Draft Mate (Draft - Measurement: The depth of a vessel's keel below the water line, especially when loaded; the minimum water depth necessary to float a ship.)
freeboard= the measurement on the side of a ship between the deck the waterline.
fathom= A unit of length equal to six feet, used principally in the measurement and
specification of marine depths.
bilge rat
matey
How about simply The Topper. It's got an R in it which sounds pirate like. All the extra words make it that much more complicated. The Avast Topper sounds great.