I believe the anti hummingbird mod in NYGM makes it so that when you stop your sub at o kts while submerged it will slowly sink and due to the slight rate of descent, the sub does not get damaged when it touches bottom (although in deep water-boat will be destroyed at crush depth)---sub needs to be going at least 1 kt to maitain depth and and 3 kts to change depth. Think the reasoning for it was more realestic submerged sub simulation. I have experianced the sinking firsthand (un-wanted) while lining up a torp shot on a revenge class at okts submerged
my wording "mod" might be wrong--it could be just changed files and code inside the larger NYGM mod and not a stand alone version. im not using Nygm right now so i can not check. I have seen past threads talking about it and i think it was discussed in the NYGM thread. I am realitivly new to posting on forums and i do not know how to insert a thread link
----sorry wish i could be more help---maybe one of the gurus around here can steer you in the right direction.