An anchored ship is not always treated the same way:
• If it is anchored in deep water but is being moved violently by wind, it takes the rule of a moving ship.
• If it is stable, it takes the rule of a stationary ship.
• If tied at the shore, sitting for Fard without an excuse is not valid.
• When standing is possible and the vessel is stably connected or supported, the prayer is treated more like prayer on stable ground.
The practical issue is real stability, not merely whether an anchor exists.