Chapter 8 origins: the MEPC.186(59) mandate
Ship-to-ship oil cargo transfers are not a new practice. Lightering of laden tankers in deep water dates from the 1960s when crude carriers outgrew US Gulf Coast harbour drafts, and parcel transfers in the Persian Gulf trades were routine commercial practice long before any IMO instrument addressed them. For the first four decades of the modern tanker industry, STS operations sat outside the MARPOL framework, governed only by the OCIMF industry guide, individual port-State rules, and the contractual structure agreed by the lightering broker.
The political shift came after the 2002 Prestige casualty off Galicia and the 2007 Hebei Spirit collision off South Korea. Neither casualty was an STS event, yet both highlighted the absence of a uniform international regime for transfers between tankers at sea. Coastal States began to file unilateral restrictions: the United States expanded its existing 60-nautical-mile lightering zones, Spain and Portugal closed waters off the Iberian coast, and Mediterranean coastal States raised bilateral concerns about transfers near beaches and protected areas. The IMO Marine Environment Protection Committee took up the issue at MEPC 56 in 2007 and tabled a draft new Chapter 8 for Annex I.
The Committee adopted Resolution MEPC.186(59) on 17 July 2009. The resolution inserted a new Chapter 8, comprising Regulations 40, 41, and 42, into MARPOL Annex I. Chapter 8 entered into force on 1 January 2011 under the tacit-acceptance procedure of Article 16 of the MARPOL Convention. Regulation 40 set the application clause and the definitions, including the definition of the POAC. Regulation 41 set the operational requirements and the Plan requirement. Regulation 42 set the notification requirement.
A transitional clause gave ships engaged in STS operations on the entry-into-force date until the next renewal of the IOPP Certificate (or 1 April 2012 at the latest) to present an approved Plan. The resolution also amended Regulation 1 (Definitions) to incorporate the new chapter’s terminology and amended the IOPP Supplement Forms A and B to add a tick-box for STS Plan approval.
The 2014 amendments adopted as Resolution MEPC.252(67) on 31 October 2014 closed two gaps. First, they clarified that the regime applies to oil tankers regardless of construction date, removing an ambiguity in the 2009 text that some operators had read as exempting pre-2011 vessels until their next renewal survey. Second, they aligned the notification template with the standard reporting format used by Regional Marine Pollution Emergency Response Centres, simplifying the burden on coastal States that already operated mandatory ship-reporting systems. No further amendments had been adopted through the 2025 MEPC session, though the working group considered alignment with alternative-fuel reporting in 2025 and may produce a further amendment in the 2026 to 2028 cycle.
Regulations 40, 41, and 42: the Chapter 8 framework
The three regulations work as a single compliance architecture. Understanding how they interlock is essential before reading the operational detail.
| Regulation | Subject | Core obligation |
|---|---|---|
| Reg.40 | Scope and application | Applies to every oil tanker of 150 GT and above engaged in STS of oil cargo at sea; lists three exclusions |
| Reg.41 | STS Operations Plan | Carry an approved Plan; conduct every transfer in accordance with it; assign a POAC; record in Oil Record Book Part II |
| Reg.42 | Notification | Notify the coastal State at least 48 hours before any STS in its territorial sea or EEZ; use the GISIS-registered contact point |
Regulation 40 defines the terms that the other two regulations use. An “STS operation” is the transfer of oil cargo between two oil tankers at sea. “At sea” includes sheltered anchorages. A “ship engaged in STS operations” is any oil tanker of 150 GT and above that carries out such a transfer as part of a commercial arrangement. The POAC is defined as “the person who has appropriate knowledge and experience to supervise and advise on the STS operation in accordance with the STS Operations Plan.”
Three exclusions sit in Regulation 40. Bunker transfers are outside the regime even where the bunker is transferred between two oil tankers, because the subject of the transfer is not oil cargo. Transfers to and from fixed or floating platforms engaged in offshore exploration or production are excluded. Emergency lightering necessary to secure the safety of the ship or save life at sea is excluded; the master may discharge cargo to a sister vessel without an approved Plan if the alternative is a structural failure or grounding, but the duty to report any resulting spill under the SOPEP regime is not suspended.
Regulation 41 scope: oil tankers of 150 gross tonnage and above
Regulation 41 applies to every oil tanker of 150 gross tonnage and above engaged in the transfer of oil cargo between oil tankers at sea. The 150 GT threshold mirrors the threshold for the Oil Record Book Part II, the crude oil washing regime, and the damage stability regime, so a small product tanker already inside the broader Annex I cargo-tank regime falls automatically inside Chapter 8.
The two ships in an STS operation each fall within the regime independently. Each must hold an approved Plan, each must hold the relevant prior approvals, and each master is independently responsible for compliance. There is no consolidated Plan covering both vessels, and the POAC is contracted separately on a per-operation basis even where a fleet operator habitually pairs the same lightering vessel with the same mother tanker.
