Conventional propulsion systems, such as propellers or water jets, work most efficiently in open water conditions. In Servogear we develop tailor-made propeller tunnels as a part of our controllable pitch propeller system, to provide greater propulsion efficiency below a hull than in open water. The propeller tunnel itself also reduces hull resistance.
Our propeller tunnel allows for larger propeller diameter with no increase of shaft angle and draught. Propeller rpm is reduced, as well as the surface pressure on the propeller blades, and the water flow entering the propeller is optimised. Together with other detail improvements, this provides the best possible working conditions - resulting in a smooth and efficient propeller thrust.
A more even loaded propeller gives a slimmer and lighter design, which means less weight and drag as well as higher efficiency. We calculate and design our propeller tunnels based on full utilisation of the flow below the hull, ensuring optimum interaction between hull and propulsor. Efficient propulsion means lower fuel consumption, more economic operation and less pollution.
Optimal Propeller Diameter
A Servogear propeller tunnel is designed according to the propeller momentum theory and will therefore secure optimal water flow through the propeller. The shape of the tunnel is designed in accordance with the contraction of water flow calculated from the propeller momentum theory. The tunnel is tailor-made for each project.
Reduced Shaft Angle
The propeller tunnel also minimizes the shaft angle and reduces the thrust variation on the propeller. This increases the lifetime of the equipment significantly. The reduced shaft angle also decreases drag caused by shaft brackets etc.
Reduced Hull Resistance
Based on experience from sea trials and model tests, a propeller tunnel normally reduces the hull's resistance in water. The reduction in resistance is caused by less transom area, which again reduces the loss in stern wave.
Typical angle between shaft and baseline: 10o. Waterflow attack angle: 10o.
Typical angle between shaft and baseline: 4o. Waterflow attack angle (catamarans): 3o