Start hereRules checked 20 October 2026
Ships lose anchors far more often than most people think. Gard, a P&I insurer, has reported that class societies see roughly one anchor lost per 100 ships a year. In the winter of 2020 to 2021, with many cruise ships laid up at anchor off the English south coast during the pandemic, the UK Marine Accident Investigation Branch (MAIB) recorded several anchor losses in a row and found that the gear was being used beyond what it was designed for.
The key fact is in the first paragraph of the IACS rule: ship’s anchoring equipment is designed for temporary mooring in a harbour or sheltered area, not to hold a ship off an exposed coast in a gale. Knowing the design limits of the anchor, the chain, the brake and the stopper is what keeps them in the hawse pipe.
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In this lesson
- Windlass, chain cable and anchor: what to check
- In plain words
- In detail
- What the rules say
- Flag and class notes
- Key numbers
- What inspectors find
- Quiz: 6 questions
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Windlass, chain cable and anchor: what to check
In plain words
Every ship carries anchors and chain sized by a formula from its size and windage (the equipment number). The windlass hoists the anchor and chain; its brake and a separate chain stopper hold the chain when it is let go or riding at anchor.
Three things keep this system safe:
- Using it within its design. The equipment is meant for temporary mooring in sheltered water, in moderate current and wind, with enough chain out.
- Maintaining it. Brakes adjusted and linings renewed, the anchor secured at sea, the gypsy, stopper and hawse pipe kept in good order.
- Surveying it. At each class special survey (every five years) the anchors and chain are ranged out in dry dock, examined and, from the second special survey, measured. Chain worn below the class limit is renewed.
In detail
What the equipment is designed for
IACS Unified Requirement (UR) A1, the basis of all IACS class rules on anchoring equipment, states that the equipment is intended for temporary mooring in a harbour or sheltered area while waiting for berth, tide and so on. It is not designed to hold a ship off fully exposed coasts in rough weather or to stop a moving or drifting ship. The equipment number formulae assume a maximum current of 2.5 m/s, a maximum wind of 25 m/s and a scope of chain of at least 6 (length paid out divided by water depth). For ships over 135 m equipment length, the alternative basis is 1.54 m/s current, 11 m/s wind and waves of up to 2 m significant height. Under normal circumstances only one bow anchor and cable are used at a time.
UR A1 Revision 7 applies to ships contracted for construction on or after 1 January 2022. Anchors and chain are manufactured to IACS UR W29 and W18.
The windlass
IACS UR A3 sets the design and test requirements for anchor windlasses:
| Item | Requirement |
|---|---|
| Holding load (design check) | 80% of the chain’s specified minimum breaking strength, or 45% if a chain stopper is fitted |
| Brake capacity | Hold 80% of the chain’s minimum breaking strength without slip or permanent deformation (45% with a stopper) |
| Chain stopper | Withstand 80% of the chain’s minimum breaking strength without permanent deformation |
| Continuous duty pull, at least 30 minutes | 37.5 d² N for grade 1, 42.5 d² N for grade 2, 47.5 d² N for grade 3 chain (d in mm), for depths to 82.5 m |
| Short-term pull (breaking out the anchor) | At least 1.5 × continuous duty pull for at least 2 minutes |
| Mean hoisting speed | At least 0.15 m/s, measured over two shots with three shots out |
| Marking | e.g. 100/3/45: chain 100 mm, grade 3, holding load 45% of chain breaking load; also maximum anchorage depth |
Example: a windlass for 76 mm grade 3 chain must pull at least 47.5 × 76² = about 274 kN continuously for 30 minutes, and about 411 kN for 2 minutes to break the anchor out.
After installation, each windlass is tested on board: braking, clutch, lowering and hoisting, proper riding of the chain over the cable lifter, passage through the hawse pipe and chain pipe, stowage of chain and anchor, and the function of the chain stoppers. The braking capacity is tested by paying out and holding the cable intermittently with the brake.
The special survey: ranging and gauging
IACS UR Z7 (hull classification surveys) requires at every special survey that the anchors and chain cables are ranged, examined and their complement and condition verified, and that the chain locker, holdfasts, hawse pipes and chain stoppers are examined and the locker pumping arrangements tested. At special survey No. 2 and every special survey after, the cables are gauged and renewed where their mean diameter is worn below the limit set by the class society.
Gauging is done at the ends of common links, where the bearing surfaces wear most. Gard’s loss prevention guidance reports that class societies typically allow up to 12% reduction of diameter; check your own society’s rule for the exact limit and how the mean diameter is calculated. Loose studs, missing or loose spile pins in joining shackles, cracks and deformed links are also reasons for renewal or repair, and welding of loose studs must only be done with the class society’s agreement.
Preventing anchor loss
From the MAIB bulletin and Gard’s guidance:
- act early and put to sea when weather deteriorates, instead of waiting for the anchor to drag;
- vary the anchor used and the amount of cable to avoid always loading the same links;
- know the coastal state’s reporting procedure for a lost anchor;
- assess anchoring equipment after heavy use, such as long lay-ups at anchor, before returning to normal service;
- secure anchors tightly at sea with tensioners or lashings;
- replace worn brake linings and adjust the band to the maintenance manual;
- buy only certified anchors and chain, and renew the fore-runner when replacing worn chain.
