What is the extent of thickness measurement at Special Survey No.4 and subsequent for a bulk carrier?
At the fourth special survey the IACS baseline adds three items. The class rules add about a dozen more. This is the survey where a programme written from UR Z10.2 alone is furthest from what the attending society will actually ask for — and the gap is not in the sections, it is in the steel nobody thinks of as cargo structure.
The short answer
- Suspect areas, and the whole deck outside the hatch line, as at the third survey.
- Three transverse sections now, not two — one of them amidships.
- Every bottom plate — the first time the bottom appears at all.
- The wind-and-water band over the full length of the ship, no longer sampled outside the cargo area.
- Shell frames in every hold, close-up, with the gauging that goes with them.
- And on a class ship, more: keel full length, sea chests, overboard discharges, superstructure decks. None of it is in the UR.
What the UR adds over the third survey
Three items, and each of them is a day of work rather than an hour.
A third transverse section. Two became three, with the amidships condition unchanged in the UR's own wording.
Every bottom plate. This is the first survey at which the bottom is on the systematic list at all — through three special surveys it appeared only where suspect areas or substantial corrosion put it there. A twenty-year ship gets its bottom gauged because the table says so, and that single line typically outweighs everything else added here.
The wind-and-water band, full length. At the third survey the band was complete inside the cargo area and sampled beyond it. Here the sampling ends: the band runs the length of the ship, both sides. UR Z10.2 R37
A double-side-skin hull takes exactly the same three additions, and so does an ore carrier — UR Z10.5 draws no distinction between them in its measurement table, whatever their close-up sheets do. UR Z10.5 R20
The statutory column matches, with one drafting quirk worth knowing when you are reading the Code rather than the UR: its close-up measurement item is not written out here at all. It points back at the corresponding item of the previous column. Miss the pointer and the column looks shorter than it is. A.1049(27)
The amidships requirement splits five ways
At the third survey four documents worded the placement of two sections four different ways. With three sections the spread gets wider, and two societies now constrain more than one of them.
| Document | Of the three sections |
|---|---|
| UR Z10.2 | One in the amidship area. The other two are unconstrained. |
| ESP Code | One should fall amidships. Same placement, softer verb. |
| DNV | At least one inside 0.5 L amidships — and all three are complete sections. |
| Lloyd's Register | Two of the three inside 0.5 L amidships. |
| ABS | All three inside the amidships 0.5 L, one of them in the amidship area. |
Read down that column and the ship's society decides how much of the hull the sections may be spread over. Under the UR three sections can be taken forward, amidships and aft; under ABS all three sit in the middle half of the ship. Those are different surveys producing different pictures of the same hull, and both are correct against their own rule. A gauging plan drafted for one and submitted to the other is rejected on geometry alone. ABS 7-A1-10 LR Table 3.1.1
The layer the UR does not carry
This is the real content of the fourth survey, and it is invisible if you read only the UR. DNV, ABS, ClassNK and LR each add a set of items that are not cargo structure at all — and they largely agree with one another.
- Keel plating over the full length — DNV, ABS and ClassNK. LR asks for the keel outside the cargo area, which is the same steel approached from the other side.
- Bottom plating beyond the cargo area — at cofferdams, at the machinery space, and at the after end of tanks. All four.
- Sea chest plating, and the shell in way of overboard discharges — the last to the extent the attending surveyor calls for. All four.
- Exposed deck outside the cargo area, plus representative plating of the first-tier superstructure decks — poop, bridge and forecastle. All four.
- Duct keel or pipe tunnel, plating and internals — ABS only. No other document in this set names it at any survey.