The flag-State Administration approves the Plan, normally through a Recognised Organisation. Approval is recorded by stamp and signature on the title page of the Plan, and the approval is cross-referenced in the IOPP Supplement under Form A or Form B as the case requires. The Administration may revoke approval at any time on evidence that the Plan no longer reflects the ship’s equipment or the operator’s procedures.
The bunker-transfer exclusion deserves emphasis. A product tanker delivering bunkers to a vessel at sea is not engaged in an STS operation under Chapter 8 even though it is transferring petroleum product between two ships. The transferred product is a fuel, not a cargo parcel. That distinction is commercially important: a chemical tanker bunkering a container ship in the Singapore Strait is not required to hold an STS Operations Plan for that operation and is not required to file the 48-hour Regulation 42 notification. The applicable regime is the Regulation 12A oil fuel tank protection framework and the relevant port-State bunkering rules.
STS Operations Plan: flag-State Administration approval
The STS Operations Plan is the single document that proves Regulation 41 compliance to a Port State Control inspector and to the POAC at the pre-transfer meeting. It must be in the working language of the master and senior officers, accessible from the bridge, and referenced in the Safety Management System under ISM Code Element 7 (Shipboard operations).
Approval follows the model used elsewhere in Annex I. The owner or manager drafts the Plan against the OCIMF industry guide and the flag-State template, submits it to the Recognised Organisation, and the Recognised Organisation reviews it for conformity with MEPC.186(59) and MEPC.252(67). The reviewer checks that the Plan contains every required element, that ship-specific information is correct (manifold spacing, fender attachment points, hose-handling crane SWL), and that the contacts list reflects the current technical superintendent and Designated Person Ashore. Approval is then granted by stamp and signature.
A Plan amendment touching an approved item, such as a change to the mooring arrangement or a change to the cargo manifold size, requires re-submission and re-approval. A change to a contacts-list entry, a working-language version, or a non-substantive correction does not require re-approval but must be entered in the revision table at the front of the Plan.
The Plan is not a generic document. Class society reviewers reject Plans that lack ship-specific particulars, that copy text from a fleet template without adjustment, or that omit the manufacturer and certificate references for the mooring fenders, transfer hoses, and dry-break couplings that the ship will actually use. A reviewer reads a Plan against the IOPP file and the ship’s mooring equipment record, and a mismatch between the Plan and the equipment list defeats approval at first review.
Four-stage operational architecture
Every STS operation under Regulation 41 follows a fixed four-stage architecture, and the Plan must address each stage explicitly. The architecture is set out in MEPC.186(59) and elaborated in the OCIMF industry guide.
Stage 1: Pre-arrival. The mother vessel and the daughter vessel exchange particulars at least 24 hours before the planned operation, longer for VLCC parcels. Each vessel transmits its draft and trim, cargo and ballast plan, deck arrangement, manifold particulars, and any defects affecting the operation. The POAC reviews both pre-arrival packages and confirms that the parcel size and the parcel sequence are within the safe envelope. The 48-hour notification to the coastal State under Regulation 42 is filed at this stage.
Stage 2: Pre-mooring contact. The two vessels rendezvous at the agreed STS area, typically a charted anchorage or a designated waypoint outside territorial waters. The Master Ship-to-Ship Transfer Checklist is completed jointly by both masters and the POAC. Yokohama-type fenders are deployed against the receiving side of the constant-heading vessel. The manoeuvring vessel approaches on a parallel course at low closing speed, contacts the fenders, and is moored alongside with synthetic fibre lines led to bitts and roller fairleads. Hoses are connected only after the joint mooring inspection is signed off.
Stage 3: Transfer. The cargo transfer follows the agreed pumping plan with continuous communication on a dedicated VHF channel. Pumping rate is ramped from a slow initial rate, increased through topping-up checks, and slowed for topping-off. The POAC monitors both manifolds and the inter-ship freeboard differential. Static-electricity bonding, inert-gas pressure on the discharging vessel, and ullage rates on the receiving vessel are logged at fixed intervals. The Oil Record Book Part II entry on each vessel is started during transfer and closed at completion.
Stage 4: Post-transfer. Hoses are drained, blown back, and disconnected. The vessels unmoor, taking care to clear the fenders and recover them on the agreed side. The master of each vessel signs off the completion certificate, and the POAC records the operation in the STS log. Both Oil Record Books are closed with code-letter H entries (cargo transfer between vessels). Any spill, however minor, triggers the SOPEP reporting chain irrespective of recovery status.
