LIGHTWEIGHT BLOCKS RACE AHEAD

With the 1997-98 Whitbread Round the World Race just about to start, robust, lightweight yacht racing hardware will yet again have to prove it is capable of doing the job.

Working closely with five of the Whitbread teams is Lewmar, who has pioneered a completely new approach to lightweight block construction in its Racing range of deck hardware. The Racing block is designed to achieve the best strength to weight ratio while remaining IMS legal. Each cheek and its constituent parts – including head block and sheave hubs – is machined from a single block of alloy, reducing the number of components and therefore the possibility of weld fixture failure.

The company says weight is always a major consideration on race boats, so it has engineered all the excess material and weight out, creating super strong blocks without sacrificing performance.

Ranging in size from 30mm to 250mm, there are two types of block available: one is equipped with roller bearings for rapid sheet (rope) trim, and the other has plain bearings to withstand high static loads.

Both blocks use a patented bayonet fixing, whose object is to provide a pulley block which is easier to assemble and needs only two locating screws to secure the head. Pulley blocks in the past have normally consisted of a rotatable sheave sandwiched between two cheeks, which were then held together by means of nuts and bolts, rivets and so on.

A major feature of the new block is the mating of the flanges of the cheeks through the middle of the sheave, through a bayonet coupling.

To provide a thrust bearing for the sheave, an annular groove is cut into each end wall of the sheave which has a mouth of restricted width. Ball bearings made from plastics such as acetal are deformed and introduced into the groove through the restricted mouth. Once inside the groove, the elements return to a spherical shape, the diameter of which is larger than the width of the groove mouth. This ensures the elements are retained within the groove. The advantage of this arrangement is that the axial thrust bearings may be assembled with the sheave before the final assembly with the cheeks.

The sheave is supported radially in relation to the cheeks by a roller bearing made up of a number of roller bearing elements, each in contact with the inner circular wall of the sheave and the outer wall of the cheek flanges.

{{Lewmar MarineTel: Havant (01705) 471841Enter 440}}