Studding sail

A studding sail, or stun'sl (pronounced stuns'l /ˈstʌnsəl/) is an extra sail on a square rigged vessel for use in fair weather. It is set outside the square sails, using stun'sl booms which run out along the yards. They came into use some time in the middle of the 17th century and by the beginning of the 19th century were usual on all square rigged sailing vessels. They started to become less common in the last quarter of the 19th century, as the economies of smaller crews and avoidance of damage to the ship's gear became more important than a fast voyage.