UK P&I Club has recently issued a Loss Prevention Bulletin regarding the care of wires and ropes on board ships.

Causes of damage to wires and ropes on board can be categorised into five types: abrasion, corrosion, crushing, cutting-in and stretch. The general condition of a wire should be monitored whenever it is in use and specific inspections should concentrate on signs of deterioration and damage.

Uses on board:The most common uses of wires and ropes on board modern vessels include:

1. Accommodation ladders and gangways

2. Cranes and hoists

3. Elevators

4. Lifeboat / rescue boat / life raft davits

5. Moorings

6. Lifting strops and slings

Causes of damage to wire ropes:There are many causes of damage to wires and ropes on board, these can be categorized into 5 types:

Abrasion:
Generally due to pulleys, sheaves, rollers and/or fairleads being seized or otherwise damaged. This is a common form of damage to mooring wires – repeated dragging by the stevedores over concrete knuckles and along the quay is probably the most common cause. Insufficient internal lubrication results in internal wear, otherwise known as fretting corrosion. Individual wires and strands rub together resulting in rust-like damage showing between the exterior strands. Crane wires are frequently found to have the individual outer strands flattened due to non-rotating or under-sized sheaves, or contact with other strands on the drum itself. Abraded wire rope, showing localised damage to individual wires

Corrosion:
Caused by unprotected wires being exposed to salt water and the elements. The smaller the diameter of the wire, the less effective the internal lubrication.

Crushing:
Uneven spooling on a drum can result in wires crossing. With load on the wire, this can lead to the lower layers of wire becoming crushed, reducing the effecting breaking strain of the wire.

Cutting-in:
Occurs when a rope buries itself when under tension beneath poorly spooled lower layers, potentially leading to jamming which could result in the wire kinking, being crushed or even counter-rotation.

Fatigue:
Fatigue is the result of frequent bending of the wire under load, particularly round under-sized sheaves, rollers, etc. and due to kinking. Fatigue is exacerbated by poor lubrication and corrosion. Fatigue results in the individual strands cracking and eventually failing.

Stretch:
More common in elevator wires, this is the result slight differences in diameter and/or elastic properties. Compensation mechanisms are usually fitted, but it can lead to wire slippage on the sheaves.

If you want to read the full Loss Prevention Bulletin click here.

Source:The UK P&I Club