Four societies adding the same five or six things, none of which the baseline mentions, is not four independent decisions. It is the baseline being a floor. A twenty-year gauging quotation built strictly from Table II will miss the machinery-space bottom, the sea chests and the forecastle deck on any of these ships — and those are exactly the plates that were never coated as well as the cargo hold was. DNV · ABS · ClassNK · LR
Close-up goes to all of them — except on one ship type
On a single-side-skin hull the frame sampling ends: every shell frame in every cargo hold, with end attachments top and bottom and the plating beside them. The rest of the close-up table — ballast tank webs and bulkheads, hold bulkheads, hatch covers and coamings, the deck inside the hatch line — repeats the third survey without change. UR Z10.2 Table I
On a double-side-skin hull the same thing happens to a different member: the frame or longitudinal sampling in the double side tanks goes from a quarter to all of them, on the side shell and on the inner side plating, forward, amidships and aft. That is the biggest single step in the double-skin close-up table anywhere. UR Z10.5 Table I/1
And on an ore carrier, nothing happens at all. Its close-up sheet does not grow here: the whole column is written as a cross-reference back to the previous one. The systematic side still takes the third section, the bottom plating and the full-length band — but the close-up scope an ore carrier reached at fifteen years is the scope it keeps. That asymmetry surprises people, and it is in the sheet, not an omission. UR Z10.5 Table I/2
Why three sections, and what they are for
Most of the table is about local wastage — is this plate still thick enough. The transverse sections are not. ClassNK says so outright: the ship's longitudinal strength is evaluated from the member thicknesses taken in the sections of the measurement table. The sections exist to rebuild the hull girder on paper. ClassNK 5.2.6-8
That explains the placement rules on this page rather than merely stating them. A section is a sampled cut through the girder; three cuts in the middle half of the ship characterise the region where bending is greatest, which is why ABS puts all three there and LR puts two. A section chosen for convenience — at a clear frame space, in an empty hold, near the gangway — satisfies the count and weakens the calculation it feeds. That is the argument to make when a section placement is being negotiated on board.
It also explains why a section is expensive on a DNV ship. DNV asks for complete sections — the whole cut, not the deck items — because a partial section does not close the girder.
The one relief, and its limit
Everything above adds. One document subtracts. A note to the LR table allows the measurement extent to be specially considered where the coatings in the cargo holds and the water ballast tanks are found in GOOD condition — and then closes the door it just opened: the extent is not to be dispensed with in its entirety. LR Table 3.1.1 notes
Two things follow. The relief is a reduction the surveyor grants, not one the owner claims — nothing in the note lets a programme arrive already reduced. And it is worth going after early: on a twenty-year ship with genuinely good coatings, this note is the only lever in the chapter that moves the number down rather than up. The corresponding IACS relief is narrower still — it is CSR-built only, and it applies to the annual reading rather than to the special survey.
What moves the answer
Substantial corrosion widens it as at every survey — Table VIII in UR Z10.2, Table IV in UR Z10.5, annex 10 in the Code, Table 13 in DNV, 7-A1-4 in ABS, Tables B5.16 to B5.20 in ClassNK. Finished before the survey is credited.
The two conditional annexes stay in force. The corrugated bulkhead between the first two holds and the side shell frames of UR S31 ships both carry their own extent, and both continue from the third survey without change.
Coating condition in a ballast tank still puts that tank on yearly examination, with gauging as the surveyor judges necessary.
And there is no fifth column. This is the last block in every table on this page — twenty-five years and thirty-five years read the same requirement as twenty. What changes after this is not the printed extent but how much of it substantial corrosion drags into the widened pattern, which on an old ship is most of it.
Sources
- UR Z10.2 Rev.37IACS — Hull surveys of bulk carriers, Feb 2023index entry →
- UR Z10.5 Rev.20IACS — Double-skin bulk carriers, Feb 2023official text ↗
- A.1049(27)IMO Res. A.1049(27) — 2011 ESP Codeofficial text ↗
- ABS Part 7ABS — Rules for Survey After Construction, Jul 2026official text ↗
- DNV Pt.7 Ch.1 Sec.4DNV — Rules for Classification: Ships, survey requirements, Jul 2022official text ↗
- LR TM GuidanceLloyd's Register — Thickness measurement and close-up survey guidance, Nov 2016official text ↗
- 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.