Striking an armor-piercing naval shell on its nose would not make it explode. The fuse in the base first needs to be armed, and then the detonator inside fired when the shell strikes its target at an extreme velocity.
The design of the German haunted ship is not anything remotely similar to what the Kriegsmarine had during WW2. The structure is typical of the Bathurst and Flower class corvettes designed by Britain.
At the beginning, when the group is in the life raft and about to board the German vessel, the captain starts banging the hull with the butt of his rifle. As he does so, the actor is clearly not hitting anything.
English text can be seen on the ship's plan, which is a simple modern photocopy on paper of a British escort's "General Arrangement" .
At 14:56 the Australian is seen looking at a large hole in one of the two lifeboats. So stating that the boats were not looked at is wrong.
No-one is seen checking the lifeboats, and finding that they have been sabotaged by being holed. Despite this, the characters mention it when they discuss what the captain did before he died.
When Jackson confronts Sinclair about withholding information, he specifies the "decapitated" body with "all the funky veins running through it" on the bridge. However, he wouldn't have known those specific details, since Teplov and Bigelow didn't say anything beyond there being a dead body.