MARPOL Annex I Reg 28: oil tanker damage stability
MARPOL Annex I Regulation 28: the side, bottom and raking damage an oil tanker of 150 GT and above must survive, and the heel, GZ and area tests it must meet.
MARPOL Annex I Regulation 28 is the subdivision and damage stability regulation for oil tankers: it requires every oil tanker of 150 gross tonnage and above delivered after 31 December 1979 to survive a prescribed side or bottom damage, at any operating draught that reflects an actual partial or full load condition, and to meet the heel, range, righting lever and area criteria of Regulation 28.3. It sits in Chapter 4 of MARPOL Annex I , in the revised text adopted by IMO Resolution MEPC.117(52) on 15 October 2004 and in force since 1 January 2007, and it has been amended twice since: by MEPC.248(66), which made a stability instrument mandatory from 1 January 2016, and by MEPC.343(78), which rewrote the watertight door wording of Regulation 28.3.1 from 1 January 2024.
The regulation is deterministic. A fixed damage box, sized from the ship’s length \(L\) and breadth \(B\), is placed along the hull, the spaces inside it are flooded at prescribed permeabilities, and the ship either meets every criterion in every case or it does not. Regulation 28 contains no residual metacentric height (GM) criterion; the 0.1 m figure in Regulation 28.3.3 is a maximum residual righting lever (GZ).
Seven paragraphs carry the rule:
| Paragraph | Subject |
|---|---|
| 28.1 | Application, and where along the length damage is assumed |
| 28.2 | Assumed extents of side and bottom damage |
| 28.3 | Survival criteria in the final and intermediate stages of flooding |
| 28.4 | Calculation assumptions: permeabilities, superstructure buoyancy, free surface |
| 28.5 | Loading and damage stability information supplied to the master |
| 28.6 | Mandatory stability instrument (MEPC.248(66), from 1 January 2016) |
| 28.7 | Bottom raking damage for tankers of 20,000 dwt and above delivered on or after 6 July 1996 |
Application: which oil tankers Regulation 28 covers
Regulation 28.1 applies to “every oil tanker delivered after 31 December 1979, as defined in regulation 1.28.2, of 150 gross tonnage and above”. The definition in Regulation 1 catches a tanker on any one of four dates: a building contract placed after 31 December 1975; in the absence of a contract, a keel laid or similar stage reached after 30 June 1976; delivery after 31 December 1979; or a major conversion contracted, begun or completed on the equivalent dates.
In practice every oil tanker in service is caught. The regulation therefore works as a fleet-wide standard, not a newbuild-only rule.
The 1 February 2002 date belongs to Regulation 27
A date of 1 February 2002 circulates in tanker stability material as the Regulation 28 cut-off. It is the applicability date of Regulation 27 on intact stability , which covers oil tankers of 5,000 tonnes deadweight and above delivered on or after 1 February 2002. Regulation 28 has no such date, and it has no deadweight threshold apart from the 20,000 dwt raking-damage paragraph in 28.7.
Loading conditions that must be checked
The damage is applied “for any operating draught reflecting actual partial or full load conditions consistent with trim and strength of the ship as well as relative densities of the cargo”. So the test is not a single design condition: a homogeneous full load at summer draught, a part cargo split across alternate tanks, and a two-grade load with dense and light cargo all count if the ship can actually sail in them.
One class of condition is excluded by the text itself. Regulation 28.1 states that “ballast conditions where the tanker is not carrying oil in cargo tanks, excluding any oil residues, shall not be considered.” A ballast passage with slops on board is therefore outside Regulation 28, although it still has to satisfy intact stability.
Who checks it
The flag Administration, or a recognized organization acting for it, approves the damage stability calculations at plan approval and the loading information supplied under Regulation 28.5. The IOPP Certificate and its Form B Supplement for oil tankers record the ship’s construction and equipment, including the stability instrument since 2016. In port, a port State control officer checks the documentation and the stability instrument under Regulation 11 of Annex I .
Where along the length the damage is assumed
Regulation 28.1 sets where the damage box may be placed, and the answer depends on the ship’s length. Longer tankers must survive damage anywhere; shorter tankers get relief at the engine room bulkheads.
| Tanker length \(L\) | Damage assumed (Reg 28.1) |
|---|---|
| Over 225 m | Anywhere in the ship’s length |
| Over 150 m, up to 225 m | Anywhere in the length, except where either after or forward bulkhead bounding a machinery space located aft is involved; the machinery space is treated as a single floodable compartment |
| 150 m or less | Anywhere between adjacent transverse bulkheads, with the exception of the machinery space |
For a tanker of 100 m or less, Regulation 28.1.3 adds a relaxation: where all the requirements of Regulation 28.3 “cannot be fulfilled without materially impairing the operational qualities of the ship, Administrations may allow relaxations from these requirements.” The relaxation is granted by the Administration case by case.
