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Innovation Links Modern Technology With Maritime Past

Schottel maintains 75-year heritage Celebrations to mark the 75th anniversary of German propulsion specialist Schottel, culminating in a spectacular fireworks display on the River Rhine, incorporated the launch of a new product and the presentation of technical papers outlining the company's latest research. MR/EN recently joined 150 guests which included customers, suppliers and distributors from around the world in a busy weekend of high technology mixed with revelry.

From a technical standpoint, the highlight of the event was the unveiling of the Schottel Twin Propeller (STP) by Sales and Marketing Director K. Peter Hammer. Developed in association with the Potsdam shipbuilding research establishment, the system consists of a 360 degree steerable propulsion unit which, in contrast to the company's popular and highly successful single screw Rudderpropeller, is equipped with two propellers of identical diameters turning in the same direction. Touted by Mr. Hammer as having a 20 percent higher level of efficiency and a significantly reduced noise level, the STP covers the entire power range for 360 degree steerable propulsion units, which makes it a favorable propulsion choice VT's latest fast attack craft for the Qatar Emiri Navy, QENS Al-Deebel, is shown being launched at the yard's Southampton shipyard.

for passenger ships, freighters, supply vessels and other vessels in the medium speed range.

For many years marine engineers have been attracted by the efficiency improvement offered by two moderately loaded propellers, in comparison with a single, highly loaded unit. However, the complex design, maintenance and sealing problems associated with a tandem arrangement of contra-rotating propellers prompted Schottel to seek a new, uncomplicated and reliable concept, and henceforth sprung the development of a two propeller/single shaft arrangement with fins located between the propellers to recover the swirl energy. The only mechanical difference between the STP and the conventional Rudderpropeller, proven in thousands of applications, is the presence of an extended propeller shaft.

Although the basic principle of the STP appears to be relatively simple, Schottel liaised with Potsdam in an effort to define the optimum propeller/ fin relationship for maximum efficiency improvement.

Model tests were carried out in the research establishment's cavitation tank, while extensive full-size trials were conducted at the company's own test pontoon.

These tests resulted in the production of a robust 360 degree steerable propulsion unit with superior efficiency. Two low-load propellers are fitted to a single shaft driven by a bevel gear system in an underwater gearbox. The front propeller attains a very high efficiency acting in 'pull' mode; the guide fins deflect the water to produce a straighter flow when it reaches the second, 'push' propeller. Further cooperation between HAL's Rotterdam VI is shown under construction at Fincantieri's Marghera yard. Schottel and Potsdam resulted in the development of special geometry for the rear propeller, enabling the unit to achieve high efficiency during exposure to inhomogeneous flow conditions stemming from both in and out of the front propeller flow. This new geometry reduced the need for a smaller rear propeller diameter — the traditional, but inefficient solution to the problem.

The configuration of the stem and underwater housing and the shape and position of the fins were also determined by extensive testing and experimentation. Not only are the fins arranged to eliminate swirl between the screws, but being aerofoil-shaped in section, they can produce a lifting force as the water passes around. This force possesses an axial component in the forward direction which is considered more than sufficient for offsetting any resistance.

The low noise and vibration levels will be particularly valuable assets for passenger vessel applications, contended Mr. Hammer, and the STP will allow either the economic efficiency to be improved or the speed to be increased with the same power. "The STP is exceedingly attractive for freighters and supply ships owing to the high efficiency and reduced fuel costs. In many instances, existing ships can be cost-effectively converted to this propulsion system.

Furthermore, we have shown that efficiencyoptimized, multi-propeller solutions do not necessarily have to be mechanically complicated and thus more trouble-prone," he stated.Emergency Propulsion Systems During the anniversary celebration, Schottel employee Uwe Gragen, a naval architect and project manager, provided an update concerning IMO's Design and Equipment Subcommittee's thoughts on the subject of emergency propulsion systems, particularly for ships carrying hazardous cargoes. He cited a number of recent incidents where he supposed vessel losses would have been prevented, had Schottel pump jets been installed at vessel bows.

Pump jets, which provide 360 degree steerable thrust, are available in a range of sizes to accept an input power of up to 3,500 kW, and the Manovriertechnishes Institut (MTD in Hamburg has reportedly calculated that many environmental disasters could have been prevented with an emergency propulsion system requiring less power than this.

IMO has concluded that an independently powered pump jet installed at the bow has no effect on the efficiency of the vessel being flush with the hull and can increase maneuverability during normal operation. Moreover, the unit's position, situated at a distance from the engine room — the most likely source of a vessel-crippling fire — is in the best position for guaranteeing maximum maneuverability with the lowest power requirements.

Interestingly, the IMO Subcommittee has commented on the fact that many tankers are under-motorized. A combination of advanced shiplines and improved propulsion enables these vessels to achieve their service speed in calm water at very low power. At Beaufort wind and Sea States 10 and 11, however, the speed attainable by these vessels is hardly enough to give the rudder any effect, and at Beaufort 12, full power is insufficient to keep station. A pump jet used in conjunction with the main engine would also reportedly solve this problem. The Schottel pump jet comprises an impeller, diffusor assembly and bottom plate. The impeller, driven through a right angle gear, sucks water via an intake funnel and diffusor into a pressure casing which is connected to the bottom plate. The water is expelled through three symmetrically arranged out- October, 1996 let nozzles in this plate, and as the whole pressure casing can be turned through 360 degrees, thrust may be directed without losses in any direction. The unit can be installed flush at any point on the ship's hull and driven by any power source.

Mr. Gragen conceded that additional safety for ships carrying hazardous cargoes cannot be realized at zero cost. "The environmental disasters caused by tanker accidents and our responsibility to future generations, however, force us to react immediately to minimize these risks," he said. Bearing in mind that a double hull is a secondary means of protection and often only provides a delay before the cargo starts to pollute, fitting an independent emergency propulsion system such as the Schottel pump jet seems a step in the right




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