What are the permissible diminution limits for bulk carriers, class by class?

Five kinds of number, and a sixth

The same warning that opens the tanker page applies here and is not repeated in full. Briefly: the eleven schemes on this page publish five different kinds of number and none of them converts into another. A percentage of as-built or original thickness on ABS, LR, ClassNK, KR and INSB. Four separate figures per member on BV and RINA — isolated area, item, group, zone — each assessed on its own and in that order, so pulling one out of the set means nothing. A diminution coefficient on DNV, where the limit is t_min = k · t_{gr_off} and the gross offered thickness is the as-built less any documented owner's voluntary addition. A computed renewal thickness on CSR, with no percentage anywhere. And a minimum renewed thickness on CCS — the steel that must remain, which is the complement of a wastage figure and reads backwards if you treat it as one. BV [4.3.4] · DNV Sec.2 [3.1.2] · CSR [2.1.1] · CCS Tbl 3.1 The full account of the five, and of what each percentage is taken of, is on the tanker page and holds unchanged here.

A bulk carrier adds a sixth kind, and it is the one this page is really about. On three members — the side frames and their brackets, the corrugated transverse bulkheads and the hatch covers and coamings — the number in the society's wastage table is not the number that governs. Each of those members carries a separate, retroactive regime built on a net thickness, and the class documents record it on the row itself, as a note that redirects you out of the table. Read the percentage and skip the note and you will pass steel that the society requires to be renewed.

The shape of these regimes is the same across the societies and it is worth learning once. A net thickness t_net is established — either from a strength calculation or, where the as-built drawings do not carry it, by subtracting a fixed corrosion addition from the as-built. Steel renewal is required where the gauged thickness is less than t_net + 0,5 mm, and the renewed thickness is the as-built, not the net. Between t_net + 0,5 and t_net + 1,0 mm there is a band in which coating applied to the manufacturer's requirements, or annual gauging, may be adopted instead of renewal. That half-millimetre-and-half-millimetre structure appears in the BV, RINA, CCS, KR and DNV texts in almost identical terms. BV Tbl 5 n.(3)/(5)/(6) · RINA Tbl 7 n. · CCS §II.3 · KR 2.(3)–(4) · DNV Sec.8

One honesty note about those regimes before they appear in sections 6, 7 and 8. The underlying IACS Unified Requirements — S18 for corrugated bulkheads, S19 for the forward bulkhead flooding case, S21 for hatch covers, S31 for side frames — are not held in this handbook's source set. What is recorded on this page is what each class document states about them: which ships, from what date, and what the class requires as a result. Where a date or an applicability limit is given below, it is quoted from the class text cited beside it, not from the UR.

Single side skin, and which column you are reading

The figures on this page are for a single side skin bulk carrier, cargo-area structure. That is not a stylistic choice. Half of what follows — the side frame regime above all — exists only because there is one skin between the hold and the sea, and it does not apply to a double side skin ship. Where a scheme's wording turns on the skin arrangement, the section says so.

ABS. The figures come from Table 1C, headed for other conventional vessels of 90 m and over built to ABS class, and specifically from the column for non-CSR bulkers, ore carriers and OBOs, contract 2018 or later. That table has six columns and four of them are not bulk carriers at all — two are containerships, split by contract date; the fifth column takes longitudinally framed vessels built before 1962, transversely framed vessels of any age and dry cargo and tank barges, all under one heading and within the length limits that heading sets; the sixth takes vessels of any age framed partly transversely and partly longitudinally. The neighbouring bulker column is contract between 1962 and 2017, and it differs by five points on several rows. For a CSR ship the individual wastage allowance comes from Part 5A/B instead. ABS 7-A1-4/35.3 Tbl 1C

LR. §1.5.3 is the Category 1 list for a non-CSR bulk carrier, and for an ore/oil or an ore/bulk/oil ship, at L ≥ 90 m. Below 90 m a bulk carrier is Category 3 and drops to §1.5.4 with the general dry cargo ships. LR's own additional criteria for bulk carrier cargo holds sit after the main list and change several figures where L > 150 m and the notation Strengthened for Heavy Cargoes is assigned — see section 4. LR §1.5 · §1.5.3

KR. Class I is a ship of 90 m and above classed at a Classification Survey during Construction after 1 July 1998. A bulk carrier does not get in on the liquid-cargo limb that catches a small tanker, so a bulk carrier under 90 m is Class II. A ship classed after construction rather than during it takes separate requirements of the Society and is outside the wear-limit table altogether. KR Annex 1-5 Tbl 1 n.1–2

INSB. A dry bulk cargo ship of L ≥ 90 m is Category 1 by name. Below 90 m it is Category 3 and shares a column with Category 2. RINA splits on a contract date of 1 June 2000: Table 7 for ships on or after, Table 8 for earlier ships, and Table 8 is a shorter table, not the same one renumbered. CSR reaches a bulk carrier at freeboard length L_LL ≥ 90 m contracted on or after 1 July 2015 — single side skin and double side skin alike, but with ore carriers, combination carriers, woodchip carriers, self-unloaders and certain cement, fly ash and sugar carriers named out of scope. INSB Tbl D n.5 · RINA Tbl 7/8 · CSR Ch 1 Sec 1

ClassNK is the one to watch on a bulk carrier, because its wastage table carries a note that removes the table. Note (v) to Appendix 3.5 states that for ships subject to the retroactive requirements for existing bulk carriers, the wastage allowance is assessed ship by ship. There is no percentage to quote for such a ship — the figure comes from that ship's own assessment. Do not substitute the table value because the note is inconvenient. NK App 3.5 (1) n.(v)

And the scopes again differ on where as well as on which ship. BV applies its criteria as a rule to the structure within the cargo area of ships over 90 m, with a 5-point increase available either for a shorter ship or for structure outside the cargo area, but never both at once. DNV Sec.2 covers structure within 0,4 L amidships and excludes ships with the class notation CSR, container ships, naval vessels, high speed and light craft, yachts and aluminium vessels, and any ship that has undergone a major conversion. INSB's global table runs from 0,5 L amidships to 0,075 L from the ends with interpolation between. BV [4.3.6] · DNV Sec.2 [1.1] · INSB Tbl D

The deck, and the deck inside the hatch line

A bulk carrier's weather deck is two different structures with two different jobs, and the tables know it. Outside the line of the hatch openings the deck is hull girder flange. Inside it — the cross deck strips between hatches, and the deck at the ends of the hatch openings — it carries almost no longitudinal stress, and every scheme that names it separately gives it a looser number.

