Polymer plain bearings replace roller bearings
Lightweight construction: Drive components for heavy duty furling systemsThe Reckmann Yacht Equipment GmbH develops and manufactures reefing systems for small to mega yachts. The company based at Rellingen near Hamburg holds a strong market share worldwide in the top segment of yacht building. Seawater-resistant, wear-resistant polymer plain bearings are used in the new generation models instead of self-made roller bearings. High-tech materials in perfect workmanship, elegant line layout and perfect finish: Sailing ships and yachts are a matter of great fascination not only for sailors, but also for many other people who are enthusiastic about technology and craftsmanship of the highest quality.
The fascination is not less if individual functional and design elements of yachts are more accurately inspected, for example, the furling system, by which the sail area is reduced during very strong winds. While reefing, every move must not only be correct, but the reefing system also has to function in every situation – which is a real challenge for the designer, because the salt water clogs the components severely and extremely high loads occur. The Reckmann Yacht Equipment GmbH has specialized in the development and production of such systems and has earned a good reputation in sailing and yacht building, and consequently a very high market share in the top segment. The range includes manual, electric and hydraulic reefing gear for vessels up to 66 meters in length. The most powerful gears that reef the sail to a length of up to 90 meters are usually custom designed and developed in close coordination with the yacht designer.
The reefing gear from Reckmann is often used in the building of top segment yachts.
The careful and thoughtful design of the reefing system is evident in the compactness of the important components: The top swirl sits on top of a reefing system and holds the sail. When the sailor rolls up the sail, the inner part of the top swirl must synchronously move along, and that too as smoothly as possible and without stick-slip effects. This places high demands on the bearing and the entire structure of the component. Dipl.-Ing. Björn Möser, Project Manager for customized reefing system: "All system components must be permanently resistant to seawater and tropical temperatures. Also, the perfect finish plays an important role in yacht building. Therefore, the housings are machined from an aluminum alloy and coated with a special anodizing film. “
In each of the components of the reefing system, "iglidur® J" plastic plain bearings provide for smooth motion without stick-slip effects.
Plain bearings resistant to seawater and wear are integrated in the top swirl (left) and also at the bottom of the universal joint (right) of the new furling system.
At least as important is the ability to withstand high mechanical loads. Björn Möser: "Large ocean-going yachts and circumnavigators have head sails with 1.000 sq.m. of area and more. In order to roll up this area, one needs to apply driving torques up to 5.500 Nm. " In these cases, extremely compact hydraulic motors with 175 bars of operating pressure, which transmit their power via a worm gear to the drive axle are used as drives. The self-locking of the gear ensures that no forces are transmitted back to the drive even from the largest sail area.
A development currently promoted by Reckmann poses even higher demands on the drives of the furling systems: Instead of the usual profiles in which the sails are attached, carbon stays that can be pretensioned up to 65 tons are used. Under these conditions, the drives and the top swirl always ensure a trouble-free furling and unfurling of the sails. The high requirements of resilience and availability of the drive components prompted Reckmann to develop and manufacture many components – even ball bearings – on its own. Björn Möser: "The bearings rotate under load and must withstand very high axial and radial forces. Originally, we used a roller bearing that absorbs the axial and radial forces. In the meantime, we use a combination of roller and plain bearings: A cylindrical roller bearing absorbs the axial forces. Radial support is provided by two plastic plain bearings that are mounted in front of and behind the roller bearing. “
The stainless steel cylindrical roller bearings are partially made by Reckmann themselves, because there are no standard products that can withstand the required load and environmental conditions. On the other hand you can rely on catalog parts for the plastic plain bearings. Here the company uses "iglidur®" bearings, which have perfectly proven themselves under the prevailing high requirements. René Achnitz, Product Manager "iglidur®" plain bearings: "At the beginning of the collaboration, we designed the bearings and ran a series of tests with several materials. We achieved the best results with the iglidur® J."
This material has already proven itself for years in many other fields of application as the fast- and slow-motion specialist with the best coefficients of friction. Moreover – and this is another important criterion in this case – the material has high dimension stability even in humid applications. After extensive in-house tests, Reckmann confirmed the results and is now using the "iglidur® J" plain bearings in the hydraulic furling systems. The bearings cope perfectly well with the high mechanical requirements. If the mechanical emergency operation of the reefing system is tested by a standard winch handle, the sailor himself is able to comprehend that the desired low-friction properties are achieved even with high pretension of the sails. Even after a long break in which the sail is not furled, the bearings rotate extremely smoothly at full load.
Reckmann is so pleased with the "iglidur®" operation that the material is also used in another new development for boats up to 100 feet in length. Here it is the universal joint of a furling system, whose electrical or hydraulic drive is installed below the deck. The reefing system itself is installed in the deck with a special swivel mount. Also in the motion axes of the gimbal mount, Reckmann uses polymer plain bearings made from this material. Björn Möser: "As a very high surface pressure occurs here as an additional parameter, we have the bearings tested extensively in the installed condition, i.e. in the universal joint, for tensile strength at a test stand with up to 32 tons. “
The end of the development has not yet been reached with these new, heavy-duty reefing system. Some super yachts, which are currently in the design phase, are again larger than the previous top models with new features integrated. Björn Möser: "Our customers – the shipyards as well as the yacht designers and sailors – are highly demanding." This is also true for Reckmann themselves. Therefore, the company is working on new reefing systems that are also characterized by ideal optics, easy operation and low friction properties, despite the high load. Here, too, Reckmann want to fall back on wear-resistant bearings.