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

• What was needed: Polymer plain bearing made of the material iglidur® J
• Requirements: High mechanical load capacity, seawater resistance, resistance to heat and UV radiation
• Industry: Shipbuilding
• Success for the customer: The material iglidur® is very dimensionally stable even in moist applications. The bearings can cope with the high mechanical requirements perfectly. Even with high pretension of the sails, the desired smooth running properties are achieved.

Reckmann Yacht Equipment GmbH specialises in the development and production of furling 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 1,000 m2 or more. To furl this surface area, drive torques of up to 5,500 Nm 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-tensioned 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 roller bearing each was used to absorb the axial and radial forces.

Today, the company relies on a combination of roller and plain bearings for the furling systems: a cylindrical roller bearing absorbs the axial forces. Radial support is provided by two plastic plain bearings mounted in front of and behind the roller 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 ambient conditions. In the case of plastic plain bearings, on the other hand, catalogue parts can be used. Here, the company uses bearings made of the material iglidur® J, which has proven itself under the given high requirements. 
The material has also proven itself for years in numerous other fields of application as a fast and slow-motion specialist with the best coefficients of friction. In addition - and this is another important criterion in this case - the material is very dimensionally stable, even in wet applications. After extensive in-house tests, Reckmann found the results confirmed and uses the plain bearings in its hydraulic furling systems. The bearings cope perfectly with the high mechanical requirements. Sailors can see for themselves that the desired smooth-running properties are achieved even when the sails are highly pretensioned 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 experience gained 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 mounted in the deck with a special ball flange. Reckmann also uses polymer plain bearings made of 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 bench with up to 32 tonnes when installed. But there is more to come: some superyachts 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 the high load. Here, too, the company intends to use wear-resistant bearing.