On the strength deck plating the local figures converge as they do on a tanker: ABS 20 % in the contract 2018 or later bulker column and the same in the 1962–2017 column — the pre-1962 longitudinally framed and transversely framed column prints 25 %; LR Category 1 20 %; KR Class I 20 %; INSB Category 1 20 %; DNV k = 0.80; BV and RINA 25 / 20 / 10 as item 1, which on the bulk carrier tables collects strength deck plating, deck stringer, sheer strake and the part of side shell plating in way of the topside tanks — a wider item than the tanker version. ClassNK is again the most permissive at 20 % of original + 1 mm, subject to its ship-by-ship note. PRS and CCS publish no local figure in the documents held. nine sources, strength deck row

The deck inside the hatch line is where the schemes separate, and by a lot. ABS gives deck plates within the line of hatches and at the ends 30 % — and prints 30 % in every one of the six columns, so contract date does not move it. LR gives it 25 %, and puts the same item under miscellaneous structural members in Table 1.5.5 at 25 % plating for Category 1. KR names it in the third row of the wear table at 25 % Class I and 30 % Class II. INSB has a row titled miscellaneous structural members including deck plates inside line of openings, 25 % Category 1 and 30 % Categories 2 and 3. So the range on this one member is 25 to 30 %, against 20 % on the strength deck five metres outboard. ABS Tbl 1C · LR §1.5.3 · KR · INSB Tbl C

Three schemes do not have this member at all, and each for a different reason worth knowing. BV and RINA carry no cross deck or deck-inside-hatch-line item in their bulk carrier tables — the item does not exist, so there is no figure to quote and the assessment falls back on the surveyor and the Society. ClassNK names effective deck plates at 30 % but does not name the deck inside the line of cargo hatch openings, and the definition of "effective deck" sits in a part of the ClassNK rules not held here, so the two cannot be equated on the evidence available. That is a gap in this handbook's sources, not in the ClassNK rules. BV Tbl 5 · RINA Tbl 7 · NK App 3.5

DNV does have the member, and puts a structural condition on it that nobody else does. Deck plating between hatches takes k = 0.80 for plate and 0.75 for stiffener, with note 1 to the table: to be specially considered if the cross deck is stiffened in the longitudinal direction in way of a vertically corrugated transverse bulkhead. That is the cross deck immediately above a corrugated bulkhead — the panel that has to carry the bulkhead's end reaction — and DNV takes it out of the table by name. DNV Sec.2 Tbl 2 n.1

The sheer strake follows the tanker pattern: ABS gives it its own line at 20 % in the contract 2018 or later column; BV, RINA and KR fold it in with the strength deck; ClassNK treats it as a shell plate; and LR §1.5.3 carries no sheer strake line, so the figure comes from Table 1.5.5, which works by frame number and strake position and gives deck-and-sheer plating 20 % for Category 1 and 30 % for Categories 2 and 3. A sheer strake reading with no strake letter and no frame cannot be assessed on the LR route. LR Tbl 1.5.5 · ABS Tbl 1C

Side shell, bottom, inner bottom and the sloping plating

On side shell plating the ABS column question bites the same way it does on a tanker and for the same reason: 20 % in the contract 2018 or later bulker column, 25 % in the 1962–2017 column and in both generic framing columns. LR, KR Class I and INSB Category 1 are at 20 %, ClassNK at 20 % + 1 mm, DNV at k = 0.80. BV and RINA give side shell plating 25 / 20 / 15 as item 6 inside a neutral axis zone criterion of 15 % — but only the part below the topside tanks. The part of side shell plating in way of the topside tanks was already collected into item 1 and is assessed in the deck zone at a group figure of 10 %. One strake, two group criteria, and the boundary is the topside tank knuckle. BV Tbl 5 items 1/6 · RINA Tbl 7 · ABS Tbl 1C

KR adds a millimetre trigger here as it does on a tanker, and the bulk carrier figures are tighter than the tanker ones. On a bulk carrier or ore carrier intended for alternate loading, a shear strength evaluation is required when the average corrosion of any strake in the side shell or longitudinal bulkhead exceeds 1,5 mm for Class I or 2,5 mm for Class II — against 2,0 and 3,0 mm for oil and chemical tankers. Alternate loading is the condition; a bulk carrier not intended for it does not pick this up. KR Annex 1-5, shear strength item 3

On the bilge, bottom and keel ABS gives bilge strake plates and bottom plates 20 % in the contract 2018 or later column and 25 % in the 1962–2017 column, and leaves the Keel Plates row empty: note 7 governs, and the keel is renewed when it reaches the minimum allowed thickness for the adjacent bottom plating. The keel has no allowance of its own on ABS, so a keel reading without the neighbouring bottom plate reading cannot be judged. BV and RINA put bilge and bottom plating and the keel plate together as item 7 at 25 / 20 / 10 in the bottom zone. LR names bottom shell plating and gives no bilge or keel line; KR names bottom shell plating in the first row. ABS Tbl 1C n.7 · BV/RINA item 7

The inner bottom is the first member on this page where the bulk carrier genuinely parts company with the tanker, and every scheme that moves, moves the same way — it gives the inner bottom of a bulk carrier more room than the same plate on a tanker. ABS gives the outermost strake and other plates of inner bottom 25 % in the contract 2018 or later column and 30 % in the 1962–2017 column, against 20 % for the same rows on the tanker table. DNV gives the inner bottom plate in bulk carriers k = 0.75, which is 25 % of the gross offered thickness rather than 20 %. That is the only departure from 0.80 for plating anywhere in its longitudinal strength table, and DNV's own revision record notes the bulk carrier inner bottom allowance being raised from 20 % to 25 % in the July 2021 revision. ABS Tbl 1C · DNV Tbl 1 inner bottom

Two conditions on the inner bottom that a summary would drop, and both change the number:

• BV subtracts a wear allowance instead of raising the percentage. The general form is t_min = (1 − W/100) t_rule − t_wc with t_wc = 0 in general — but t_wc = 1,5 mm for inner bottom plating not protected by a continuous wooden ceiling, on ships contracted for construction on or after 1 January 2001 and assigned one of the service notations bulk carrier, bulk carrier ESP without the CSR additional service feature, ore carrier ESP, combination carrier/OBO ESP or combination carrier/OOC ESP. The item percentage stays at 20 %; the limit moves by a millimetre and a half. Whether a ceiling is fitted is a survey observation, not a drawing lookup. BV [4.3.1] t_wc · Tbl 5 item 10
• LR raises the percentage, but only on a heavy-cargo ship. Inner bottom plating is 20 % for Category 1 in the main §1.5.3 list, and 25 % under the additional criteria applicable only to bulk carrier cargo holds where the ship length L > 150 m and the notation Strengthened for Heavy Cargoes is assigned. Both conditions, not either. The same pair of conditions moves hopper sloping plating from 20 % to 25 %. LR §1.5.3 additional criteria · Tbl 1.5.5 n.4.2

On the topside and hopper tank sloping plating ABS splits the top strake of the topside tank sloping plating into its own row at 20 % and puts the rest into the other-plates row — 20 % contract 2018 or later, 25 % 1962–2017. BV and RINA split it the other way: topside tank sloped plating including horizontal and vertical strakes is item 4 in the deck zone, hopper tank sloped plating is collected with the inner bottom as item 10 in the bottom zone, both at 25 / 20 / 10. KR names both in the first row at 20 % Class I. ClassNK names no sloping plating at all, and INSB has no sloping-plating item either — on INSB such plating falls into the longitudinal structural members plating row at 20 % Category 1 where it contributes to longitudinal strength. ABS · BV/RINA items 4/10 · KR · NK · INSB

