User report - Polymer plain bearings in yacht reefing systems: Seawater-resistant, resilient

Reckmann Yacht Equipment GmbH specialises in the development and production of reefing systems that reduce the sail area in very strong winds. The company has made a name for itself in the top segment of sailing with its manual, electric and hydraulic reefing systems. It also implements particularly powerful systems for ships up to 66 metres in length, which can reef sails up to 90 metres long.
To ensure that the reefing system works in every situation, the careful design of the reefing systems takes centre stage. This is particularly evident in the top swivel, which sits at the top end of a reefing system and holds the sail. When the sailor furls the sail, the inner part of the top swivel must move synchronously - as smoothly as possible and without any stick-slip effect. This places high demands on the bearing and the entire design of the component. In addition, salt water and the tropical climate, which are very hard on the components, pose particular challenges for the designer.
Most important, however, are the enormous mechanical loads that act on the bearing points. Large ocean-going yachts and circumnavigators have headsails with a surface area of 1,000m2 or more. To furl this surface area, drive torques of up to 5,500Nm must be applied. The high forces require drives consisting of extremely compact hydraulic motors with an operating pressure of 175 bar. And a current development that Reckmann is driving forward places even higher demands on the drives of the furling systems: instead of the usual profiles in which the sails are attached, carbon stays are used that are pre-loaded to up to 65 tonnes. Under these conditions, the drives and top swivels must ensure that the sails can be furled and unfurled without any problems at all times.
The high demands on the load capacity and availability of the drive components mean that Reckmann develops and manufactures many components in-house - even the ball bearings. The bearings rotate under load and have to absorb very high axial and radial forces. Originally, one rolling bearing each was used to absorb the axial and radial forces.

Today, the company relies on a combination of rolling and plain bearings for the reefing systems: a cylindrical roller bearing absorbs the axial forces. Radial support is provided by two plastic bearings, which are mounted in front of and behind the rolling bearing.
Reckmann builds some of the stainless steel cylindrical roller bearings itself because there are no standard products that can withstand the required loads and environmental conditions. In contrast, catalogue parts are available for the plastic bearings. Here, the company uses bearings made from the material iglidur J, which has proven itself under the given high requirements. 
The material has been proving itself for years as a fast and slow-motion specialist with the best friction coefficients in numerous other fields of application. In addition - and this is another important criterion in this case - the material is dimensionally stable, even in wet applications. After extensive in-house testing, Reckmann found the results confirmed and uses plain bearing in its hydraulic furling systems. The bearings cope perfectly with the high mechanical requirements. Sailors can see that the desired smooth running characteristics are achieved even with high sail pretension by testing the mechanical emergency operation of the reefing system using a standard winch handle. Even after a longer break, during which the sail was not reefed, the bearings turn extremely smoothly under full load.
Reckmann is so satisfied with the results that the material is also being used in another new development for boats up to 100 feet in length. This is the universal joint of a furling system whose electric or hydraulic drive is installed below deck. The reefing system itself is assembled with a special ball flange in the deck. Reckmann also uses polymer plain bearings from iglidur in the movement axes of the gimbal mounting. As a very high surface pressure also occurs here, the plain bearings were extensively tested on the tensile test rig with up to 32 tonnes when installed. But there is more to come: some super yachts currently in the design phase are even larger than the previous top models. Reckmann is therefore working on new reefing systems that are also characterised by their perfect appearance, simple operation and smooth-running properties despite their high load. Here too, the company intends to use wear-resistant bearings.