Lewmar Blocks

Correctly sizing blocks is one of the most critical tasks for safe maneuvering. An undersized block strains under load and increases friction, making it tiring to trim sheets and halyards. Lewmar designs solutions based on bearings that reduce dynamic friction under tension, a detail that matters greatly when sailing in strong winds.

When selecting hardware, the first parameter to look at is the safe working load (SWL). Do not confuse it with the breaking load (BL), which represents the extreme limit before failure. The block must operate within its nominal working range to guarantee a long service life. Also consider the material of the cheeks and sheave, especially if the boat is exposed to sun and salt for extended periods.

At Nautiba we review your technical request before confirming the order. If you are unsure which model best suits your mainsheet system or the turning circuit in the cockpit, we help you verify the dimensional specifications. The goal is to supply the exact part based on your deck configuration, minimizing uncertainty during installation.

The line must run smoothly. If the line is too thick for the sheave groove, mechanical efficiency drops. Always verify the maximum line diameter permitted by the manufacturer for each specific block.

Selection Criteria and System Maintenance

• Evaluate the SWL rating based on the sail area and boat type, not just the line diameter.
• Check the compatibility between the attachment type and the existing deck mounting point.
• After each season, rinse the bearings with fresh water to remove salt crystals.
• Periodically check for cracks in the cheeks, especially if the block is made of plastic or anodized aluminum.

How do I choose the correct working load?

Calculate the maximum load the line will need to bear in strong wind conditions. Make sure the block's safe working load exceeds that value, applying a safety factor appropriate to the type of cruising or racing.

Is a plastic or aluminum sheave better?

The choice depends on use and load. Technical plastic is light and does not corrode, making it ideal for many cruising applications. Aluminum is preferable when high working loads and greater long-term mechanical strength are required.

Can I replace an existing block with one from a different brand?

Yes, but you must verify that the footprint, the attachment type, and the line diameter are compatible. If you have doubts about mechanical compatibility, contact our technical support before purchasing.

What to do if the sheave does not turn freely?

Wash the block thoroughly with fresh water and use a marine-specific spray lubricant that does not attract dirt. If the problem persists, the internal bearing may be worn or damaged.