Where a bulk carrier has a longitudinal bulkhead, BV and RINA have nothing for it — the bulk carrier tables carry no longitudinal bulkhead item; the item exists only in their oil tanker tables. ABS prints top strake, bottom strake and other plates, all 20 % in the contract 2018 or later column and 20 / 25 / 25 % in the 1962–2017 column. LR gives plating 20 % and longitudinals 25 %. ClassNK and KR split by bulkhead type: a deep tank bulkhead takes 20 % + 1 mm on NK and 20 % Class I on KR, and any other watertight bulkhead plating takes 25 % on both. BV/RINA no item · ABS Tbl 1C · LR · NK · KR

Longitudinals and bottom girders

On deck, side and bottom longitudinals the spread is the same ten points as on a tanker and for the same reason — the schemes simply do not agree, and none of the documents held explains itself. ABS 20 % in the contract 2018 or later column and 25 % in the 1962–2017 column, in a single internals row that also collects girders, transverses, struts, bulkhead webs and stringers, brackets and hatch side girders — a bulk-carrier-specific addition to the row that the tanker table does not have — with no split between web and flange. LR 25 % for strength deck, side shell, bottom shell, inner bottom, hopper sloping and topside sloping longitudinals alike. DNV k = 0.75 for stiffeners with girders and stringers at 0.80. KR 25 % Class I and 30 % Class II. INSB 25 % in both category columns. ClassNK 30 %, the most permissive. ABS · LR · DNV · KR · INSB · NK

BV and RINA split web from flange as always — web 25 / 20, flange 20 / 15 — but on a bulk carrier the group figure is 10 % for every longitudinal group named: deck longitudinals, side shell longitudinals in way of the topside tanks, bilge and bottom longitudinals, and longitudinals connected to the inner bottom and hopper tank sloped plating. On the tanker tables the side shell longitudinals sat in the neutral axis zone at 15 %; on the bulk carrier tables the side longitudinals that are listed are the topside ones, and they are in the deck zone at 10 %. Same society, different ship, different group criterion. BV Tbl 5 items 2/3/8/11 · RINA Tbl 7

Two exceptions that a summary would flatten. KR pulls longitudinals attached to the strength deck plating and the sheer strake out of the 25 % row and into the first row at 20 % Class I and 20 % + 1 mm Class II. ClassNK does the same for flat bar longitudinal beams on the sheer strake and strength deck, which take 20 % + 1 mm rather than the 30 % that covers webs and faces of frames, longitudinal beams, stiffeners and brackets. On both societies the tightest stiffener on the ship is the one welded to the deck. KR Annex 1-5 Tbl 1 · NK App 3.5 (1)

BV and RINA give bottom girders their own item at 25 / 15 / 10 — an item figure of 15 % where almost every other plating item in the table sits at 20 %, and one of the tightest item figures anywhere in the bulk carrier set. DNV does not tighten the girder in the same way, but it does add a strength check on the same member: on a single skin bulk carrier of L > 150 m carrying cargo of density 1,78 t/m³ or more, the shear strength of the bottom girders in hold No.1 is also checked to IACS UR S22. Hold No.1, single side skin, heavy cargo, over 150 m — four conditions, all of them on the sheet or not at all. BV/RINA item 9 · DNV Sec.4 Tbl 1 n.1

Two reading rules apply across this whole section and are worth stating once. LR Table 1.5.5 note 6 and INSB Table C note 3 both hang the limit on an average: work a plate out over its whole area, work a stiffener out over the span between its supports, and compare that figure. One low reading does not condemn the member. And on CSR the corrosion addition of a stiffener is set by the location where it lands on the attached plating, not by where the web sits — an inner bottom longitudinal in a double bottom ballast tank and one in a duct keel take different values. LR Tbl 1.5.5 n.6 · INSB Tbl C n.3 · CSR [1.2.3]

Side frames and end brackets

This is the member that catches surveyors out, and it catches them out in a specific way: the wastage table gives a perfectly ordinary-looking percentage, and on a large part of the world fleet that percentage does not govern. On a single side skin bulk carrier the cargo hold side frames and their end brackets carry a retroactive regime of their own, applied by schedule to ships that were already in service when it came in.

Start with what the tables print, because it is what a reader will find first. ABS puts frames, brackets and hatch side girders in the internals row at 20 % in the contract 2018 or later column and 25 % in the 1962–2017 column, with no web-and-flange split. LR gives cargo hold shell frames and end brackets 20 %. ClassNK gives web, face and bracket of hold frames 25 % — a separate band from the 30 % that covers other frames, so ClassNK already treats the hold frame as a different member. DNV gives frames and stiffeners k = 0.75 on both web and flange. INSB gives cargo hold transverse frames and end brackets 20 % Category 1 and 25 % Categories 2 and 3. BV and RINA give item 18 side shell frames web 25 / 20, flange 20 / 15, brackets 20 / 15. ABS · LR · NK · DNV · INSB · BV/RINA item 18

Now the notes that take those figures away. KR gives the frames row the only entry in its whole wear table that pairs a percentage with an absolute floor: web, face and brackets of frames in a cargo hold or tank, 20 % of original thickness or 1,5 mm, whichever is greater for Class I, and 25 % or 2,5 mm, whichever is greater for Class II. On a thin frame web the millimetre figure is the one that bites — on a 10 mm web, 20 % is 2,0 mm and the floor does nothing, but on a 6 mm web 20 % is 1,2 mm and the 1,5 mm floor governs instead. KR then adds that ships subject to IACS UR S31 carry the separate requirements of Pt 7 Ch 3 Sec 17. KR Annex 1-5 Tbl 1, frames row

BV attaches note (4) to item 18: where a single side skin ship carries the service notation bulk carrier ESP and its side frames were not built to Part II Ch 08 Sec 8-03 as that section stood in the BV Rules edition of 1 April 1998 or in any edition after it, the renewal criterion — and the alternatives to renewing, which are reinforcement and coating — for the side shell frames and their brackets sits in Ch 6 Sec 2 [5], and in Ch 6 App 1 [5], not in the wastage table. The note goes further and says what the table is still good for on such a ship: thickness measurements of flanges and side shell plating not covered by that chapter, and of additional intermediate frames fitted to comply with an ice class notation, are still assessed against the table. So on a caught ship the frame web comes out of the table and the flange stays in. BV Tbl 5 n.(4)

