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#Industry News

More info released on Voith Linear Jet

German propulsion company Voith has released further details of it revolutionary Linear Jet system at Seawork 2015.

Voith Turbo’s marine manager, Mark Harvey, said: “We believe the Voith Linear Jet is a significant breakthrough in world marine propulsion systems that takes the best elements of two existing technologies, the conventional screw propeller and water jets.”

In developing the Linear Jet the company looked at the problems associated with these two existing systems, heavy weight and complication with the water jets and relatively low efficiency with the screw propeller. The Linear Jet has the propeller operating in a tunnel with an associated stator that recovers some of the propeller thrust energy in the same way as a water jet but the complex control systems of the jet required to achieve steering and reverse have been removed. By operating the propeller in the more controlled environment there have been significant efficiency gains over a conventional propeller.

One of the main challenges in the development was in the design of the nozzle in which the propeller operates to reduce its resistance as much as possible whilst at the same time increasing the propeller thrust. The final concept has the nozzle fixed into a semi-tunnel shaped into the hull similar to that found on many propeller-driven vessels in order to get a more horizontal propeller shaft and to reduce the draft. This semi-tunnel feeds the water flow into the nozzle where it is accelerated by the propeller. A conventional rudder located behind the nozzle provides steering and the propeller in the nozzle can operate effectively in reverse.

The interior of the nozzle is tapered as it runs aft whilst its exterior has a distinctive curve, the result of extensive testing to find the optimum shape. The nozzle can be fully integrated into the hull semi-tunnel so that the bottom of the nozzle is on slightly lower that the hull draft. This affords good protection for the propeller and the nozzle can be constructed from material compatible with the hull materials, composite, aluminium or steel. The propeller in the Linear Jet has larger clearances than those used on water jets which will reduce any erosion problems.

Another benefit of the Linear Jet design is that the stator inside the nozzle also provides a support bearing for the propeller shaft so the no shaft brackets are required. The maintenance requirements are low with a water lubricated bearing on the stator. Marine growth is also reduced and would be easily accessible for diver clearance compared with the problems that marine growth can cause for water jets.

The Linear Jet is claimed to make significant reductions in noise and vibration, give a good increase in the available bollard pull and to produce higher top speeds with the same engines and hull design. Tests have shown that significant fuel savings can be made with the Linear Jet. Voith plan to offer this Linear Jet in versions that can absorb power outputs from 500 kW up to 25,000 kW which should make it an effective propulsion system for a wide variety of vessels and it remains efficient at speeds up to 40 knots.

Details

  • Germany
  • Voith

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