Grim's idler
The Grim idler is a development by Otto Grim (born December 22, 1911 in Groißenbrunn ; † June 21, 1994 in Meiendorf ), professor at the Technical University of Hamburg-Harburg .
The purpose of this stator is to extract energy from the propeller jet of ships and convert it into additional thrust, which is transmitted to the ship via the propeller shaft and thrust bearings. This means that twisting energy that would otherwise be lost is converted into usable propulsion and, as hydrodynamic and practical studies have shown, fuel consumption can be reduced by up to 10% with the same driving performance .
The stator is a non-powered, combined turbine and propeller wheel with seven, but mostly nine, slender blades (flukes), which are mounted on the propeller shaft (tail shaft) behind the active propeller of the ship and rotate freely in the same direction. It has a diameter up to 20% larger than the driven propeller. The inner part of the blades is designed as a turbine for turning the stator, the outer part as a propeller for generating thrust. The stator is designed so that it rotates at 30% to 40% of the propeller speed during normal travel.
In 1969, the ship propeller manufacturer Schaffran manufactured its first system with the Grim idler. In 1980 the federally owned research ship Gauss was equipped with a guide wheel; private shipping companies did not begin to use the guide wheel for new ships until 1982. From 1982 to 1989 the Cologne propeller manufacturer Ostermann delivered another 80 idlers to various shipyards . In 1983, the Bremen volcano built the 45,051 GRT Pharos (build no. 1037), which was then the world's largest ship with a Grim's idler.
In practice, however, the stator turned out to be insufficiently simple, robust and low-maintenance. The complicated shape, breaks due to vibrations, cavitation , tightness and storage problems at the additionally loaded end bearing of the drive shaft then led to the provisional end for the stator. For optimal efficiency , the propeller should be built as large as possible, so there is often no space for an even larger stator. Reducing the size of the propeller in favor of a Grim's stator would not increase the overall efficiency of the propeller-stator combination, but in most cases even reduce it. In practice, however, this problem should rarely occur. No Grim idlers are currently being installed. With further developed idlers, however, once these problems have been resolved and the price of crude oil continues to rise, the situation could change again.
A well-known example of the use of Grim's idler was the Queen Elizabeth 2 , which was fitted with idlers from the Dutch company Lips during its renovation at Bremerhaven's Lloyd Werft in 1986 . Idler wheels that were around 16% larger were used (DGL / D propeller = 6.70 m / 5.80 m = 1.16). Even during the test drives after the conversion, damage occurred due to broken idler blades, which led to the tests being aborted and later to the removal of the idlers.
swell
- O. Grim: Propeller and Vane Wheel . Journal of Ship Research 24 (4), pp. 203-226 (1980).
- Dubbel: manual of technology.
- Hansa - Schiffahrt - Schiffbau - Hafen, 1985, p. 1279 ff.
- Klaus J. Meyne in Ship & Harbor . 1986 8 H. 9.
Individual evidence
- ↑ Hamburg University of Technology : Shipbuilding series : "Commemorative publication on the occasion of the 100th birthday of Prof. Dr.-Ing.Dr.-Ing.Eh Otto Grim", March 2012
- ↑ Michael vom Baur, Klaus J. Meyne: The Grim'sche Leitrad - Chronicle of an Innovation . In: Hansa , part 1 in volume 6/2012, pp. 59–62 and part 2 in volume 7/2012, pp. 30–33, Schiffahrts-Verlag Hansa, Hamburg 2012.