RINA says the same thing in its own table and is blunter about it. Table 8 note (4), for ships contracted before 1 June 2000 subject to the retroactive requirements of Ch 6 Sec 2 [7], states that the 20 % web figure is not to be used and the specific value from the structural assessment applies instead, while the flange figures still apply. That is the clearest statement in any of the documents held of what the retroactive regime does: it deletes one cell of the table for that ship and leaves the rest standing. RINA Tbl 8 n.(4)

LR attaches note 4.3 to Table 1.5.5: on a single skin bulk carrier contracted for construction before 1 July 1998 undergoing re-assessment of its cargo hold shell frames under the Provisional Rules for Existing Ships — IACS UR S31 — the measurements are compared against the minimum thickness values in the ship's own evaluation records, not against the 20 % in §1.5.3. On such a ship the office needs a document that is specific to that hull, and if it is not on board the assessment cannot be completed from the rulebook. LR Tbl 1.5.5 n.4.3

PRS is the one society in this set that publishes the whole regime itself, in Publication 63/P, and it is the best available statement of what UR S31 actually requires. The ships it reaches are single-deck bulk carriers fitted with topside and hopper tanks, whose cargo spaces are meant mainly for dry bulk, and whose construction did not follow sub-chapter 20.5 of PRS Part II — Hull. On such a ship it governs the frames and the brackets on the side shell, in every cargo hold that a single side bounds. Single-deck OBO carriers take the same treatment on the same members. Where a ship fails the definition in one or more holds, or parts of holds, the requirements do not apply to those individual holds. The renewal thickness is not a percentage:

t_REN = the GREATEST of
  (a) t_COAT − t_C          t_COAT = 0.75 · t_20.5
  (b) 0.75 · t_AB           t_AB = as-built thickness
  (c) t_REN,d/t             web depth / R   (zones A and B only)
  (d) t_REN,S               where a strength check is required

R = 65 √k  symmetrically flanged frames      55 √k  asymmetrically flanged
R = 87 √k  symmetrical lower brackets        73 √k  asymmetrical lower brackets

t_C, mm    L=100 m   L=150 m   L=200 m      (linear interpolation between)
  holds other than No.1, span and upper brackets   2.0   2.0   2.0
  holds other than No.1, lower brackets            2.5   3.0   3.0
  hold No.1, span and upper brackets               2.0   3.0   3.0
  hold No.1, lower brackets                        3.0   3.5   4.0

Read the shape of that and the reason for the whole regime is visible in the numbers. The corrosion addition grows with ship length, it is larger at the lower brackets than over the span, and it is largest of all at the lower brackets of hold No.1 — 4,0 mm on a 200 m ship against 2,0 mm over the span of any other hold. That is the corner of the ship where a side frame connects to the hopper in the foremost hold, and the regime allocates its steel accordingly. Note also that criterion (c) is a slenderness limit, not a corrosion limit: the frame is renewed if its web gets too thin for its depth, which means the same wastage is acceptable on a shallow frame and not on a deep one. PRS Pub 63/P §2.1.2 · Tbl 2.1.1

And the schedule — which ships, from when. PRS Publication 63/P states it in full for bulk carriers: compliance is to be assessed and any steel renewal, reinforcement or coating performed by the due date of the first intermediate or special survey after 1 January 2005 for ships that were 15 years of age or more on that date; by the due date of the first special survey after 1 January 2005 for ships that were 10 years or more; and by the date the ship reaches 10 years of age for ships that were under 10 years on that date — and then at every subsequent intermediate and special survey. Completing an intermediate or special survey before 1 January 2005 whose due date fell after it does not postpone compliance, though an intermediate survey whose window straddles 1 January 2005 can be accepted. For OBO carriers the same three-limb schedule runs from 1 July 2005. PRS Pub 63/P §1

Two conditions in the same publication that a technician meets on the ship rather than in the office. On an ice-strengthened bulk carrier the intermediate frames are not counted when considering compliance, and the renewal thicknesses for the additional ice structure are set case by case; if the ice notation is later withdrawn, the ice strengthening structure — tripping brackets excepted — is not considered to contribute to compliance. And where the measured thickness falls below the slenderness criterion at the lower part of the frame, tripping brackets fitted to the publication's own requirements may be accepted as an alternative to renewing the frame, in which case criterion (c) drops out of the calculation. Two existing tripping brackets not quite in the specified positions may be accepted as equivalent, provided the bracket thickness is not less than the frame web thickness. If tripping brackets are fitted, say so and gauge them. PRS Pub 63/P §1.1 · §2.1.2.1 b)

Put together, it comes to this. Take a single side skin bulk carrier not built to the side frame scantlings the class documents name (sub-chapter 20.5 of PRS Part II — Hull, which PRS's own footnote records as covering IACS UR S12, or Part II Ch 08 Sec 8-03 of the BV Rules 1 April 1998 edition). On that ship, five of the eleven schemes redirect the side frame web out of their own wastage table: BV, RINA, LR and KR explicitly, and ClassNK through its ship-by-ship note for existing bulk carriers subject to the retroactive requirements. PRS publishes no wastage table of its own and gives Publication 63/P as the criterion directly. ABS, DNV, INSB and CCS carry no such redirection on the frames row in the documents held. If the ship is caught, the percentage on this page is not the number, and the number is in the ship's own evaluation records. Ask for them before the sheet is closed, not after.

File note on the PRS source: the copy of Publication 63/P held prints July 2008 in its running head, and the source registry carries no revision for it. Treat the figures above as the PRS text held and confirm against the current publication before they are relied on.

Corrugated transverse bulkheads

The second member with a regime of its own, and there are in fact two regimes on it, applying to different ships and doing different things. Both are recorded on the bulkhead row of the class tables and both are easy to walk past.

The plain-plating figures first. LR gives cargo hold transverse bulkhead plain plating and stiffeners 25 %. KR gives watertight bulkhead plating other than a deep tank bulkhead 25 % Class I and 30 % Class II. INSB gives plating 25 % Category 1 and 30 % Categories 2 and 3. ABS puts the transverse bulkhead in the shared other-plates row at 20 % contract 2018 or later and 25 % in the 1962–2017 column. BV and RINA give item 17 plating 25 / 20 / 15, stiffener web 25 / 20, stiffener flange 20 / 15. DNV alone changes the coefficient with the construction: plane bulkhead k = 0.75, corrugated k = 0.80 on flange and web. A double skin bulkhead — two plate flanges tied by vertical webs — is not in the table body at all: the note under the table says such a bulkhead should have k = 0.80. DNV hedges there and the page hedges with it; read it as guidance, not as a table value. LR · KR · INSB · ABS · BV/RINA item 17 · DNV Tbl 2

Then the corrugated parts, which are a different member with different numbers. LR sets these out separately and by hold function, and the range is wide: corrugated plating of transverse bulkheads within holds designed to be fully filled with salt water ballast — a deep tank — 25 %; within holds designed to be partially filled, 15 %; the aft transverse bulkhead of the forward hold, 15 %; the remaining transverse bulkheads, 20 %; and all plain plating including stool plating, 25 %. INSB publishes the same four-way split in the same words on Table C note 1 for dry bulk cargo ships with corrugated bulkheads. So on both societies the corrugated bulkhead of a partially-filled hold, and the one at the after end of hold No.1, are held to 15 % — the tightest plating percentage anywhere on this page, ten points tighter than the plain plating a metre away on the same bulkhead. LR §1.5.3 additional criteria · INSB Tbl C n.1

Which hold is designed to be partially filled, and which bulkhead is the aft bulkhead of the forward hold, are facts about the ship's loading manual and its general arrangement. Neither is visible from inside the hold with a probe in your hand. This is the point on the whole page where the office most often has to go back and ask.

