Unmanned Aircraft. The Ad astra is an unmanned aircraft that requires a creature with an intelligence of 12 or highter to pilot it, otherwise it cannot hover. Whilst a creature is piloting. Ad Astra's intelligence, Wisdom and Charisma scores are replaced with that of the creature, and any effects that would affect these stats instead targets the piloting creature. The pilot assumes full control of Ad astra's movement when piloting, and can use any of their class features or racial abilities, provided the aircraft is also capable of doing so. If the creature stops piloting for any reason ( such as being knocked away from the helm) then the Ad astra's stats return to normal and the construct becomes inert again.

Crew capacity. The Ad astra has space enough for a crew of 10 people and 8 passengers.

Hull

Armor Class 13

Hit Points 250 (damage threshold 10)

Movement: Sail

Armor Class 12

Hit Points 100; -10 ft. speed per 25 damage taken

Speed (air) 15 ft.; 5 ft. while travelling into the wind; 25 ft. while travelling with the wind.

Speed (water) 35 ft.; 15 ft. while travelling into the wind; 50 ft. while travelling with the wind.

Lift. Gravity gem. In the center of the lower deck is a 10-foot-tall cylindrical device called a harnersser inside it lies a gravity gem. 

Armor Class 25

Hit Points 60

Lift. Ascend 60 ft or Descend 60ft. If the Gravity gem is destroyed or removed from the harnersser the ship can no longer levitate.

Weapon: Ballista

Armor Class 15

Hit Points 50

Ranged Weapon Attack:  +6 to hit, range 120/480 ft., one target. Hit: 16 (3d10) piercing damage.

Weapon: Harpoon Gun

Armor Class 15

Hit Points 50

Ranged Weapon Attack: +6 to hit, range 120/480 ft., one target. Hit: 16 (3d10) piercing damage.

In addition to dealing the damage on hit the harpoon also impales the target. While impaled, the target can't take any actions on its turn other than trying to free itself from the harpoon, which requires a successful DC 15 Strength check. If the check succeeds, the target takes 5 (1d10) piercing damage as the harpoon is pulled free and is no longer impaled. If a harpoon is attached to the gun by a rope, a creature impaled on that harpoon can't move farther away from the gun or increase its altitude until it frees itself. A creature within reach of the gun's winch can use its action to reel in a harpooned creature, pulling it up to 20 feet closer to the gun.

On its turn, the airship can take 3 actions, choosing from the options below. It can take only 1 action if it has only two crew. It can't take these actions if it has no crew.

Fire Ballista. The airship can fire its ballista. The ballista has a 90-degree arc of fire (side to side, and up and down).

Harpoon Gun. The airship can fire its spring-loaded harpoon gun. The harpoon gun comes with a winch, a 500-foot coil of hempen rope and has a 90-degree arc of fire (side to side, and up and down). Although it fires harpoons instead of bolts, the gun is considered a ballista. Tying a rope to the harpoon takes an action.