What is "shifting backstays"

Shifting \Shift"ing\, a.

1. Changing in place, position, or direction; varying; variable; fickle; as, shifting winds; shifting opinions or principles.

2. Adapted or used for shifting anything.

   Shifting backstays (Naut.), temporary stays that have to be let go whenever the vessel tacks or jibes.

   Shifting ballast, ballast which may be moved from one side of a vessel to another as safety requires.

   Shifting center. See Metacenter.

   Shifting locomotive. See Switching engine, under Switch.