Oil Tanker Ship-to-Ship Transfers: Plan the Whole Encounter

First, establish what kind of transfer is proposed

14 October 2026 — A ship-to-ship (STS) fixture may be described in commercial terms as a cargo movement between two tankers. Operational planning needs a narrower first question: what activity, ships and location are involved? The IMO’s published MARPOL Annex I Chapter 8 text addresses transfers of oil cargo between oil tankers at sea involving oil tankers of 150 gross tonnage and above. Its stated exclusions include bunkering, certain transfers associated with offshore production or storage facilities, and transfers necessary to secure a ship’s safety or save life at sea. Do not assume that a procedure written for an oil-cargo STS operation answers every question about bunkering or an offshore installation.

Location matters independently of that definition. An operation near a coast may face requirements beyond the international STS provisions. The UK Maritime and Coastguard Agency’s notice, for example, describes separate controls for transfers in its permit area and notification for relevant operations in UK controlled waters. That example is a reason to identify the coastal jurisdiction early, not a set of UK conditions to apply indiscriminately worldwide.

IMO Resolution MEPC.186(59): MARPOL Annex I Chapter 8, Prevention of Pollution During Transfer of Oil Cargo Between Oil Tankers at Sea · Maritime and Coastguard Agency, MSN 1829 (M): Ship to Ship Transfer Regulations 2020

Make the approved plan usable before scheduling the encounter

For an operation within Chapter 8’s scope, the IMO text calls for an Administration-approved STS operations plan, written in the ship’s working language, and for the tanker to comply with that plan. It also addresses the qualifications of the person in overall advisory control. These are distinct from a commercial nomination: a proposed date and quantity do not establish how two particular ships will manoeuvre, moor or respond if conditions change.

A useful planning exchange therefore identifies both ships, the oil and intended quantity, the proposed area, whether the ships will be at anchor or underway, the expected duration, the STS service provider or adviser, and the contacts who can resolve operational changes. The industry STS safety checklist starts with receipt of a joint plan of operations, effective communications, exchange of ship-handling characteristics, review of weather forecasts, a crew briefing and an agreed contingency plan. Treat these as checks that give the ships a common operating picture, rather than paperwork to collect after arrival.

IMO Resolution MEPC.186(59): MARPOL Annex I Chapter 8, Prevention of Pollution During Transfer of Oil Cargo Between Oil Tankers at Sea · Ship to Ship Transfer Safety Checklist: Before Operations Commence

Keep notification separate from permission

The IMO Chapter 8 text says an oil tanker subject to its provisions planning an STS operation in a MARPOL Party’s territorial sea or exclusive economic zone is to notify that Party at least 48 hours before the scheduled operation. The specified notice includes ship identifiers and arrival estimates; the proposed start time and position; whether the transfer is at anchor or underway; oil type and quantity; planned duration; the service provider or adviser’s details; and confirmation that an STS plan is aboard. It also calls for an updated arrival estimate if the tanker’s estimate for the STS area changes by more than six hours.

That notice is not a universal permit. The MCA notice, as a jurisdiction-specific example, describes a written application at least 72 hours before a proposed transfer in the UK permit area, alongside its separate 48-hour notification provisions for specified operations in UK controlled waters. Before fixing the operational timetable, establish which authority must receive what, whether approval is needed, and who will transmit revisions. Do not substitute the IMO notification interval for a local application requirement.

Treat approach and mooring as their own phase

Cargo cannot begin safely merely because both ships have reached the same position. The industry checklist places checks before run-in and mooring: visually inspect and correctly rig fenders, agree course and speed information and the method of controlling speed where applicable, ready mooring equipment and personnel, establish communications with the other ship, and monitor surrounding traffic. Its earlier checks include testing manoeuvring and navigational equipment and reviewing weather forecasts.

The practical handover is from the joint plan to the bridge and deck teams. Confirm which arrangements apply to this pair of ships and this location; distinguish an anchored encounter from one conducted underway. The MCA’s STS guidance highlights common language, communications channels and bridge-team roles, and asks that contingency planning address deteriorating weather, mooring-rope failure, pollution and fire. A weather or equipment change should prompt a fresh decision against the agreed plan, not an assumption that the original approach remains suitable.

Ship to Ship Transfer Safety Checklist: Before Operations Commence · Ship to Ship Transfer Safety Checklist: Before Run-In, Mooring and Cargo Transfer · Maritime and Coastguard Agency, MSN 1829 (M): Ship to Ship Transfer Regulations 2020

Check the cargo interface before opening the flow

Once alongside, the focus changes without ending the navigational watch. The industry checklist’s pre-transfer checks include effective mooring and fendering, blanking unused cargo connections, readiness of firefighting and spill-response equipment, plugging scuppers and save-alls, securing applicable sea connections and overboard discharges, and confirming cargo monitoring, gauging and alarm settings. It lists inert-gas and vapour-balancing checks with applicability qualifications; their presence on a checklist should not be read as a claim that every tanker has identical equipment.

Use those checks to settle practical questions between the ships before transfer: who is monitoring each side of the connection, how an abnormal condition will be communicated, and what the agreed plan requires before resuming after an interruption. Maintain the distinction between the two ships’ cargo responsibilities and the adviser’s overall advisory role. The IMO requirement to follow the ship’s STS plan remains the governing reference for an operation within Chapter 8’s scope; a generic checklist supports, but does not replace, that ship-specific document.

Plan the separation and the record, too

Completion of pumping is not completion of the encounter. The industry checklist’s post-disconnection checks include securely blanked hoses or manifolds, a cleared transfer side, exchanged cargo documents, communications with both ships’ mooring personnel, and an agreed method of letting go and separating. The MCA likewise stresses planning and briefing the unmooring and departure manoeuvre. Reserve time and attention for those steps rather than treating departure as an automatic sequel to the final cargo figure.

Finally, close the operational trail. For STS operations within its scope, the IMO Chapter 8 text calls for records to be retained aboard for three years and made readily available for inspection. Preserve a coherent account of the operation alongside the notices, revisions and shipboard records relevant to the voyage. The central planning lesson is simple: the fixture describes the cargo movement, but the STS plan must carry the two ships through notification, approach, transfer and separation.