propulsors
operating in ice. The motor is fed by a pulse width modulating (PWM) drive designed to provide high torque at low shaft speeds, an important factor in achieving a good capability to free a stalled propeller in ice. With a 100 per cent shrink-fitted stator, efficient cooling is secured from the surrounding sea water, providing substantial thermal inertia to absorb peak loads during ice milling. ››› ››› The shaft bearings exploit the latest roller bearing technology. All seals resisting sea water are of the environmentally friendly type, such that a single seal failure will not create oil spillage into the sea.
A stainless steel propeller is designed to cope with the tough environment imposed by operating in ice conditions, its individual bolted-
on blades enabling easy replacement in the event of damage.
Wärtsilä’s new Ice Pod propulsor also targets vessels operating in polar conditions, the ABS- approved azimuthing thruster designed to withstand severe loading and help cut through 1m-thick ice. The group’s R&D department applied 3D modelling to determine forces and dynamic loads so that pod dimensions could be calculated and optimised.
The 2,500kW electric motor drives a 2.3m-diameter propeller. The overall unit is formed by three elements: the pod and propeller; the can, which interfaces the thruster to the hull; and an inner part containing the upper gearbox whose output shaft is connected to the motor.
Wärtsilä’s Ice Pod Voith logs orders for VITs, VIPs, VSPs and VWTs
Recent orders booked by Voith Turbo call for thrusters for offshore, passenger vessel and yacht applications. The German specialist claims to be the only manufacturer producing thrusters with ratings of 1,500kW based on permanent magnet synchronous motor technology.
The principle of a thruster with a permanently-
excited electric motor housed in the hollow shaft and with no maintenance requirements due to seawater-lubricated bearings is increasingly appreciated, says Voith. Since the start of series- production in 2008, the company has sold more than 55 units, most of which are in service.
Voith Inline Thrusters (VIT) and Voith Inline
Propulsors (VIP) feature rim drives which combine electrical, mechanical and hydrodynamic elements to achieve a compact unit with low vibrations for smooth running. Swing-out Azimuth stern thrusters, a variation of the VIP, can be extended from the hull and rotated through 360 degrees without limitation. The units are reportedly in demand for dynamic positioning,
yacht and
offshore applications. With an inner propeller diameter of 2,300mm, the VIT is currently claimed to be the most powerful of that type. Among recent references is an offshore
A Voith Water Tractor driven by two VSP propulsors
wind farm jack-up vessel under construction at the Cosco Shipyard in China for the Danish company A2SEA. The installation will comprise a VIT unit as well as three Voith Schneider Propellers (VSP). • A fifth Voith Water Tractor (VWT) has joined a fleet of such tugs deployed in the Israeli port of Haifa, supporting the safe berthing of container ships. With a bollard pull of 70 tons, Ilan has a higher capacity than the existing vessels Ariel, Eithanah 2, Edvah and Amatzia 2, which have respective ratings of 30, 35 and 55 tons. Like all VWTs, the tugs are powered by Voith Schneider Propeller
systems, Ilan featuring
two VSPs (type 32R5/265-2), each driven by a 2,670kW engine. For the first time, however, Voith not only delivered the complete propulsion system but also provided the basic design of the tug in co-operation with the shipbuilder. Voith
undertook the complete steel project planning for structure, performed all
necessary strength calculations, compiled the stability documentation and provided the design and arrangement of anchor, towing and mooring equipment.
A VSP propulsion solution was selected by
Ostensjo of Norway for a new eco-friendly class of platform supply vessel, citing four years’ favourable experience with installations on the PSV Edda Fram. Two VSP 32R5 ECR- 300-2 propulsors will drive a new 93m-long vessel scheduled for delivery from the Gondan yard in Spain in September 2013. A Voith roll stabilisation system is also specified.
Multi-thruster sets for offshore construction vessels
A backlog of large azimuth thrusters booked from Rolls-Royce for offshore projects includes an outfit of 12 systems for propelling and dynamic positioning a construction/pipelaying
70 I Marine Propulsion I February/March 2012
vessel completing for Allseas at Daewoo Shipbuilding & Marine Engineering. Pieter Schelte will be deployed in decommissioning work in the North Sea on delivery in 2014.
With a length of 360m and a breadth of 118m, the vessel will have a full load displacement of almost 900,000 tonnes; the hull blends a barge-like structure aft with a ›››
www.mpropulsion.com
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