Proposed Canon
Seafarer is a special related to running a ship and gives the relevant knowledge. It adds the total move of all seafarers on a ship designated as crew, and divides that by a number determined by the ship's condition and design to determine the ship's own move. Seafarers also add to the attack power of a ship's Shockmancy beam weapons.
Count Topotato, a Warlord without the Seafarer or water-capable specials, was leading a Haggar corvette. He drowned trying to lead a squad of Aquabats in underwater combat. He was profoundly stupid, so probably didn't know he needed one or both specials to do so.