Regulation 42: the 48-hour notification
Regulation 42 carries the notification requirement and sits alongside Regulation 41 within Chapter 8. It requires the master of the oil tanker engaged in the STS operation to notify the State within whose territorial sea or exclusive economic zone the operation is to take place at least 48 hours before the planned operation. The notification is not optional and is not waived by short-notice charter changes; a transfer that proceeds without 48 hours’ notice is a Regulation 42 breach even where the operation itself is otherwise compliant.
The 48-hour minimum accommodates unforeseen circumstances. Regulation 42 accepts that operational realities may shorten the lead time and permits a notification “as far in advance as possible” where 48 hours is not achievable, provided the master records the reason and the coastal State is informed at the earliest opportunity. Coastal States typically waive the 48-hour requirement for emergency transfers necessary to prevent grounding or structural failure but enforce it strictly for commercial lightering.
The notification template carries a fixed set of fields: the name and IMO number of each vessel, the position of the planned operation, the planned start and finish times, the name of the POAC, the name of the operator, the cargo grade and quantity, and a confirmation that both vessels hold approved Plans. The MEPC.252(67) amendment aligned this template with the standard format used by Regional Marine Pollution Emergency Response Centres. Coastal States may require additional national-law fields, particularly insurance evidence and pollution-response standby arrangements, and the master must supply those fields where the receiving State has communicated its requirements through the IMO Global Integrated Shipping Information System (GISIS).
The notification is addressed to the contact point of the coastal State as registered in GISIS. For operations in international waters where no coastal State exercises jurisdiction over the area of operation, no Regulation 42 notification is filed. The POAC and both masters retain the obligation to comply with Regulation 41 in full and to log the operation in the Oil Record Book.
Per-state notification rules and exclusion zones
Coastal-State practice on STS operations diverges sharply, and a fleet operator running a worldwide lightering business needs a per-State matrix to keep the master compliant.
The United States maintains the longest-standing restrictions. Under 33 CFR Part 156 and the lightering zone regulations issued under the Oil Pollution Act 1990, STS operations involving cargo bound for or originating in the US are restricted to designated lightering zones, primarily off the Texas and Louisiana coasts in the Gulf of Mexico, with the inner boundary at 13 nautical miles from the baseline. Transfers within 13 nm of the US coast are prohibited except under an emergency exemption issued by the Captain of the Port. Notification is required at least 24 hours in advance to the cognisant Coast Guard Sector and runs in parallel to the IMO 48-hour notification; both must be filed.
United Kingdom waters are governed by the Merchant Shipping (Ship-to-Ship Transfers) Regulations 2010, which require notification to the Maritime and Coastguard Agency at least 14 days in advance for first-time operations at a designated location and 24 hours for subsequent operations at the same location. Designated locations are charted, and operations outside designated locations are prohibited within the UK Pollution Control Zone except by specific Secretary of State authorisation.
Spain and Portugal prohibit STS oil cargo transfers within their territorial seas and exclusive economic zones following the Prestige casualty, except for emergency lightering. The Strait of Gibraltar carries an additional restriction: transfers in the eastern approaches to the Strait are subject to bilateral coordination between Spain and Morocco, and the Bay of Gibraltar itself is subject to UK Gibraltar territorial waters rules.
Mediterranean special-area implications under the Annex I special-areas regime raise the bar on operational discharge but do not in themselves prohibit STS transfers. Coastal States bordering the Mediterranean special area apply national rules ranging from outright prohibition (parts of the Italian and French coast) to designated-area authorisation (Greek archipelago, Maltese waters).
Persian Gulf practice favours STS over harbour discharge for VLCC cargoes destined for transhipment. Khor Fakkan and the Sohar approaches in Oman and the UAE carry no special prohibition, and the commercial preference is driven by avoidance of harbour fees and time saved over a port call. Notifications are filed with the relevant national maritime authority through the GISIS template.
Singapore permits STS operations only at designated anchorages under the Maritime and Port Authority of Singapore authorisation regime. Notifications run through MPA, and the POAC must hold MPA-recognised credentials.
A flag-State Administration’s approval of an STS Operations Plan does not waive any of these national-law requirements. The master remains responsible for verifying coastal-State authorisation for every operation, and the operator’s compliance department typically maintains a per-State checklist as an annex to the Plan.
POAC: Person in Overall Advisory Control
The POAC is the senior practitioner who runs the operation. MEPC.186(59) requires a POAC to be present and in advisory control for the duration of the operation, from pre-arrival through unmooring.
The POAC is contracted by the lightering operator, typically separately from the masters of the two vessels. The POAC’s role is advisory: the master of each vessel retains command authority and may overrule the POAC at any time on safety grounds. The POAC coordinates the two vessels, monitors the manifold and freeboard, ensures the pre-transfer checklists are completed, and interfaces with the coastal-State authority where authorisation has been granted.
