I would take it to mean the Admiralty has 11 Admirals in it. There are probably an equal number of Vice Admirals and more Rear Admirals, and if the position is occupied, 1 Fleet Admiral. The lower ranks would just hold less voting power, like the Southern Liberty Navy High Command, with the Fleet Admiral presumably having veto power. The Queen herself could probably totally override the board as commander-in-chief, though she'd probably not want to interfere too much.