Thinking of it by center of gravity makes it simpler. Some day I'll do some
calculations now that sort of understand that part.
Aren't there vertical separators in the ballast tanks on large submarines? I
was thinking that if the center of gravity was low enough so that in a worst
case scenario tilt would be 70 degrees, and the ballast tanks had vertical
separators with a width of half the height with bottom wents exactly in the
middle, that it could work. According to my calculations at 70 degrees the
ballast tank could fill to 82.5% with air before it starting blowing air out of
the bottom.
I suppose having vertical separators like this would require multiple valves
for the different chambers and wouldn't be practical for a small psub, but
psubs don't have multiple compartments inside anyway.
Would it work to have the bottom hole in the aft ballast tank all the way aft
and then connect that to a short pipe which would run to the forward end of the
tank? That way if the sub was angled straight down water couldn't enter the
tank because it would have to come up through the pipe which is filled with
pressurized air. And if the sub was pointed straight up the pipe would be
filled with water but the hole in the tank is at the bottom side so air
wouldn't bubble out and water couldn't really get it. Having the hole at one
end of the tank is good if the sub is tilted one way but will make the ballast
tank unusable if it is tilted the other way. Would this pipe method be a way of
having the best of each at the same time? One draw back I see is that if the
sub is tilted straight down the pipe would prevent water from entering the
tank, but it would not allow an already flooded ballast tank to be blown. So
maybe put the hole in the middle and have the pipe. That way it helps you in
one direction and doesn't do any harm in the other. Could it work?
Alex
Alec,
Whether the sub goes vertical is going to depend upon where the center
of gravity ends up after flooding and any shifting of equipment that
might occur (jimk makes a good point here). Think of the flooding as
not adding weight but reducing buoyancy and changing the center of
gravity. Assuming you weighed enough and had some weights inside for
trim that could be moved you could potentially move the center of
gravity to balance the sub even if the forward compartment had flooded.
Realistically that forward compartment would have to be a rather small
volume to balance it out this way, but theoretically it would work.
The soft ballast tanks are definitely a problem if the sub tilts to the
point that you lose buoyancy from them, however you always have your
emergency drop weight which you can let go of. The sub should be
configured such that dropping the emergency weights will allow the sub
to surface even if the soft ballast tanks are flooded. Whether it will
do the same with a compartment flooded depends on whether that situation
was planned for.
Jon
On 4/17/2012 8:53 PM, Alex wrote:
> I've been thinking about what happens if you have a water tight
> bulk head in the middle and the forward or aft compartment floods. Or possibly
> with 3 compartments with forward or aft flooded.
>
> Does the submarine go almost vertical? And the most important part of this is
> what happens to the external soft ballast tanks. If the tank has a bottom vent
> in the middle and it becomes vertical, it will only fill up half way with air
> before it bubbles out.
>
> Worst case scenario: Let's say you have a sub with huge ballast tanks on the
> bow and stern that can surface even if it is fully flooded inside. Let's say
> that the forward ballast tank is damaged and the forward compartment is
> flooded. The unflooded aft compartment and stern ballast tank should be enough
> to surface. But will the stern ballast tank work with the bow pointed way
down?
>
> Alex
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