The 225 m band covers the large crude carriers. A VLCC with a rule length of about 330 m, a Suezmax of about 270 m and most Aframax tankers must survive damage that straddles the engine room bulkhead, while a medium-range product tanker of about 180 m sits in the middle band and can treat its aft machinery space as one compartment.
Assumed side and bottom damage extents
Regulation 28.2 fixes the size of the damage box. Every capped dimension is “whichever is less”, so the formula governs a small ship and the cap governs a large one. \(L\) is the length as defined in Regulation 1 and \(B\) the breadth, both in metres.
Side damage (Reg 28.2.1)
| Direction | Extent |
|---|---|
| Longitudinal | \( \tfrac{1}{3}L^{2/3} \) or 14.5 m, whichever is less |
| Transverse | \(B/5\) or 11.5 m, whichever is less, measured inboard from the ship’s side at right angles to the centreline at the level of the summer load line |
| Vertical | From the moulded line of the bottom shell plating at centreline, upwards without limit |
The longitudinal formula reaches the 14.5 m cap at \(L = 43.5^{3/2} \approx 286.9\) m. The transverse cap of 11.5 m is reached at \(B = 57.5\) m. Because the transverse extent is measured at the summer-load-line, the box penetrates the same distance whatever the draught being tested.
Bottom damage (Reg 28.2.2)
Bottom damage has two columns, one for the forward part of the ship and one for the rest. Treating the whole bottom with the forward figures overstates the assumed damage aft.
| Direction | Within 0.3L from the forward perpendicular | Any other part of the ship |
|---|---|---|
| Longitudinal | \( \tfrac{1}{3}L^{2/3} \) or 14.5 m, whichever is less | \( \tfrac{1}{3}L^{2/3} \) or 5 m, whichever is less |
| Transverse | \(B/6\) or 10 m, whichever is less | \(B/6\) or 5 m, whichever is less |
| Vertical | \(B/15\) or 6 m, whichever is less, measured from the moulded line of the bottom shell plating at centreline | \(B/15\) or 6 m, whichever is less, measured the same way |
The 5 m caps govern almost every seagoing tanker. The longitudinal formula exceeds 5 m once \(L\) passes about 58.1 m, and \(B/6\) exceeds 5 m once \(B\) passes 30 m. Aft of the forward 0.3L, a product tanker and a VLCC are therefore assumed to suffer the same 5 m by 5 m bottom breach.
Extents worked for five tanker sizes
The figures below apply Regulation 28.2 to representative principal dimensions. They are arithmetic on the formulas, not data for any named ship.
| Size | \(L\) (m) | \(B\) (m) | Side, long. | Side, trans. | Bottom fwd, long. | Bottom fwd, trans. | Bottom aft, long. × trans. | Bottom, vertical |
|---|---|---|---|---|---|---|---|---|
| Small coastal | 100 | 17 | 7.18 m | 3.40 m | 7.18 m | 2.83 m | 5.00 × 2.83 m | 1.13 m |
| MR product | 183 | 32.2 | 10.74 m | 6.44 m | 10.74 m | 5.37 m | 5.00 × 5.00 m | 2.15 m |
| Aframax | 240 | 42 | 12.87 m | 8.40 m | 12.87 m | 7.00 m | 5.00 × 5.00 m | 2.80 m |
| Suezmax | 270 | 48 | 13.92 m | 9.60 m | 13.92 m | 8.00 m | 5.00 × 5.00 m | 3.20 m |
| VLCC | 330 | 60 | 14.50 m | 11.50 m | 14.50 m | 10.00 m | 5.00 × 5.00 m | 4.00 m |
Two results stand out. Only the VLCC reaches the 14.5 m and 11.5 m side caps and the 10 m forward bottom cap. And the vertical bottom extent of \(B/15\) never reaches its 6 m cap in this range, since that would need a breadth of 90 m.
Lesser damage, bulkhead spacing and recesses (Reg 28.2.3 to 28.2.6)
Four further rules shape the damage case set:
- 28.2.3, lesser damage. If a damage of lesser extent than the maximum would give a more severe condition, that damage is considered. A narrow breach that floods a wing ballast tank on one side only can produce more heel than the full-width box that also reaches the centre tanks.
- 28.2.4, closely spaced bulkheads. For tankers over 150 m, where damage involving transverse bulkheads is assumed under 28.1.1 or 28.1.2, transverse watertight bulkheads must be spaced at least the longitudinal extent of side damage apart to be considered effective. Where they are closer, “one or more of these bulkheads within such extent of damage shall be assumed as non-existent for the purpose of determining flooded compartments.”
