What is Blocks & Sheaves?
Blocks are pulleys used throughout a sailboat's rigging system to redirect lines and provide mechanical advantage. They can be fixed, swivel-mounted or incorporate cam cleats for line control.
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What it is
Blocks are pulleys used throughout a sailboat's rigging system to redirect lines and provide mechanical advantage. They can be fixed, swivel-mounted or incorporate cam cleats for line control. Blocks may include bearings, which are ideal for applications involving frequent movement, or be plain (without bearings), which are better suited for static or steady loads.
What it does
Blocks reduce friction when lines run through them, making it easier to handle heavy loads like raising sails or trimming sheets. By providing mechanical advantage through multiple-purchase systems, blocks allow sailors to control large sails with manageable effort. Well-maintained blocks ensure smooth line movement and efficient sail control.
Why it matters
Blocks are fundamental to every aspect of sail handling. Worn or seized blocks create excessive friction that makes sail trimming difficult and can damage lines. Failed blocks during sail handling can lead to loss of control, especially in heavy weather. Smooth-running blocks mean easier sail changes, better sail trim, and less physical strain on the crew. On racing boats, efficient blocks can mean the difference between winning and losing. Blocks are designed for specific line diameters and rated for load capacity. Blocks may be rated for the breaking strength (the load at which the block will start to fail and deform) or safe working load (the maximum load the block can handle while still working as designed). Generally, the safe working load is around half the breaking strength. It is generally recommended to install blocks whose safe working load is above the expected maximum load for your application. This allows the block to handle unexpected and shock loads
General Maintenance
After sailing, rinse blocks with fresh water, especially after salt exposure, to remove salt and dirt. Apply a manufacturer-recommended marine-grade lubricant to ball bearings to maintain smooth performance, and replace any blocks that show cracking, delamination, or significant wear. During the sailing season, inspect blocks monthly to ensure the sheaves rotate freely without binding, and check for deformation, cracks, excessive wear, or grooves caused by line friction. Also verify that mounting hardware is secure and replace any worn shackles or bolts. Once a year, disassemble serviceable blocks for a thorough cleaning and re-lubricate the bearings with marine-grade lubricant. Blocks are designed for specific line diameters and rated for load capacity. Blocks may be rated for the breaking strength (the load at which the block will start to fail and deform) or safe working load (the maximum load the block can handle while still working as designed). Generally, the safe working load is around half the breaking strength. It is generally recommended to install blocks whose safe working load is above the expected maximum load for your application, as this allows the block to handle unexpected and shock loads.
Common Issues
- Sheaves or bearings seizing due to salt accumulation and lack of lubrication
- Worn sheaves with grooves that chew up lines
- Cracked or UV-damaged shells, especially on older composite blocks
- Cracking of cheek plates under high loads
- Mounting hardware working loose or corroding
- Beckets or attachment points wearing through
- Sideplates bending under load on undersized blocks
- Thin lines jumping the sheave and wedging the block against the cheek plate
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