The Collaborative International Dictionary of English v.0.48:

Boottopping \Boot"top`ping\, n.
   1. (Naut.) The act or process of daubing a vessel's bottom
      near the surface of the water with a mixture of tallow,
      sulphur, and resin, as a temporary protection against
      worms, after the slime, shells, etc., have been scraped
      off.
      [1913 Webster]

   2. (Naut.) Sheathing a vessel with planking over felt.
      [1913 Webster]