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Originally Posted by Dr.Sid
Just an idea how to determine real sub lift coeficients. Have you ever heard about diving sub without filling the ballast tanks ? It should be possible, at some speed and pitch angle. Or the opposite .. surfacing sub with tanks full (and staying surfaced).
I understand both maneuvers are nonsense, but maybe somebody ever this, even theoretically.
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Nonsense maybe, but lets think this out.
Diving with the ballast tanks bown dry:
MAYBE, if you had bowplanes (they would be under the surface and thus effective).. and were going flat out on the surface, you MIGHT be able to push the bow down enough to get the water flowing over the hull, thus turning the upper hull into a massive plane surface. The old nuke boats of before the Albacore hulls (pre 637 hulls) had this problem at high speeds. They had to be careful at high speed putting angles on the hull less they lose depth control. I do believe that the rounded hull surface all but eliminated the issue.
They also have a LOT of reserve bouyancy designed into the hull. I do not think you could do this if you tried.
Surfacing the boat with the ballast tanks full:
Yes, easily. You just drive the ship up using the planes and the engines. Once on the surface you have the surface tension of the water to help support you (this is the same thing that allows a needle to 'float' on the suface of the water.
One term for surfacing without blowing the tanks is called 'broaching'. We hate doing it as when you have fairwater planes, you can make a rather LOUD noise and REALLY shake the boat when the planes come down back into the water.