- 28.2.5, bulkheads on tankers of 150 m or less. Where damage between adjacent transverse bulkheads is assumed under 28.1.3, no main transverse bulkhead, and no transverse bulkhead bounding side tanks or double bottom tanks, is assumed damaged unless the spacing of the adjacent bulkheads is less than the longitudinal extent of side damage, or there is a step or recess in a transverse bulkhead of more than 3.05 m in length within the extent of penetration. The step formed by the after peak bulkhead and the after peak top is not regarded as a step.
- 28.2.6, pipes, ducts and tunnels. Where these lie within the assumed extent of damage, arrangements must stop progressive flooding through them to compartments other than those assumed floodable for that case.
Rule 28.2.6 is where a design passes or fails in detail. A cargo line or a ballast main running through a wing tank inside the damage box is an extra flooding path unless its valves, non-return fittings or routing keep the flooding inside the assumed boundary.
Raking damage for large tankers (Reg 28.7)
Regulation 28.7 adds a bottom raking damage assumption for oil tankers of 20,000 tonnes deadweight and above delivered on or after 6 July 1996. Raking damage models a long, shallow tear along the bottom from a grounding at speed, as opposed to the short local breach of Regulation 28.2.2.
| Direction | Tankers of 75,000 dwt and above | Tankers of 20,000 dwt and above, below 75,000 dwt |
|---|---|---|
| Longitudinal | 0.6L measured from the forward perpendicular | 0.4L measured from the forward perpendicular |
| Transverse | \(B/3\) anywhere in the bottom | \(B/3\) anywhere in the bottom |
| Vertical | Breach of the outer hull | Breach of the outer hull |
For the 330 m VLCC in the table above, the raking extent runs 198 m aft from the forward perpendicular and 20 m across. For the 240 m Aframax, assuming it is above 75,000 dwt, it runs 144 m. The vertical extent is a breach of the outer hull only, so the spaces opened are those between the outer bottom and the inner bottom of the double hull required by Regulation 19 along that length.
Until 1 January 2016 this paragraph was numbered 28.6. MEPC.248(66) inserted the new stability instrument paragraph as 28.6 and renumbered raking damage as 28.7, changing the cross-references in Regulations 19.2.2, 20.1.2 and 20.4 to match. Older plan approval documents, class guidance and tank arrangement studies that cite “28.6” for raking damage refer to what is now 28.7. A stub covers bottom raking damage as a concept across instruments, and Regulation 20 carries the matching provisions for existing tankers.
Survival criteria (Reg 28.3)
Regulation 28.3 states the conditions a tanker must meet once the assumed damage has flooded. There are five subparagraphs, and the numerical ones apply in the final stage of flooding:
| Subparagraph | Requirement |
|---|---|
| 28.3.1 | Final waterline, taking account of sinkage, heel and trim, below the lower edge of any opening through which progressive flooding may take place |
| 28.3.2 | Angle of heel due to unsymmetrical flooding not more than 25 degrees, or 30 degrees if no deck edge immersion occurs |
| 28.3.3 | Righting lever curve with a range of at least 20 degrees beyond equilibrium, a maximum residual righting lever of at least 0.1 m within that range, and an area of at least 0.0175 metre radians within that range |
| 28.3.4 | Stability during intermediate stages of flooding to the satisfaction of the Administration |
| 28.3.5 | Equalization arrangements requiring mechanical aids not credited |
Final waterline and progressive-flooding openings (Reg 28.3.1)
The final waterline must lie below the lower edge of any opening through which progressive flooding may take place. The regulation lists what counts. Air pipes, and openings closed by weathertight doors or hatch covers, count as progressive-flooding openings. A tank vent or a weathertight door to the accommodation that ends up under the final waterline therefore fails the case outright.
MEPC.343(78), adopted 10 June 2022 and in force from 1 January 2024, replaced the 28.3.1 text. The openings that may be excluded are now:
- watertight manhole covers and flush scuttles;
- small watertight cargo tank hatch covers which maintain the high integrity of the deck;
- remotely operated sliding watertight doors;
- hinged watertight access doors with open or closed indication locally and at the navigation bridge, of the quick-acting or single-action type, that are normally closed at sea;
- hinged watertight doors that are permanently closed at sea;
- sidescuttles of the non-opening type.
The two hinged watertight door categories in 28.3.1 are the 2022 addition.
Heel limit (Reg 28.3.2)
The angle of heel due to unsymmetrical flooding must not exceed 25 degrees. It may be increased up to 30 degrees “if no deck edge immersion occurs”. Unsymmetrical flooding is the norm for side damage on a double hull tanker: the box floods the wing ballast tank on one side and possibly the cargo tank inboard of it, with nothing on the other side.
