"We're taking damage sir!" "Medic!!!" "We have flooding sir!" "Medic!!!" "Bulkheads have been compromised sir!"... glub glub glub...
The depth of you boat shows the depth below the keel, so if you have 53 foot below your keel and dive to 60, you will hit bottom. Your boat generally sits at a 14 foot depth when surfaced, so you would need at least 76 foot (generally) to dive to PD. To help shorten your career in subs, the SH4 submarine is not designed to be able to sit on the bottom and "hide" - and will take damage continuously when you are in contact with the bottom, no matter how 'gentle' you are.