The POAC qualification is not codified in IMO instruments. Regulation 40 defines the POAC as a person with “appropriate knowledge and experience to supervise and advise” on the operation in accordance with the Plan. The operational baseline for what constitutes appropriate knowledge comes from the OCIMF industry guide: a master mariner certificate of competency, three years’ tanker command experience, and a logged record of supervised STS operations as POAC-in-training before solo POAC duty. Some flag States issue a national POAC endorsement; Singapore’s MPA is among those that require MPA-recognised POAC credentials for operations within its jurisdiction.
Major lightering operators and the leading STS service companies maintain in-house POAC qualification matrices that typically exceed the OCIMF baseline. The POAC labour market is small globally. Roughly 800 to 1,200 active POACs cover the worldwide commercial-lightering trade, concentrated in the US Gulf, the Persian Gulf, the Mediterranean, and the Singapore Strait. Day rates for 2025 to 2026 run from about USD 1,800 to USD 3,500 plus travel and standby for typical commercial work, with VLCC-class operations at the upper end. Insurance underwriters typically require evidence of POAC qualification on the cover note as a condition of enhanced-risk cover.
Mooring: Yokohama fenders and dynamic positioning
The mooring arrangement carries the largest single share of operational risk in an STS transfer and the largest single share of Plan content. The two vessels are moored side-by-side with the constant-heading vessel maintaining heading by main engine and rudder (in deeper water) or by anchor (in sheltered water), and the manoeuvring vessel is brought alongside on a parallel course at controlled closing speed.
Yokohama-type pneumatic fenders are the industry standard for separation. They are large air-filled rubber cylinders, typically 3.3 metres in diameter and 6.5 metres long for VLCC work. The fender count and arrangement scale with vessel size: a Suezmax-to-Aframax operation may use four fenders, a VLCC-to-Suezmax operation typically uses six, and the largest VLCC-to-VLCC operations use eight. ISO 17357-1:2014 carries the type-test and certification standard, and each fender carries a manufacturer plate referencing the ISO test and the date of manufacture. Fenders are replaced or recertified at the manufacturer-specified interval, typically five years.
The fenders are positioned at the parallel mid-body of the constant-heading vessel and secured with primary and back-up pendants to the bitts and mooring deck. Secondary fenders are positioned forward and aft of the parallel mid-body to absorb pitch and yaw motion. The fender arrangement is recorded in the Plan with a deck-plan diagram showing fender positions, primary and secondary attachment points, and the certified working pressure of each fender unit.
Mooring lines run from the manoeuvring vessel through roller fairleads to the constant-heading vessel’s bitts. Synthetic fibre ropes are standard, and the line plan is set out in the Plan with the number, size, and material of each line. Dynamic positioning is not commonly used for oil-cargo STS transfers because the constant-heading vessel maintains heading by conventional means, but DP-equipped daughter vessels may use DP for the approach phase to reduce closing-speed risk. The tanker mooring STS calculator is a planning tool for line count and working-load allocation.
Cargo manifolds and dry-break couplings
The cargo manifolds of the two vessels must align in plan view at the moored condition. The OCIMF Manifold Recommendations (5th edition, 2018) set the standard manifold spacing at 3.0 metres centre-to-centre for tankers, and the Plan must record the actual spacing and confirm the chosen mating vessel falls within the compatibility envelope.
Dry-break couplings are the industry-preferred manifold connection for STS work. A dry-break coupling carries an integral shut-off valve in each half of the coupling and seals automatically on disconnection, preventing the residual cargo in the hose from spilling at uncoupling. The coupling is rated for the maximum cargo working pressure of the transfer hose, typically 15 bar for crude-oil work, and is type-approved by Class. The Plan records the coupling manufacturer, the certificate reference, and the maximum working pressure.
Reducer flanges are carried on board where the manifold flange size of the manoeuvring vessel does not match the manifold flange size of the constant-heading vessel. Standard manifold flange sizes are 8, 10, 12, and 16 inches under ANSI 150 and ANSI 300 ratings. The Plan records the carried reducer set and confirms that the operator’s lightering trade lane is covered by the available reducers.
Transfer hose certification
Transfer hoses are the consumable item of the STS regime and are subject to the most rigorous certification within the operation. Each hose is type-tested under EN 1765:2016 (for oil and petroleum products) or under the OCIMF guidelines for SPM hoses as applied to STS work.
Each hose carries an individual serial number, a date of manufacture, a hydrostatic-test record, and a Certificate of Compliance issued by the manufacturer. Hydrostatic tests are repeated annually at 1.5 times the maximum allowable working pressure. Vacuum tests verify the integrity of the inner liner. Electrical-continuity tests verify bonding-strap integrity. The hose is stripped and re-tested every five years or after any damage event. The Plan records the certificate reference for each hose carried, and the records are presented to the POAC at the pre-transfer meeting.
