Screw propulsion machinery was lighter in weight, thus improving fuel economy; Screw propulsion machinery could be kept lower in the hull, reducing the ship's centre of gravity and making it more stable in heavy seas; By taking up less room, propeller engines would allow more cargo to be carried; Elimination of bulky paddle-boxes would lessen resistance through the water, and also allow the ship to manoeuvre more easily in confined waterways; The depth of a paddlewheel is constantly changing, depending on the ship's cargo and the movement of waves, while a propeller stays fully submerged and at full efficiency at all times; Screw propulsion machinery was cheaper.[24]