Sent: Wednesday, November 24, 2004 6:35 PM
When a submarine dives it basically has to be heavy overall to break the surface tension on the hull. Also, when diving from an aircraft you have to get down in a helluva hurry.
On the surface when the boat is rigged for dive there is a tank that holds 5,000 pounds of water called the negative tank. When the tank is full you are heavy by that amount over your diving trim on diving. and it gets you down in a hurry, ---- like from fully surfaced to 60 feet (periscope depth) in 35 seconds.
At some point usually at about 45 feet when you have broken the surface tension on the hull, and plan on leveling off at 60 feet you have to blow the water from this tank to sea to stop your downward motion and reach your diving trim.
On the other hand when you are going deep in a helluva hurry to avoid a bomb from an aircraft, you may not blow the tank until you are at say 100 feet. Now mind you, you are blowing this tank to sea against the outside sea pressure, which goes up in a hurry as you goe down.
You have to use a lot of high pressure air from your 3000 psi airbanks to clear this tank if you blow it too deep. You never blow this tank completely dry or you would put up a big air bubble. So you blow it almost dry, then vent the air off of the top of the tank, back into the boat.
When we old submariners pass mail back and forth we usually close with some old submarine expression, such as "Blow Negative" "Open The Outer Doors" (torpedo tube doors), Or "Pump From After Trim to Forward Trim" .
Sent: Wednesday, November 24, 2004 7:25 PM
I sent this to a cousin that asked me what I meant by "Blow Negative".
full order should be "blow negative to the mark", which left water in the tank,
but we never used it as it was assumed you were blowing it to the mark.
Up Periscope !!!