Residual righting lever, range and area (Reg 28.3.3)
The core criterion reads in full:
“The stability in the final stage of flooding shall be investigated and may be regarded as sufficient if the righting lever curve has at least a range of 20º beyond the position of equilibrium in association with a maximum residual righting lever of at least 0.1 metre within the 20º range; the area under the curve within this range shall not be less than 0.0175 metre radians. Unprotected openings shall not be immersed within this range unless the space concerned is assumed to be flooded. Within this range, the immersion of any of the openings listed in subparagraph 3.1 of this paragraph and other openings capable of being closed watertight may be permitted.”
Read against a damaged righting lever curve , that sets three numbers measured from the equilibrium heel \( \theta_e \):
$$ \theta_{\text{range}} \geq 20^{\circ} \text{ beyond } \theta_e, \qquad \max_{\theta_e \leq \theta \leq \theta_e + 20^{\circ}} GZ(\theta) \geq 0.1 \text{ m}, \qquad \int_{\theta_e}^{\theta_e + 20^{\circ}} GZ \, d\theta \geq 0.0175 \text{ m rad} $$The area is taken “within this range”, the 20 degrees beyond equilibrium. It is not the area to the angle of vanishing stability or to a downflooding angle, which is how a general damage stability summary sometimes paraphrases it. An unprotected opening that immerses inside the 20 degree range ends the curve there unless the space behind it is assumed flooded.
Intermediate stages and equalization (Reg 28.3.4 and 28.3.5)
Regulation 28.3.4 requires the Administration to be satisfied that stability is sufficient during intermediate stages of flooding, but sets no numbers. Each Administration, or the recognized organization acting for it, applies its own criteria to those stages.
Regulation 28.3.5 states that “equalization arrangements requiring mechanical aids such as valves or cross-levelling pipes, if fitted, shall not be considered for the purpose of reducing an angle of heel or attaining the minimum range of residual stability”. The same subparagraph allows spaces “linked by ducts of a large cross-sectional area” to be considered common. A passive cross-connection between port and starboard double bottom tanks can count; a cross-flooding valve that someone must open cannot.
Why there is no GM criterion
Regulation 28.3 contains no requirement for a minimum residual metacentric height. The text quoted above is the whole stability criterion, and its 0.1 m is a maximum residual righting lever within the 20 degree range. A tanker may have a positive metacentric height in the damaged condition and still fail 28.3.3 if the GZ curve never reaches 0.1 m before the range ends.
A metacentric height criterion does appear in tanker stability, but for the intact ship: Regulation 27 requires an initial metacentric height GMo of not less than 0.15 m, a test separate from Regulation 28 and from the general intact stability criteria. Importing a GM figure into the damaged condition misstates Regulation 28.
Calculation assumptions (Reg 28.4)
Regulation 28.4 fixes the inputs to the flooding calculation: the permeability of each kind of space, the treatment of superstructures above the damage, and the free surface corrections.
Permeabilities (Reg 28.4.2)
Regulation 28.4.2 sets the permeability, the fraction of a space’s volume that floodwater can occupy:
| Spaces | Permeability |
|---|---|
| Appropriated to stores | 0.60 |
| Occupied by accommodation | 0.95 |
| Occupied by machinery | 0.85 |
| Voids | 0.95 |
| Intended for consumable liquids | 0 to 0.95 |
| Intended for other liquids | 0 to 0.95 |
Cargo tanks fall under “other liquids”. A cargo tank’s permeability is therefore not fixed at zero, nor at 0.95; the regulation gives a range of 0 to 0.95. MSC.1/Circ.1461 explains how the range is applied: the permeability of a partially filled compartment “should be consistent with the amount of liquid carried in the compartment” (Table 2 footnote), and under paragraph 6.4.3, whenever damage penetrates a tank containing liquids, its contents are assumed completely lost and replaced by seawater up to the level of the final plane of equilibrium.
Superstructure buoyancy (Reg 28.4.3)
The buoyancy of any superstructure directly above the side damage is disregarded. The text continues: “The unflooded parts of superstructures beyond the extent of damage, however, may be taken into consideration provided that they are separated from the damaged space by watertight bulkheads and the requirements of subparagraph .1 of this regulation in respect of these intact spaces are complied with. Hinged watertight doors may be acceptable in watertight bulkheads in the superstructure.”
Free surface (Reg 28.4.4 and 28.4.5)
The free surface effect is calculated at an angle of heel of 5 degrees for each individual compartment. The Administration may require or allow free surface corrections at a greater angle for partially filled tanks.
For consumable liquids, Regulation 28.4.5 assumes that at least one transverse pair or a single centreline tank of each type has a free surface, and the tanks chosen are those where the effect is greatest.
Information to the master (Reg 28.5)
Regulation 28.5 requires the master of every oil tanker to which it applies, and the person in charge of a non-self-propelled oil tanker, to be supplied in an approved form with two things: information on loading and distribution of cargo necessary to ensure compliance with Regulation 28, and data on the ability of the ship to comply with the damage stability criteria. Regulation 28.5.2 adds that the data include the effect of any relaxations allowed under 28.1.3. In practice the data take the form of approved loading conditions with their damage results, a limiting KG or GM curve, or both.
