You cite the Excelsior class. Okay, here's a cross section where the length of 469 meters is shown in 695 pixels, with 4 pixels for deck height. So (469/695)*4 ylelds 2.6954 meters (8.86 feet) deck to deck. That is a bit tight, but not severe. When I do these I usually determine number of decks looking at 3.5 to 4 meters deck to deck, whatever in that range can fit the exterior clues.