Ability lacked by landlubbers

• Sailors' equilibrium
• Freedom from mal de mer
• Sailor's need
• Good standing in the Navy?
• Sailor's asset
• What landlubbers lack
• Ability to adjust one's balance to the motion of a ship
• Sailor's bearings
• Good sailors have them

Wiktionary Word definitions in Wiktionary
n. (alternative spelling of sea legs English)