New tug class introduced to the market TUGS AND SALVAGE
A
NEW RAstar class of high-performance ASD terminal/escort tugs have been
introduced by Robert Allan Ltd, of Canada. Fuelled by the demands of the many LNG terminal operations coming into play at the present time, the RAstar class tugs have been developed to offer good ship-handling, escort, and sea-keeping performance at exposed terminal locations. This new class of tugs can trace its genesis to
the VSP escort tug Ajax designed for Østensjø Rederi AS in 1996. The unique features incorporated into that hull form enabled a significant improvement in indirect towing performance, but the unforeseen advantage was that this hull shape would also provide a very significant advantage in sea-keeping. Based on this success, Robert Allan Ltd
began a programme of internal research and model testing into the performance and behavioural characteristics of this type of hull form. A key assignment in 2004 led to the
development of a major ASD escort tug design, featuring the same general sponsoned style of hull form. This design then served as a model for the next generation of tugs, which have been designated as the RAstar class. The model testing programme was
performed at the Vizon-SciTec Model Basin Facilities, in Vancouver, under the direction of Alan Reynolds of Offshore Research Ltd. The testing included basic speed/power characteristics in calm seas and in waves, as well as manoeuvring, sea-keeping, and indirect escort towing performance. Most recently the programme has been extended to examine the effects of tug-ship interactions on towline forces in a seaway. The RAstar hull form incorporates a
significant outward flare (or sponson) on the upper hull sides. When the tug is heeled over under influence of the towline during an escort operation, the ‘weather’ sponson is submerged and a large righting force is generated to improve the stability, thus increasing the towline force. In addition, the hull has a large foil-shaped skeg, also designed to provide increased indirect forces. Although these hull and appendage
design features were developed to provide increased escort performance, the sea- keeping characteristics have also shown very significant improvements over more conventional hull forms. The RAstar hull forms provide dramatic
TECHNICAL PARTICULARS ACP Z-TECH 6000 TUG
Length, oa…....................................27.40m Beam, moulded …............................11.65m Depth, hull moulded …......................5.00m Draught, maximum….........................5.33m Bollard pull...................60tonnes minimum Speed...........................12.5knots minimum Classification…............................Lloyd’s Register 100 A1 Tug, LMC, UMS
24 This ACP Z-Tech 6000 tug was built for operation in the Panama Canal.
TECHNICAL PARTICULARS RASTAR CLASS TUGS
2800 Length, oa
Beam, moulded Depth, moulded
28.20m 12.60m 5.30m
Maximum draught 5.20m Bollard pull Speed
3200
32.00m 12.80m 5.45m 5.35m
3400
34.00m 14.50m 6.20m 6.95m
3600
36.00m 14.20m 6.05m 5.75m
3800
38.00m 14.50m 6.10m 5.10m
3900
39.10m 14.70m 6.10m 5.75m
65tonnes 75tonnes 90tonnes 95tonnes 100tonnes 100+tonnes 13.0knots 13.3knots 13.5knots 14.0knots 14.5knots
15knots
reductions in roll amplitude and accelerations, and the large skegs provide significant roll damping. As part of the model testing programme to
verify the performance of the RAstar hull forms, and to be able to state with confidence that the motions of this new design were a real improvement over existing tugs, a model of a similar size of standard tug was also built, and the motions of the two hull forms were measured in identical wave conditions for a unique vessel-to-vessel comparison. The seakeeping predicitions for the
RAstar class tug indicate that this form of vessel provides an exceptionally stable and comfortable platform for the crew. A significant reduction in motions is predicted in comparison to the more standard tug type, and will significantly reduce crew stress and fatigue, thereby improving overall operational safety and effectiveness. Currently RAstar class designs are under
contracted development for tugs of 28m, 32m, 34m, 36m, 38m and 39m, with from 65tonnes to 100tonnes bollard pull.
First of series tugs delivered Meanwhile, in other news the first three of a series of new Z-Tech 6000 class ship-handling tugs have reported for duty with the Panama Canal Authority (ACP). The first tug arrived
in Panama in late January 2007, the second and third in February. The next series of tugs are currently building, with deliveries starting in the third quarter of 2007. Designed by Robert Allan Ltd, these new
high-performance tugs are based on the standard successful Z-Tech 6000 class design, but were specifically adapted to the operational needs of ACP for the busiest ship channel in the world. The total fleet of eight new tugs is being built by Cheoy Lee Shipyards Ltd, of Hong Kong, at its Hin Lee Shipyard facility, in China. The Z-Tech design combines the best
performance features of an Azimuthing Stern Drive (ASD) tug with those of a Z-drive tractor tug. The Z-Tech has a large skeg forward, providing a high indirect steering force, and enabling directionally stable operation in both ahead and the astern tractor modes. The working deck forward is relatively low
and flat, creating a safer working space, yet still leaving sufficient room to install/withdraw the Z-drive units from aft of the house. For seagoing operations or for line towing, the Z- Tech with its high, rounded stern, works stern- first in tractor mode. A single control station serves both harbour
ship-handling duties (facing forward over the working deck), and transiting or towing voyages (facing astern).
SHIP & BOAT INTERNATIONAL MAY/JUNE 2007
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