Bas,
I would think that since the torpedorohr go through Tauchzelle 5, and the vanes are aft of the frame 106 collision bulkhead, inside Tauchzelle 5, that any bubbles generated by a shot would not end up there. Bubbles would go forward of that bulkhead. Some might rise into the Wasserdichte Bock (bow buoyancy tank), perhaps.
I also have read that the piston that pushes the torp out of the tube greatly reduces the amount of air that gets expelled from the boat.
When doing a surface shot, it is my understanding that this piston is not used, but bubbles would not be a major concern at that point.
Thanks for the response, but I do not think that would be the answer.
My odd idea was that it was some sort of degaussing equipment to protect magnetic pistols (but that makes little sense either - the vanes are too far aft, and there is no empirical data saying degauss equipment was ever carried.)
So far I have been told they are strengthening vanes. I know if I designed a boat that would be subject to explosions and possible grounding, I would want to protect the explosive warheads. That Would make sense!
Cheers, mates!
Topher VIIC