This is rarely useful, simply because it's incredibly difficult to earn a Great Admiral before the Renaissance Era - sea battles are just so rare in the early game, and Barbarian fights don't count towards earning Great Admiral points.

One interesting perk of the Great Admiral is the fact that he can traverse ocean tiles, regardless of whether or not you've researched Astronomy. This may be used to a crushing effect by a skilled player, or it may be wasted by an unskilled one! Note that the Admiral is consumed when using this ability. What's different is its ability to instantly repair every naval and embarked unit in the same hex, as well as in adjacent hexes. The Great Admiral is used similarly to the Great General - as a combat booster, but in sea warfare.

The unit is expended after performing this action.

Repair Fleet (Instantly heals all ships within one tile).

Naval Leadership (15% Combat bonus to all Ships within 2 tiles).

The number of points required increases with each successive Admiral. Appears when water-based military units generate enough Great Admiral points (by earning XP in battles against non-Barbarian opponents). A Great Person specialized in naval warfare.

Great general civ 5