Hello Mr. Tore,
Referring to the attached drawing...
1. In order to establish the final air pressure inside the saddle tanks while on the surface; The diesel exhaust blowing pressure is 0.5 atmospheres above atmospheric pressure of 1.0 atu. Therefore, the saddle tank internal air pressure will be 1.5 atu after the exhaust blowing.
2. The water level inside the saddle tanks will be just above the top of the Kingston ports; the saddle tank's Kingston valves are open to the sea while the U-Boat is on the surface or submerged (water ballast configuration).
3. The air in the saddle tanks will remain captured in the saddle tanks until the vent valves located at the top of the saddle tanks are opened, then and only then will water level rise inside the saddle tanks while the U-Boat is on the surface.
4. It is established that the compensating water outlet pipe is positioned near the very bottom of the saddle tank and well below the standing water level inside the saddle tank. So, there is no means for the ballast tank air to escape from the saddle tank unless the saddle tank is vented.
5. If we compare the water pressure from the surface to the water level at the bottom of the saddle tank where the Kingstons are open to the sea, and then to a point outside the ballast tank at the same water level; the water pressure would be exactly the same.
6. Therefore, the water level inside the compensation pipe going to the selector valve which is open to the atmosphere would be at the sea level. This would be the water line established by the U-Boat's buoyancy (displacement) Vs the weight of the U-Boat.
This would be the same principle with the following test; if we took a water glass and drilled a hole through the bottom center and placed a straw through the hole until it lined up with the top edge of the glass, then we turn the water glass upside down and partially submerge it into a bath tub filled with water. The air in the glass would be slightly compressed as we forced the glass into the water, and the water level in the straw would match the water level in the bath tub. If we had a means of balancing the glass, then it's weight would establish the water line for the glass in the tub...
What do you think?
Kind regards,
Don_