Shifts and expedients of camp life, travel & exploration

by William Barry Lord; Thomas Baines

SINGLE AND COMPOUND BLOCKS.

To make a single block, take a piece of good sound wood of medium density, and of a kind that will not easily split. Elm is much used at home: oak will do very well; so will also the stinkwood of Africa, and others of like quality in other countries. Let it be, for instance, 7in. long, 4in. wide, and 3in. thick; suppose it is to carry a rope of 1in. in diameter, properly called a 3in. rope, all ropes being measured by their circumference. Gauge along each of the narrow sides two parallel lines 1in. apart and 1in. from each edge, and draw lines across at 1in. from each end; then, taking a brace and an inch centre-bit, insert the centre so that its cutter shall just come within the cross-line at either end; bore the holes half through, and between them bore two other holes with the same bit, thus taking out nearly all the wood between the lines: reverse the block, and bore in like manner from the other side; take a chisel and mallet and clean away all the intermediate parts, and you will have a sheave hole 5in. long and 1in. wide. Clean it up with a file or rasp. Then, drawing a longitudinal line along the centre of each of the broader sides, mark it at 3in. from one end and 4in. from the other on each side, and, placing the centre of the bit on these marks, bore through each side for the pin-hole.

Then for the sheave select a log of the hardest wood conveniently obtainable; lignum vitæ is generally used, but many kinds of acacia would answer very well. See that it is large enough to cut away all the sap wood, and leave a heart 4in. in diameter; trim this to a circular form, saw off a disc 1in. thick, fix it in a lathe, and with a gouge or half round rasp or file sink a hollow all round the edge. If you have not a lathe, saw the disc not quite off, and, while it is still attached to the log, make the hollow on the edge and saw it off when finished; bore an inch hole in the centre, place it in the shell, drive a pivot of hard wood right through, and you will find that at one end of the block the sheave very nearly fills the hole, while at the other a vacancy of about an inch is left to reeve the rope through.

Then, with a gouge or half round rasp, sink hollows in the outside of the shell along the centre line toward each end, and across the ends, to receive the strop; round off the corners and edges as neatly as you wish, and you will have a serviceable block like Fig. 1 ([p. 384]). Sometimes iron pivots are used, but these are a trifle smaller than the wooden ones; ¾in. iron would do, but then an iron socket ought to be let into the sheave as in Fig. 2. Some sheaves have small iron rollers let into them to run round on the pivot, and so diminish the friction; but a traveller need not work to such a nicety as this.

The snatch-block.

The snatch-block has already been two or three times mentioned, and perhaps this is a good opportunity to show its form, which is given in Fig. 3. The shell is longer and stouter than that of a common block, and in one side of it is cut the “natch” from which it takes its name; it is iron bound, but part of the strop is fashioned into a hasp, which is opened when the bight of a rope is to be passed into the natch and shut down upon its staple and forelocked to keep the rope from coming out should the strain be suddenly released.

Signal block.

Fig. 4 is a very useful kind of block for signalling; it has ten or more sheaves side by side, and as many lines running over them; in fact it ought to have as many sheaves as there are flags. It is kept in the signal locker with the halyards always rove, and each flag bent on to its own line. When required for use one end of the peak down-haul is bent on to the cleat in the centre, as shown in the figure, and it is hoisted to the peak end; the flags required are then sent up, care being taken to hoist each to such a height that they may read properly one under the other in the required order. These being done with are hauled down and others sent up, and much confusion and loss of time is saved by thus avoiding the necessity of bending on and unbending the several flags from one pair of halyards.