286

NICHOLLS S SEAMANSHIP AND NAUTICAL KNOWLEDGE

9. From the following information construct a figure to scale and
by means of triangles of forces find (1) the stress on the cargo gin;
(2) the thrust on the derrick; (3) the tension on the span; (4) the load
on the span block; (5) the load on the leading block at the heel of the
derrick when given length of derrick 25 feet; heel to span block on mast
20 feet; length of span 18 feet; angle the fall makes at the heel block 92
degrees; weight to be lifted 10 tons, using a single wire fall.

Ans. (1) Stress on gin block 18J tons.

(2) Thrust on derrick heel 22£ tons.

(3) Tension on span 9 tons.

(4) Load on span block 13-| tons.

(5) Load on heel block 14 tons.

10. What do you consider to be the best arrangement of derrick
or derricks when loading or discharging a bag cargo?

11. Describe the cargo gear you would rig when loading (a) slings
of goods weighing about 5 cwt.; (&) heavy goods weighing 1 ton per sling.

12. A beam weighing 30 cwt. is supported in slings attached to
shackles on upper flange of beam and 12 feet apart. If the legs of the
sling are 8 feet long, find the stress on each leg.

22| cwt.

A Cargo Gin.

Fig. 28.

A Cargo Hook,