Hose-handling cranes on each vessel must lift the hose to the manifold without bending below the manufacturer’s minimum bend radius. The Plan records the crane SWL and reach for the hose set actually carried. Hose strings are typically three to five hose lengths joined by butterfly couplings, with float collars positioned to keep the string clear of the water during connection and disconnection.
STS Operations Plan: content elements
The Plan content is set out in MEPC.186(59) and elaborated by the OCIMF industry guide. A flag-approved Plan addresses each of the following elements explicitly, with ship-specific particulars rather than generic text.
Identification of personnel. Names and certificates of competence for the master, chief officer, chief engineer, and the personnel designated to operate the manifold, the cargo control room, and the mooring stations. The POAC certificate is referenced.
Pre-transfer ship suitability check. A checklist confirming the ship’s IOPP Certificate is current, the SOPEP is on board, the cargo equipment is in working order, the mooring equipment is certified and in date, and there are no open defects affecting the operation. The check is signed by the master before the pre-arrival notification is filed.
Mooring. The deck-plan diagram of fender positions, mooring-line plan, and the limits of acceptable wind, swell, and current. The Plan sets out the closing speed limits for the approach, typically not more than 0.3 metres per second at first contact for a Suezmax-class manoeuvring vessel, and the abort criteria.
Cargo transfer. The pumping plan, the maximum and minimum transfer rates, the inert-gas pressure window, and the topping-off procedure. The transfer-rate ramp profile is set out as a table.
Communications. The dedicated VHF channel for the operation, the back-up channel, the language of the operation (English by default), and the emergency-stop signal.
Emergency procedures. The actions on cargo overflow, on hose rupture, on mooring failure, and on fire. The Plan cross-references the SOPEP for spill response and the SOLAS muster list for fire and abandonment.
Industry guidance reference. A formal reference to the OCIMF Ship to Ship Transfer Guide for Petroleum, Chemicals and Liquefied Gases (1st edition, 2013) and, where applicable, the CDI Ship to Ship Transfer Guide for Chemicals, confirming the procedures in the Plan are drawn from those publications.
The Plan does not require the operator to disclose commercial information such as charter rates or POAC fees.
Class society oversight
Plan approval and survey verification rest with the flag-State Administration but are normally delegated to a Recognised Organisation under IACS. The IACS member societies cover the bulk of the world tanker fleet: DNV (Oslo), Lloyd’s Register (London), American Bureau of Shipping (Houston), Bureau Veritas (Paris), Nippon Kaiji Kyokai / ClassNK (Tokyo), Korean Register (Busan), RINA (Genoa), China Classification Society (Beijing), Russian Maritime Register of Shipping (St Petersburg), and Indian Register of Shipping (Mumbai).
Each society publishes a Plan-review checklist drawn from MEPC.186(59) and maintains a panel of senior surveyors qualified to attend STS operations as flag-State witness where the flag State requires witnessing for new-Plan approval. Plan re-approval after a substantive amendment is normally handled remotely from the plan-approval office, with on-board verification at the next periodic survey.
A Plan that has not been amended since first approval, where the ship has changed manager or substituted equipment, will not pass renewal survey. A non-conformity is raised against the IOPP file, and the corrective action is confirmed before the IOPP Certificate is endorsed. The most frequent first-review rejection reasons are: a fleet-template Plan without ship-specific particulars; missing fender or hose certificate references; and an equipment list on the Plan that does not match the equipment physically on board.
SOPEP integration (Regulation 37 cross-link)
The STS Operations Plan does not stand alone. Spill response is covered by the Shipboard Oil Pollution Emergency Plan under Regulation 37, and the STS Plan must cross-reference the SOPEP for the response architecture rather than duplicate it.
The SOPEP four-section structure provides the reporting flow that any STS spill triggers. A spill at the manifold, a hose rupture, or an unmooring incident with cargo loss runs through the SOPEP Section 2 reporting matrix to the coastal State, the flag State, and the Designated Person Ashore. Section 3 of the SOPEP carries the action steps for the master and the mate, including the immediate stop-pumping signal the POAC issues over the dedicated VHF channel.
For STS work, the SOPEP must explicitly address STS operational scenarios: a manifold overflow during topping-off, a hose burst, a connection rupture during disconnection, and a fender failure leading to hull contact. Most flag States accept a generic SOPEP covering these scenarios under the broad heading of cargo-transfer events; some require an STS-specific annex to the SOPEP referencing the STS Plan.
The OPRC 1990 framework underlying the SOPEP applies to STS spills as it applies to any oil spill. Regional Marine Pollution Emergency Response Centres are notified through the same OPRC reporting flow. Pollution-response standby arrangements at the lightering location are not mandatory under MEPC.186(59) but are commonly required by the coastal State as a condition of authorisation, with a tug or workboat carrying booms and skimmers held within the lightering area for the duration of the operation.
