Hello, friends.
I'm currently searching for crash dive speed of various subs, especially the fastest records with 'skilled crew'. I could find some resources, like a memoir of Japanese I-41, stating that the sub could reduce diving time by 40 secs with extensive training.
Then what about the u boats? I could see the evaluation of U-570 by RN(25-30 secs), however, I believe it could be faster than that. (The estimated crash diving speed to periscope depth of I-41 was 50 secs, but they managed to reduce it. XP)

So, is there anyone to help me find the record of crash dive time for u boats (type vii, I hope) to take themselves down underwater with the skilled crew? Any sources (memoir, statement, etc...) would be great for me.