What is the extent of thickness measurement at the annual survey for a bulk carrier?

The column is empty, and it is empty everywhere

Across the whole set — the two IACS requirements, BV, KR, ClassNK — the annual survey has no scheduled measurement. Not a reduced list, not a sampled list: no list. Every annual gauging obligation is conditional on something else being true first. UR Z10.2 · BV · KR

This matters more than it sounds, because it inverts how the survey is planned. For a special survey the extent is known before the ship arrives and the question is how to execute it. For an annual survey the extent is unknown until someone has looked — so the plan cannot be drawn in advance, only the capacity to respond to what the overall survey turns up.

There is one partial exception, and it is worth knowing. ClassNK does print an annual gauging line, though it is still conditional: the members in ballast tanks are gauged where extensive corrosion is found at the internal examination that applies to bulk carriers over five years of age, and the hatch covers and coamings where the surveyor considers it necessary. It is the only document in the set that names the item in an annual table rather than leaving it wholly to the trigger clauses. ClassNK B3.6

The three routes in

One — the surveyor calls for it. The standing phrase across all five documents. It is discretionary in four of them and defined in one, which is the subject of the section after next.

Two — extensive corrosion is there to be seen. A separate limb, not a restatement of the first: it does not depend on the surveyor forming a view about future wastage, only on the condition being visible now. In practice this is the limb that produces unplanned gauging on an annual survey.

Three — the record from earlier surveys. Two distinct obligations, and they are not the same obligation. Areas marked suspect at a previous survey are examined. Areas found to have substantial corrosion at a previous survey are gauged. One is an eye survey, the other is readings, and the difference is what the annual report has to show. UR Z10.2 §3.2.4.1

The third route is the one that compounds. A ship that reached substantial corrosion at its last special survey carries an annual gauging obligation on those areas for the rest of the cycle — so a single finding at fifteen years generates work at sixteen, seventeen, eighteen and nineteen. That is the cost of a substantial-corrosion entry that is almost never priced when it is first recorded.

The close-up ladder, and the step that is not where people expect

Close-up survey at the annual has its own schedule, and gauging follows it, so this is where the predictable work sits.

• From ten years: at least a quarter of the frames in the forward cargo hold — the lower third of the side frame where it meets the shell, its end bracket, and the plating alongside. An overall survey of all holds runs with it.
• From fifteen years: the same members, the same quarter, but taken in the forward hold and one further hold the surveyor picks.

The step between the two bands is the second hold. The percentage does not move — BV and KR both make the point in their own notes, and it is worth carrying because the instinct is to expect the sampling rate to climb with age. It does not; the number of holds does. BV Tab 1 · KR 202. 4

And there is a widening clause attached to it. Where that close-up shows remedial measures are needed, the survey extends to all shell frames and adjacent plating in that hold, and to a sufficient extent in every remaining hold. ClassNK puts a number where the others leave "sufficient": a minimum of a quarter of the frames in each remaining hold. That converts a two-hour item into a full survey, and it is decided on board. UR Z10.2 · ClassNK B3.5

One society defines the trigger. The rest leave it open

"Where the surveyor considers it necessary" is the phrase that decides the whole annual survey, and four of the five documents leave it exactly there. KR does not. A note in its table sends the reader to a clause in the Guidance that sets out when gauging may be called for, on four grounds:

• wastage that is evident, or that is suspected;
• an area that is prone to rapid wastage;
• no hard coating present, or its condition in doubt;
• anything already listed in the preceding clause of that Guidance article.

Two of those four have nothing to do with measured thickness. An area prone to rapid wastage qualifies on its geometry and its service, not its condition; a coating whose condition is in doubt qualifies on the absence of evidence. So on a KR ship the question at an annual survey is not only "is this thin" but "is this the kind of place that goes thin, and can we see whether it has". That is a different conversation, and it is written down. KR Guidance Ch 1, 801. 3

For a technician the practical value of that clause is that it works as an agenda. Under any of these rules the same four questions are the ones a surveyor is actually weighing; KR is simply the document you can point at while asking them.

