CAKGO SLINGS 285

Shackles.—Shackles to be legibly stamped with their safe working
load and their identification number.

Information as follows to be supplied when ordering cargo lifting
blocks. Description of block Fittings. Number of sheaves Type of
sheave. Size of rope. Safe working load. Remarks.

QUESTIONS.
1. Sketch a derrick and name the gear on it.
2. How would you go about putting the gear on a derrick and getting
it upended ready for working cargo?
3 What is meant by the t{parallelogram of forces"?
4. Draw the following to scale:—
Length of derrick, 50 feet.
From heel of derrick to span on the mast, 40 feet
Angle between derrick and mast, 30°.
Weight suspended from the end of the derrick, 3 tons
From your figure find the approximate thrust on the heel of the
derrick and the strain on the span.
Am.—3-8 and 1*85 tons.
5. The same derrick is lowered to make an angle of 60° with the
mast. What will the relative thrust and strain be now?
Ans.—3-8 and 3-3 tons.
6. A span between two masts is formed by two pendants, one
pendant makes an angle of 40° with the vertical and the other makes
an angle of 60° with the vertical A load of 6 tons is suspended from
the span, find by construction the load on each pendant.
Ans—5-5 and 3-9 tons.
7. A span is formed by two pendants from two masts, one at an
angle of 30°, the other at an angle of 80°, to the vertical. Find the tensioc
on each arm of the span when supporting a weight of 4 tons.
Ans.—2J and 4J tons.
8. A derrick at an angle of 50° is supported by a topping lift at an
angle of 40° to a vertical mast. Find the thrust on the derrick and the
tension on the lift when a weight of 6 tons is hanging from the head of
me derrick.
Ans,—3J and 4J tons.