The Collaborative International Dictionary of English v.0.48:

Seaworthiness \Sea"wor`thi*ness\, n.
   The state or quality of being seaworthy, or able to resist
   the ordinary violence of wind and weather. --Kent.
   [1913 Webster]

WordNet (r) 3.0 (2006):

seaworthiness
    n 1: fitness to traverse the seas [syn: seaworthiness,
         fitness]