Now the first retroactive regime — UR S19, the flooding case on the bulkhead between the two foremost holds. ABS note 8 to Table 1C hands the whole judgement away. Where UR S19 reaches the corrugated transverse watertight bulkhead dividing holds 1 and 2, the surveyor assesses that bulkhead against S19 and not against the table. It has to be shown compliant to begin with, then shown compliant again at every Intermediate Survey and at every Special Periodical Survey — Hull. BV note (3) and RINA note (3) both send the bulkhead between the two foremost cargo holds, on ships subject to the retroactive schedule, to the criteria in Ch 6 Sec 2 of their own rules. DNV Sec.4 note 2 states the condition in engineering terms: on a single side skin bulk carrier of L > 150 m carrying cargo of density 1,78 t/m³ or more, the vertically corrugated transverse bulkhead between forward holds 1 and 2 shall satisfy the flooding requirements of UR S19. KR records that ships subject to URs S19 and S23 carry the additional guidance of Annex 1-5 Table 9. PRS Part I §5.1.3.6 names UR S18 for the corrugated transverse bulkhead as the applicable criterion but publishes no figure of its own. ABS Tbl 1C n.8 · BV/RINA n.(3) · DNV Sec.4 Tbl 2 n.2 · KR · PRS

And the second — UR S18, the net thickness rule that applies to all the corrugated bulkheads on a caught ship, not just the forward one. CCS states its scope more completely than any other document held — five conditions and one exclusion, and the ship has to meet all of them. Length 150 m and over. A single deck, with topside and hopper tanks. Watertight transverse bulkheads of vertical corrugated construction. Solid bulk cargo at a density of 1,0 t/m³ or more. And a contract for construction on or after 1 July 1998. The exclusion: a double skin bulk carrier is outside it, unless S18.1 brings the ship back in. On such a ship, where the as-built drawings do not carry the net thickness, CCS computes it as the as-built less a corrosion addition of 3,5 mm; renewal is required where the gauged thickness is less than t_net + 0,5 mm, and the renewal thickness is the as-built thickness; between t_net + 0,5 and t_net + 1,0 mm coating or annual gauging may be adopted instead. CCS Ch 3 §II.3.1

BV and RINA carry the same net thickness rule with their own applicability wording, and the two differ in a way worth reading closely. BV's second bullet to note (3) catches ships assigned the notation bulk carrier or self-unloading bulk carrier, contracted on or after 1 July 1998, with transverse vertically corrugated watertight bulkheads, of L ≥ 150 m, intended for dry bulk cargo of density 1,0 t/m³ or above where the unloading system maintains watertightness during seagoing operations — and on those ships all bulkheads are renewed below t_net + 0,5 mm, with t_net taken from the strength criteria at Pt D Ch 4 Sec 3 [6.1] as that clause stood in BV's July 2021 edition. ABS states the same regime in one line as note 9: bulk carriers for which UR S18 applies to the corrugated transverse watertight bulkheads comply with the steel renewal provisions of S18. BV Tbl 5 n.(3) · RINA Tbl 7 n.(3) · ABS Tbl 1C n.9

ClassNK does it with a flat millimetre figure and a date that is not a contract date. For a transverse watertight bulkhead in a cargo hold complying with Chapter 31A of Part C, where the application for Classification Survey during Construction was submitted to the Society before 1 July 2007, the renewal thickness is t_renewal = t_as-built − 3,0 mm. For an application submitted on or after that date, the renewal thickness is the value shown on the approved structural drawings under 31A.3.6 of Part C — so on a newer ship the number is on the drawing and nowhere else. Watertight bulkhead plates outside that scope fall back to 25 % of original thickness under the 2014 Guidance. Note the date: it is the application date, not the contract date and not the keel date, and it is the only society on this page that keys the regime to it. NK Pt B Guidance B1.3.1-4

On a CSR bulk carrier none of this applies and the arithmetic is the corrosion addition again — but the corrugated bulkhead is where CSR's one-side values are heaviest on the whole ship. In a dry bulk cargo hold on a BC-A or BC-B ship, the upper part of the transverse bulkhead takes 2,4 mm, the lower stool sloping, vertical and top plate takes 5,2 mm, and other parts take 3,0 mm. On any other bulk carrier the same three are 1,0, 2,6 and 1,5 mm. Those are one-side values. Two of them make the member, and the second one is whatever is on the other face — the stool interior, a ballast tank, a void — so a lower stool sloping plate on a BC-A ship starts from 5,2 mm on the hold side before anything is added for the other. Whether the ship is BC-A, BC-B or neither, and where the "upper part" boundary falls, are inputs — the notation is on the class certificate, and the full one-side grid is in table T10. CSR Ch 3 Sec 3 Tbl 1

Hatch covers and coamings

The third retroactive regime, and the one where the percentage in the table is furthest from the number that governs. The wastage tables are generous here: ABS puts hatch covers, hatch coamings and brackets in one row at 30 % in every column; LR gives cargo hold hatch cover plating, cover stiffeners, coaming plating and coaming stiffeners 25 % each; KR gives hatch cover and hatch coaming, both including stiffeners, 25 % Class I and 30 % Class II; INSB gives plating 25 / 30 % and stiffeners 25 % in both columns, with no separate coaming line at all; BV and RINA give hatch cover top plating 25 / 20 / 15, skirt plating and stiffeners 25 / 20, coaming plating 25 / 20 and coaming brackets 30 / 25. ABS · LR · KR · INSB · BV/RINA items 12–16

Every one of those figures is overridden on most of the bulk carrier fleet in service. The regime is UR S21, it is stated by the societies in millimetres rather than per cent, and it has two date windows, not one.

