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| Submarine Art, Danijel Frka |
When war threatened in 1914 submarines had come a long way from the H L
Hunley, the first submarine to sink a warship way back in the American Civil
War, but to understand them today requires the same knowledge of basic physics
that it did then. Too often, if the forces acting upon a submarine became
unbalanced, whether on the surface or below it, the boat could suddenly
disappear and never be seen again.
A toy boat will float in a bowl of water because the buoyancy (force) of the
water is greater than the gravity (force) pulling it down. If you flood it, it
will sink because you have increased its mass, and thus the force of gravity
pulling it under becomes greater than its buoyancy. If you half flood it and
give it a good push it will pop up at one end or the other.
The inept Chief tried frantically to hold the boat on Schnorkel depth,
but she rose and fell like a see-saw. In despair I took over and said…”Just
hold her at thirteen metres”. Within a few minutes the boat again lost her
stability…she tilted up sharply and shot to the surface… I shouted, “Both
diesels emergency ahead! Open all vents. All men to the bow.” The diesels
knocked wildly, the boat rocked hard. For a few seconds…the sea held the boat
in a crazy position, then she sank slowly, steadily…she swung into a forty
degree down angle…At eighty metres I managed to level her off and establish her
trim.
‘Iron Coffins’ by Herbert Werner Cassell 1969
In this case, the forces of buoyancy and gravity were correct but they were
not evenly balanced or ‘trimmed’. Submarines of both World Wars One and Two had
main ballast tanks, fore and after tanks and a range of smaller tanks for
trimming. Take the U-96 in Das Boot, for example. Why did it sink in the
Straits of Gibraltar?
Breach in the diesel room, breach in the motor room…E-motor bilge making
water fast…The bow heaviness jams me back against the forward wall of the
control room. Are we descending faster than usual? “Boat out of control, can’t
hold her,” whispers the Chief. No more buoyancy, only gravitational pull.
‘Das Boot’ Lothar Gunther Bucheim 1973 Piper Verlag GmbH Munich
Actually, Bucheim is incorrect here. The force of buoyancy was still present
but the force of gravity was greater. So, why did it eventually rise?
“Respectfully report to Herr Kaleun – water taken aboard has been pumped
into regulator cells – possible to expel it outboard with compressed air”…then
I notice: no more water in the control room.”
Within the pressure hull of a submerged submarine air pressure (force per
area) could change for a variety of reasons.
The effects of carbon dioxide were made worse by the steady build-up of
pressure from high-pressure air leaks compounded by venting internal tanks,
torpedo tubes and the heads (toilet) after blowing. When the boat did at last
surface it was a prudent precaution to hold on to the captain’s legs when he
opened the hatch: there was a real danger of him being shot out like a human
cannonball and lost over the side.
'Submarines at War 1914-1918’ Richard Compton-Hill
Periscope Publishing Ltd. 2004
