It is form and function that dictates good tug design. The tugs working in the port of Hong Kong do so in a very particular set of conditions. The development of the port as an enclave with land in short supply, let to the lightering of ships where by cargo is loaded and unloaded between vessels in the middle of the harbour. This continued even after the advent of containers. The port maintains 58 moorings for this purpose and 2.9 million TEUs were handled in this fashion in 2001. Typically these are loaded by cranes with their own derricks mounted forward. The containers are stacked several high and then the lightering barge puts its own lines to a tug and is towed to a sorting yard ashore. A lighter barge carries in the range of 240 TEUs of full containers and over 300 TEUs of empties. These operations are supported by more than 1000 barges and 250 tug boats.
Competition is intense in Hong Kong and the costs of boats doing these short hauls has to be contained. As a result, many of the boats are single-engined vessels. Fortunately Hong Kongs long maritime history and communities of fishing families has built a population of excellent boat handlers. All barge movements by tugs are done "on the wire" with the barge putting its line out to the tug, where the eyed end of the bridle is placed on a towing hook.
This March Zhuhai Shipbuilding Industry Company, located at the mouth of the Pearl River in the southern part of Chinas Guangdong province, has a new single screw tug under construction for a Hong Kong customer, Transward Ltd.. While it appears rather like most new Hong Kong tugs above the waterline, the addition of a steerable nozzle will be a distinctive feature below the water line. Ducted nozzles of the kort type typically add 30 percent to a tugs thrust and bollard pull. But the nozzle on this new boat has a longer profile than is conventional and it is mounted on the rudder stock so that it can also steer the tug. This is not new technology as steerable nozzles have been around almost as long as nozzles, but with most tugs being built as twin propeller boats, it is interesting to see that the single steerable nozzle still has a place.
Power for the new 27.5 by 24.4-metre tug will be a Cummins V-12 KTA38 M1 putting 1000 HP (746 kW) into the Nico 7:1 gear. The hull is built with a .5 metre between frames and a moulded depth of 3.9 metres. With the steerable nozzle enclosing a 2.1-metre propeller the draft will be 2.88 metres.
In these times of high tech azimuthing Z-drives and cycloidal drives, there are those who might think that any boat that doesnt at least have twin propellers is antiquated. One fleet operator in the US Pacific northwest continues to operate single screw line haul boats and has a hard time getting captains who can manoeuver the boats away from the dock. But in Hong Kong where excellent boat handling is a way of life, a steerable nozzle will give this new tug a distinct advantage in spinning loaded container barges around in heavy traffic.
For further information contact:
Mr Fred Chen