M6062M
–
04/ 2007
Calculation of loading of a snatch blocks
The maximum Wor king Load Limit (WLL) w ritten on the side of the block is the maximum load that
should be exerted on the block and its connecting fitting.
This total load value F varies w ith the angle (
α
) betw een the incoming and departing lines to the
block. The follow ing table (A) indicates the factor to be multiplied by the line pull to obtain the total
load F on the block.
A lways ensure :
F < pulley WLL
F < anchoring point resistance.
IMPORTANT REMARK
: In case on a 3 legs block assembly, add to
the above calculated effort the load applied on the becket.
The total
value of the calculated effort m ust be strictly lower to the
working load lim it (WLL) of the block and the resistance of the
anchorage point where the block is fitted.
Wire rope strength reduction
The ratio =
betw een the pitch diameter of the sheave and the w ire rope
diameter, called the w inding ratio, alters the tensile strength in the
w ire rope as hereafter - table (B) :
* Values for information only, depending on the construction of the wire rope.
For more information, please ask your wire rope supplier.
Winding
ratio
Reduction
*
6
21%
8
17%
10
14%
15
11%
20
9%
Angle
α
Effort applied on
suspension
“F”
0°
w inch WLL x 2
15°
w inch WLL x 1,98
30°
w inch WLL x 1,95
45°
w inch WLL x 1,85
60°
w inch WLL x 1,73
90°
w inch WLL x 1,41
120°
w inch WLL x 1
150°
w inch WLL x 0,52
180°
w inch WLL x 0
Ta
b
le
(
A
)
Ta
b
le
(
B
)
Example for EH
if
α
= 0°
F = 2 x winch WLL + becket loading
F
Pitch Ø (= BOG Ø + 1 w/r Ø)
i
Wire rope Ø
Becket
Suspension
10
