Source : Webster's Revised Unabridged Dictionary (1913)

Capsize \Cap*size"\, v. t. & i. [imp. & p. p. {Capsized}; p. pr.
   & vb. n. {Capsizing}.] [Cf. Sp. cabecear to nod, pitch,
   capuzar, chapuzar, to sink (a vessel) by the head; both fr.
   L. caput head.]
   To upset or overturn, as a vessel or other body.

         But what if carrying sail capsize the boat? --Byron.

Source : WordNet®

capsizing
     n : (nautical) the event of a boat accidentally turning over in
         the water