1. Propeller Diameter: It is observed that the speed of the shaft and the propeller diameter are very closely related. A low shaft speed (given diameter) is very beneficial from efficiency point of view. However, it leads to high shaft torque subsequently large shafts and gearboxes. Therefore, while designing the propeller a balance must be found to ensure its performance.
Generally, propulsive efficiency can be increased by installing propellers with large diameters. However, the diameter behind the ship is limited by the draught of the vessel. Optimization of propeller design is done to meet the balance.