SECTION IV.

RIGGING AND ROPES.

CHAPTER I.

THE rigging and ropes of a modern steamship still constitute a very important part of the vessel's equipment, notwithstanding the almost total abolition of sail area, and its extinction as a propelling agent in the present day steamer.

Generally too little attention is devoted to what are considered the minor details of a steamship's rigging, by those best qualified to determine the sizes of ropes and blocks, and the arrangement of tackles on a mechanical basis. The array of derricks around the masts and kingposts of a freighter, with their varying loads of from 2 to 50 tons, exemplify the necessity for a closer acquaintance with the staying, guying and tackling of these appliances, to ensure that the whole of the system shall be designed throughout on an uniform basis.

RIGGING.

By the term "rigging" is generally denoted the standing rigging, or that part whose function is to stay or support the masts, spars and funnels, and comprises the shrouds, guys, pendants, bowsprit shrouds, jib-boom guys, stays and backstays. These supports are now invariably made of galvanized wire rope, either iron or mild steel, the latter being employed where strength and lightness are desired, or where heavy working derricks are fitted. A special quality called plough steel, is sometimes used when exceptionally great loads have to be lifted. Indeed, it will often be found cheaper to employ plough steel in these cases, as the number of shrouds or stays may thereby be reduced, thus effecting a greater saving in the quantity required than the extra cost in quality has involved.

Wire Rope. As its name implies, wire rope is manufactured from small steel or iron wires, twisted into strands, six of which (usually) are laid up around a tarred hemp centre, the strands having a wire heart where strength is more important than flexi

bility, otherwise where used as running gear and flexibility is a necessity they also have a hempen centre. The number of wires constituting a strand varies with the degree of flexibility required, 19 wires to a strand being ordinary flexible rope, and 37 wires extra flexible, such as would be used for derrick topping lifts. Steel wire rope for ship rigging should always be galvanized, otherwise it deteriorates rapidly, and where it is used for running gear, it should be soaked in boiling tallow and linseed oil, a process which will add much to its life.

Great care must be used at all times in handling it so as to avoid sharp nips or kinks, either of which is fatal. For this reason when used as hawsers, wire rope must be stowed on a reel having a core of suitable diameter, and in the case of running rigging, the proper diameter of sheave for a given size of wire is important. An undersized sheave shortens the life of the best rope, and by distorting the fibres, weakens its strength.

Approximate diameters of sheaves for extra flexible steel wire rope, are given in the table on page 381.

Splices. Splices in wire rope, such as are necessary around thimbles and elsewhere, weaken its strength from 10 to 15 per cent. It is necessary, therefore, to take account of this in fixing on the safe working load. Likewise in ordering the lengths of rope, allowance must be made on net sizes for the number of splices worked.

Thimbles. — In working eyes in the ends of wire rope, it is necessary that the fibres forming the inside of eye should be protected from the destructive effect of a link or shackle pin bearing on same. To guard against this, the splice is worked around heart shaped eyes or thimbles. These, like the sheaves, must be of a suitable size for a given circumference of rope.