- The SWL of a union purchase rig must be calculated in accordance with the classification societies or dock labour regulations. In the absence of the above, the code of safe working practices for merchant seamen recommend that the SWL. Should not exceed one-third the SWL. Of the smaller derrick.
- The operating angle of the derrick should preferably be not less than 30 degrees to the horizontal and under no circumstances should it be less than 15 degrees.
- The maximum included angle between the cargo wires should not exceed 120 degrees so that forces in the rig are kept to a minimum. To ensure this the slings used in the operations should not be unduly long and winch men must not lift the loads above the guard rails beyond the minimum required for safety.
- Runner wires should not be allowed to rub against the hatch coamings or guard rails as this will result in their deterioration.
- Winchmen should be experienced and should co-ordinate well.