The first window: contracted from 1 July 1998 to 1 January 2004. Read the two ends off the society you are working to, because they are not worded alike: BV and RINA open theirs "on or after 1 July 1998", KR opens its own "after 1st July 1998" and closes it "before 1st January 2004". A ship contracted on 1 July 1998 itself is inside the BV and RINA windows and outside KR's. KR sets the window out most explicitly. For hold hatch covers of bulk carriers contracted in it and designed by the Rules Pt 4 Ch 2: for single skin covers and for pontoon covers, KR renews the plate once wear passes 1,5 mm — the same point as t_net + 0,5 mm, its net thickness being the required thickness with the corrosion addition taken off. Where the wear is between 1,0 and 1,5 mm, coating applied to the manufacturer's requirements or annual gauging may be adopted instead. For the internal structural members of pontoon covers, gauging is required when plating renewal is being done or when the surveyor judges it necessary from the corrosion or deformation condition, and renewal follows where the wear exceeds 1,5 mm. In the same window, CCS still controls the renewal thickness of the cargo hold hatch coaming the old way — 75 % of as-built for L ≥ 90 m and 70 % below 90 m — a minimum renewed thickness, not a wastage percentage. RINA note (4) covers the same pre-2004 window for all cargo hatch covers with the t_net + 0,5 mm rule. KR Annex 1-5 2.(3) · CCS §II.3.2 · RINA n.(4)

The second window: contracted on or after 1 January 2004, and here the scope widens from bulk carriers to all bulk carriers, ore carriers and combination carriers. What it covers on those ships is every cargo hatch cover, together with the forward and the side coamings of any hatch standing on a deck that the Load Line Convention puts in position 1. Three of the documents held print the corrosion additions themselves, and they agree on the values:

• Single skin hatch cover — all structure, plating and secondary stiffeners, t_c = 2,0 mm.
• Double skin hatch cover — the outer plating 2,0 mm; internal structures 1,5 mm. The documents that print the value do not describe that plating in the same words: DNV names the top and the bottom plating, CCS the roof and the base plate, ClassNK the top, the side and the bottom plating. Where a skirt is gauged, record it on its own line — only the ClassNK wording plainly reaches it.
• Hatch coaming and coaming stays — 1,5 mm.

Those figures are printed identically by DNV, CCS and ClassNK, and the renewal rule sits on top of them in the same form each time: renewal where the gauged thickness is less than t_net + 0,5 mm, coating or annual gauging available between t_net + 0,5 and t_net + 1,0 mm, and the renewed thickness the as-built. ClassNK writes it as a formula, t_renewal = t_as-built − t_c + 0,5 mm, which is the same rule rearranged, and adds a condition on the date that the others do not: it catches covers of bulk carriers not complying with Part CSR-B or CSR-B&T contracted on or after 1 January 2004 or at the beginning stage of construction on or after 1 January 2005. Two ways in, not one. DNV Sec.8 Tbl 1 · CCS §II.3.2 · NK Pt B B1.3.1-3(2)

Three details on this row that decide cases:

• The coaming has its own, tighter wear figure. KR requires steel renewal for coamings on bulk carriers, ore carriers and combination carriers contracted from 1 January 2004 to 1 July 2024 where the gauged thickness is worn more than 1,0 mm — against 1,5 mm for the cover — with the coating alternative between 0,5 and 1,0 mm. Same rule, half the wear, because the coaming's corrosion addition is 1,5 mm and not 2,0. A cover and a coaming gauged in the same visit are judged against different millimetre figures. KR Annex 1-5 2.(4)(C)
• The internal structure of a double skin cover has no half-millimetre band. Where the plating is being renewed, or where the surveyor calls for it on the corrosion or deformation condition, the internals are gauged — and BV, RINA and CCS all state that renewal is then required where the gauged thickness is less than t_net itself, not t_net + 0,5 mm. The band that applies to the plating does not apply inside the cover. BV n.(5)/(6) · RINA n.(4)/(6) · CCS §II.3.2
• The forward covers came in earlier. DNV's Sec.8 table note 2 records that UR S21 applies to vessels with a contract date on or after 1 January 2004, and to hatch covers forward of 0,25 L on or after 1 July 1998. A ship contracted in 2001 can therefore be inside the regime at the forward covers and outside it aft. DNV Sec.8 Tbl 1 n.2
• BV's notation list is the gate, not the ship type. Note (5) catches ships with the service notations bulk carrier ESP, bulk carrier BC-A ESP, BC-B ESP or BC-C ESP contracted on or after 1 July 1998; note (6) catches BC-A, BC-B, BC-C, ore carrier ESP, combination carrier/OBO ESP and combination carrier/OOC ESP contracted on or after 1 January 2004. Both add the same fallback: if t_net is not available, the as-built less the total corrosion addition can be used. BV Tbl 5 n.(5)–(6)

LR and ABS both point at the regime rather than restating it: LR note 7 sends bulk carriers contracted on or after 1 July 1998, CSR ships excepted, to the evaluation of scantlings of cargo hold hatch covers under UR S21, and bulk carriers, ore carriers and combination carriers contracted on or after 1 January 2004 to S21.6.2 for the coamings; ABS note 10 sends the hatch covers of bulk carriers to which UR S21 applies to the steel renewal provisions of S21.6. PRS Part I §5.1.3.6 names UR S21 as the applicable criterion, with Revision 6 for ships contracted on or after 1 July 2024, and publishes no figure of its own. On all four, the percentage in the wastage table is not the answer for a caught ship. LR Tbl 1.5.5 n.7 · ABS Tbl 1C n.10 · PRS §5.1.3.6

The hull girder

Everything above is conditional on the hull girder, and on a bulk carrier one of the triggers fires much earlier than it does on a tanker.

ABS states it as the condition on the whole of Table 1C: the individual wastage allowances are acceptable provided the hull girder section modulus is not less than 90 % of the greater of the modulus required at new construction or by 3-2-1/3.7.1(b). Note that the Table 1C notes stop at that; the technical-office trigger for ships of 130 m and over ten years is on the tanker table, not this one. ABS Tbl 1C n.4

BV and RINA publish the same zone figures as on a tanker — deck zone 10 %, neutral axis zone 15 %, bottom zone 10 %, each evaluated separately — and the zone column does the same two jobs. It is the escape hatch: a group of items may exceed its own criterion where the average of the whole zone does not exceed the zone figure. And it is the hull girder proxy: BV's note 1 to §4.3.5 states that the zone criterion rests on the current hull girder section modulus being not less than 90 % of the rule modulus within 0,4 L amidships, and that when the zone criterion is used the assessment is made against the original modulus rather than the rule modulus. On RINA, Table 8 — ships contracted before 1 June 2000 — publishes only deck zone 10 % and bottom zone 10 % and leaves the neutral axis zone blank, so an older RINA bulk carrier has no neutral axis zone criterion to fall back on. BV [4.3.5] n.1 · RINA Tbl 7/8 zone

DNV is where the bulk carrier difference bites. The two modulus tests are the same as on a tanker — the reduced section modulus not less than 90 % of the required modulus based on design bending moments, and not less than 90 % of the minimum rule modulus. What is different is what the ultimate strength trigger catches: a global longitudinal buckling check of the vertical hull girder ultimate bending capacity is required when the average reduction of deck or bottom structures exceeds 5 % on a single deck vessel of L > 150 m. A conventional bulk carrier is a single deck vessel by definition, so that trigger fires on most of the fleet at one quarter of the local 20 % allowance. Outside 0,4 L amidships a separate table allows an average reduction of deck or bottom of 10 % over the first and last tenth of the length, interpolated over the next tenth. DNV carries one more strength check that belongs on this row rather than in the local table: note 3 to the transverse-member table of its 1A1 section puts the floors in hold No.1 through the same IACS UR S22 shear check as the bottom girders in section 5, on a single skin bulk carrier over 150 m carrying cargo at a density of 1,78 t/m³ or more. Girders and floors, same hold, same UR, two notes. DNV Sec.2 [3.1.4] · Sec.4 Tbl 2 n.3