Ballast tanks: a yearly cycle is imposed, not scheduled

No ballast tank is examined at an annual survey because of the calendar. A tank appears there only if an earlier special or intermediate survey put it on a yearly cycle — and the condition for that is written out.

A ballast tank goes onto the yearly cycle where any one of three things is true: its hard protective coating has fallen below GOOD and has not been renewed; a soft or semi-hard coating was applied instead of a hard one; or it never had a hard coating at all. The tank is then examined every year and gauged as the surveyor deems necessary. BV and KR carry the same three-limb condition in their own clauses. UR Z10.2 §2.2.3.1 · BV · KR

The double bottom is carved out, and by a change of verb. For a ballast tank that is not a double bottom tank the annual examination is required. For a double bottom tank in the identical coating state the rule says it may be. One word separates an obligation from a discretion, and it is easy to read past — but it decides whether a double bottom in poor coating condition is on the list every year or only when someone decides it should be.

The consequence for planning is that the annual gauging load on a given ship is set years earlier, at the survey that assessed the coatings. A coating assessment is therefore not a report line — it is a commitment of work across the remaining cycle.

The two reliefs, both narrow

The CSR-built relief. The yearly reading may be dropped for an area whose coating was applied to the coating maker's requirements and has been kept in good condition. IACS, BV, KR and ClassNK all carry it, and all four attach it to ships built to the Common Structural Rules. A pre-CSR ship does not get it, whatever the state of its coatings. KR words it tightest of the four, naming the hard protective coating and the GOOD grade explicitly. UR Z10.2 · BV · KR · ClassNK

The hold-coating relief. Where the hard protective coating in the cargo holds is found in GOOD condition, the extent of both the close-up survey and the gauging may be specially considered. This one is not restricted to CSR ships — it is the more widely available of the two, and it is the lever that actually reduces the close-up ladder above. UR Z10.2 §3.2.4.1 d) · BV

Both are worded as things that may be granted, not claimed. Neither can be built into a quotation in advance — but both are worth raising at the opening meeting, because a coating assessment made without them in mind tends to get made once and then relied on for four years.

Where the widened pattern lives

Once a reading lands in the substantial-corrosion band the annual survey stops being an annual survey for that area: the extent goes to the widened grid, and the additional readings are completed before the annual survey is credited. Not at the next survey, not as a recommendation.

Which grid depends on the document, and the way each one files it says something about how the rule set is built:

• IACS — Table VIII in UR Z10.2, Table IV in UR Z10.5. In the requirement itself.
• BV — five grids, Tab 12 to Tab 16, split by structure rather than by ship: bottom and side shell; hold transverse bulkheads; deck structure and hatch covers; double bottom and hopper; and the remainder.
• ClassNK — Tables B5.16 to B5.20, reached through the special survey article.
• KR — not in the Rules at all. The grid sits in the Guidance, split by ship type: Table 14 for a single-side-skin bulk carrier, Table 18 for a double-skin one, with separate tables again for tankers and chemical carriers.

The KR arrangement is the one to watch when the Rules are the only document on board. Its annual survey clause tells you the extent increases and points at a table that is somewhere else — so a ship carrying the Rules without the Guidance has the trigger and not the answer. KR Annex 1-5

Sources

1. UR Z10.2 Rev.37IACS — Hull surveys of bulk carriers, Feb 2023index entry →
2. UR Z10.5 Rev.20IACS — Double-skin bulk carriers, Feb 2023official text ↗
3. BV NR467 Part ABureau Veritas — Rules for the Classification of Steel Ships, Part A, Jul 2026official text ↗
4. KR Part 1Korean Register — Rules and Guidance for the Classification of Steel Ships, Part 1, 2026official text ↗
5. ClassNK Part BClassNK — Rules and Guidance for the Survey and Construction of Steel Ships, 2022official 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.

Related questions

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