Which IACS UR covers thickness measurement for my ship type?
Two questions settle it. What does the ship carry, and does it have a double skin? Everything else follows from the application clause of the UR you land on.
The short answer
- Oil tanker: double hull sends you to Z10.4, anything else to Z10.1.
- Bulk carrier: double side skin sends you to Z10.5, anything else to Z10.2.
- Chemical tanker: Z10.3, if the cargo tanks are part of the hull.
- Gas carrier: Z7.2. General dry cargo: Z7.1, but read its exclusion list first.
- Everything else — ro-ro cargo ships and refrigerated cargo ships, livestock carriers and deck cargo ships, and the dedicated trades, meaning container, wood chip and cement carriers: no Z10, no Z7.1. Z7 and the society's own rules govern. Z7.1 §1.1.1
- Z7 applies to every self-propelled ship on top of whichever of the above you land on.
The routing table
Z7 carries the routing clause itself. It pairs seven ship types with seven documents, in matching order, for the extra requirements on hull structure, piping systems and ballast tanks: a tanker goes to Z10.1, a bulk carrier to Z10.2, a chemical tanker to Z10.3, a double hulled tanker to Z10.4, a double side skin bulk carrier to Z10.5, a general dry cargo ship to Z7.1, and a liquefied gas carrier to Z7.2. UR Z7 §1.1.3
| Ship | UR | Application clause |
|---|---|---|
| Oil tanker, not double hull | Z10.1 | Self-propelled oil tankers other than double hull oil tankers as defined in Z10.4 §1.1.1 |
| Oil tanker, double hull | Z10.4 | All self-propelled double hull oil tankers |
| Bulk carrier, single side skin | Z10.2 | Self-propelled bulk carriers other than double skin bulk carriers as defined in Z10.5 §1.1.1 |
| Bulk carrier, double side skin | Z10.5 | All self-propelled double skin bulk carriers |
| Chemical tanker | Z10.3 | Self-propelled chemical tankers with an IMO certificate of fitness, cargo tanks integral to the hull |
| Liquefied gas carrier | Z7.2 | All self-propelled ships carrying liquefied gases in bulk |
| General dry cargo ship | Z7.1 | Self-propelled, 500 gt and above, carrying solid cargoes — with nine exclusions, see below |
| Every self-propelled ship | Z7 | Applies to all self-propelled vessels, additional to whichever UR above governs |
Source for the whole table: application clauses, each UR §1.1.1
Single skin or double: the line that moves you
The tanker pair and the bulk carrier pair are each written as one UR for the double-skinned ship and one for everything else. The wording runs the same way both times: Z10.1 takes oil tankers other than double hull oil tankers as Z10.4 defines them, and Z10.2 takes bulk carriers other than double skin bulk carriers as Z10.5 defines them. So the definition that decides your job lives in the UR you are not reading. Z10.1 §1.1.1 · Z10.2 §1.1.1
For a bulk carrier the test is not the width of the wing space. A ship counts as double skin when all cargo holds are bounded by a double-side skin, whatever that skin measures. A narrow wing void still makes it a Z10.5 ship. Z10.5 §1.2.1
Combination carriers are inside the bulk carrier definition, and a single-skin combination carrier picks up Z10.1 as well as Z10.2 — the ship is surveyed as a bulk carrier and as a tanker. Z10.2 §1.2.1 fn.1
Hybrid ships: two URs on one hull
Ships built with some holds single side skin and others double are common enough that both URs carry the same instruction from opposite sides. Z10.2 says the Z10.5 requirements apply to the cargo holds of double side skin and their associated wing spaces. Z10.5 says Z10.2 applies to the cargo holds of single side skin. One ship, two rule sets, split by hold. Z10.2 §1.1.6 · Z10.5 §1.1.2
General dry cargo ships have the same arrangement. Where a ship has holds of both constructions, Z7.1 applies only to structure in way of the single-side-skin cargo hold region. Z7.1 §1.1.2 Plan the survey hold by hold, not ship by ship — the extent table you work to changes as you move aft.
