In the old days a lot of people were given names we do not use anymore. It was supposed to confer certain qualities upon the child. Thus girls may be named Hope, Charity, Honor, Mercy Chastity, etc. It isn't such a jump for boys to be named Preserved, Honor, Manly, etc. If O'Brian's Killick was a son-of-a-gun (i.e., born on a warship) then it is likely he would have been named Preserved in hopes that he would not end his days badly.