A wire rope rarely fails without warning. Broken wires, a shrinking diameter or rust bleeding from the valleys usually show up several inspections earlier, if someone measures them against a limit. This guide sets out the ISO 4309 discard criteria for cranes, falls and mooring wires, and shows how to record every rope examination in Marine Inspection so the discard call is never a guess.
Ship wire rope inspection to ISO 4309: every defect is scored against its own discard limit
ISO 4309 rates each kind of deterioration as a share of its discard criterion, from slight to discard. When one mode reaches 100%, or several at the same spot add up to 100%, the rope comes off.
Where ISO 4309 wire rope discard criteria apply on board
ISO 4309 is written for crane ropes, but its method is the common benchmark for most running wire on a ship. Each rope also sits under its own rule set, and the maker’s manual takes priority where it is stricter. See how one register covers all four groups.
ISO 4309 + ILO C152
Lifting appliances thoroughly examined at least every 12 months and load tested at least every 5 years. The provision crane inspection guide covers the examination cycle.
SOLAS III/20.4
Inspected periodically, especially where they pass through sheaves; renewed on deterioration or within 5 years; turned end for end at no more than 30 months unless the flag accepts inspection instead.
MSC.1/Circ.1620
Removed before failure against the maker’s criteria. Our anchor and mooring equipment guide covers the wider mooring system.
Maker’s manual
Accommodation ladder, pilot hoist and hatch cover wires follow the maker’s limits, usually built on the same ISO method.
How to run a wire rope examination: daily, periodic and special
ISO 4309 splits rope inspection into three levels, each with a different person and depth. The periodic examination is the one that sets the discard decision, and it must end with a record stating the longest interval before the next one. You can set that interval as a due date straight from the result.
Trained operator
- The length to be used that day
- End attachments and terminations
- Correct seating on drum and sheaves
- Repeat after any change in reeving
Competent person
- Full length, or working length plus at least five wraps on the drum
- Drum anchorage, terminations, sheave sections, crossover zones
- Broken wires, diameter, corrosion, deformation
- Record with the maximum interval to the next examination
Before work resumes
- After any incident that may have damaged the rope
- After the crane has been idle for more than three months
- After shock loading or a rope jumping a sheave
Broken wire discard criteria: counting over 6d and 30d
The broken-wire limit depends on the rope’s construction. Count the load-bearing outer wires (n), find the rope category number (RCN) in the standard, then compare visible breaks over two lengths: 6 times and 30 times the nominal diameter. For a 20 mm rope that is 120 mm and 600 mm. Ask us to show the broken-wire count logged against each length.
| Example rope | Section of rope | Discard at, over 6d | Discard at, over 30d |
|---|---|---|---|
| RCN 01, single-layer rope, n ≤ 50, ordinary lay | Over steel sheaves or a single-layer drum | 2 wires | 4 wires |
| RCN 01, same rope | Multi-layer drum crossover zone | 4 wires | 8 wires |
| RCN 21, rotation-resistant, 4 outer strands, n ≤ 100 | Over steel sheaves or a single-layer drum | 2 wires | 4 wires |
Two worked examples taken from the standard’s broken-wire charts. Lang lay ropes and other RCNs have their own values; always read the line for your rope.
Valley breaks
Two or more breaks in the valleys between strands within one lay length (about 6d) point to internal damage.
Breaks at a termination
Two or more broken wires at or next to a socket, ferrule or splice.
Localized grouping
Breaks crowded into one or two strands can justify discard below the chart values.
Isolated installation breaks
Breaks from shipping or fitting are not counted, but are logged and any protruding ends removed.
Trend the count. Breaks usually accelerate near end of life, and ISO 4309 Annex F uses the rate of increase to set the next inspection date.
Diameter reduction discard thresholds by rope type
Uniform diameter loss is worked out as (reference diameter − measured diameter) ÷ nominal diameter × 100. The limit is tighter for steel-core and rotation-resistant ropes, because they have less room to lose before strength falls away. Put the formula in the inspection form and let the app score it automatically.
| Rope type | Slight 20% | Medium 40% | High 60% | Very high 80% | Discard 100% |
|---|---|---|---|---|---|
| Single-layer, fibre core | 6 to <7% | 7 to <8% | 8 to <9% | 9 to <10% | ≥10% |
| Single-layer steel core, or parallel-closed | 3.5 to <4.5% | 4.5 to <5.5% | 5.5 to <6.5% | 6.5 to <7.5% | ≥7.5% |
| Rotation-resistant | 1 to <2% | 2 to <3% | 3 to <4% | 4 to <5% | ≥5% |
Local decrease: discard
A sudden waist in one spot usually means a failed core or a sunken strand. ISO 4309 calls for discard, whatever the uniform figure says.
Local increase: investigate
A bulge of 5% or more on steel-core rope, or 10% or more on fibre-core, can mean core swelling or internal corrosion. Investigate and consider discard.
Stop judging ropes from memory
Reference diameter, broken-wire counts and severity scores for every crane, fall and mooring wire, on one screen.
Rope corrosion: external, internal and fretting
Salt air makes corrosion the defect that ends most ship ropes, and it often hides under grease. Clean the section before you judge it, without solvents that strip the lubricant out of the core. If you want photo evidence attached to every corrosion rating, we can show you.
