The Collaborative International Dictionary of English v.0.48:

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