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BLOCKS

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If the hauling part comes away from the standing block it is said to be rove to disadvantage ... A fall rove through a single standing block. No mechanical ... – PowerPoint PPT presentation

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Title: BLOCKS


1
BLOCKS TACKLES
By Lt (SCC) C Penny RMR Crawley Detachment
2
BLOCKS
  • A block is a portable pulley made from
  • Metal
  • Or wood metal
  • Synthetic resin bonded fibre (SRBF)
  • Most naval blocks are now SRBF.

3
PARTS OF A BLOCK
EYE
CROWN
TALLY PLATE
SWALLOW
SHEEVE
CHEEK
BECKET
TAIL or ARSE
4
BLOCK CLASSIFICATION
  • Wooden blocks are classified by their size.Which
    is
  • their length from crown to tail in millimetres
  • Wooden blocks will take a rope one tenth its
    size
  • Metal SRBF blocks are classified by size of
    rope which each is designed
  • Blocks may have more than one sheave
  • A single having one sheave
  • A double having two sheaves and so on

5
TYPES OF BLOCK
Synthetic resin bonded fibre
Metal Clump
Internal Bound
Metal (Cast Type)
Stropped
Metal (Built up type)
6
METAL BLOCKS
  • Built up of steel plates fittings
  • Shells have binding which supplies strength
  • cheeks of light plating
  • Some metal blocks have their shells are cast in
    one piece
  • Metal blocks vary considerably in quality and
    finish for the job they perform

7
SRBF BLOCK
  • Built up of steel bindings
  • Cheek plates sheave made of synthetic resin
    bonded fibre
  • Designed to be used with both man made natural
    ropes
  • Can be single, double ,triple, or snatch blocks -
    with proof loads of 2,4, 8 tons
  • You should not use wire ropes with this block nor
    should it be oiled or greased

8
INTERNAL BOUND
  • Has a shell partly of wood and partly of metal
  • Is the modern type of wooden block
  • It has a metal binding (fork shaped) this
    incorporates the eye or hook Becket when fitted
  • This block is now mainly superseded by the
    synthetic resin bonded fibre block (SRBF)

9
I.B. BLOCK
10
SNATCH BLOCKS
  • These are single blocks metal or SRBF with a gate
  • Allows a bight of rope or line to be accepted
    directly into the block
  • Not to be used if a solid block could do the job
  • Should not be used if safety of life depended on
    them as gate may open

11
SNATCH BLOCKS
12
STROPPED BLOCK
  • Now rarely found in service
  • Shell made entirely of elm
  • Old fashion wooden block held in position by a
    strop passed around its shell
  • Strop is seized into a thimble eye at the crown
  • The strop thus strengthens the shell and the block

13
CLUMP BLOCK
  • Can be made of wood or metal
  • Has an exceptionally large swallow
  • It will take rope one sixth of its size
  • metal clump blocks are designed to take chain

14
PURCHASES TACKLES
  • A purchase is a mechanical device by means of
    which an applied pull or force is increased it
    may be a system of levers, revolving drums or
    wheels geared to one another, Or a combination of
    blocks or pulleys rove with rope or chain.
  • A Tackle pronounced Taycle is a purchase
    consisting of a rope rove through two or more
    blocks in such a way that the force of any pull
    applied to its hauling part is increased by an
    amount depending upon the number of sheaves in
    the blocks, and the manner in which the rope is
    reeved through them.

15
PARTS OF A TACKLE
POINT OF ATTACHMENT
STANDING BLOCK
STANDING PART
RUNNING PART
HAULING PART
MOVING BLOCK
16
MECHANICAL ADVANTAGE VELOCITY RATIO
  • The amount by which the pull on the hauling parts
    multiplied by the the tackle is called the
    mechanical advantage (MA) and if friction were
    disregarded this is equal to the number of parts
    at the fall at the moving block
  • Mechanical advantage is only gained at the
    expense of the speed of working. In the second
    diagram you will see the weight will be raised
    only half a metre for every metre movement at the
    hauling part
  • So the the ratio between the the distance moved
    by the hauling part and that moved by the moving
    block is known as the velocity ratio (VR) and it
    is always equal to the amount of falls at the
    moving block

17
ADVANTAGE DISADVANTAGE
  • If the hauling part comes away from the moving
    block it is said to be rove to advantage
  • If the hauling part comes away from the standing
    block it is said to be rove to disadvantage
  • So if possible always rig a tackle so that the
    hauling part comes away from the moving block and
    make the moving block the one with the most
    amount of sheaves

18
LOAD ON THE STANDING BLOCK
  • The load on the standing block, and therefore on
    the fitting to which it is attached, is dependant
    on the (MA) of the tackle used. This is
    calculated by adding the pull required on the
    hauling part to the weight which is being moved,
    The greater the (MA) the less will be the load on
    the standing block.

19
SINGLE WHIP
  • A fall rove through a single standing block
  • No mechanical advantage gained
  • Used for hoisting light loads
  • Used when speed of hoisting is required

20
RUNNER
  • Consists of a rope through a single moving block

21
DOUBLE WHIP
  • Is used for hoisting
  • Consists of two single blocks
  • Standing part made fast to or near to the upper
    block
  • It cannot be rove to advantage

22
GUN TACKLE
  • This is the term usually applied to a purchase
    consisting of two single blocks but it is not
    used for hoisting
  • The standing part of the fall is always attached
    to one of the blocks

23
LUFF
  • A purchase of 24mm or greater in size
  • Consists of a double and a single block
  • The standing part of the fall is attached to the
    single block

24
TWO FOLD PURCHASE
  • Consists of two double blocks
  • Is a useful general purpose tackle

25
THREE FOLD PURCHASE
  • Consists of two treble blocks

26
TEST OF KNOWLEDGE
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