Page 5: of Maritime Reporter Magazine (January 1989)

PROPULSION

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IqbqdM j >' i i i 500th Voith Water Tractor,

First Of New Generation,

Now Under Construction* —Report Available—

Over the years, numerous experi- ments have taken place in ship towage. One concept, however, has remained unchanged, that being the

Voith water tractor. This year the 500th Voith water tractor is under construction, which provides an ide- al opportunity to reflect on what led to the development of this tug type and its ever increasing prominence within the towage industry.

The problems and risks involved in ship-handling are well known.

With the development of the Voith-

Schneider propeller, it was possible to depart from traditional ideas, i.e., of having the screw and rudder aft, and to venture to design a system which initially takes into account the problems encountered in ship- handling.

The special characteristics of the

Voith-Schneider propulsion system which created an effective solution to existing problems are reviewed, as follows: - The axis of rotation of the pro- peller is perpendicular to the thrust plane. - Within this plane the thrust can be infinitely varied in magnitude and direction. - The blade profiles are arranged parallel to the axis of rotation and are therefore untwisted along their entire length. Thus zero thrust is clearly defined when the blade pitch is nil. - Propeller pitch and thus thrust are controlled in respect of magni- tude and direction according to rec- tangular coordinates. By a combina- tion of the two coordinates, thrust changes can pass quickly through zero without creating any extra- neous thrust in undesired direction. - Because of its vertical axis, the propeller position can be chosen to optimize the correlation with the hull in respect of a particular task. - The VSP is extremely robust due to the very low rotational speed of the rotor.

The free arrangement of the

Voith-Schneider propeller under the vessel was ruled out because of the possible problems of grounding, lateral contacts and the crossing of chains and towlines. These poten- tial problems were, however, coun- tered with a guard plate which pro- tects the blades and at the same time acts as a nozzle plate.

It was now possible to arrange the propellers forward ahead of the cen- ter of rotation of the vessel, giving it an active front steering which is comparable to a car with front- wheel drive and steering. The tow-

General layout of a modern Voith water tractor. ing gear was shifted aft behind the center of rotation of the vessel and a stabilizing fin arranged under it.

Thus, the tractor principle came into being which still exists funda- mentally unchanged today.

The introduction of the Voith water tractor in ship-handling ser- vice proved to be a significant step toward improving ship safety. The first vessel of a new generation, now under construction in Antwerp, will be the 500th Voith water tractor to be built and in the 35-year history of this type of vessel, operational in about 100 ports around the world.

For further information and a free copy of the article on the 500th

Voith water tractor

Circle 46 on Reader Service Card *The above article is taken from an es- say, "500th Voith Water Tractor—A Brief

Review," by Dipl.-Ing. U. Sturmhofel, proj- ect manager in the Marine Engineering

Division at J.M. Voith GmbH, Heidenheim.

COSCO To Set Up

Own Repair Yard

China's largest maritime carrier,

China Ocean Shipping Co. (COS-

CO), plans to set up its own repair yard and will locate a 100,000-ton dock at a newly acquired site at

Nantong in central Jiangsu province near the mouth of the Yangtze Riv- er. The facilities will be used to maintain the more than 600 vessels in Cosco's fleet. The site has a front- age of 1,000 yards, and a water depth of 65 feet. Circle 318 on Reader Service Card

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Modern, sleek luxury

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Charming nostalgia (stemwheeler or sidewheeler) C. 150 passengers

D. 49 to 100 passengers

January, 1989 7