You have not mentioned in your question compared to what will the ships float lower or higher. I assume it is non-tropical water.
Tropical water is water that lies in the region between the tropics. The temperature of the water here is higher compared to non-tropical waters and does not fall below 25 C.
As the temperature of water increases, the molecules move further apart and its density decreases.
A ship floats in water when the buoyancy of the water is equal to the weight of the ship. In case this cannot happen if the mass of the ship is too high or its structure is such that it is not able to displace a sufficient quantity of water, the ship will not float.
When a ship moves from non-tropical waters to tropical waters as the density of water decreases a larger volume of water has to be displaced for the ship to remain afloat. This would mean that a larger structure of the ship will be submerged in the water and it will float lower.