snap shackles
attached. These lines could then be wrapped around the guard rail wherever
necessary and snapped back to themselves for lift in case of a flooded or
partially flooded pod. The swimmer does that, and you should be able to
figure how many buoys and what size to compensate for the unplanned loss
of buoyancy. The idea is to spot the buoys where needed for lift to bring
the sub level and steady on the surface before opening the hatch if that turns
out to be necessary. Bailing out would be an absolute last-ditch measure offshore, and
never done to my knowledge, even with an extinguished fire on board and
the boat full of smoke, which I did once. That's what the BIBS and scuba masks
are for, to keep you breathing and clear eyed until the topside crew can
save you and the million dollar underwater pickup truck. We surely didn't want
to lose one of those subs, and didn't. It was never even close. Planning is the
key. Phil and his crew do vacuum checks on the void spaces (pods and
hull) before every dive. We didn't do that, but I'm betting we would today.
It's just too simple and elegant a solution to ignore. A couple of minutes
while buttoning up will check for leaks and set your O-rings so that this
wouldn't or at least shouldn't ever be a problem. Vance -----Original Message----- Vance, I am interested in your comment that “if flooded it would
stand the sub on its tail.” Is that a must to avoid? How many subs are able to have a
compartment flooded and not come up on some obscure angle? I.e. If a
battery pod is flooded would it not make a sub come up on its side so
that the hatch if opened would flood? I am not being facetious but
concerned about mine’s ability to come up with a compartment flooded. I
haven’t done the calcs yet but what designs would qualify as same. My
philosophy or belief was as long as you can get to the surface you are
rescueable. Interested in your comments on this one. Hugh From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org]
On Behalf Of vbra676539@aol.com You can't dfepend on neutral buoyany for a module as you describe.
It will need to have a variable ballast tank and fairwater tanks to hold the
unit up on the surface. Along with the controls for that system, you will need
intake and exhaust and cooling valves interconnected to the pressure hull
(or controlled in the module by reach rods), PLUS your electrical distribution
to the control panel for charging and/or hotel loads, including propulsion. AND
you will need an additional dropweight to offset the volume of your
propulsion/charging center, as it will be way aft of your CG/CB and might stand
the sub on its tail or thereabouts if flooded. Nothing to it. Vance -----Original Message----- Hi Jens. That's what I was thinking. We were sailing last weekend
on San Francisco Bay with a friend and his 26 foot boat has a little two
cylinder diesel motor. My thought was to use a pressure vessel with a bolt-on
end cap dome, and install a small diesel motor, generator, and fuel tank in it.
Make the "unit" completely separate from the cabin hull with a
"disk type" thru-hull for cable and controls. The unit could provide
power for running electric motors OR have a propeller shaft coming out the back
end ( OR both.) It would need to be neutrally buoyant as a unit so the sub
could dive even if it was removed. This "power module" could easily
be bolted to the sub and removed as a unit if it needed repair or maintenance.
Cooling would be an issue but if the motor was water cooled, just a water pump
and plumbing would be needed.....no radiator. The small two cylinder diesel on my friend's boat pushed his boat
at about 5 knots at 3/4 speed and he said it will run for days on a tank of
fuel. I think the motor brand was a "Universal". Probably made in
China but a quick search on Google would show what's available in a compact
motor that was water cooled. I designed my sub to accept a small 20 horse outboard on the rear
transom plate for long distance surface transit. The cables and wires will
pass through a small electrical thru-hull, and for steering the motor has a
link to the electric thrusters/rudders linkage. The outboard is small enough to
be put inside the sub if needed but most likely will be loaded onto the surface
boat when diving. A permanent diesel electric "module" seems like a fairly
simple thing to fabricate, and the sub could still be used with or without it. Frank D. __________ Information from ESET NOD32 Antivirus, version of virus
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