Detection of Leaks
Do you have any idea what happens to the people working on board a ship or submarine once it has been completely submerged? They are definitely looking for cracks and crevices through which water could run off. Why? If there are any holes in the boat, then the conditions that they are in are pretty dangerous.
It does not matter how large the hole or leak is; it must be patched up or repaired in a reasonable length of time, and it must be done as rapidly as is physically possible. For them, the question of whether or not they will live is an existential one.