help
 

im in the boat at the suface at the air pocket and i have the the hammer now when ever i go for the other stuff down there i sufficate what do i do next

Next step ain't easy. Take a deeeep breath and dive into the door opposite to where you found the hammer.

As far as I remember:
* immediately go right and swim to the end
* there, turn left and swim almost until the end
* just before the end, at the last crosspoint turn right and immediately left again. You should come to a small room with a ladder going up to a lock.

Use the hammer at the lock to break it, this will make it. Good luck!