Blocks with rolling elements are an engineering development of the plain bearing block.
Ball Bearing Blocks are ideal for running rigging applications where the line needs to run fast through the system and where the line needs constant fine tuning adjustment under load e.g. racing sheets - "release, pump, tension, release, pump, tension"
Ball Bearings in blocks are designed to rotate freely and can be identified by the fantastic whizzing sound they make when they are spun by hand under no load.
Ball Bearings are a set of multiple, relatively small diameter, spherical balls encapsulated in a ball 'race or cage' between the sheave and the rotating axle. The inner and outer ball race holds the balls captive and allows them to roll so freely that they are as close as you can get to frictionless. The hardened, round surfaces of the spherical balls can handle both radial and thrust loads. The minimal contact surface area between the small spherical balls is the reason for their negligible resistance to movement. However, because the load bearing surface is also low, ball bearings are susceptible to distortion when subjected to heavy force.
The picture shows a Harken ball bearing block, a ball bearing and a Selden ball bearing block.
Ball bearing block features:
- Virtually frictionless sheave rotation for free running lines
- Outstanding response under dynamic loads
- Ultimate performance and functionality for racing
- Suitable for rapid release and continual tuning
- Excellent durability with Delrin/Torlon ball bearings
Parts of a Yacht Rigging Block, traditional and modern