IOPP Certificate renewal-survey verification
The STS Operations Plan is verified by the Recognised Organisation at every renewal survey of the International Oil Pollution Prevention (IOPP) Certificate. The IOPP renewal survey is the five-yearly survey covering the full Annex I scope, and Plan currency is one of the audit items.
The surveyor reviews the Plan’s revision table, verifies the approval stamp date, confirms the Plan reflects the ship’s current equipment configuration, and checks the contacts list against the operator’s current technical superintendent and Designated Person Ashore. A Plan that has not been amended since first approval where the ship has changed manager or substituted equipment will not pass the renewal survey, and a non-conformity is raised against the IOPP file.
Common findings at renewal survey include: an expired Plan where the operator has changed flag without re-submitting under the new flag; a missing approval stamp where a fleet template was issued under an older approval that does not extend to the specific vessel; and equipment misalignment where the Plan references fender or hose particulars that do not match the equipment currently on board. Each of these findings is corrected before the IOPP Certificate is endorsed, and a major non-conformity may delay the issue of the renewed Certificate.
The Annual Survey under the IOPP regime touches the Plan only lightly, normally confirming that the Plan is on board and that the contacts list is current. A material change between annual surveys triggers an interim re-approval submission through the Recognised Organisation, with the revised Plan in place before the next STS operation.
Lightering vs reverse lightering
The operational vocabulary distinguishes two basic patterns.
Conventional lightering transfers cargo from a fully-laden inbound vessel to a smaller daughter tanker that then takes the parcel into a draft-restricted port. The pattern is the standard practice on the US Gulf for VLCC inbound cargoes destined for Texas and Louisiana refineries that lack the harbour draft for a fully-laden VLCC. The mother vessel reduces parcel by parcel until her draft permits a port call or, in some cases, returns to load the next voyage without ever discharging at a US port. The US Gulf lightering economics support a fleet of dedicated daughter Aframaxes and Suezmaxes operating on lightering charters out of Galveston, Houston, and the Louisiana Offshore Oil Port sea-buoy.
Reverse lightering loads an outbound vessel from a daughter that has accumulated cargo from one or more shore loadings. The pattern is common in the Persian Gulf where shore terminals load smaller parcel tankers that then transfer to a VLCC at anchorage at Khor Fakkan or off Fujairah, and in the Mediterranean for transhipment to Suezmaxes destined for Asian markets. Reverse lightering allows a VLCC to load a full cargo without ever entering a draft-restricted port, saving harbour fees, inbound pilotage, and loaded turnaround time.
Regulation 41 treats both patterns identically. The Plan does not distinguish between conventional and reverse lightering, the four-stage architecture applies to both, and the 48-hour notification is required for both. The POAC and the masters treat the constant-heading vessel as the mother and the manoeuvring vessel as the daughter irrespective of which is the discharging and which is the receiving party. The OCIMF guide uses constant-heading and manoeuvring terminology rather than mother/daughter to avoid the directional ambiguity in reverse-lightering arrangements.
CDI alignment for chemicals
The Chemical Distribution Institute (CDI) operates the parallel guidance for chemical-cargo STS operations. The CDI Ship to Ship Transfer Guide for Chemicals is referenced where the cargo is a noxious liquid substance under MARPOL Annex II, and for parcel-tanker operations carrying both oil-cargo parcels and chemical parcels the master must reference both guides.
Alignment between the OCIMF and CDI guides was formalised by a 2014 memorandum of cooperation and is reflected in the OCIMF guide’s chapter on chemicals. The alignment ensures that a parcel tanker engaged in mixed-cargo STS work follows a single set of pre-transfer checklists, a single mooring procedure, and a single emergency-response architecture irrespective of which specific cargo is being transferred at any given hour. The Plan approved under Annex I Regulation 41 may incorporate by reference the chemical-cargo procedures in the corresponding Annex II Procedures and Arrangements Manual.
Commercial implications: VLCC lightering economics and insurance
The commercial architecture of STS operations rests on three pillars: lightering economics for VLCC trades, the POAC labour market, and the insurance position.
VLCC lightering economics. A laden VLCC carrying 2 million barrels of crude oil cannot enter most US Gulf refining ports at full draft, and a port call at the Louisiana Offshore Oil Port requires a short shuttle in any case. Lightering 1 million barrels into two Suezmax daughter vessels at the offshore lightering area allows the VLCC to enter Texas City or Houston, deliver the residual parcel, and depart without the time and fuel cost of a partial discharge at LOOP and a separate lightering operation. The economics typically favour STS by USD 200,000 to USD 500,000 per VLCC voyage on the US Gulf trade and by similar margins on the Persian Gulf to Asia trade.