What the rules say
- IACS UR A1 paragraph A1.1.1 states that the anchoring equipment is intended for temporary mooring of a ship within a harbour or sheltered area, and A1.1.2 that it is not designed to hold a ship off fully exposed coasts in rough weather or to stop a moving or drifting ship. 1
- IACS UR A1 paragraph A1.1.4 bases the equipment number on a maximum current of 2.5 m/s, a maximum wind of 25 m/s and a minimum scope of 6. 1
- IACS UR A3 paragraph 3.1.5 requires the windlass brake to withstand a pull of 80% of the chain’s specified minimum breaking strength without permanent deformation or brake slip, or 45% where a chain stopper is fitted. 2
- IACS UR A3 paragraph 3.1.6 requires a chain stopper, if fitted, to withstand 80% of the chain’s minimum breaking strength without permanent deformation. 2
- IACS UR A3 paragraphs 3.1.2 to 3.1.4 set the continuous duty pull by chain grade and diameter, a short-term pull of at least 1.5 times that for 2 minutes, and a mean hoisting speed of at least 0.15 m/s. 2
- IACS UR A3 section 5 requires each windlass to be tested on board after installation for braking, clutch function, hoisting, lowering, chain riding and stowage. 2
- IACS UR Z7 paragraph 2.2.4 requires anchors and chain cables to be ranged and examined at every special survey and, from special survey No. 2, the cables to be gauged and renewed where worn below the society’s limit. 3
Flag and class notes
- The detailed wear limits for chain are in each class society’s rules, not in an international convention. Ask your RO for the limit and the gauging method before dry dock, and take part in the measurements yourself, as Gard recommends. 4
- The UK MAIB (Safety Bulletin SB1/2021) issued safety lessons after multiple cruise ship anchor failures in autumn and winter 2020 to 2021. 5
- Flags’ and port States’ requirements to report a lost anchor vary. Check the coastal state’s requirements and your flag’s notices.
Key numbers
| What | Value |
|---|---|
| Design current and wind | 2.5 m/s and 25 m/s, scope of at least 6 1 |
| Windlass brake holding, no stopper | 80% of chain minimum breaking strength 2 |
| Windlass brake holding, stopper fitted | 45% 2 |
| Chain stopper | 80% of chain minimum breaking strength 2 |
| Continuous duty pull, grade 3 chain | 47.5 d² N for at least 30 minutes 2 |
| Short-term pull | 1.5 × continuous duty pull for 2 minutes 2 |
| Mean hoisting speed | At least 0.15 m/s 2 |
| Ranging | Every special survey; gauging from special survey No. 2 3 |
| Typical class wear allowance | Up to 12% of diameter (check your class) 4 |
| Anchor losses seen by class societies | About 1 per 100 ships per year 4 |
What inspectors find
- Brake linings worn and bands not adjusted, so the brake slips below its rated holding load. 4
- Anchors not secured at sea, hammering in the hawse pipe and loosening spile pins. 4
- Loose studs and wear at link ends found when the chain is ranged. 4
- Equipment used beyond its design during long periods at anchor in exposed waters. 5
FAQ
Can I anchor in 100 m of water?
The windlass design figures assume anchorage depths down to 82.5 m with ordinary stockless anchors. Deeper anchoring needs a windlass designed for it (the marking shows the maximum anchorage depth) and careful planning.
Should the brake or the stopper hold the cable at anchor?
UR A3 allows the brake to be designed for only 45% of the chain’s breaking strength when a stopper is fitted, so the stopper is meant to take the riding load. Follow your SMS and the maker’s instructions.
Can we weld a loose stud ourselves?
No. Gard advises consulting the class society first, because welding studs is risky. Often it is better to scrap that length or replace the link with a joining shackle.
When is the chain measured?
At special survey No. 2 and every special survey after that, during dry dock when the cable is ranged.
Quiz6 questions
Sources
- 1
IACS Unified Requirement A1, Anchoring equipment, Rev.7 (September 2020) Corr.1 (September 2021), section A1.1 (copy hosted by ABS). https://ww2.eagle.org/content/dam/eagle/regulatory-news/2022/IACS-UR-A1.pdf
- 2
IACS Unified Requirement A3, Anchor windlass design and testing, Rev.1 (June 2019), sections 3 to 6 (copy hosted by Türk Loydu). https://turkloydu.org/pdf-files/iacs-karar-ve-csr-degisimleri/iacs-es-gereklilikleri/UR_A3_Rev1_TR_EN.pdf
- 3
IACS Unified Requirement Z7, Hull classification surveys, Rev.26, paragraph 2.2.4 (copy hosted by Türk Loydu). https://www.turkloydu.org/pdf-files/iacs-karar-ve-csr-degisimleri/iacs-es-gereklilikleri/UR_Z7_Rev26_TR_EN.pdf
- 4
Gard, Loss of anchors and chain (loss prevention article, 9 February 2011). https://gard.no/insights/loss-of-anchors-and-chain/
- 5
UK Marine Accident Investigation Branch, Safety Bulletin SB1/2021, Multiple cruise ship anchor failures during autumn/winter 2020 to 21 (30 March 2021). https://www.gov.uk/maib-reports/safety-warning-about-multiple-cruise-ship-anchor-failures
Rules checked 20 October 2026. VSL Safety is not an approved training provider and doesn't issue certificates. These lessons don't replace STCW training, or the manufacturer's training and certification that service technicians need.
