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Thrusting towards a half century of service

Azimuth thrusters have established a wide role during nearly half a century at sea

by Malcolm Latarche I

n three years’ time, the azimuthing thruster will celebrate its golden jubilee in oceangoing service, celebrating the installation in 1967 of two 342kW Schottel Rudderpropellers in the tug Janus, bringing the device out of the inland waterways by giving it a higher powered role. But they date from 1950, since their invention by Josef Becker, the founder of German propulsion specialist Schottel. The first versions were not installed in the hull in any conventional way but were fitted on inland vessels as an oversize outboard motor similar to the company’s modern Navigator units. A demonstration of the manoeuvrability conferred by thrusters will be on show in

Hamburg in June this year at the ITS 2014 Tug, Salvage & OSV Convention and Exhibition when a number of tugs fitted with Schottel thrusters will perform a ‘ballet’ in Hamburg harbour

as a finale to the convention.

Schottel will also be showcasing the latest version of the Schottel Rudderpropeller at the exhibition. Today the basic concept and technology has been adapted and improved by Schottel and several other system makers and can be found on an increasing number of ships of all types. Over the years since the initial thruster was built by Schottel, tugs and small ferries have been joined by offshore ships and rigs as vessels where


as its sole means of self-propulsion. But its thrusters are not intended to move it around the ocean. Having no main engine of its own, Prelude will be towed between employments and its trio of thrusters are there for precise and accurate manoeuvring into position before the risers are connected.

azimuthing thruster propulsion system is preferred over the more conventional propeller and rudder of other ship types. Soon it could even be claimed that the largest vessel in the world relies on thrusters as the 488m FLNG Prelude now under construction at Samsung’s yard in Geoje, South Korea, will be fitted with three of them

Schottel’s hybrid debut

With hybrid power systems being very much a matter of debate for many ship types, it seems somehow appropriate that for Schottel, a pioneer of

thruster development, the first

application for the new thruster it will be showcasing at the ITS 2014 Tug, Salvage & OSV Convention and Exhibition in Hamburg later this year will be in a hybrid tug. The new thrusters are a variant of the

company’s Rudderpropeller series SRP 3000 and 4000 and feature power-take-in (PTI). The tug is the first in the ‘Efficient Double-ended DYnamic’ (EDDY) tug and workboat series and is being built by Holland Shipyards to a concept design developed by Baldo Dielen Associates. More specifically, the tug is a 30-65 type with the numbers signifying a length of 30m and a bollard pull of 65 tonnes. Main power for the tug’s propulsion comes

from a pair of Mitsubishi S16R diesel main engines coupled directly to a pair of Schottel SRP 3000 propulsion units. With the SRP PTI series the PTI is a permanent electric magnet motor providing 460kW at 1,100 rpm for manoeuvring and transit operation up to 10 knots without the main engines running. Power

66 I Marine Propulsion I April/May 2014

for the PTI motors is provided by two Scania DI 16 diesel generators. Because tugs are required to perform a wide variety of tasks across their entire power spectrum, they rarely need to operate for long at or near the high power levels required for

Modern thrusters come in many forms; the original rudderpropeller type with its Z-drive operation is still around in large numbers but the simple L-drive is more frequently used and the permanently-outside thruster has been joined by retractable and swing-up types that are taken inside the hull when not in use so as to reduce drag. Some thrusters are fixed, some push and others pull. Podded propulsion systems are thrusters where even the motor is moved outside of the hull. But it is the tunnel thruster that is the most common and found on every type of ship. Some manufacturers have developed products that can perform as both a tunnel thruster and an azimuthing thruster. In these

optimum engine performance. The PTI solution adapts to the task at hand. It eliminates the part load operation from the main diesel engines and takes over for transit and idling. The system allows for an easy switch between engine and PTI during tug operation so that the power of the PTI can be added to the diesel engine in the boost mode for maximum bollard pull or high torque requirements at partial loads. An additional benefit is that the main engines can be considerably smaller in size thus reducing capital and running costs. The PTI option also permits a high level of redundancy as there is an electric motor in addition to the main diesel engine. The EDDY tug will not be the first hybrid tug that Schottel has had a hand in. What is claimed as Europe’s first true hybrid tug, the 2010-built Rotor tug RT Adriaan, re-entered service with the KOTUG fleet

in the port of

Schottel’s SRP 3000 PTI thruster is one of its newest designs (credit: Schottel)

Rotterdam two years ago having undergone conversion from conventional diesel drive to a diesel/battery hybrid with its Caterpillar engines supplemented by a lithium-ion battery pack. A 500kW TECO-Westinghouse motor/generator is installed in each shaftline close to the flexible coupling of the tug’s trio of Schottel SRP 1215 FP azimuth thrusters.

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