The evening before, some of our senior rates will dress up as Davy Jones, The Bears, and the Police, and go from mess to mess to learn who has yet to have crossed the equator. As it comes, a high trial is held for those whose names are written, headed by Neptune, his beautiful wife, and the judge.
They'll have their heads shaved, and are dunked in the ceremonial pool. Some other ships have minor changes to some degree, and back when my dreams took place, it was more custom for the men to be dunked overboard than in a pool. But it seems very little changed over the last three centuries, as near as I can tell.