This is the paragraph a stability booklet and loading computer answers to for damage stability. It sets no longitudinal strength criterion; bending moment and shear force in the damaged condition are not part of Regulation 28.
Mandatory stability instrument (Reg 28.6, from 1 January 2016)
Regulation 28.6, inserted by MEPC.248(66) adopted 4 April 2014, entered into force on 1 January 2016. Its operative sentence is: “All oil tankers shall be fitted with a stability instrument, capable of verifying compliance with intact and damage stability requirements approved by the Administration having regard to the performance standards recommended by the Organization”.
The application dates are:
- Tankers constructed on or after 1 January 2016: fitted from delivery.
- Tankers constructed before 1 January 2016: at the first scheduled renewal survey of the ship on or after 1 January 2016, but not later than 1 January 2021.
An instrument already on board that is capable of verifying compliance need not be replaced. The Administration issues a document of approval for the instrument, and that document is subject to control under Regulation 11, so a port State officer can ask for it.
The same resolution added items 5.7.5 and 5.7.6 to Form B of the Supplement to the IOPP Certificate. Regulation 28.6 uses “constructed” for its cut-off, while Regulation 28.1 uses “delivered”, so the two dates are read under their own definitions. A stub tracks the tanker stability instrument requirement across MARPOL, the IBC Code and the IGC Code.
Waivers under Regulation 3.6
MEPC.248(66) also added Regulation 3.6 to the exemptions and equivalents regulation . The Administration may waive the Regulation 28.6 instrument, if the tanker is loaded in accordance with the conditions approved by the Administration taking into account the guidelines developed by the Organization, for:
- a tanker on a dedicated service with a limited number of permutations of loading, so that all anticipated conditions have been approved in the stability information given to the master;
- a tanker where stability verification is made remotely by a means approved by the Administration;
- a tanker loaded within an approved range of loading conditions;
- a tanker constructed before 1 January 2016 provided with approved limiting KG or GM curves covering all applicable intact and damage stability requirements.
A Regulation 3.6 waiver covers the Annex I Regulation 28.6 instrument only. A chemical tanker’s separate stability instrument requirement under IBC Code paragraph 2.2.6 is not waived by it.
Instrument types and verification guidance
Regulation 28.6 names no type of instrument. The types are defined in Part B 4.1.3 of the 2008 IS Code , adopted as MSC.267(85) on 4 December 2008:
| Type | Function (IS Code Part B 4.1.3) |
|---|---|
| Type 1 | Intact stability only |
| Type 2 | Intact stability, and damage stability checked against “a limit curve … or previously approved loading conditions” |
| Type 3 | Intact stability, and damage stability by “direct application of pre-programmed damage cases” |
A Type 1 instrument cannot satisfy Regulation 28.6 alone, because the regulation requires verification of damage stability too. None of the three types concerns the accidental oil outflow parameter of Regulation 23 , which is a design property of the tank arrangement and not something an instrument recalculates for each loading.
Two circulars sit under the requirement. MSC.1/Circ.1229 of 11 January 2007 is the guideline for approving stability instruments. MSC.1/Circ.1461 of 8 July 2013 is the guidance on verifying damage stability for oil, chemical and gas tankers: Part 1 applies to tankers constructed on or after 14 June 2013 and Part 2 to all tankers. It accepts compliance shown by approved loading conditions, approved limit curves, or a Type 2 or Type 3 instrument, and its footnote 4 recommends a Type 3 instrument.
Amendment history and the old Regulation 25
Tanker damage stability has sat under two regulation numbers in MARPOL Annex I, and much of the confusion around Regulation 28 comes from the 2007 renumbering.
| Date | Instrument | Effect on tanker damage stability |
|---|---|---|
| Before 1 January 2007 | Original Annex I | Damage stability held in Regulation 25, “Subdivision and stability” |
| 1 February 1999 | MEPC.75(40), adopted 25 September 1997 | Added Regulation 25A, “Intact stability” |
| 1 January 2007 | MEPC.117(52), adopted 15 October 2004 | Revised Annex I: subdivision and damage stability becomes Regulation 28; Regulation 25 becomes “Hypothetical outflow of oil”; Regulation 25A becomes Regulation 27 |
| 1 January 2016 | MEPC.248(66), adopted 4 April 2014 | New 28.6 stability instrument; raking damage renumbered 28.7; new Regulation 3.6 waivers |
| 1 January 2024 | MEPC.343(78), adopted 10 June 2022 | 28.3.1 rewritten to exclude hinged watertight doors that meet set conditions |
The renumbering has a trap for anyone reading pre-2007 documents. “Regulation 25” in a 1990s plan approval letter means damage stability; in the revised Annex I it is hypothetical outflow , a different calculation based on the damage assumptions of Regulation 24 . The Regulation 13F double hull rules and Regulation 13G phase-out of the original Annex I, introduced by MEPC.52(32) on 6 March 1992 and accelerated by MEPC.111(50) on 4 December 2003, became Regulations 19 and 20 of the revised Annex.
