What does UR Z10.5 require for double-skin bulk carriers, in plain language?
Z10.5 is the enhanced-survey rule for bulk carriers whose cargo holds are bounded by a double side skin. On a hybrid ship it does not cover the whole vessel — the single-side-skin holds go back to Z10.2.
The short answer
- Who it covers: every self-propelled double skin bulk carrier — all cargo holds bounded by a double-side skin, whatever the width of the wing space.
- Hybrid ships: where some holds are single side skin and some double, UR Z10.2 applies to the single-side-skin holds.
- Cycle: Special Survey every 5 years, annual within ±3 months of the anniversary, intermediate at or between the 2nd and 3rd annual.
- Close-up: Table I/Sheet 1 for double skin bulk carriers, Sheet 2 for ore carriers. Gauging: Table II. Substantial corrosion: Table IV. TM firm: Table VI.
- Current text: Rev.20 applies to surveys commenced on or after 1 July 2024.
What counts as a double skin bulk carrier
The definition has two halves and technicians usually remember only the second. A double skin bulk carrier is a ship built generally with a single deck, double bottom, topside tanks and hopper side tanks in the cargo spaces, intended primarily to carry dry cargo in bulk — ore carriers and combination carriers included — and every one of whose cargo holds has a double-side skin around it. How wide the wing space is does not enter into it: a narrow wing void still counts. The same clause records that ore carriers and combination carriers are not covered by the IACS Common Structural Rules. UR Z10.5 §1.2.1
The rule covers hull structure and piping in way of cargo holds, cofferdams, pipe tunnels, void spaces, fuel oil tanks inside the cargo length area, and all ballast tanks. It is additional to the classification requirements for the rest of the ship, which sit in UR Z7. For a combination carrier with longitudinal bulkheads, extra requirements come from Z10.1 or Z10.4. One definition changes how you count tanks on the sheet: a double side tank is a separate tank even when it is open to the topside tank or the hopper side tank. A space used for both cargo and salt water ballast is treated as a ballast tank once substantial corrosion has been found in it. UR Z10.5 §1.1.3 / §1.2.2
A transverse section here takes in every longitudinal member: the plating, the longitudinals and the girders, at the deck and the sides, at the bottom and the inner bottom, on the hopper sides, the inner sides and the top wing inner sides, and on the longitudinal bulkheads. Substantial corrosion is wastage over 75% of the allowable margins, or on a CSR ship a measured thickness between tren + 0.5 mm and tren. Cargo length area is the part of the ship containing the cargo holds and the adjacent fuel tanks, cofferdams, ballast tanks and void spaces. UR Z10.5 §1.2.6 / §1.2.11
Hybrid ships: where Z10.5 stops and Z10.2 starts
The application clause settles this in one sentence. For bulk carriers with hybrid cargo hold arrangements — some holds of single side skin, others of double side skin — the requirements of UR Z10.2 apply to the cargo holds of single side skin. Z10.5 does not stretch over the whole ship because most of it is double skin, and Z10.2 does not take the whole ship because one hold is single skin. The split is hold by hold. UR Z10.5 §1.1.2
In practice that means the single-side-skin holds bring the Z10.2 side shell frame regime with them — the frame and bracket close-up and gauging that has no equivalent in Z10.5, because a double skin hold has no cargo-hold side frames to gauge. Everything else on the ship — the ballast tanks, the hatch covers, the deck plating, the transverse sections — is scoped by Z10.5. Get the survey programme to state which holds fall under which rule before the gauging starts, because the sheet layouts differ. See K3.3 for the Z10.2 side.
