Hi SG
Thanks for that, I knew I'd seen a pic somewhere, doh!
I suspect that this is not original but it could be a copy of an original, see attached port and starbord vents from U 534, albeit small and poor quality pics.
I count 12 slats, 14 including the outer edge on the starboard and an undefined number on the port, possibly as few as 7. The port vent is not currently visible and the starboard vent no longer exists now there is just a hole in the hull. The starboard vent appears to be retained by 10 countersunk screws, which seems now likely than the 4 bolts on the U 505s vent. The port vent however was in pooor condition when the photo was taken, at the time she was being moved to Birkenhead. which would imply that it was original. The starboard one seems a little too good to be the original, I do know she spent 3 years being "inspected" at Hirtshals dry dock and a lot of panels were cut out and refitted/replaced (looking for the alleged gold?), or it could have survived in good condition in silt.
I would love to know where Revel get 7 and Eduard get 8 slats.
If only there was a dry dock picture like you where looking for, it would help resolve the mystery.
Regards
Jon