I'm sure someone like Sam will correct me on this, but looking at the profile of BB's
deckplans it seemed like the Orlop Deck - which formed the top of the forepeak tank - was about 25 feet above the top of the double bottom at the rear (Water Tight Bulkhead 'A') but sharply reduced due to the upward curve of the keel towards the prow, where the height appeared to be about 12 to 15 feet.