Swerves at sea (4)
I believe the answer is:
yaws
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">swerves at sea</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for yaws that I've seen before include "Doesnt go straight; tropical disease" , "Goes off course (ship); tropical disease" , "Deviates" , "course changes" , "Moves unsteadily" .)