POAC labour market. The small global POAC pool drives a tight market for senior tanker masters with logged STS experience. Lightering operators on long-term lightering charters typically employ a small number of staff POACs and contract day-rate specialists for peak operational periods. Day rates run at roughly USD 1,800 to USD 3,500 plus expenses depending on vessel class and location as of 2025 to 2026.
Insurance considerations. Hull and machinery underwriters and P&I clubs treat STS operations as an enhanced-risk activity, with cover typically conditioned on (a) evidence of an approved STS Operations Plan, (b) evidence of a qualified POAC, (c) compliance with the OCIMF industry guide, and (d) compliance with the coastal-State notification requirements. A breach of any of these conditions typically excludes cover for the resulting loss. The major International Group P&I clubs publish loss-prevention guidance for members and offer advisory support to operators preparing first-time Plans for new lightering trades.
The commercial market also includes specialist STS service companies that operate fleets of fenders, hoses, dry-break couplings, and POAC pools as a turn-key service to occasional lighterers, with regional operators in the Persian Gulf, Singapore, and the Mediterranean.
Notification timing and fender count: the two key numbers
Two relations govern the numbers an STS Operations Plan must satisfy: the notification lead time and the fender count. The first is a hard regulatory minimum; the second is an empirical operational envelope.
The notification minimum is fixed by Regulation 42 at 48 hours before the planned operation. That threshold came out of coastal-State emergency-response readiness analysis in the MEPC 56 to MEPC 59 working group. Forty-eight hours is the lead time a coastal State needs to position pollution-response standby assets, confirm authorisation under any national-law overlay, and communicate operational restrictions back to the master before the operation starts.
The fender-count envelope is empirical and scales with vessel size: roughly 4 fenders for a Suezmax-to-Aframax operation, 6 for a VLCC-to-Suezmax operation, and 8 for the largest VLCC-to-VLCC work. The envelope derives from full-scale measurement of wave-induced relative motion between two moored tankers. The motion envelope scales with LOA and beam through the response amplitude operator (RAO) of each vessel, and the fender count is set so that the cumulative compression energy of the fender array exceeds the maximum credible relative-motion energy at the lightering location’s design wave height. The precise count is set in the Plan as a function of LOA, beam, and the wave and wind envelope of the lightering location.
The two figures rest on stated conditions. The regulatory regime assumes both vessels meet Annex I structural requirements, the operation runs in waters where the coastal State has been notified or where no coastal State exercises jurisdiction, a qualified POAC is present, and weather stays inside the Plan’s operational envelope. A breakdown of any one triggers an abort. The fender-count envelope assumes the fenders are within manufacturer recertification date, that air pressure has been verified before deployment, and that the attachment points are within their certified SWL.
Worked example: VLCC-to-Suezmax off the Texas Gulf coast
A 320,000 dwt VLCC with LOA 333 m, beam 60 m, and fully laden draft 22.5 m lighters a half-cargo parcel into a 158,000 dwt Suezmax of LOA 274 m, beam 48 m, partial-load draft 14.0 m at receipt. The lightering location is a designated zone 18 nm offshore, water depth 32 m, design significant wave height 1.5 m.
Notification runs at least 48 hours before the operation to the US Coast Guard Sector (under 33 CFR Part 156) and to the IMO contact point under GISIS (under Regulation 42). Both notifications are mandatory and run in parallel. The fender set is 6 primary Yokohama 3.3 m by 6.5 m fenders along the parallel mid-body of the VLCC, with 2 secondary fenders forward and aft.
Mooring uses 8 synthetic fibre lines to the VLCC’s bitts, each 80 m long, breaking strength 90 tonnes. The manifold connection is 12-inch ANSI 150 with a dry-break coupling at the daughter manifold and a 16-inch reducer at the VLCC manifold. The transfer rate ramps from 1,500 m³/h to a maximum of 7,500 m³/h at full flow, then ramps down to 800 m³/h for topping-off. The POAC is engaged separately on a USD 2,800 day rate plus standby.
A single-parcel transfer of 80,000 m³ runs at the maximum rate for about 11 hours. Ramp-up, ramp-down, and topping-off bring the transfer time to 14 to 16 hours. The full operation, including approach, mooring, transfer, unmooring, and departure, occupies about 24 to 30 hours. These durations are planning estimates: actual time turns on pump availability, inert-gas pressure window, and any weather hold.
Abort triggers and emergency response
The Plan handles three principal failure modes during a live transfer. A sudden weather deterioration triggers an abort sequence that stops pumping, drains the hose, disconnects, and unmoors before the wind and wave envelope is breached, with the master of each vessel retaining authority to abort independently of the POAC. A hose rupture triggers the immediate stop-pumping signal on the dedicated VHF, closure of the manifold valves, and the start of the SOPEP reporting flow. A fender failure aborts the operation; hull contact is assessed, and the SOPEP is activated if any cargo loss is identified.
