a root has low unwind sail
main_topsail is sail. fore_and_aft_sail is not sail. fore_and_aft_sail is sail. staysail is not fore_and_aft_sail. topsail is sail. head_sail is not sail. staysail is fore_and_aft_sail. topsail is not sail. main_topsail is not sail. spanker is not fore_and_aft_sail.