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

Two surveys, one name

Almost everything written about the intermediate survey describes the first version of it — the light one. That description is correct for exactly one intermediate survey in a ship's life, the one at seven and a half years. Every later one is a different animal.

The break is at ten years and it is sharp. Below it the rule sets a short list of its own. Above it the rule stops listing and points backwards: the requirement becomes whatever the last special survey required. There is no gradual middle band. UR Z10.2 §4.2

The practical consequence runs the wrong way round from how budgets are usually built. A ship's fourth intermediate survey costs what its third special survey cost. Planning it as a mid-period formality — one crew, two days, a few suspect areas — is how a survey ends up extended alongside.

Under ten years: suspect areas, and enough to judge the close-up

The systematic requirement in this band is a single item: the areas found suspect at earlier surveys. Not a section, not a strake, not a plate class. If the ship has no suspect areas on record, the systematic column is empty. UR Z10.2 §4.2.2.3

The work therefore comes from the second item — readings at the close-up areas, taken to a depth that lets the surveyor say how far general and local corrosion have gone. Those areas are the shell frames of the forward hold and of one further hold the surveyor picks, with their end attachments and the plating beside them, and the transverse bulkheads of those holds. UR Z10.2 §4.2.2.2

Two societies put a number on the frames where the UR does not. BV and ClassNK both set the close-up at a minimum of a quarter of the side shell frames in those two holds. The UR leaves the proportion to the surveyor, which in practice means the plan is negotiated rather than calculated. BV Tab 3 · ClassNK B4.4

On a double-side-skin hull the close-up in the holds is not even automatic. It arises where the overall survey of the holds gives the surveyor reason to extend into selected areas of the structure — so a clean overall survey can leave this column genuinely empty. That is the one place in the chapter where a gauging requirement is contingent on what an eye survey finds first. UR Z10.5 §4.2.2

Over ten years: the previous special survey, minus a named few things

Above ten years the rule repeats the preceding special survey in full — the systematic column, the close-up column, and the measurements that go with both. It applies in both age bands above ten, so the survey does not grow again at fifteen; it simply tracks whichever special survey came last. UR Z10.5 §4.2.3

What comes out is a closed list, and it is worth having it exactly, because every conversation about reducing this survey ends up here:

• Internal examination of the fuel oil tanks is not required.
• Pressure testing of tanks is not required.
• Both come back if the attending surveyor considers them necessary.

That is the whole of it in the IACS text, and BV states the same two exclusions in the same terms. Nothing about the thickness measurement is subtracted. A programme that assumes the intermediate is "the special survey at a discount" has the relationship backwards: it is the special survey with the tank-entry and testing overhead trimmed, and the gauging left intact. BV Ch 4 Sec 2 [3.2.1]

ClassNK reaches the same place by a mechanism worth understanding, because it shows what a "repeat" really means in a rule book. Its clause does not describe the survey at all — it substitutes articles, replacing the intermediate gauging article with the special survey one. The substitution carries a single exception: the article that evaluates longitudinal strength from the transverse sections does not come across. So a ClassNK intermediate survey repeats the special survey's measurement extent but not its hull-girder assessment. ClassNK 4.1.1-2

Ballast tanks, and the one lever that reduces the extent

The ballast tanks are where the intermediate survey earns its keep, and they are also the only place in this survey where the extent can be argued down rather than up.

The relief is stated in two conditions and both have to hold: the close-up survey satisfies the surveyor that the structure has not lost thickness, and the hard protective coatings are still in GOOD condition. Where both are true the extent may be specially considered. BV carries the identical two-condition test in its table notes; ClassNK allows the number of measurement points to be reduced on the same basis. UR Z10.2 · BV · ClassNK

Read the condition carefully before relying on it. It is not "the tank looks acceptable" and it is not "the coating was good at the last survey" — it is a judgement the attending surveyor makes at this survey, on both counts, having done the close-up first. The relief therefore cannot be built into a programme in advance; it can only be earned during one. On a double-skin hull there is a second, separate relief keyed to the hold coating as UR Z9 defines it. UR Z10.5 §4.2.2.3

The mirror image also applies, and it is the more common outcome: a tank whose coating has gone from GOOD goes onto yearly examination, with gauging where the surveyor judges it necessary, and stays there until the coating is made good. One tank failing its coating assessment can therefore add gauging to four annual surveys, not just to this one.

Over fifteen years: the dry dock, and the lower portions

Above fifteen years the intermediate survey includes a survey in dry dock, and a specific piece of work is attached to it: the lower portions of the cargo holds and of the water ballast tanks are taken through overall survey, close-up survey and gauging — if that has not already been done. UR Z10.5 §4.2.4 · BV [3.3.1]

The definition of lower portions is given rather than left to judgement: the parts of the structure that lie below the light ballast waterline. BV states it in the same terms. That is a definition worth carrying to the ship, because it is a waterline the crew do not routinely mark and it is not the summer load line.

BV also removes an option here: below fifteen years the bottom survey may be taken in dry condition or in the water as applicable, and above fifteen the in-water alternative is gone. BV Ch 4 Sec 2

Where the documents diverge

A ship exactly fifteen years old is not named by either BV heading. One clause is headed for ships between ten and fifteen years of age, the next for ships over fifteen — so the boundary year falls between two headings rather than inside one. The class renewal table in the same document has no such gap: its columns are written with the inequalities explicit. This is a drafting artefact rather than a policy, and the answer on board comes from the renewal table's boundaries — but it is the kind of thing that costs an afternoon if it is discovered during the survey instead of before it. BV [3.2] · [3.3]

ClassNK makes the hatch covers unconditional. Its close-up table ties the hold frames and transverse bulkheads to ships over five years of age, but the plating and stiffeners of every hatch cover and coaming carry no age qualifier at all — they are in scope at every intermediate survey, including the first. ClassNK B4.3

The CCS measurement guidelines set no intermediate extent of their own. The clause that carries the heading is a referral to the CCS Rules and contains nothing else; the same is true of the ballast tank and cargo hold clauses beside it. The one place the Guidelines do speak in their own words is narrow — the double-side-skin void space of a bulk carrier over twenty years old and of 150 m in length and above. Anyone using the Guidelines as the working document for an intermediate survey has to go to the Rules for the answer. CCS Ch Seven IX

What moves the answer

Substantial corrosion widens the extent here exactly as it does at a special survey — Table VIII in UR Z10.2, Table IV in UR Z10.5, Tab 12 to Tab 16 in BV, Tables B5.16 to B5.20 in ClassNK — and the extra readings are finished before the survey is credited.

There is a documented alternative to that widening, and it is CSR-built only. Where an area of substantial corrosion has been identified, it may instead be coated to the coating maker's requirements and then examined every year to confirm the coating is holding, or gauged every year. IACS, BV and ClassNK all carry it. It trades one large job now for a small one every year, and it is not available to a ship built before the Common Structural Rules.

The previous special survey is the input, so its scope decides this one. Above ten years the way to control the cost of an intermediate survey is to have controlled the special survey that precedes it — the sections chosen there are the sections repeated here, two and a half years later.

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. ClassNK Part BClassNK — Rules and Guidance for the Survey and Construction of Steel Ships, 2022official text ↗
5. CCS TM GuidelinesCCS — Guidelines for thickness measurement, Ver.6.6, Mar 2025official text ↗
6. UR Z9IACS — Coating condition in ballast tanksofficial 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.

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