Quantcast Types of Tackle - 14043_120

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Figure  4-24.—Single-whip  and  runner  tackle. TYPES OF TACKLE Tackles   are   designated   in   two   ways:   first, according to the number of sheaves in the blocks that are used to make the tackle, such as single whip or twofold  purchase;  and  second,  by  the  purpose  for which the tackle is used, such as yard tackles or stay Figure 4-25.—Gun tackle. tackles.  In  this  section,  we’ll  discuss  some  of  the different  types  of  tackle  in  common  use:  namely, single whip, runner, gun tackle, single luff, twofold purchase,  double  luff,  and  threefold  purchase.  Before proceeding, we should point out that the purpose of the letters and arrows in figures 4-24 through 4-30 is to indicate the sequence and direction in which the standing part of the fall is led in reeving. You may want to refer to these illustrations when we discuss reeving of blocks in the next sections. A  single-whip  tackle  consists  of  one  single- sheave block (tail block) fixed to a support with a rope passing   over   the   sheave   (figure   4-24.)   It   has   a mechanical  advantage  of  1.  If  a  100-pound  load  is lifted,  a  pull  of  100  pounds,  plus  an  allowance  for friction,  is  required. A  runner  (figure  4-24)  is  a  single-sheave  movable block that is free to move along the line on which it is reeved.  It  has  a  mechanical  advantage  of  2. A  gun  tackle  is  made  up  of  two  single-sheave blocks (figure 4-25). This tackle got its name in the old days because it was used to haul muzzle-loading guns back into the battery after the guns had been fired  and  reloaded.  A  gun  tackle  has  a  mechanical advantage of 2. To lift a 200-pound load with a gun tackle  requires  100  pounds  of  power,  disregarding friction. Figure  4-26.—Inverted  gun  tackle. 4-16



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