|
| Crosby's
"Rigging with Snatch Blocks" Calculator |
 |
Tackle Block Information
Continued:
Example B
(Calculation for determining total load value for mechanical advantage
system.)
Hoisting system lifting 1,000 lbs. using a traveling block. The mechanical
advantage of traveling block C is 2.00 because two (2) parts of load
line support the 1,000 lb. weight. (Note that this example
is simplified for determination of resultant load on blocks. Lead line
pull will be greater than shown due to efficiency losses.) (To
determine single line pull for various bearing efficiency see “How
to Figure Line Parts” page 296..
To
Determine Line Pull:
Line Pull = 1000 lbs.
¸ 2.00 = 500 lbs.
To determine total
load on traveling block C:
C = 500 lbs. x 2.0 = 1,000 lbs.
(line pull)(Factor 0° angle)
To determine total load
on stationary block D:
D = 500 lbs.
x 1.87 + 500 lbs. = 1,435 lbs.
(line pull) (dead
end load)
(Factor 40° angle)
To determine total
load on block E:
E = 500 lbs. x .84 = 420 lbs.
(line pull) (Factor 130° angle)
To determine total
load on block F:
F = 500 lbs. x 1.41 = 705 lbs.
(line pull) (Factor 90° angle) |
|
| The
Reeving of Tackle Blocks |
|
In reeving of tackle blocks,
there are many methods. The method discussed below is referred to as
“Right Angle” reeving. Please consult your rigging manual
for other methods of reeving.
RIGHT ANGLE REEVING
In reeving a pair of tackle blocks, one of which has more than two sheaves,
the hoisting rope should lead from one of the center sheaves of the
upper block to prevent toppling and avoid injury to the rope. The
two blocks should be placed so that the sheaves in the upper block are
at right angles to those in the lower one, as shown in the following
illustrations.
Start reeving with the becket or dead end of the rope. Use
a shackle block as the upper one of a pair and a hook block as the lower
one as seen below.
Sheaves in a set of blocks revolve at different rates of speed. Those
nearest the lead line revolve at the highest rate of speed and wear
out more rapidly.
All sheaves should be kept well lubricated when in operation to reduce
friction and wear.
"Right Angle" Reeving
Diagram |
|
CAUTION