Medevac at Sea: How a Maritime Medical Evacuation Actually Works

What actually happens in a medevac at sea?

A medevac at sea — sometimes spelt medivac — is the emergency transfer of a sick or injured person from a vessel or offshore installation to definitive care ashore, with clinical support en route, coordinated through the state's rescue services rather than by the operator alone. The word itself, and how it differs from a casevac, is glossary territory; this article is about the process — what happens, in what order, and who decides, between "we have a casualty on board" and a patient in a hospital bed.

Every maritime medevac runs through the same five phases, whatever the flag or sea area: the alarm is raised and a remote clinician assesses the case; a decision is made and rescue assets are tasked; an evacuation route is chosen; the evacuation itself is executed; and the patient is handed over to shore-based care. Each phase has a different owner — which is precisely why the process confuses people who assume the vessel operator, or the company, is running it.

The framework underneath is international. The IMO regards medical assistance at sea as an integral part of search and rescue, and its guidance (MSC/Circ.960) describes the system as five elements working together: rescue coordination centres, a telemedical assistance service (TMAS), means of intervention at sea, shore-based reception arrangements and common operational procedures.

Who decides: the chain from deck to coastguard

The chain starts on board. The master — or on an offshore site, the offshore installation manager or site manager through the site's emergency response plan — raises the alarm, typically to the coastguard's rescue coordination centre, which IMO guidance calls the natural first contact for a captain facing a medical problem on board. In the UK, HM Coastguard coordinates all maritime search and rescue operations through its network of rescue coordination centres.

The first substantive step is almost always a telemedical consultation, not a launch. The RCC connects the vessel to a TMAS doctor, who takes a history, assesses the patient remotely and recommends a course of action: treat on board, divert, or evacuate. Under MSC/Circ.960 the responsibilities are cleanly divided — the TMAS doctor "has full authority to recommend evacuation on medical grounds", while on board "the captain is responsible for examining the patient, administering treatment and the final decision". That final authority is protected in law: SOLAS regulation V/34-1 provides that the owner, charterer or company "shall not prevent or restrict the master of the ship from taking or executing any decision which, in the master's professional judgement, is necessary for safety of life at sea…".

Crucially, the decision to launch a SAR asset belongs to neither the master nor the company: the RCC organises the evacuation "to the extent of its capacities" and coordinates the operation. A shipowner cannot order up a rescue helicopter; it can only request one, and the coastguard weighs that request. IAMSAR Volume III is explicit that the benefits of a medevac "must be weighed against the inherent dangers of such operations to both the person needing assistance and to the rescue personnel" — which is why the RCC will ask for a structured picture before tasking anything: vessel identity and contact details, the patient's name, age, vitals, the nature of the illness or injury, symptoms, and every medication already given.

The evacuation routes — and when each is chosen

IMO guidance notes that the means used for a medical evacuation "are generally the same maritime or aeronautical means used for rescue operations" — there is no dedicated medevac fleet waiting offshore. In practice four routes cover nearly every case, and the choice is driven by clinical urgency, distance, weather and what is actually available on the day.

A SAR helicopter hoist is the fastest route for a time-critical casualty within range, and brings a paramedic-crewed aircraft to the patient. A vessel diversion — altering course to the nearest suitable port — is the default when the condition allows hours rather than minutes, with the RCC advising the master on the most suitable port given the patient's condition. In offshore wind, the site's own marine assets add a third route: a crew transfer vessel or an SOV's daughter craft can land a casualty to a waiting ambulance. And where a nearby ship carries better medical capability, or a rendezvous shortens the distance, a ship-to-ship transfer can bridge the gap.

The helicopter hoist, from the ship's side

Once a helicopter is tasked, the vessel gets a briefing — IAMSAR Volume III, carried on the bridge of most ships and now in its 2025 edition, contains the standard script. The crew clears a pick-up area, preferably on the port stern; masts and booms that can be lowered are lowered, loose gear is secured, unnecessary people are kept clear, and the ship's radar goes to standby just before the aircraft arrives. At night, deck lighting is directed at the pick-up area but never at the helicopter, which would degrade the pilot's vision. On arrival, the vessel alters course to put the wind about 30 degrees on the port bow and holds a steady course with steerageway, giving the pilot — who flies the hover from the starboard side — clean air over the deck.

Two rules from the manual are drilled because getting them wrong is dangerous. First, static electricity: the helicopter builds a charge in flight, so the rescue device or its trailing static line must touch the vessel before anyone touches it. The UK MCA's guidance on helicopter assistance (MGN 325) adds that the hook handler should wear rubber gloves and rubber-soled shoes for the same reason. Second, the hi-line: in poor weather or confined deck areas the helicopter may lower a weighted line for the crew to guide the winch hook — the line is hauled in only when the helicopter crew instructs, and, in the manual's own capitals, "THE LINE MUST NOT BE ATTACHED TO THE VESSEL". Securing the hoist wire or trail line to the ship couples a hovering aircraft to a moving vessel; if the operation must be broken off, the line is paid out immediately, clear of obstructions.

