midship beam

from The Collaborative International Dictionary of English v.0.48

Midship \Mid"ship`\, a.
   Of or pertaining to, or being in, the middle of a ship.
   [1913 Webster]

   {Midship beam} (Naut.), the beam or timber upon which the
      broadest part of a vessel is formed.

   {Midship bend}, the broadest frame in a vessel. --Weale.
      [1913 Webster]