Page 12: of Maritime Reporter Magazine (May 1999)

INVESTMENT IN DESIGN diesels of the widest-bore types, albeit with something less than the maximum number of cylinders, would be needed to guarantee schedule-keeping up to a top speed capability of 25-knots. An open- top configuration is being investigated, with special consideration of strength and seaway behavior.

A subsequent advance to 15,000-TEU, while technically viable in GL's view, would be subject still further to logisti- cal and port factors, and would neces- sarily demand turnround productivity possibly as great as 300 moves per hour and necessitating provisions for simulta- neous working of the vessel from both sides.

Such a behemoth of the liner trades, calling at a minimum number of main- line hubs, could spawn a requirement for vessels of 3,000-5,000-TEU to serve regional pivots and feeders of up to 1,500-TEU to sweep the minor ports.

Draft is a key control on future size, since access to many of the major termi- nals and ports requires that a vessel should draw no more than 46 ft. (14 m).

Interrelated with this criterion, Suez

Canal parameters dictate a maximum beam of 190 ft. (58 m) for a draught of 46 ft. (14 m).

On the basis of these considerations, believes HDW's Andreas Kraus, the top capacity for a future generation of con- tainerships in the foreseeable future would probably be around 11,000-TEU rather than 15,000-TEU, assuming a reasonable deadweight-to-slot relation- ship.

Speaking in London at the 'Design and Operation of Container Ships' con- ference organized by The Royal Institu- tion of Naval Architects (RINA), Kraus said that studies under the Container

Transport Systems of the Future pro- gram demonstrated the economic advan- tages of the 8,000-TEU size.

Evaluations of various designs from 4,970-TEU upwards at different speeds indicated the competitiveness of the 8,000-TEU type as regards fuel con- sumption per slot and nautical mile, with the best performance at 22 knots. Over- all transport costs, including transship- ment and hinterland stages, were also demonstrated to be lowest for an 8,000-

TEU vessel at 22 knots.

From a global logistics point of view, the German research project indicated an optimum service speed of between 24 and 25 knots for the largest linehaul ves- sels. In his joint presentation at the recent RINA gathering with Marc

Lebrun from Bureau Veritas entitled 'Design consideration of very large con- tainerships,' Wartsila NSD Switzer- land's Barend Thijssen confirmed the potency of the Sulzer RTA96C diesel. A single, 12-cylinder model, the most powerful engine in the company's exist- ing two-stroke range, direct-coupled to a single fixed-pitch propeller, could ensure the requisite speed for ships as large as 9,000-TEU.

It was pointed out that technical stud- ies including vibration analysis had demonstrated the feasibility of 13- and 14-cyUnder versions of the wide-bore engine design. In 14-cylinder format, the RTA96C would deliver 76,860-kW (104,580-bhp) at 100-rpm.

The question is whether a propeller that can transmit so much power is tech- nically feasible. "Today's containership propellers are coming closer and closer to the limits set by propeller-induced vibrations and by the manufacturing of the propeller itself," argued Thijssen and Lebrun.

From a two-stroke perspective, it is felt that the alternatives for ships in excess of 9,000-TEU are a twin-engine, twin-screw configuration, or a contra- rotating propeller arrangement. The con- siderable impact on capital costs of two massive low-speed engines instead of a single unit, however, could be a deter- rent in other than the most extreme sizes, i.e. of a minimum 13,000-TEU, it was suggested.

The contra-rotating propeller system option thereby warrants closer examina- tion by the industry.

Where enormous power concentra- tions are involved, it is felt that this holds certain potential benefits relative to a conventional single screw arrange- ment through higher propulsive efficien- cy, and therefore reduced installed power requirement and operating costs, and by offering a degree of redundancy and extra operational flexibility.

Circle 234 on Reader Service Card 12 Maritime Reporter/Engineering News

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