Blocks & Buoys Lewmar

Focus primarily on the safe working load (SWL)—this is the relevant value for continuous operation. The breaking load is the safety margin and not a “working target.” Select the block/trolley so that the rope diameter, sheave diameter, shackle/bolt size, and the expected load at the attachment point are all compatible. For cruising yachts, a safety margin above the SWL is usually recommended, especially for mainsheets, downhalers, stretchers, and highly loaded sheaves.

The block must match the rope diameter—too small means increased friction, poorer operability, and faster wear on the rope. Pay attention to the maximum rope diameter specified by the manufacturer and avoid selecting a size that’s “right at the limit.” For highly loaded trim lines or frequent winching, a larger sheave diameter is worthwhile for smoother running and less sheath abrasion.

Stainless steel (A4/316) is very robust and corrosion-resistant, but heavier. Aluminum saves weight and is very strong, but requires attention regarding contact corrosion (e.g., aluminum on stainless steel)—insulating washers, sealants, and clean installation help here. Composite/plastic is lightweight, dampens noise, and is often highly corrosion-resistant; for heavily loaded positions, selecting the correct series/load class is crucial.

Correct alignment (no diagonal pull), suitable shackles/brackets, and clean stops are important to ensure the block does not “work” against deck fittings. Route lines so that the entry angle is correct and no side load is placed on the bearing/sheave. For taljes, appropriate cleat positions and short free line runs help reduce slamming in rough seas.

For high-load fittings, always ensure proper load distribution: use through-bolts with large washers or a backing plate. Carefully seal deck penetrations (cleanly deburr, fill/seal if necessary) to prevent water from entering the sandwich core. Use seawater-resistant screws (A4/316) and secure nuts against loosening. After the first few trips: Re-inspect the screw connections.

Check bolts/split pins, shackles, swivels, bearings, and washers for play, cracks, nicks, and smooth operation. Rinse salt off regularly with fresh water. Lubricate sparingly and use the correct lubricant for the bearing (follow manufacturer’s instructions); dirt-trapping “permanent greases” are not suitable for all applications. Do not use aggressive or acidic cleaners. If there is significant wobble, cracks, or excessive play: repair the component (if possible) or replace it—this prevents costly consequential damage to the rigging and deck fittings.

For trimming and frequent readjustment, a block with a clamp is practical because it can be operated without an additional clamp. A becket allows for greater leverage or flexible attachment points. Snap shackles are useful when quick release is required (e.g., for certain trimming or dinghy applications)—pay particular attention here to sufficient SWL and safe operation under load.