Good to see these photos. I wonder if you know why one of the boats has a different arrangement of free-flooding/limber holes?Some magazine scans of the good old 091.
401 started with a long line, 402 was also long then 403 went with a line of dotted holes, then went back to a long line in 404 and 405. I think 401 was retrofitted with the short holes sometime after. They are trying to experiment which configuration of sink holes would produce the less noise both hydrodynamically --- water flowing around the holes as the sub moves forward --- as well as the noise as the water is either absorbed and ejected from the ballast tanks when the sub sinks or rises.Good to see these photos. I wonder if you know why one of the boats has a different arrangement of free-flooding/limber holes?
One of them has a series of open oblong slots whereas the others appear to have long continuous lines. Is one an old idea which is being replaced with a new design?