The survey cycle
Special Surveys at 5-year intervals, with a maximum 3-month class extension in exceptional circumstances; the survey may be commenced at the 4th Annual Survey, or earlier provided the whole thing finishes inside 15 months. Concurrent crediting of a space to both the Intermediate and the Special Survey is not acceptable. Annual Surveys within ±3 months of the anniversary; the Intermediate Survey at or between the 2nd and 3rd Annual Survey. UR Z10.5 §2.1 / §4.1
At the Special Survey all cargo holds, all ballast tanks including double bottom and double side tanks, pipe tunnels, cofferdams, void spaces bounding cargo holds, the decks and the outer hull are examined, backed by gauging and testing. The dry dock survey is part of it and covers the lower portions, below the light ballast water line. Fuel oil tanks in the cargo length area are surveyed on a sliding scale: none at Special Survey No.1, one at No.2, two at No.3, half of them with a minimum of two at No.4 and after. Peak tanks are internally examined at every Special Survey, and from No.3 on one deep fuel oil tank in the cargo area is included if fitted. UR Z10.5 §2.3.1
Coating condition drives the annual work. Any ballast tank that is not a double bottom tank goes onto annual examination, with gauging as far as the surveyor sees necessary, in three cases: the hard coating is found below GOOD condition and nobody renews it; a soft or semi-hard coating has gone on instead; or no hard coating was ever applied when the ship was built. Double bottom ballast tanks in that state may be examined annually. Rev.20 extends the same logic to the double-side skin void spaces, once a bulk carrier is past 20 years of age and measures 150 m in length or more: POOR coating that is not renewed puts those voids on the annual list. UR Z10.5 §2.2.3.3 / §3.4
The Intermediate Survey grows with age. At 5–10 years: overall survey of representative ballast tanks — the selection must include the fore and aft peak tanks — an overall survey of all cargo holds, overall and close-up survey of suspect areas from previous surveys, and gauging sufficient to establish general and local corrosion levels at those areas. From 10 years on it is the previous Special Survey extent, without internal examination of fuel oil tanks and without pressure testing of all tanks unless the attending surveyor asks. Over 15 years a dry dock survey becomes part of the Intermediate Survey. UR Z10.5 §4.2 + Tbl V
Close-up survey extent, by Special Survey number
Table I has two sheets. Sheet 1 is the double skin bulk carrier grid below. Sheet 2 is a separate grid for ore carriers, built around web frame rings in ballast wing tanks and wing void spaces rather than transverse webs in water ballast tanks — check which sheet your ship falls under before you scope the job.
| Survey | Water ballast tanks | Double side tanks | Cargo holds, hatches, deck |
|---|---|---|---|
| SS No.1 age ≤ 5 | One transverse web with its plating and longitudinals, in two representative tanks of each type — must include the foremost topside and double side ballast tanks on either side | — | Two selected cargo hold transverse bulkheads with the internal structure of upper and lower stools; all hatch covers and coamings, plating and stiffeners |
| SS No.2 5 < age ≤ 10 | One transverse web with plating and longitudinals in each tank; forward and aft transverse bulkheads with their stiffening, in one transverse section, taken through the topside tank, the hopper side tank and the double side ballast tank on one side only | 25% of ordinary transverse frames, or 25% of longitudinals on a longitudinally framed ship, taken on the side shell plating and the inner side plating, forward, at mid-tank and aft — in the foremost double side tanks | One transverse bulkhead in each cargo hold with stool internals; all hatch covers and coamings; every deck plate and the structure under it, inside the hatch opening line, between all cargo hold hatches |
| SS No.3 10 < age ≤ 15 | All transverse webs with plating and longitudinals in each tank; all transverse bulkheads with stiffening in each tank | Same 25% sample, now in all double side tanks | All cargo hold transverse bulkheads with stool internals; all hatch covers and coamings; all deck plating and under-deck structure inside the hatch line |
| SS No.4+ age > 15 | All transverse webs and all transverse bulkheads, in each tank | All ordinary transverse frames, or all longitudinals, taken on the side shell plating and the inner side plating, forward, at mid-tank and aft, in all double side tanks | As for the 10–15 year band |
Source for the whole table: UR Z10.5 Tbl I/1 Cargo hold transverse bulkheads are surveyed close-up at four levels: above the inner bottom and above the line of gussets and shedders on ships without a lower stool; above and below the lower stool shelf plate and above the shedder plates; above mid-height; and below the upper deck plating adjacent to the upper wing tank, or below the upper stool shelf plate. Where hatch covers have no access to the internals by design, the close-up and gauging are done on the accessible parts.
Where a hard protective coating in a cargo hold, as defined by Z9, is found in GOOD condition, the extent of close-up survey and gauging may be specially considered — and the same allowance applies to areas in spaces where the coating is GOOD. The surveyor can also push the other way and extend the close-up survey. UR Z10.5 §2.2.3.2 / §2.3.4
Thickness measurement extent, by Special Survey number
Watch the phrase “outside line of cargo hatch openings” in this table. On a bulk carrier the deck transverse sections are taken in the deck strips outboard of the hatch coamings, not across the hatch itself.
| Survey | Within the cargo length | Wind-and-water strakes |
|---|---|---|
| SS No.1 age ≤ 5 | Suspect areas only | — |
| SS No.2 5 < age ≤ 10 | 2 transverse sections of deck plating outside the line of cargo hatch openings | Strakes in way of those two sections; plus selected strakes outside the cargo length area |
| SS No.3 10 < age ≤ 15 | Each deck plate outside the hatch line; 2 transverse sections, one of them amidships, outside the hatch line; all wind-and-water strakes | Selected strakes outside the cargo length area |
| SS No.4+ age > 15 | Each deck plate outside the hatch line; 3 transverse sections, one of them amidships, outside the hatch line; each bottom plate | All strakes, full length |
Source for the whole table: UR Z10.5 Tbl II Suspect areas are gauged at every one of these surveys, and at every survey from No.2 on, every member subject to close-up survey under Table I/Sheet 1 or Sheet 2 is gauged for general assessment and recording of the corrosion pattern.
