High thrust at low speed
If high thrust at low speeds is important for you, then a nozzle is the best solution. The lifting action of the nozzle profile tends to pull the nozzle forward. How does this work?
On rudder propellers with a nozzle, the velocity of the water flow is increased and the pressure is reduced. As a result, the thrust and the torque of the propeller decreases slightly, while a circulation with inward-directed force takes place. This force provides for a forward-acting element, giving the nozzle a positive thrust which is generally larger than the reduced thrust of the propeller. Due to the small clearance between the nozzle and the tip of the propeller blade, the tip vortices are reduced thereby increasing efficiency. However, the frictional resistance of the nozzle increases as the speed increases, and will eventually become greater than the additional thrust. The nozzle is thus ideal for providing greater pulling power for heavy loads, but less suited for high speed vessels.
The advantages summed up of a nozzle compared to an open propeller:
20 to 25% more thrust at low speeds
The nozzle provides the propeller some protection
Higher "bollard pull"
Air intake at shallow draft can be avoided by placing an anti-vortex plate above the propeller.