If a winchman comes down, the deck party follows his instructions. If the stretcher must be moved from the pick-up area to load the patient, the cable is unhooked first and the loose hook laid on deck for the helicopter to retrieve. When the patient is strapped in and ready, the deck signals the winch operator, tends the trail line as the stretcher rises to stop it swinging, and finally tosses the line's end gently over the side. None of this is improvised on the day — MGN 325 expects ships to hold contingency plans and run drills against a helicopter operations checklist before they ever need one.

Preparing the casualty — stabilisation, tagging, documents

While the aircraft or boat is in transit, the on-board team's job is to make the patient transferable. IAMSAR's instructions are practical: move the patient to the pick-up area if required, keep the RCC updated on any change in condition, and ensure the patient is "tagged to show details of any medication which has been administered" — the receiving crew must know what is already on board the patient, chemically speaking.

The paperwork travels too. The manual calls for the patient's seaman's papers, passport, medical record and other necessary documents to be prepared "in a package ready for transfer with the patient" — personal luggage stays behind, since loose items can foul the winch cable or the rotors. For the hoist itself, the patient is strapped into the stretcher face-up, wearing a lifejacket if their condition permits. Where a telemedical service has been managing the case, a concise clinical summary — presentation, observations over time, treatments and responses — is what turns a handover from a guess into a briefing.

How long does a medevac take? Offshore timelines and realities

The honest answer: longer than most emergency response plans assume. The UK's SAR helicopter fleet — ten Bristow-operated bases flying S-92 and AW189 aircraft for HM Coastguard — launches well within 15 minutes of an alert, but launch is not arrival. Transit at a cruising speed of around 145 knots, locating the vessel, the hoist sequence itself and the flight to a receiving hospital all add up; a casualty 100 nautical miles offshore can be more than an hour from the nearest base even before anything happens on scene.

Nor is a helicopter guaranteed. SAR aircraft serve a whole region, and the offshore wind industry's own emergency response guidance (G+ IOER) warns duty holders not to assume one will be free to respond to a renewable-energy incident when it is needed. The marine fallback is slower still: shore-based rescue craft top out around 25 knots, so the run to a far-offshore wind farm is measured in hours, not minutes. Night, fog and sea state can close off routes entirely — which is why the evacuation-route decision is made case by case, on the day, by the RCC.

For offshore wind operators the planning consequence is direct: the site's medical emergency response cannot be built on the assumption of a 30-minute helicopter. G+ guidance expects response times to be evaluated and provision matched to them — and the industry's incident experience shows why the waiting time matters: in the G+ data, around three quarters of cases needing medical intervention were dealt with at the site, with roughly a quarter going on to evacuation.

Telemedicine at both ends of the medevac

The single biggest lever in the whole process sits at the start. IMO guidance is unusually blunt about why TMAS exists: "to avoid, as far as possible, the need for evacuation, which, although sometimes essential, is by its nature dangerous and expensive" — evacuations should be "reserved for medically justified cases". The data bears out how often remote assessment settles the question: in Swedish TMAS records, the share of seafarer consultations ending in evacuation fell from 18% in 1997 to 14% in 2007 — meaning more than four in five cases were resolved without anyone leaving the ship — and Turkish TMAS figures from merchant cargo ships show roughly one contact in ten leading to a medevac. Most radio medical consultations end with treatment on board, not a helicopter.

When evacuation is warranted, the same remote clinician earns their keep twice more: during the wait, guiding stabilisation and monitoring while the asset is in transit and flagging deterioration to the RCC; and at handover, supplying the receiving hospital with a documented clinical course rather than a verbal fragment shouted over rotor noise. What happens after the patient lands — treatment, the fit-to-fly assessment and the journey home — is a separate, slower chain of its own: medical repatriation, with its own logistics and costs.

The pattern across the whole process is consistent: the master or site holds the duty, the TMAS doctor holds the clinical recommendation, and the coastguard holds the assets. A crewing or HSE manager cannot control the weather or the helicopter's other taskings — but they can control how early a clinician sees the case, how well the crew is drilled for the deck work, and how completely the patient's story travels with them. Those are the parts of a medevac that go right by preparation, not luck.

Sources

• IMO MSC/Circ.960 — Medical Assistance at Sea: RCC/TMAS roles, TMAS doctor's authority, master's final decision, avoiding evacuation
• IAMSAR Manual Volume III, Mobile Facilities (2016 edition full text) — MEDEVAC request information, hoist procedures, hi-line technique, casualty preparation
• IAMSAR Manual Volume III, 2025 edition (current) — Witherbys product listing
• UK MCA MGN 325 (M) — Helicopter Assistance at Sea: contingency plans, drills, shipboard checklist, static discharge precautions
• SOLAS Chapter V, Regulation 34-1 — Master's discretion
• HM Coastguard — coordination of all UK maritime search and rescue
• Bristow — UK Search and Rescue: 10 bases, S-92/AW189 fleet, launch within 15 minutes
• MCA presentation, UK SAR Helicopter Service (Damien Oliver) — S-92 and AW189 radius of action and cruising speed
• G+ Integrated Offshore Emergency Response (IOER) good practice guidelines, 2nd edition — marine asset speeds, SAR helicopter availability, share of cases managed locally
• Westlund et al. (2016), International Maritime Health — Swedish TMAS 1997–2012: seafarer evacuation rates 18% to 14%
• Çakır (2021), Ocean & Coastal Management — Turkish TMAS: 4,668 consultations, 471 evacuations from merchant cargo ships