Two clauses add work that is easy to miss because it is not in the table. Transverse sections are chosen where the largest reductions are suspected or where deck plating readings point, and one of them is to be in the amidships area. Separately, representative gauging is required to establish both general and local corrosion levels in the transverse web frames of all water ballast tanks, and gauging of the transverse bulkhead plating to establish its corrosion level. That extent may be specially considered where the close-up survey shows no structural diminution and the hard protective coating is still efficient. UR Z10.5 §2.4.5 / §2.4.6
Substantial corrosion, the TM firm, and where the points are defined
Substantial corrosion triggers Table IV, four sheets covering bottom, inner bottom and hopper structure; deck structure including cross deck strips, hatchways, hatch covers, coamings and topside tanks; the structure in double side spaces, which also serves the wing void spaces of ore carriers; and transverse bulkheads in cargo holds. Representative rows:
- Bottom, inner bottom and hopper plating: a minimum of three bays across the double bottom tank including the aft bay, plus measurements around and under all suction bell mouths — five-point pattern on each panel between longitudinals and floors.
- Hatch covers: side and end skirts at three locations each, and three longitudinal bands — the two outboard strakes and the centreline strake — five-point measurement at each location and in each band. Hatch coamings: each side and each end, one band on the lower 1/3 and one on the upper 2/3.
- Double side spaces: on the upper strake, and on the strakes that sit in way of the horizontal girders, read the plating between every pair of transverse frames or longitudinals across at least three bays; on all other strakes, every third pair over the same bays. Frames and longitudinals: three readings across the web, one on the flange.
- Cargo hold transverse bulkheads: a band at about mid height and a band adjacent to the upper deck or below the upper stool shelf plate, five-point pattern over one square metre of plating. Lower stool: bands within 25 mm of the welded connection to the inner bottom and to the shelf plate, five-point between stiffeners over one metre length.
Source: UR Z10.5 Tbl IV/1–4 The extended measurements are taken before the survey is credited as completed. On CSR-built ships the identified substantial-corrosion areas may instead be coated to the coating manufacturer's requirements and examined annually to confirm the coating is still good — or they are gauged at annual intervals. UR Z10.5 §2.4.2
Gauging is carried out by a firm certified by the Classification Society under Table VI: the firm submits its organisation, experience, technicians' careers — operators qualified to a recognised industrial NDT standard — equipment and calibration procedures, an operators' guide, the training programme, and a record format matching Annex II; then an audit; then an onboard demonstration with satisfactory reporting. The certificate is renewed or endorsed at intervals not exceeding 3 years, and can be cancelled where measurements were improperly carried out or improperly reported. The surveyor witnesses the gauging, the firm attends the survey planning meeting, and gauging in close-up areas is done at the same time as the close-up survey. UR Z10.5 §7.2 / Tbl VI
The points are defined in §7.3 and its Table 1, with Figures 4 to 9 giving the locations. That clause applies to CSR-built ships; otherwise the individual Society's rules govern. Table 1 states that “selected” plates on deck, tank top, double bottom and in the wind-and-water area means a single point on one out of three plates; all deck, tank top and bottom plates and wind-and-water strakes take at least two points per plate at the 1/4 extremities or in areas of average corrosion; a transverse section of deck plating outside the hatch line takes two single points on each deck plate between the ship's side and the hatch coaming. Transverse section measurements are taken on both port and starboard sides. Where the rule says one transverse bulkhead in each cargo hold, the close-up and gauging are done on one side of the bulkhead, chosen from the overall survey of both sides, and the surveyor may call for the other side in case of doubt. The report gives location, measured thickness and original thickness, date, equipment, personnel and qualifications, signed by the operator; the surveyor reviews it and countersigns the cover page. UR Z10.5 §7.3 Tbl 1 / §7.4 The per-plate patterns are in K6.2.
Scoping a hybrid bulk carrier on the drawing
Draft Operator lets you tag each hold as double skin or single side skin, so the Z10.5 holds and the Z10.2 holds carry their own point patterns on the same shell expansion — ⊞ Hold → Skin type.
Open Draft OperatorSources
- UR Z10.5 Rev.20IACS — Hull surveys of double skin bulk carriers, Feb 2023official text ↗
- UR Z10.2IACS — Hull surveys of bulk carriers; governs the single-side-skin holds of a hybrid ship (Z10.5 §1.1.2)index entry →
- UR Z7IACS — Hull classification surveys, the base rule Z10.5 sits on top of (Z10.5 §1.1.3)official text ↗
- IACS CSRIACS Common Structural Rules — renewal thickness referenced by Z10.5 §1.2.11; ore and combination carriers are outside CSRofficial 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.