The density of water is affected by its salinity, temperature, and pressure. The more saline the water, the denser it is. This is because salt water contains dissolved minerals, which increase the water's density. The warmer the water, the less dense it is. This is because warm water molecules move faster and take up more space than cold water molecules. The greater the pressure, the denser the water is. This is because pressure forces water molecules closer together.
In the open ocean, the water is typically very saline, cold, and under high pressure. This combination of factors makes ocean water very dense. When a ship enters a body of fresh water, the water is typically less saline, warmer, and under less pressure. This combination of factors makes fresh water less dense than salt water. As a result, the ship displaces less water in fresh water and sinks deeper into the water.
A deeper draught means a greater immersion of the hull and hence an increase in resistance. Thus, the speed will decrease and the propeller efficiency will decrease because of the increased slip of propeller.
