Possible Clues:

• In the main, they provide support
• In the main one finds them strangely ageless
• Ability to resist sickness on boat
• In the main people find them a steadying influence
• Eagles fly South and sailors soon get them
• Ability to walk on a ship
• Members with ability to survive rough voyages
• Good thing to find on a boat
• Good standing with sailors?
• Sailor's balance