Answer: trysail

AnswerCrossword Clue
TRYSAILIt keeps a vessel windward in a storm
TRYSAILCanvas.
TRYSAILShip's special canvas
TRYSAILAid for upwind maneuvers
TRYSAILIt's attached to a mast in storms
TRYSAILIt's hoisted on a brig in high winds
trysailtriangular or quadrilateral sail having its luff hooped or otherwise bent to a mast, used for lying to or keeping a vessel headed into the wind; spencer