Lifting Gear

LIFTING GEAR

A purchase is the rope that has been reeved between blocks of s tackle. Strength of the purchase : 1. Breaking Strain 2. Safe Working Load (WLL)

Breaking Strain – the ultimate strain on a rope at failure (kilograms) Safe Working Load – the maximum load that should be applied to a rope.  

Fibre rope = 1/6 of the breaking strain Steel Wire Rope = 1/5  of the breaking strain

Rope SWL x 6 = breaking strain SWR x 5 = breaking strain

Ropes are not supplied in 20.4 mm so use 22mm. Formulas are not valid for worn or damaged ropes If no SWL is marked on sheaves then rope size is the largest size that can be run through the sheave. The diameter of sheaves used for fibre ropes should be :  

when hand operated at least six times the diameter of the rope when power operated at least twelve times the rope diameter

Diameter of sheave is measured from bottom of groove. Wire rope blocks generally referred to as steel blocks.

There should be a plate attached to the cheek of the block showing :   

Serial number SWL Last test date

Rope must match the size of the sheave to avoid crushing, kinking and deformation

For wire ropes the sheave diameter should be :  

non power operated blocks – ten times the diameter for power operated blocks – twenty times the diameter

Rough rule of thumb for shackle SWL is 4D squared where D is diameter of the  body in mm.

Do not allow shackles to pull at an angle Hooks :     

Moused Swivels Not stretched or distorted Sufficiently large opening for rope used Don’t overcrowd the hook – use shackle

To find the Mechanical Advantage of a purchase count the number of ropes at the moving block. If a tackle has a MA = 2 then a force of one tonne applied at the hauling part would exert a force of 2 tonne at the load to be moved A tackle is rigged to disadvantage when the hauling part comes from the fixed block. When rigged to advantage MA = number of sheaves in block + 1 Stress (S)

=

WEIGHT (W) MECHANICAL ADVANTAGE (MA)

The stress on the hauling part of the tackle. PLUS FRICTION per sheave of 10% of the weight being lifted.

Stress

=

WEIGHT + FRICTIONAL COMPONENT MECHANICAL ADVANTAGE (MA)

W STRESS

+

= MA

 N x W 10

A TACKLE ROVE TO DISADVANTAGE TAKES MORE EFFORT TO MAKE THE LIFT. Slings :   

Fibre rope Wire rope Chain

Fibre rope slings :

1. lifts without scratching 2. protects load surface 3. flexible

Chain strength :

It is common to allow a strength factor of 5 for chain. Grading of chain :   

Grade 1 – Mild Steel Grade 2 – Special Quality Steel Grade 3 – Extra Special Quality Steel

With the ISO standards grade 3 is mild & 4 – 9 are high tensile SWL = 3 D squared x Grade Safe slinging of loads :   

having correct SWL connecting the load securely keeping the load safe when suspended

Under no circumstances should the angle between the slings exceed 120 Where a sling is marked with SWL this relates to angles up to 90 Chain Blocks :   

High tensile steel SWL marked on block and hook Brake

Stores Crane Manifold Crane – positioned adjacent to liquid fuel transfer manifold for recovering shore connection lines for liquid transfer.    

SWL around 2 tonnes Auto brake on power stop Swivel with no overhauling weight Local operation.

Dancing Roller limit switch to detect runner slackness out of driver view. Bulk Cargo grab activation may be electric, electro-hydraulic or by wire rope and sheaves. Union Purchase is a rig in which a  pair of derricks is used in combination, the derricks being fixed and the cargo runners being coupled in such a way that the load may be swung from a position vertically under one derrick to a position under the second.

“Proof Load” specified in Marine Orders Part 32 – Cargo Handling Equipment Appendix 5. Shackles :    

Check crown & pin for wear – no more than 10% Check pin for straightness Check that pin is seated Check that shackle is not opening up

Hook throat opening no more than 5%stretch

Plate of steel block :   

Serial Number SWL Last Test Date.

Proof Load basically SWL plus a bit LEL – UEL : Propane Butane Hydrogen Petrol

2.1% - 9.5% 1.6% - 8.0% 4.0% - 74% 1.0% - 7.5%