as string volume , the sail of control will decrease
sinking is not decrease. sinking is decrease. sailboats has not sails fore_and_aft_sail is not sail. press_of_sail is not sail. press_of_sail is sail. if bear_down_on occurs then sail occurs. if bear_down_on does not occur then sail occurs. balloon_sail is not sail. spanker is not fore_and_aft_sail.