Another way to detect water beneath the keel I did not see mentioned.
Order crash dive... when you hear a loud bang and scraping sounds well youve found the bottom !
Of course this makes you vunderable to detection as well
edit 08/01/05
Almost forgot ... If you implode before you reach the bottom the depth beneath the keel exceeds the structural capacity of your sub. Which makes the detection issue irrelavant. :rotfl: