to ride a portoise

from The Collaborative International Dictionary of English v.0.48

Portoise \Por"toise\, n. [Perhaps fr. OF. porteis portative,
   portable.] (Naut.)
   The gunwale of a ship.
   [1913 Webster]

   {To lower the yards a-portoise}, to lower them to the
      gunwale.

   {To ride a portoise}, to ride an anchor with the lower yards
      and topmasts struck or lowered, as in a gale of wind.
      [1913 Webster]