Harken Black Magic Series Instruction Sheet

I N S T R U C T I O N S H E E T
N15W24983 Bluemound Rd., Pewaukee, WI 53072-4974 USA
Tel: 262-691-3320, Fax: 262-701-5780 • Web: www.harken.com, Email: harken@harken.com
WARNING! Strictly follow all instructions to avoid an accident,
damage to your vessel, personal injury or death.
See www.harken.com/manuals for additional safety information.
Block load increases when the line turns at a greater angle. Block loads
double when the line turns 180 degrees. See example below. Select blocks
carefully.
5000 lb
(2268kg)
3800 lb
(1723kg)
7000 lb
(3175kg)
Angle of
deflection Load factor
30°
45°
60°
75°
Black Magic Footblocks

Block Loading vs Angle of Deflection

Example shows single
footblock with a sheet
load of 5000 lb (2268kg)
5000 lb
(2268kg)
5000 lb
(2268kg)
5000 lb
(2268kg)
Angle of
deflection
52% 90°
76% 105°
100% 120°
122% 135°
8650 lb
(3923kg)
10000 lb
(4535kg)
Angle of
Load factor deflection
141%
159%
173%
185%
5000 lb
(2268kg)
5000 lb
(2268kg)
5000 lb
(2268kg)
5000 lb
(2268kg)
Load factor
150° 193%
160° 197%
180° 200%
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