Regulation 28 and the other Annex I tanker regulations
Chapter 4 of Annex I tests the cargo area of an oil tanker against several separate standards. Regulation 28 is the one about whether the ship stays afloat and upright; the others are about how much oil escapes or how the tanks are arranged.
| Regulation | Question it answers |
|---|---|
| Reg 18 | Segregated ballast tanks and their protective location |
| Reg 19 | Double hull and double bottom dimensions protecting cargo tanks |
| Reg 23 | Probabilistic mean oil outflow performance |
| Reg 24 and Reg 25 | Assumed damage and hypothetical outflow |
| Reg 26 | Cargo tank size limits |
| Reg 27 | Intact stability in port and at sea |
| Reg 28 | Survival after side, bottom and raking damage |
A Regulation 23 or Regulation 25 outflow result says nothing about survival, and a Regulation 28 pass says nothing about outflow. The damage boxes of Regulation 24 and Regulation 28 also differ, so a damage case built for one is not reused for the other without checking the extents.
The double hull is where the two meet in design. The wing tank width and double bottom height of Regulation 19 set what the side and bottom damage boxes flood: a box shallower than the double bottom floods only ballast, while one wider than the wing tank reaches the cargo tank. Tanker designers size the protective spaces against both regulations at once, together with segregated ballast capacity.
Chemical tankers and gas carriers
A chemical tanker certified under the IBC Code meets the damage stability requirements of IBC Code chapter 2, in the text revised by MSC.176(79) of 10 December 2004 and in force since 1 January 2007. The damage extents in 2.5.1, the permeabilities in 2.7.2 and the survival criteria in 2.9 use the same figures as Regulation 28. The extents in 2.5.1 are common to all three ship types; the ship type governs other chapter 2 requirements, including cargo tank location under 2.6.
MARPOL Annex II does not hold the chemical tanker damage rules. In the revised Annex II adopted by MEPC.118(52), Regulation 16 is “Measures of control” and Regulation 11 is “Design, construction, equipment and operations”, which points to the IBC Code. An oil and chemical tanker therefore meets Regulation 28 for its oil cargoes and IBC chapter 2 for its chemical cargoes, with the same numerical criteria in both.
The IGC Code for gas carriers , in the version adopted by MSC.370(93) on 22 May 2014 and in force from 1 January 2016, uses the same 20 degree range, 0.1 m maximum residual righting lever and 0.0175 metre radian area in 2.7.2.1. It differs in one respect: the 20 degree range may be measured from any angle commencing between the position of equilibrium and 25 degrees, or 30 degrees where no deck immersion occurs. Regulation 28.3.3 measures it from equilibrium.
Both codes also carry a stability instrument requirement. For the IBC Code it is paragraph 2.2.6, added by MSC.369(93) of 22 May 2014 and in force from 1 January 2016, the same date as Regulation 28.6.
SOLAS probabilistic damage stability does not apply to oil tankers
SOLAS Chapter II-1 Regulation 4.1, in the text adopted by MSC.216(82) on 8 December 2006 and in force for ships constructed on or after 1 January 2009, applies the subdivision and damage stability requirements of Parts B-1 to B-4 to cargo ships of 80 m in length and upwards, “but shall exclude those cargo ships which are shown to comply with subdivision and damage stability regulations in other instruments developed by the Organization.”
An oil tanker that complies with MARPOL Annex I Regulation 28 is one of those ships. It is not assessed against the attained and required subdivision indices of the SOLAS probabilistic method . The explanatory notes to the SOLAS damage stability regulations, MSC.281(85) of 4 December 2008, revised by MSC.429(98) of 9 June 2017, address SOLAS only and do not interpret Regulation 28.
The two methods also answer different questions. The SOLAS index weighs the probability of each damage and of survival given that damage; Regulation 28 asks whether the ship survives one fixed damage, wherever it falls within the permitted zone, with a pass or fail result. The general principles of subdivision and floodable length underlie both, but neither result substitutes for the other.
Load Lines type A freeboard flooding test
A tanker assigned a type A freeboard under the International Convention on Load Lines faces a separate flooding test. Regulation 27 of the 1988 Load Lines Protocol, as amended by MSC.143(77) of 5 June 2003 and in force from 1 January 2005, requires a type A ship over 150 m in length to withstand flooding at an assumed permeability of 0.95, with 0.85 for a machinery space.