ClassNK requires 90 % of the rule-required hull section modulus for L_f ≥ 130 m under the current rule set, dropping to 80 % at L_f ≤ 60 m with interpolation between, and holds ships built to the 1964–1972 rule versions to the full rule requirement with no reduction. The same appendix carries a shear trigger that the bending table does not print: ClassNK calculates shear strength once the average corrosion of any strake in the side shell, or in a longitudinal bulkhead, passes 2,5 mm on an ore carrier or on a bulk carrier intended for alternate loading — against 3,0 mm on an oil or chemical tanker. Same alternate-loading condition as KR's trigger, and the figure is KR's Class II figure, a millimetre looser than KR Class I. INSB uses its positional table: over 0,5 L amidships for a Category 1 ship, topside plating 10 %, topside longitudinals 15 %, bottom plating 10 % single bottom and 15 % double bottom, bottom longitudinals 15 %; at 0,075 L from the ends the same five read 20 / 25 / 20 / 20 / 25 %, interpolated between. INSB's note 2 is worth reading on a bulk carrier specifically: the topside area comprises the deck outside the line of openings, the stringer and the sheer strake including rounded gunwales, with their associated longitudinals — so the cross deck is not in the topside area and does not carry its figure. NK Tbl 4 · NK App 4-5 6(2) · INSB Tbl D n.2

CSR checks the deck and bottom zone section modulus at 90 % of the value at gross offered thickness and the neutral axis zone area against the gross figure less 0,5 t_c, at special surveys once the ship is over 10 years of age, with a screening rule that passes the section without the zone-area calculation where the reduction of all contributing items is under 10 % for the deck and bottom zones and under 0,5 t_c at the neutral axis. The zone item lists are set separately for bulk carriers and for oil tankers, so a bulk carrier's deck zone is not the tanker's deck zone. CSR Ch 13 Sec 2 [2.2.2]

LR, KR, PRS and CCS publish no hull girder percentage in the documents held. LR gives a strength deck residual buckling thickness in Table 1.5.6 but no modulus or area figure. KR Pt 1 Ch 3 106. 1 (2) names oil tankers of 130 m and upwards and sets the criteria by separate requirements of the Society which are not held — so for a bulk carrier the only published KR trigger on this row is the shear strength evaluation at 1,5 mm Class I and 2,5 mm Class II average strake corrosion, on ships intended for alternate loading. PRS Part I §5.1.3.6 and CCS Chapter Three §I.1 both refer out of the document held. LR · KR 106.1(2) · PRS · CCS §I.1

A defect in the DNV text

This is recorded because a technician or an office reading the document will hit it, and the honest thing is to say what is printed rather than quietly fix it.

DNV-CG-0182, Edition July 2022 — the newest edition held — carries a Section 10 covering pitting, groove and edge corrosion on oil tankers and bulk carriers built under the IACS Common Structural Rules. Within it, under the heading 3 Edge corrosion, sits clause [3.2] Average thickness. Its one operative sentence is set out here inside quotation marks and word for word, because the wording is the whole point of this section: "The average measured thickness across the breadth or height of the stiffener shall be less than what it is defined in IACS CSR (and this is usually shown on the approved drawing)." Nothing in it has been tidied or shortened. That is the sentence carried at PDF page 34. DNV-CG-0182 Sec.10 [3.2] · PDF p. 34

Read at face value that clause requires the average measured thickness to be below the CSR figure — which would make a sound stiffener non-compliant and a wasted one acceptable. It reads backwards against every neighbouring criterion in the same section of the same document:

• [2.3], one clause earlier and on the facing page, makes the CSR general-corrosion renewal criterion a floor for plating: the average taken across any section has to stay at or above it. Same test, pointing the other way.
• [2.3] and [3.1] both set their measured-thickness criteria as t_m ≥ 0.7 (t_as-built − t_{vol add}) and t_m ≥ t_ren − 1 — minimums, not maximums.
• [4.1] does the same for groove corrosion, t_m ≥ 0.75 (t_as-built − t_{vol add}) and t_m ≥ t_ren − 0.5, and [4.2] sends larger grooved areas to be assessed on the general corrosion criteria using the average measured thickness.

Every other statement of the same idea in Section 10 is a lower bound. The intent of [3.2] is plainly that the average measured thickness across the stiffener shall not be less than the CSR figure — and this handbook does not silently correct a source, so the clause is reported as printed and the reading is flagged.

What to do with it. Work to the intent — the average measured thickness across the breadth or height of the stiffener is a floor, not a ceiling — and confirm it with the attending surveyor before it decides a case. Do not quote [3.2] as printed in a report, and do not quote it as corrected either without saying that you have read it against the rest of the section. If the case turns on it, the surveyor should raise it with DNV.

Scope note: DNV-CG-0182 Sec.10 applies to local corrosion on oil tankers and bulk carriers built under IACS CSR, so this defect is not specific to bulk carriers. It is recorded here because Sec.10's only ship-type-specific subsection, [2.2] Side structures of bulk carriers, names bulk carriers, and because edge corrosion of stiffener webs and flanges is the single side skin side frame problem. And it must be re-read in the current DNV edition, which is not held — the wording may already have been corrected.

The full grid

This page reads the bulk carrier dataset — fourteen members against eleven schemes — in the order a technician works down the hold, and stops to explain where the explanation is in a source. It is not the whole grid. Every cell, with its clause, its PDF page and the conditions attached to it, sits in handbook table T01 — Permissible diminution, class by class, which carries the same eleven schemes across oil tankers, bulk carriers and general dry cargo ships.

Open T01 — permissible diminution, all 451 cells ↗

The page gives the reading; the table gives every cell. The CSR corrosion-addition values quoted here in one-side form belong in full to handbook table T10 — CSR renewal thresholds, not to either of them.

What this means when you fill the sheet

Nothing on this page can be applied to a bare millimetre value. On a bulk carrier the list of what has to travel with the reading is longer than on a tanker, because three of the members carry regimes that turn on the ship's history rather than on its structure.

The one field whose absence makes the whole set unusable is the as-built thickness at the point gauged. Not per member and not per strake — per point, because a strake changes thickness along its length and the hopper knuckle is not the plate above it. ABS, LR, ClassNK, KR, INSB and CCS all compute from it. DNV computes from it less the documented voluntary addition. CSR subtracts the corrosion addition from it. Every one of the net-thickness regimes in sections 6, 7 and 8 falls back to "as-built minus the corrosion addition" when the drawings do not carry t_net — which is most of the time. Without the as-built there is no denominator and no scheme on this page produces an answer. Everything else in the list below can be recovered from the ship's papers afterwards; the as-built at the point you gauged cannot.

