1) Suitability 2) Suitableness 
A body of water, such as a river, canal or lake, is navigable if it is deep, wide and slow enough for a vessel to pass. Preferably there are few obstructions such as rocks or trees to avoid. Bridges must have sufficient clearance. High water speed may make a channel unnavigable. Waters may be unnavigable because of ice, particularly in winter. Nav...
• (n.) The quality or condition of being navigable; navigableness. • (n.) The quality or condition of being navigable; navigableness.
Nav`i·ga·bil'i·ty noun [ Confer French navigabilité .] The quality or condition of being navigable; navigableness. 
[n] - suitability for the passage of a ship or aircraft
noun the quality of being suitable for the passage of a ship or aircraft