That test is a condition of freeboard assignment and sits under a different convention. Passing it does not demonstrate Regulation 28 compliance, and the reverse also holds; the damage extents, the loading conditions and the criteria are separately specified. The freeboard and reserve buoyancy that a type A assignment produces is still an input to Regulation 28, because it fixes the summer load line at which the side damage penetration is measured.
United States overlay: 33 CFR 157.21 and 46 CFR 172.065
The United States applies tanker damage stability through its own regulations, and they diverge from Regulation 28 on one point that matters. 33 CFR 157.21, part of the 33 CFR Part 157 rules for tank vessels, sets the final waterline test, the 25 degree heel limit (30 degrees without deck edge immersion) and a 20 degree range with a maximum residual righting lever of 0.1 m.
46 CFR 172.065 applies the same 225 m and 150 m location bands, an 85 percent machinery permeability, and in paragraph (g)(3) a “maximum righting arm … at least 3.94 inches (10 cm)” through the 20 degree range. Neither section carries the 0.0175 metre radian area criterion of Regulation 28.3.3. A US-flag tanker approved to the CFR criteria alone has therefore not shown compliance with the area requirement that the MARPOL text imposes.
46 CFR 172.070 separately requires tank vessels of 5,000 DWT and above contracted after 3 December 2001 to meet the intact stability requirements of the revised Annex I. The US figures above are from the eCFR text published on 1 September 2026.
Damage case set and verification in practice
A Regulation 28 submission is a matrix: every permitted damage location, for each type of damage, against every loading condition in which the ship can actually sail with oil in its cargo tanks. Each cell must pass all of 28.3.1 to 28.3.3 and the Administration’s intermediate-stage criteria.
The damage locations follow from the length band in 28.1 and the bulkhead positions. For a tanker over 225 m the side damage is assumed anywhere in the length, including at the engine room bulkheads, so the case set has to cover every location that opens a different combination of compartments. The bottom cases are built twice, once with the forward 0.3L extents and once with the 5 m extents elsewhere, and the raking case is added for tankers within 28.7.
The loading conditions come from the trading pattern. Homogeneous full load, part cargo, multi-grade loads with tanks slack, and departure and arrival states of consumables all enter, but ballast conditions without oil in cargo tanks do not. Regulation 28.1 makes partial load conditions part of the test as well as full load, and Regulation 28.4.4 adds the free surface of each slack compartment.
Damage results reach the ship in one of three forms, matching the instrument types and the MSC.1/Circ.1461 options:
- a finite list of approved loading conditions, each checked against every damage case;
- a limiting KG or GM curve against draught, below which any condition is taken to comply;
- a Type 3 instrument that applies the pre-programmed damage cases directly to the condition the chief officer enters.
MSC.1/Circ.1461 states its own reason for preferring the third route. Footnote 4 recommends an approved Type 3 stability software on board “to avoid difficulties associated with developing suitable KG/GM limit curves and their restriction on operational capacity”. Its paragraph 4.3.3 notes that any change of filling level, draught, trim or cargo density might have a major influence on the result of a damage case.
Regulation 28 compliance links to the other stability inputs a deck officer handles: the hydrostatic and Bonjean data , the KN cross curves used to construct the damaged GZ curve, trim and list in the flooded state, and the capacity and sounding tables behind every tank’s free surface. A change to any of them after delivery, such as a lightship change from a conversion, changes the inputs to the approved damage stability information.
Common misstatements of Regulation 28
The same errors recur in tanker stability material, and each one can be checked against the text:
- “A residual GM of 0.10 m.” Regulation 28.3 has no GM criterion; the 0.1 m is a maximum residual righting lever.
- “Applies to tankers delivered on or after 1 February 2002.” That is Regulation 27. Regulation 28 applies to tankers delivered after 31 December 1979, which in practice is every tanker in service.
- “Full cargo tanks have permeability 0.” Regulation 28.4.2 gives liquid spaces 0 to 0.95, and MSC.1/Circ.1461 6.4.3 assumes a damaged tank’s contents are lost and replaced by seawater.
- “Bottom damage is B/6 or 10 m along the whole bottom.” Aft of the forward 0.3L the caps are 5 m longitudinal and 5 m transverse.
- “Regulation 28.5 is a bending moment criterion.” Regulation 28.5 requires loading and damage stability information for the master. Regulation 28 sets no longitudinal strength criterion; hull girder strength is governed by class rules.
- “MSC.337(91) governs stability instruments.” MSC.337(91) is the Code on Noise Levels on Board Ships . The relevant references are Regulation 28.6, IS Code Part B 4.1.3, MSC.1/Circ.1229 and MSC.1/Circ.1461.
- “Annex II Regulation 16 holds the chemical tanker damage rules.” The rules are in IBC Code chapter 2; Annex II Regulation 16 is measures of control.
