Luff-tackle, double and single block: doubled. If the double block is movable, trebled. Two double blocks: power × 3⅓. Double and treble blocks: power × 4. Two treble blocks: power × 4½. Whip upon whip (single Burton): trebled. When one tackle is applied to another, the power obtained is found by multiplying their respective values together. No advantage is gained by using a greater number of sheaves than two treble blocks in one fall. The power is equal to the weight divided by the number of ropes (standing parts) attached to the lower block, or by twice the number of rising pulleys (sheaves). KNOTS, HITCHES, ETC. =Thumb-knot= (Fig. 108).--Used to prevent the end from unfraying, or to prevent its slipping through a fall. =Figure-eight Knot= (Fig. 109).--Used to prevent the end from unfraying, or to prevent its slipping through a fall. [Illustration: FIG. 108.] [Illustration: FIG. 109.] [Illustration: FIG. 110.] [Illustration: FIG. 111.] [Illustration: FIG. 112.] =Reef-knot= (Fig. 110).--For joining two ends of rope or chain together. =Singlesheet Bend= (Fig. 111).--For joining dry ropes of unequal size. =Doublesheet Bend= (Fig. 112).--Same for wet ropes. =Draw-knot= (Fig. 113).--Same when it may be required to cast them loose. =Running-knot= (Fig. 114).--To form a loop that will draw taut. [Illustration: FIG. 113.] [Illustration: FIG. 114.] =Bowline= (Fig. 115).--To form a loop at the end of a rope which will not slip. =Half-Hitch.=--For securing the loose ends of lashings. =Two Half-hitches= (Fig. 116).--For making fast a rope-end to an object. =Clove-hitch= (Fig. 117).--Two half-hitches, used for commencement and finish of lashings; making fast the end or the bight of a rope to any object. [Illustration: FIG. 115.] [Illustration: FIG. 116.] [Illustration: FIG. 117.] [Illustration: FIG. 118.] =Timber-hitch= (Fig. 118).--Used on pieces of timber, or in making fast to spars, where the weight will keep the rope taut. =Round Turn= and =Two Half-hitches= (Fig. 119).--For making fast a rope so that the strain shall not jam the hitches. =Fisherman's Bend= (Fig. 120).--For making fast where there is give and take motion, as when a boat is at anchor. [Illustration: FIG. 119.] [Illustration: FIG. 120.] [Illustration: FIG. 121.] =Lever-hitch= (Fig. 121).--For drawing pickets, fixing rounds of rope-ladder, bars to, or loops on, drag-ropes. =Man's Harness-Hitch= (also Fig. 121).--Loop to pass over shoulder. To fix a rope with a weight on it rapidly to a block. [Illustration: FIG. 122.] [Illustration: FIG. 123.] =Cat's-paw= (Fig. 122).--At the end or in the middle of a rope for hooking on a block. =Blackwall Hitch= (Fig. 123).--Simple hitch with pliable rope and fixed weight. Used to transfer the strain from one rope to another, or to secure a tackle to a rope for a horizontal pull. =Stopper Hitch= (Fig. 124).--To shift the strain off a rope temporarily.