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Tackling the rotor tug challenge

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Author(s): Jesper Nielsen, Sales Manager for the Maritime Division of FORCE Technology

Across the world, there is an increased demand for advanced simulator-based tools that can assist tug operators and ports in determining the best type, size, number of tugs and the strategies to be used for a given tug operation.

Simulations, including type-specific tug simulations, are a strategic focus area for FORCE Technology. It has been cooperating with a large number of tug operators and ports on training and port studies for the past 10 years. Considerable amounts of development funds have been used specifically to develop tug-related simulation systems based on towing tank tests and advanced mathematical models.

The studies in which we have seen a requirement for involving advanced tug simulation include: escort operations for large tankers when approaching terminals; towing out of large newly built ships from yards; assistance to Liquefied Natural Gas (LNG) carriers to and from terminals positioned offshore; and tug assistance in new or modified ports that will accommodate larger vessels in the future such as large LNG carriers, container vessels, cruise ships or tankers.

At FORCE Technology, we operate nine simulators, four of which are full mission systems and three are dedicated tug simulators. All simulators can be coupled, and all can easily be transformed and used as either tugs or other types of vessels. Pictured is a new compact tug simulator where 27 52inch monitors with full HD resolution in a 360 degree array have been used to provide a very large field of view (see Figure 1). The simulator can be used to simulate a specific Azimuth Stern Drive (ASD), Voith Schneider propeller (VSP) or rotor tug and includes a vast selection of handles, winch and engine controls and instruments including overhead panels.

FORCE Technology has 50 years of experience in conducting comprehensive maneuvring and simulation studies. FORCE Technology conducts about 30 engineering studies every year in our simulator centre in Copenhagen, Denmark. The studies are conducted in order to ensure safe and efficient navigation of different types of vessels in existing or planned port facilities. The simulation studies have different objectives which could include operations such as the placement of navigational aids; evaluation of breakwater layout and alignment, including width and alignment of approach channels; evaluation of arrival/ departure conditions for existing or new port facilities. They can also include: ship motions in both frequency and time domains giving accurate assessment of risks; mooring studies; controllability of vessels at limited water depth; operational guidelines, as well as determination of tug type, size and number best suited for a specific operation.

Simulation studies involving rotor tugs

For the past years, we have performed an increasing number of simulator-based studies involving rotor tugs. The rotor tug concept was developed by the Dutch company Kooren in the late 1990s and first used to handle the large-windage-area car carriers in the Bremerhaven locks. The rotor tug can be described as a ’conventional’ tractor tug with two azimuth thrusters fore and the aft skeg replaced by a third azimuth thruster unit. This configuration of propulsion and steering units gives the high-powered rotor tug extreme maneuvrability and the ability to work efficiently in narrow spaces. For training and port studies, it is important that the mathematical models used are very precise and accurate. Based on data from physical tank tests, naval architects and engineers have produced different sizes of rotor tugs.

The mathematical models produced at FORCE Technology include complex features such as ship to ship interaction between the assisted ship and the tugs; tug performance in waves; fender interaction in three dimensions; modelling of the towing line; description of ship mass, inertia, time constants; deep/shallowwater hydrodynamics; aerodynamic forces (derived from our database of wind tunnel tests) and wave-induced motions. The simulation studies performed involving rotor tugs have primarily been for the operation of very large bulkers and LNG carriers where the tugs have been instrumental to their safe approach and departure.

 

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