I had previously read that many sailors served under pseudonyms - possibly to avoid repercussions if they decided to desert ship and were later re-impressed into the Navy. A letter enclosed with the will of Robert Kissack (1781 - see www.manxnotebook.com/famhist/wills/1781_rk.htm) would appear to indicate that the practice was widespread - can others offer any other documented examples (it would certainly appear to make searching Naval records considerably more awkward)