Whats the best way to get fastest dive time

[verticalization]

I have a quick question about running decks awash, not to get too far off topic, but.. i tried doing it for the first time in my last patrol, calm seas.. i set 7m depth

my boat kept the depth perfect, however.. i couldn't get the crew on the bridge, i had to be at atleast 6m before they would pop back up again

is there any way to keep the crew on deck? with decks awash?