284

NICHOLLS'S SEAMANSHIP AND NAUTICAL KNOWLEDGE

pin and sheaves, any shackle, eye, hook, becket or permanent
attachment to any block

Marking.—Blocks shall be stamped with (a) Maker's name or trade
mark; (6) Identification number; (c) Safe working load in tons

Safe Wot fang Load —The S W L shall be the maximum load which
in ordinary working can be safely lifted by the block In the case of
single sheave blocks used singly or in combination the load on the pin
or eye of the block shall not exceed half the test load under any conditions
of working.

Factor of Safety —The factor of safety shall not exceed one-fifth of
the calculated breaking load of the material or any part of the block
This factor of safety is intended to allow for additional stress due to
friction, acceleration of load and shock.

Test Load —All blocks to be tested by the application of the following

loads without showing any deformation, visible cracks, flaws or defects.

*
Single sheave blocks......4- times the S W.L.

Multiple sheave blocks up to 20 tons, 2 times the S W L.

20 to 40 tons, S W.L. +20 tons.
„ „ over 40 tons, 1-J times S W L.

Sheaves.—The diameter to be the outside measurement of the
sheave. Pins to be secured to prevent rotation. Depth of groove to be
not less than the diameter of the rope. Angle of flare of groove 50° to
60°.

Where the angle of embrace is 90° or more it is recommended that
the minimum diameter of the sheaves for various sizes of rope shall be as
follows:—

Under 2" wire. 10" sheave.
2"to2|" „ 12" „
2fto3" „ 14" „
3" to 4" „ 16" „
Over 4" „ 18" „
The mimmum diameter of sheaves for any
other conditions should be not less than four
times the circumference of the wire used.

Ail nuts to be securely locked and sheaves
and swivel heads to be provided with sufficient ng e ° m
lubrication.

- Bechets to be capable of carrying at least half the load on any one
sheave*