Then, in the order the sections above needed them:

• Single side skin or double side skin, hold by hold. The PRS side frame regime does not apply to a hold that fails the definition even where the rest of the ship is caught, and BV's note (4) is written for single side skin ships. This is a per-hold fact, not a per-ship one.
• Contract date — and for ClassNK, the application date. ABS Table 1C splits at contract 2018; RINA at 1 June 2000; the hatch cover regime at 1 July 1998 and again at 1 January 2004, with DNV catching covers forward of 0,25 L from the earlier date; KR Class I at classification during construction after 1 July 1998; CSR at contract 1 July 2015. ClassNK keys the corrugated bulkhead regime to the date the application for Classification Survey during Construction was submitted, which is not the contract date and not the keel date, and its hatch cover regime to contract on or after 1 January 2004 or beginning of construction on or after 1 January 2005.
• Age at 1 January 2005 — for the side frame schedule. Whether the ship was under 10, 10 or more, or 15 or more years old on that date decides by which survey compliance was due, and 1 July 2005 is the equivalent date for an OBO carrier.
• Hold number, and hold function. Hold No.1 has its own corrosion additions in the PRS side frame table and its own bulkhead in the S19 regime. Which holds are designed to be fully filled with salt water ballast, which are designed to be partially filled, and which bulkhead is the aft bulkhead of the forward hold, decide whether the LR and INSB corrugated figure is 25, 20 or 15 %. That is a ten-point range decided by the loading manual, not by the probe.
• Cargo density and notation. The S18 regime turns on solid bulk cargo of density 1,0 t/m³ or above; DNV's bottom girder and forward bulkhead checks turn on 1,78 t/m³ or more; LR's inner bottom and hopper figures turn on the notation Strengthened for Heavy Cargoes together with L > 150 m; BV's notes turn on the exact service notation, BC-A, BC-B, BC-C, ore carrier ESP and the rest. Copy the notation string off the certificate rather than writing "bulk carrier".
• Whether a continuous wooden ceiling is fitted over the inner bottom. On BV this is worth 1,5 mm off the limit on a ship contracted on or after 1 January 2001 with one of the named notations. It is a survey observation and nothing in the drawings will tell the office whether the ceiling is still there.
• Whether tripping brackets are fitted to the side frames, and their thickness. Under the PRS side frame regime they can remove the slenderness criterion from the calculation entirely — but only if the office knows they exist and what they gauge.
• Hatch cover construction: single skin, pontoon or double skin, and for a double skin cover whether the point is on the plating or on the internal structure. The corrosion addition is 2,0 mm on the plating and 1,5 mm inside, and the internal structure has no half-millimetre band above t_net at all. Record cover and coaming separately — they are judged at different millimetre figures on the same ship.
• Web separately from flange on every frame, bracket and longitudinal. BV and RINA hold the flange tighter than the web throughout; the PRS side frame criteria are written for the web with the flange assessed under the table; DNV splits web from flange on web frames and floors. A single "side frame: 7.4 mm" entry cannot be assessed on any of them.
• Enough points to average, and the strake identity. LR Table 1.5.5 note 6 and INSB Table C note 3 both make the maximum diminution an average over the plate area or the length between supports. KR's shear trigger is an average per strake. BV's group and zone criteria are averages of averages. One low reading is not a failure on those schemes, and one high reading is not a pass.

Two habits that pay for themselves on a bulk carrier specifically. Ask for the ship's own evaluation records for the side frames before the hold survey, not after. If the ship is inside the S31 regime, the numbers the readings will be judged against are in that document and nowhere in any rulebook, and a sheet closed without them has to be reopened. And record the compartment on both sides of every plate, even on a non-CSR ship — hold one side and topside tank the other is not the same member as hold one side and sea the other, and it is the field most often missing when the office has to go back and ask.

Last thing, and it is the same on every ship type: none of these figures is a target. Every maximum LR publishes already has five more years of average corrosion built into it, and LR says so. It then calls a plate or a stiffener substantially corroded once wastage passes 75 % of the permissible diminution — so the extra close-up and gauging work starts at three-quarters of the number on this page. What counts as substantial corrosion in the other ten schemes is a separate question with its own page. LR TM Guidance §1.5

Sources

1. ABS Pt 7 App 1 Sec 4ABS Rules for Survey After Construction, Part 7 — July 2026official text ↗
2. BV NR467 Pt A Ch 2 App 3Bureau Veritas NR467 Rules for the Classification of Steel Ships, Part A — R26, July 2026official text ↗
3. LR TM Guidance Pt 1 Ch 5Lloyd's Register Thickness Measurement and Close-up Survey Guidance, Part 1 — Version 7.3, November 2016 (older edition held)official text ↗
4. NK Guidance App 3.5ClassNK Guidance for Undergoing Class Maintenance Surveys — 2014 edition (older edition held)official text ↗
5. NK Pt B Guidance B1.3.1ClassNK Rules and Guidance for the Survey and Construction of Steel Ships, Part B — 2022 edition (older edition held)official text ↗
6. RINA Pt A Ch 2 App 2RINA Rules for the Classification of Ships, Part A Ch 2 App 2 — 1 July 2024 interactive set (older edition held)official text ↗
7. DNV-CG-0182DNV-CG-0182 Allowable thickness diminution for hull structure — Edition July 2022 (older edition held)official text ↗
8. KR Pt 1 Annex 1-5KR Rules and Guidance for the Classification of Steel Ships, Part 1 — 2026 editionofficial text ↗
9. PRS Pt I §5.1.3.6PRS Rules for the Classification and Construction of Sea-going Ships, Part I — January 2026official text ↗
10. PRS Pub 63/PPRS Publication 63/P — Replacement Criteria for Side Shell Frames and Brackets in Single Side Skin Bulk Carriersofficial text ↗
11. INSB Pt I Ch 3 Sec 13INSB Rules and Regulations for the Classification and Construction of Steel Ships, Part I — Issue 04 Rev.03, December 2024official text ↗
12. CCS TM Guidelines Ch 3CCS Guidelines for Thickness Measurement of Hull — Ver. 6.6, March 2025official text ↗
13. CSR Pt 1 Ch 13IACS Common Structural Rules for Bulk Carriers and Oil Tankers — 1 January 2024 version, in force 1 July 2024official 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

• How do I read a thickness limit?K5.1
• What counts as substantial corrosion in each class?K5.2
• What are the permissible diminution limits for oil tankers, class by class?K5.3
• What are the permissible diminution limits for general dry cargo ships?K5.5
• What are the pitting acceptance criteria in each class?K5.6
• How is CSR renewal thickness calculated?K5.7
• What thickness limits apply to ships under 90 m?K5.8