Chemical tankers split the same way, along the cargo length instead of hold by hold. Where a chemical tanker is constructed with both integral and independent tanks, Z10.3 applies only to that portion of the cargo length containing integral tanks. A combined gas carrier / chemical tanker with independent tanks within the hull is surveyed as a gas carrier, which routes the ship to Z7.2. Z10.3 §1.1.1 Independent tanks carried on deck are outside Z10.3 either way; Z7 covers them. Z10.3 §1.1.2
Ships no Z10 covers
Z7.1 looks like the catch-all for dry cargo, and it is not. It reaches general dry cargo ships that are self-propelled, of 500 gt and upwards that carry solid cargo, and then removes nine categories. Struck out are: any ship already subject to Z10.2 or Z10.5; container carriers, wood chip carriers and cement carriers in dedicated service; ro-ro cargo ships; refrigerated cargo ships; livestock carriers; deck cargo ships; and any general dry cargo ship whose double side skin runs the length of the cargo area and the full height of the hold to the upper deck. Z7.1 §1.1.1
A container ship, a car carrier or a reefer therefore has no Z10 and no Z7.1. The gauging extent comes from Z7 and from the attending society's own rules, and it is thinner than the ESP grids — which is exactly why those jobs are quoted differently and why the survey programme matters more, not less.
Two exceptions worth carrying in your head. An excluded ship type still picks up Z7.1 §2.6 and §3.3 if it is fitted with a single cargo hold. Z7.1 §1.1.1 fn.1 And a double-side-skin dry cargo ship that reverts to single skin over a few frame spaces — at a hold entrance, or in the forebody at the forward end of the foremost hold — may be given special consideration rather than being excluded outright. Z7.1 §1.1.1 fn.3
Where the extent tables live
Landing on the right UR is half the job. The numbers you actually work to sit in the enclosures at the back, and they are numbered differently from one UR to the next.
| UR | Minimum extent at special survey | Extent at substantial corrosion |
|---|---|---|
| Z10.1 | Table II | Table IV, four sheets requirement |
| Z10.2 | Table II | Table VIII, five sheets requirement |
| Z10.3 | Table II | Table IV requirement |
| Z10.4 | Table II | Table IV, five sheets requirement |
| Z10.5 | Table II | Table IV, four sheets requirement |
| Z7 | Table 1 | Table 2 guidance |
| Z7.1 | Table II | Table III guidance |
| Z7.2 | Table II | Table V guidance |
The third column is not the same kind of document in both families. In the Z10 series it is a requirement — Table IV in Z10.1, Z10.3, Z10.4 and Z10.5, Table VIII in Z10.2 — each titled Requirements for extent of thickness measurements at those areas of substantial corrosion, Z10.2 reading "of extent" and Z10.5 adding "of double skin bulk carriers within the cargo length area". In the Z7 series it is guidance: Z7 Table 2, Z7.1 Table III and Z7.2 Table V all carry the title Guidance for Additional Thickness Measurements in Way of Substantial Corrosion. Z7 T2 · Z7.1 T III · Z7.2 T V
Source: the table list at the front of each UR. Enclosures p.3, except Z7.2 p.2 and Z7 Contents p.1
Two bulk carrier annexes sit outside that pattern and catch people out. Z10.2 Annex III carries the gauging of the vertically corrugated transverse bulkhead between holds 1 and 2, for ships that have to comply with UR S19. Annex V carries the side shell frames and brackets, for ships under UR S31. Neither is in Table II — a survey planned from Table II alone will miss both. Z10.2 §1.1.4 · §1.1.5
Before the gangway
Settle the UR at the office, not in the tank. The ship's particulars give you the type and the construction; the two hybrid clauses decide whether you are working to one table or two. Get it wrong and the report comes back.
What Z7 adds on topSources
- UR Z7 Rev.29 Corr.1IACS — Hull classification surveys, May 2024official text ↗
- UR Z7.1 Rev.15 Corr.1IACS — General dry cargo ships, May 2024official text ↗
- UR Z7.2 Rev.8IACS — Liquefied gas carriers, May 2019official text ↗
- UR Z10.1 Rev.25IACS — Hull surveys of oil tankers, Feb 2023official text ↗
- UR Z10.2 Rev.37IACS — Hull surveys of bulk carriers, Feb 2023index entry →
- UR Z10.3 Rev.20IACS — Hull surveys of chemical tankers, May 2022official text ↗
- UR Z10.4 Rev.18IACS — Double hull oil tankers, Feb 2023official text ↗
- UR Z10.5 Rev.20IACS — Double skin bulk carriers, Feb 2023official text ↗
- A.1049(27)IMO — 2011 ESP Codeofficial text ↗
Class-society and IMO documents are indexed and linked, never re-hosted. Where a class rule is stricter than the IACS baseline, the class rule governs.