VOITH’s New Propulsion System: The Voith Linear Jet (VLJ)

By Peter Pospiech at November 23, 2012 06:59
Filed Under: Company News, drive systems

The new Voith Linear Jet gives naval architects new ways to optimize their vessel designs while still delivering top speeds of 40 knots. The key difference to conventional propellers is the VLJ's much smoother and quieter operation even at high speeds and a larger range of applications: Not only is the propulsion system useful for high speeds, but it is also ideally suited to low-speed cruising. The Voith Linear Jet combines the advantages of waterjets (at high speeds) with those of conventional propellers (at low speeds) in one propulsion system. The high degree of efficiency achieved in both areas of application makes it the perfect solution not only for fast catamarans but also for yachts, coast guard vessels or ferries.
Low installation complexity, low sensitivity to marine growth, sustained high efficiency across the vessels' speed range and high bollard pull are borrowed from the propeller side. Reduced vessel draft, the ability to reach high speeds with high efficiency and low noise and vibration levels are borrowed from the waterjet side.

Voith's all new Linear Jet propulsion drive

A Voith press release stated, “The Voith Linear Jet takes away some of the disadvantages of traditional waterjets, without compromising the vessel’s top and sprint speed ability. The considerable higher efficiency at low-end cruising speeds will provide a positive design spiral for light weight craft. Smaller fuel tanks for the same range, reduce vessel displacement resulting in increased hull efficiency with ensuing increased range and top speed” and “this gives a VLJ equipped ship a considerable range advantage against its waterjet sister vessel. Typical VLJ applications will be any ship with a mixed operating profile between low speed cruising and sprint speeds like Navy and Coastguard vessels and Yachts. Ferries operating at sustained speeds around 30 knots employing high-speed or medium speed Diesel or LNG engines will also benefit of this new propulsion option.”  Thus, Voith claims that their VLJ is capable of providing the speed characteristics of a jet drive, when the drives are designed to remain immersed to avoid cavitation and close to the hull to reduce the drag profile, is also validated (like its predecessors, the new vessel is a fast catamaran hull design).
The Voith Linear Jet (VLJ) is a fully submerged customshaped deceleration / acceleration nozzle with a stator section aft of the rotor. The stator section cancels rotor-induced swirl, and through that, optimizes the acceleration of the jet stream and the rudder inflow. The submerged position eliminates the requirement for a long inlet tunnel resulting in linear in- and outflow and low marine growth sensitivity.

The Voith Linear Jet combines the best properties of propellers with the
best properties of waterjets.

The resulting benefits of this natural flow path without redirections are increased efficiency and reduced noise and vibration levels. For each vessel application a thorough hull integration study is performed and in combination with the special nozzlefastening mechanism, it maximizes nozzle thrust generation and minimizes nozzle drag up to high speeds.

Application Examples of the new Voith propulsion system

The main application envelope of the Voith Linear Jet is between 25 and 40 knots. Outside this speed range other features like the reduced draft versus a propeller or a higher bollard pull can make the Voith Linear Jet the preferred option.
e.g. Wind service support vessel with Voith Linear Jet
Bollard pull, maneuverability and transit efficiency are main operational requirements for a workboat like a wind service support vessel. Optimized nozzles for bollard pull are available in the VLJ range. To obtain favorable transit efficiency with these high-bollard pull nozzles, a vessel-optimized hull integration study is standard for these applications. The high VLJ bollard pull values with the favorable transit efficiency allow vessel operation in higher sea states and increase the vessel's effective operational hours per year. When increased bollard pull and transit speed values are not required, then a one-size smaller engine may be considered.

Wind service support vessel with Voith Linear Jet

e.g. Fast ferry equipped with Voith Linear Jet
Fuel burn reduction and fast berthing in port maximizing the number of daily departures will make the ferry service profitable. The low VLJ installation complexity increases availability and lowers maintenance costs. A study conducted for a 4 x 2 880 kW, 30-knot ferry comparing traditional waterjets with the Voith Linear Jet showed a total 804 kW lower power requirement for the Voith Linear Jets. With a fuel burn of 220 g per kWh and a fuel price of US$ 750 per ton, the fuel costs for 2500 annual operation hours is reduced to US$ 331 650. The time required for safe approach of the jetty is minimized with navigation and yaw rate signals linked to the thrust allocation algorithms.

Fast ferry equipped with Voith Linear Jet

Graphs: courtesy of Voith

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