- “SOLAS probabilistic rules apply alongside Regulation 28.” SOLAS II-1 Regulation 4.1 excludes ships that comply with damage stability rules in other IMO instruments.
- “The area is measured to the downflooding angle.” Regulation 28.3.3 takes the area “within this range”, the 20 degrees beyond equilibrium.
Limitations
This article reports the text of Regulation 28 as adopted by MEPC.117(52) and amended by MEPC.248(66) and MEPC.343(78). Any later amendment adopted by the Marine Environment Protection Committee would change it, and the consolidated IMO text in force on the date of use is the authority, not this summary.
Regulation 28.3.4 leaves the intermediate-stage criteria to the Administration, and Regulation 28.1.3 leaves relaxations for tankers of 100 m or less to the Administration. Both vary by flag and by the recognized organization acting for it, so the criteria applied to a particular ship are found in its approved stability documents, not in the regulation.
Unified interpretations by IMO or by the classification societies through IACS refine how terms such as “unprotected opening” are applied. They are not summarized here and are read directly from the issuing body. The same applies to the damage stability rules of individual classification societies and to regional port State control practice under the Paris MoU and the Tokyo MoU .
The worked extents are arithmetic on representative dimensions. A real damage case set also depends on bulkhead positions, tank boundaries, piping routes and approved loading conditions that only the ship’s own calculations contain. Nothing here replaces the approved stability information required by Regulation 28.5 or the instrument approved under Regulation 28.6.
Frequently Asked Questions (FAQs)
Which oil tankers does MARPOL Annex I Regulation 28 apply to?
Does Regulation 28 contain a minimum residual GM criterion?
Why is the bottom damage smaller aft of the forward 0.3L?
What is raking damage under Regulation 28.7?
Are ballast conditions checked against Regulation 28?
What permeabilities does Regulation 28.4 prescribe?
By when did existing oil tankers have to carry a stability instrument?
Can the stability instrument requirement be waived?
Does Regulation 28 require a Type 2 or a Type 3 stability instrument?
Does SOLAS Chapter II-1 probabilistic damage stability apply to an oil tanker?
What damage stability rules apply to chemical tankers?
How does the IGC Code criterion for gas carriers differ from Regulation 28?
Is the type A freeboard flooding test the same as Regulation 28?
What was Regulation 25 of MARPOL Annex I before 2007?
Are small tankers of 100 m or less given any relaxation?
How are watertight doors treated in the final waterline check?
Can cross-flooding arrangements be credited to reduce the heel?
Do pipes and ducts inside the damaged zone matter?
Must a lesser damage be checked if it is worse than the full extent?
How is free surface handled in the damaged condition?
Is the buoyancy of the superstructure counted after side damage?
Does a double hull under Regulation 19 automatically satisfy Regulation 28?
Which document on board shows Regulation 28 compliance?
What does a port State control officer look for on damage stability?
Is MSC.337(91) the stability instrument guideline?
How does the US rule differ from Regulation 28?
Does a major conversion bring an older tanker under Regulation 28?
Related Articles
- MARPOL Annex I: prevention of pollution by oil
- MARPOL Convention
- Damage stability
- Probabilistic damage stability
- MARPOL Annex I Regulation 27: intact stability
- MARPOL Annex I Regulation 19: double hull
- MARPOL Annex I Regulation 23: accidental oil outflow
- MARPOL Annex I Regulation 24: damage assumptions
- Stability booklet and loading computer
- IBC Code
- IGC Code
Sources
- IMO Resolution MEPC.117(52), adopted 15 October 2004: Amendments to the Annex of the Protocol of 1978 relating to MARPOL 1973 (Revised MARPOL Annex I), Regulation 28 Subdivision and damage stability, in force 1 January 2007
- IMO Resolution MEPC.248(66), adopted 4 April 2014: Amendments to MARPOL Annex I (mandatory carriage requirements for a stability instrument, new Regulations 3.6 and 28.6), in force 1 January 2016
- IMO Resolution MEPC.343(78), adopted 10 June 2022: Amendments to MARPOL Annex I (watertight doors, Regulation 28.3.1), in force 1 January 2024
- IMO Resolution MSC.267(85), adopted 4 December 2008: International Code on Intact Stability, 2008, Part B 4.1.3 stability instrument types
- IMO Resolution MSC.216(82), adopted 8 December 2006: Amendments to SOLAS Chapter II-1, Regulation 4.1 exclusion of ships complying with damage stability regulations in other IMO instruments
- IMO Resolution MSC.176(79), adopted 10 December 2004: Amendments to the IBC Code, chapter 2 damage assumptions, flooding assumptions and survival requirements
- IMO Resolution MSC.143(77), adopted 5 June 2003: Amendments to the Protocol of 1988 relating to the International Convention on Load Lines, Regulation 27