Blocks, also known as pulleys, are available with plain, roller or ball bearings. Select the bearing type according to the use that the block will serve onboard.
The plain bearing block, mainstay of the running rigging on a cruising yacht, is developed from the traditional dead eye which has no moving parts and originated as a piece of hardwood e.g. lignum vitae with carefully grooved holes through it. Things have gone full circle with the advent of the modern-day low friction ring equivalent.
Plain bearing actually means that the sheave rotates directly on a simple central axle i.e. the transverse pin between the cheeks of the block. The sheave (pulley wheel) may have a load bearing bush, also known as a bushing or sleeve bearing. A bush is added to reduce friction and resultant wear. The bush that bears the load is the origin of the term Plain Bearing.
The picture shows a Barton plain bearing block, a sheave with a bush fitted and a sheave with no bush.
Plain bearing block features:
- No ball bearings, no roller bearings !
- Simple construction with only one moving part, the least possible to construct a serviceable pulley.
- Low maintenance
- The sheave rotates directly on a simple axle pin which may have a load bearing bush - sheaves have a groove designed to sympathetically accept rope or wire and are machined from nylon, aluminium alloy, brass or similar materials.
- Cost effective - reasonably priced compared with ball bearing or roller bearing blocks.
- Excellent for high static loads – blocks with bearings will run faster under light load and cope much better with fine tuning adjustment under extreme load
- Excellent all round, multi-purpose functionality
- Excellent working life – no bearings to be crushed and/or fall out
Parts of a Yacht Rigging Block, traditional and modern