Be vigilant when you are handling lines by capstan. Warning of a dangerous strain is given by the creaking, stretch  and  reduction  in  circumference  of  the  line  when you are using nylon lines. BLOCK  AND  TACKLE A block consists of a wooden or metal frame (or shell) containing one or more rotating pulleys called sheaves. When a line or wire is reeved through a block or a pair of blocks, the whole arrangement becomes a tackle. Usually, the purpose of a tackle is to multiply the force applied on the hauling part of the fall. The number of times it is multiplied, disregarding friction, is the mechanical  advantage  of  the  tackle. Every  tackle  contains  a  fixed  block,  attached  to some solid support, and a movable block, attached to the  load.  The  force  applied  at  the  hauling  part  is multiplied, excluding friction, as many times as there are parts of the fall at the movable block. A block ordinarily is referred to by the number of sheaves it contains: for example, single sheave, double sheave, triple sheave. Its size is determined by the length of its frame (in inches). The frame is the main body of the block, and contains the metal strap support- ing the pin on which rotates the sheave(s). Multiple- sheave  blocks  usually  have  both  inner  and  outer  straps. The closed upper end of the strap on a wooden block holds  the  hook  or  shackle;  the  other  end  accommodates the becket, for securing the end of the fall. Wooden blocks are used exclusively with line; they are never used with wire. Blocks for wire normally are all-steel, heavy-duty, roller-bearing blocks, either self- lubricating  or  equipped  with  fittings  for  grease  guns. A snatch block is a single-sheave block, a part of which (strap) opens on a hinge so a line may be layed in the block. Fairleading, causing a line or wire to lead angularly around an obstruction and then straight to some desired point, is the usual purpose of a snatch block. See Boatswain's Mate, Volume 1, NAVEDTRA 10101, for further discussion on the blocks and tackle. STANDING   RIGGING Standing  rigging,  usually  of  6  by  19  galvanized high-grade plow-steel wire rope, is used to support the masts. The fore-and-aft supports are called stays, and the supports running athwartships are called shrouds. Stays and shrouds are set up at the lower end with turnbuckles, and those in the line of fire of the guns are also fitted with pelican hooks so they may be moved quickly. Vibration often causes turnbuckles to back off, To prevent this, keepers are installed on turnbuckles in standing  rigging. All standing rigging is grounded to the ship's struc- ture with a bonding strap to eliminate the effects of charges  in  rigging  induced  by  electromagnetic  radia- tion. When you make any adjustments to the shrouds and stays, the bonding straps must be disconnected to prevent damage and/or breaking. Upon completion of adjustments  they  must  be  reconnected. If shrouds and stays are allowed to become slack, their  effectiveness  is  reduced.  Standing  rigging  should, therefore,  be  inspected  periodically  and  tightened  if necessary.  The  following  procedure  should  be  observed when  considerable  adjustments  are  required: 1. Disconnect bonding straps. Loosen turnbuckles to slack all shrouds and stays so no unbalanced forces are applied to the mast. 2.   Take up the slack as uniformly as possible until sag is eliminated from all stays and shrouds, and turn- buckles are hand-tight. Measure the distance between the ends of the turnbuckle bolts. 3. Tighten each turnbuckle so it is shortened by a distance equal to 1 inch for each 60 feet of stay length. Reconnect  the  bonding  straps. Insulators should present clean surfaces. They should not be painted, tarred, varnished, or coated in any way. All electrical bond straps on standing rigging should  be  inspected  for  damage,  broken  or  missing fittings,  and  excessive  deterioration  at  points  of  contact between  dissimilar  metals  as  specified  by  the  PMS periodicity  and  procedures.  Deficiencies  should  be reported to the work center supervisor and/or division officer. DECK  SAFETY LEARNING OBJECTIVE: Explain the impor- tance of deck safety. Lines must never be made fast to capstans or gypsy heads, but only to fittings such as cleats or bitts pro- vided for that purpose. When hawsepipe covers are removed for any purpose, a safety guard must be installed  forward  of  each  hawsepipe  to  prevent personnel handling lines from stepping or falling into the opening. When heaving around or veering the anchor cable, only authorized personnel may remain on the 4-44