Manoeuvring vessels around in tight spaces is not always as easy as it might seem.
Even the most experienced skipper needs to apply skill and care, especially when navigating in strong currents and vessel-congested waters.
Maintaining a secure and stable position is crucial, for example, when vessels are involved in delicate and often complex offshore oil and gas operations.
Drillships and floating production storage and offloading (FPSO) vessels must retain full control when docking and departing, whatever the wind conditions or currents.
There are many reasons for the maritime sector to be grateful for dynamic positioning.
Since it was introduced more than 40 years ago, dynamic positioning (DP) has provided a safe and reliable way to ensure vessels maintain their secure position during offshore operations. DP is a computer-controlled system to automatically maintain a vessel’s position and direction by using its own propellers and thrusters.
Usually located on the front and back as well as both sides of the vessel, thrusters have an important role to play in maintaining position from every direction. Satellite communications and information about wind and weather conditions are transmitted to the computer system, helping it to control the vessel’s movements. Using this information, the computer automatically engages the thrusters to counter and overcome any changes in the vessel’s position.
Large vessels usually have one or more tunnel thrusters – also known as bow thrusters – built into the bow, below the waterline. Most thrusters are driven by electric motors although some are hydraulically-powered. As well as keeping a ship securely in place, thrusters are extremely useful in helping vessels to dock without tugboat assistance – saving operators and owners time and service costs.
Initially used mainly in the bows of ferries and tugs, these versatile control devices quickly became must-have installations in offshore oil servicing vessels and larger ocean-going craft. They enable unassisted manoeuvring alongside oilrigs, other vessels, loading platforms and docks, and provide precise control at slow speeds. Tunnel thrusters are now an integral component in ships and marine applications around the world where precision vessel control is imperative.
Now a new tunnel thruster, developed by marine engineers at global power systems company Rolls-Royce, is described as being more powerful and easier to maintain than existing thruster technology. Innovative permanent magnet tunnel thrusters (TT-PM, see photo alongside) are positioned at the front and back of vessels and provide sideways thrust for manoeuvring and maintaining a stable position in rough seas.
Rolls-Royce is a leader in the integration of technologically-complex systems for offshore oil and gas merchant and naval surface and submarine vessels. As proud developers of the cutting-edge TT-PM system, the company claims it provides several key advantages over conventional thrusters, including:
* a 25 per cent increase in power output from same-size propellers
* a significant reduction in noise and vibration
* it can be removed underwater, saving owners and operators from dry
docking.
Other claimed benefits include the freeing up of space directly above the thruster where traditional tunnel thruster motors are located, and a symmetrical design that gives equal thrust to port or starboard. It is available in 1,600mm and 2,000mm diameters.
The new thruster features a permanent magnet motor in a rim which drives the propeller in the centre. The permanent magnet comprises a stator carrying electrical coil windings and a rotor fitted with strong permanent magnets. A rotating magnet field is created by the stator which interacts with the fields of the permanent magnets on the rotor – which generates force to drive the motor round, providing mechanical power.
Rolls-Royce says the thruster has been through an intensive test programme over several months and has demonstrated its reliability, high performance and operational efficiency.
A Norwegian shipping company has now placed an order with Rolls-Royce for a “unique package of advanced ship equipment” which will include the first commercial delivery of tunnel thrusters powered by permanent magnet technology. The equipment is for an offshore construction vessel being built in Turkey for Volstad Shipping AS (see image below).
The advanced ship equipment also includes the innovative new Rolls-Royce Unified Bridge which features a simplified range of controls, panels and displays for on-board systems. The technically-advanced bridge layout provides significantly improved ergonomics and easier operation to enhance operator and crew safety and improve task efficiency. Rolls-Royce is also providing Volstad with azimuth-thrusters, engines, dynamic positioning, automation, navigation, drives, switchboards and electric motors.
“Volstad Shipping will receive a vessel that incorporates innovative technology from the control centre at the top with the Unified Bridge, down to the very latest thruster technology below the waterline,” said John Knudsen, Rolls-Royce president offshore. “Our offshore team has worked closely with the ship owner and designer to develop the advanced equipment and features on this vessel.”
Here are some more technical details about the new permanent magnet tunnel thruster. And if you want to compare its performance with retractable steerable thrusters (also known as drop-down thrusters) you may find this article interesting.
Main photo courtesy CellsDeDells