Mark Borgerson <
mborg...@comcast.net> wrote:
>In article <
5127b92f....@news.supernews.com>,
fair...@gmail.com
>says...
>>
>> Mark Borgerson <
mborg...@comcast.net> wrote:
>>
>> >If the outside pressure is 3000PSI and your air is at
>> >6000PSI, you don't blow a lot of water out of the
>> >ballast tanks in an emergency! (You can only displace water
>> >equivalent to the volume of the HP air tanks.)
>>
>> You don't need to blow the tanks dry... you only need to blow enough
>> to get you moving in the right direction.
>>
>> We had the theoretical capability to blow our tanks dry all the way
>> down to test depth... But procedure was to blow only enough to ensure
>> positive buoyancy and to vent if we were rising too fast or were
>> unable to control our angle with the planes. (Emptying the banks had
>> various operational consequences - acceptable in extremis, but the
>> procedures were designed to avoid stumbling into those consequences.)
>>
>OTOH, at or near that critical depth, if you can only displace
>as much water as the volume of your HP air bank,
True from a purely mathematical point of view. Operationally, as you
point out below, test depth is set at some fraction of HP air bank
pressure.
>you're in deep trouble when interior flooding approaches the volume
>of the HP air tanks. The question then is how much volume the
>designers want to allocate to the HP air banks. I suspect that,in
>most subs, the volume of the HP air banks is only a small fraction
>of the internal volume.
True.., but there are other considerations.
HP air banks can be, and are, generally put in places not useful for
much else or where they won't interfere significantly with other
installations. (I.E. frame bays and ballast tanks.) Also, flooding
can kill by other mechanisms than overcoming ballast capability...
Thresher was likely disabled by no more than a few tons or tens of
tons of water. A boat can also be killed if there is sufficient water
at the ends to overcome the boats ability to control pitch (either via
the control surfaces or the trim system), and that amount is generally
far less than the total ballast capability.
Which is why we generally stay well above test depth if there's no
pressing need to go down there, and why we're always prepared at a
moments notice to get shallow by any means necessary. (Getting
shallow reduces the flooding rate.) There's also other lines of
defense (three systems of pumps in US boats, able to operate all the
way down to test depth, as well as the ability to pressurise the
compartment being flooded). HP and Emergency blow are just part of an
integrated strategy...
Submarine design is generally done on a very pragmatic basic - "look,
we've done all we can but there are edges and corners we can't
cover... if you can't deal, unvolunteer". There's a reason why
submariners are considered brave, and utterly lunatic.
>The Dolphin is probably exceptional in the ability to dive to a point
>where outside pressure is half the pressure in the HP tanks. For most
>boats I would guess that the HP air is pressurized to 5 or 6 times the
>outside pressure at normal test depth. (HP air at 6000, PSI, outside
>pressure at 1000PSI--equivalent to about 2000 feet depth.)
Correct in principle, though obviously (as often is the case in this
group) more details are not available.