Final answer:
The buoyant force on a boat is greater in fresh water compared to salt water, as a boat must displace a larger volume of fresh water to float due to its lower density, which means the weight of displaced fresh water is greater than that of the displaced salt water for the same boat.
Step-by-step explanation:
When a boat floats in both fresh water and salt water, the buoyant force is related to the density of the liquid the boat is floating in. Since salt water has a greater density than fresh water, a boat will displace less salt water to achieve the necessary buoyancy to float. However, the buoyant force itself depends on the weight of the fluid that is displaced. Therefore, because a boat displaces a larger volume of fresh water to float (since fresh water is less dense), the weight of the displaced water, and hence the buoyant force, will be greater in fresh water compared to salt water for the same boat.
According to Archimedes' principle, the buoyant force on an object submerged in a fluid is equal to the weight of the fluid that is displaced by the object. Therefore, if a ship floats higher in salt water than in fresh water, it indicates that the ship is displacing less volume of salt water due to its higher density. But since the buoyant force is a measure of the weight of the displaced fluid and not its volume, the buoyant force would be greater in fresh water as this requires displacing a greater volume (and hence weight) of water to support the same ship.