Successful sea trials for first VLJ equipped vessel

FEBRUARY 5, 2015 — Trearddur Bay, a 21 m x 7 m wind farm service catamaran that is the first vessel propelled by the new Voith Linear Jet (VLJ) propulsion system, has successfully completed sea trials in the Solent, achieving 31 knots with 8 tonnes DWT.

The vessel is the latest to be designed by BMT Nigel Gee Ltd for Turbine Transfers and was built by Aluminium Marine Consultants (AMC) on the Isle of Wight.

The Voith Linear Jet (VLJ) is an innovative propulsor unit combining the best properties of conventional propellers with the best properties of conventional waterjets. It consists of an advanced ducted propeller combined with a stator positioned in the duct aft of the propeller, in a similar arrangement to that of a waterjet.

Manufacturer Voith Turbo describes it as “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.”

Trearddur Bay is fitted with two VLJ 900 propulsory powered by twin MTU 10V2000M72 engines offering very high efficiency and lower fuel consumption.  For the same installed power the VLJ can provide a bollard pull significantly higher than that of a waterjet or conventional fixed pitch propellers.

Ed Dudson, BMT Nigel Gee’s Technical Director commented: “Trearddur Bay’s successful sea trials demonstrate BMT Nigel Gee’s ability to combine robust, proven hull forms with innovative propulsion systems to new solutions for this fast growing market.”

BMT Nigel Gee says the VLJ equipped catamaran has performed convincingly all along the line and by far surpassed the expectations ofTurbine Transfers Ltd, a subsidiary of well-known workboat operators Holyhead Towing Company.

The vessel will take service technicians to offshore wind farms at sites all around Europe, initially at the Westernmost Rough site off the Humber for Dong Energy.

The catamaran achieved a trials speed of 30 knots, above expectations, compared to 26.5 knots for a near sister with jet propulsion. Even if the current installed ten cylinder 900 kW diesels were replaced for eight cylinder 720 kW diesels the economical service speed of 25 knots required by Turbine Transfers would still be met.

“The vessel is achieving more thrust at high speeds, and when stopped in the water and pushing on a wind turbine than with conventional systems, while achieving significantly lower noise and vibration levels,”sayd Alistair Knowles, Marine Superintendent at Turbine Transfers. “Furthermore it improves our green credentials through substantial fuel and emission savings in our operations.”

Voith engineers designed and developed the VLJ exclusively by computer, applying the CFD (Computational Fluid Dynamics) method.