Diesel boats aren't allowed to be underwater in bad weather ... they can't handle the underwater surges that occur on batteries alone.
There was a Typhoon in WWII that rolled up the deck of a US Navy carrier, you can imagine what it would have done to a round bottom boat.
My sea story is too long to tell right now, but I have been in force nine weather on a diesel boat in the Gulf of Alaksa and it is no fun.
Gotta protect those bow planes ...