The regulatory basis is narrow and exact. MARPOL Annex I Regulations 40, 41, and 42 within Chapter 8 are the parent regulations. MEPC.186(59) is the adopting resolution. MEPC.252(67) is the 2014 amendment. The OCIMF Ship to Ship Transfer Guide for Petroleum, Chemicals and Liquefied Gases (1st edition, 2013) is the operational industry guidance, with CDI guidance for chemicals and coastal-State law applying per State.
The recurring findings at IOPP renewal survey and at Port State Control inspection are predictable. They include: a Plan stamped under an old flag after the ship has changed flag; a Plan referencing a fender or hose set no longer carried; a contacts list not updated for a manager change; absence of a POAC qualification certificate at the pre-transfer meeting; a 48-hour notification filed less than 48 hours before the operation; and failure to log the operation in the Oil Record Book Part II under code-letter H. Each finding is correctable, and each one recurs across the fleet.
Regulatory reference table: Chapter 8 obligations
| Requirement | Regulation | Key detail |
|---|---|---|
| Applicability | Reg.40 | Oil tankers >=150 GT; cargo transfers only |
| STS Operations Plan | Reg.41 | Flag-State Administration approved; on board |
| Working language | Reg.41 | Language of master and senior officers |
| POAC | Reg.40, Reg.41 | Present and in advisory control throughout |
| Notification | Reg.42 | >=48 hours to coastal State in whose TS/EEZ |
| Oil Record Book | Reg.17 | Code-letter H entries on both vessels |
| IOPP verification | Reg.11 | Plan checked at every renewal survey |
| Exclusions | Reg.40 | Bunkering; offshore platforms; emergency lightering |
| Adopting resolution | MEPC.186(59) | Adopted 17 July 2009; in force 1 January 2011 |
| 2014 amendment | MEPC.252(67) | Adopted 31 October 2014; notification template |
Limitations
The Regulation 41 regime is narrower than practitioners often assume, and the figures in this article carry stated caveats.
First, scope. MARPOL Annex I Chapter 8 governs the transfer of oil cargo between two oil tankers of 150 GT and above. It does not govern bunker transfers, transfers to or from fixed or floating offshore platforms, or emergency lightering to save the ship or life at sea. The operational detail, the checklists, the closing-speed limits, and the mooring arithmetic live in the OCIMF industry guide and the CDI guidance, neither of which has direct force of law. A Plan can satisfy MEPC.186(59) and still fail an underwriter’s audit against the OCIMF guide; the two are distinct standards with distinct gatekeepers.
Second, jurisdiction. Flag-State approval of a Plan does not waive coastal-State requirements, and those requirements split sharply. The 48-hour IMO notification under Regulation 42 runs in parallel to, not in place of, national notification: 24 hours to the US Coast Guard Sector under 33 CFR Part 156, 14 days to the UK MCA for a first-time operation at a designated location, outright prohibition inside Spanish and Portuguese waters. In international waters where no coastal State exercises jurisdiction, no Regulation 42 notification is filed at all, yet the full Regulation 41 operational regime still binds the master.
Third, weather and fendering practicalities. The fender-count relation is an empirical envelope, not a closed-form result. It assumes a design significant wave height and a verified fender condition; a real operation that meets the count on paper can still be unsafe if the swell period resonates with the moored-pair RAO or if a fender has lost pressure. The closing-speed limit of about 0.3 m/s at first contact for a Suezmax-class manoeuvring vessel and the abort window are the controlling practical limitations, and both shrink fast as the sea state rises.
Fourth, exemptions and residual risk. The emergency-lightering exemption lets a master discharge without an approved Plan when the alternative is structural failure or grounding, but it does not suspend the duty to report a resulting spill. Several hazards sit outside the Plan entirely: political-risk events such as sanctions changes affecting cargo origin or port-State seizure on national-security grounds, severe weather with onset shorter than the abort window, and fire on either vessel during transfer, which falls into the SOLAS fire-safety regime rather than the STS Plan.
Fifth, the commercial numbers are estimates. The POAC day rates (USD 1,800 to USD 3,500), the POAC pool size (roughly 800 to 1,200 active globally), the VLCC lightering saving (USD 200,000 to USD 500,000 per voyage), and the worked-example transfer durations are working figures drawn from the commercial-lightering trade as of 2025 to 2026. They move with charter-market conditions, fuel prices, and the specific lightering lane, and should be treated as planning ranges rather than fixed values.
See also
- MARPOL Annex I: prevention of pollution by oil
- MARPOL Annex I oil pollution prevention overview
- Regulation 12A oil fuel tank protection
- Regulation 17 Oil Record Book
- Regulation 28 damage stability
- Regulation 33 crude oil washing
- Regulation 37 SOPEP
- MARPOL Annex II noxious liquid substances
- MARPOL Convention
- ISM Code