Bulk carrier crane hoist rope
A nine-year-old hoist rope parted while discharging a wind turbine component in Houston, with damage put at USD 3–5 million. Heavy corrosion sat under the grease, where annual visual surveys could not see it. The operator now renews crane wires every five years.
Rescue boat crane wire
A 14-month-old wire parted and the boat fell about three metres. The lubricant used did not reach the core, so internal corrosion ran unchecked. MAIB urged removing old grease at inspections and using a penetrating lubricant.
Wire rope deformation and damage: immediate discard signs
Some defects need no counting at all. ISO 4309 states that any rope in a dangerous condition is discarded at once, and the cards below show where that line falls. The same visual cues are worth adding to the cargo handling equipment inspection checklist, so they are checked before every lift. Turn them into a free digital checklist.
Kink or tightened loop
Permanent strand displacement; strength cannot be restored.
Strand fracture
A complete strand broken anywhere along the rope.
Heat damage
Heat colouring or burnt-off grease; two or more arc-struck wires.
Basket or birdcage
Outer strands opened away from the core; remove the section or the rope.
Core or strand protrusion
Core or a strand forced out between the outer strands.
Protruding wire loops
Wires standing out in loops; a single removable king wire may be tolerated.
Waviness
Discard at a gap of d/10 on rope that runs over sheaves or drums, or d/3 on rope that never does.
Flattening or bend
Severe bends over a sheave: immediate discard. Milder flattening: inspect more often or discard.
Combining defects: the ISO 4309 severity method
Real ropes rarely have just one problem. Annex G of ISO 4309 has the inspector express each deterioration mode as a percentage of its own discard limit, then add the modes found at the same position. Below are two illustrative cases at a single point on a fibre-core crane rope. See the combined score worked out in the app.
Case A · keep in service, shorten interval
40% combined · breaks 20% + diameter 20% · medium
Case B · discard
120% combined · breaks 40% + diameter 20% + corrosion 60%
Case B’s corrosion bar is capped at the meter edge. Where magnetic rope testing (MRT) finds more breaks than the eye, the MRT count is used.
Wire rope inspection schedule for ship cranes, falls and mooring wires
Pull the levels together into one routine for each rope group. Intervals tagged Rule come from regulation; the rest are ISO guidance or common practice and should follow the maker where it is stricter. For falls, compare with the davit and brake checks in our SOLAS LSA readiness guide, and load the whole schedule as recurring jobs.
| When | Cranes | Lifeboat and rescue boat falls | Mooring wires | Basis |
|---|---|---|---|---|
| Before use / daily | Working length, terminations, spooling | Visual at drills and launching | Visual before mooring | ISO guidance |
| Monthly | Diameter at marked points, lubrication | Visual, sheave areas, lubrication | Full-length examination, grease | Practice |
| Periodic (competent person) | Full ISO 4309 examination, severity scored | Full length incl. drum and sheaves | Broken wires, diameter, corrosion | ISO guidance |
| 12 months | Thorough examination of lifting appliance | Annual thorough examination of davit and winch | Review against maker’s criteria | Rule |
| 30 months | — | Turn end for end (or inspect, if flag accepts) | End-for-end if worn at one end | Rule |
| 5 years | Load test of lifting appliance | Renew falls, or sooner on deterioration | — | Rule |
| After any event | Special inspection; after 3+ months idle | After shock load or sheave jump | After a surge or overload | ISO guidance |
How Marine Inspection tracks each wire rope to its discard date
A single pass or fail tells nobody when the rope will reach its limit. Marine Inspection keeps a life timeline for each rope: certificate, reference diameter, then every examination scored on the ISO 4309 scale, so the trend shows when to order the replacement. The example below is illustrative.
Diameter down 3.1% (high) plus three valley-side breaks over 30d. The trend reaches the limit before the next periodic examination, so the interval has been halved and the spare ordered.
Wire rope inspection and ISO 4309 FAQs
What is ISO 4309?
ISO 4309:2017 is the international standard for the care, maintenance, inspection and discard of wire ropes on cranes. It sets discard criteria for broken wires, diameter loss, corrosion and deformation, plus a method for combining them.
How many broken wires mean a wire rope must be discarded?
It depends on the rope construction. For a common single-layer rope with up to 50 outer wires running over steel sheaves, the limit is 2 visible breaks in 6 rope diameters or 4 in 30. Two or more valley breaks in one lay length, or two at a termination, mean discard whatever the rope.
What diameter reduction requires discard?
10% for single-layer fibre-core rope, 7.5% for steel-core or parallel-closed rope, and 5% for rotation-resistant rope, measured from the reference diameter taken after running in.
How often must lifeboat falls be renewed?
Under SOLAS III/20.4, falls are renewed when deterioration makes it necessary or at intervals of not more than 5 years, whichever comes first, and turned end for end at no more than 30 months unless the flag accepts periodic inspection instead.
Can grease hide wire rope corrosion?
Yes. In the 2022 NTSB crane case, heavy corrosion was only visible once the grease was removed. Clean the inspection points first, and use a penetrating lubricant that reaches the core.
Does ISO 4309 apply to mooring wires?
Not formally; it is a crane standard. Mooring wires are retired against the maker’s criteria under MSC.1/Circ.1620, though many fleets use ISO-style limits such as 10% broken wires over 10 diameters. Marine Inspection lets you set a different limit set per rope group.
Measure once, trend forever, discard on time
Give every crane rope, fall and mooring wire its own history, severity score and next due date across the fleet.
