MAIB Annual Report 2025: what its structure means for survey vessel operations

What the MAIB has put on the record

The Marine Accident Investigation Branch published its Annual Report 2025 on 30 September 2026. The report covers the branch’s activities during 2025. According to the accompanying release, it contains:

• a statement from the Chief Inspector of Marine Accidents
• an overview of the accidents reported to the branch
• a summary of the investigations it started
• details of the publications it issued
• the recommendations made in 2025, with an update on their status
• updates on open recommendations made in previous years

The release contains no figures and says nothing about survey vessels, accident types or recurrence. We attribute no statistics or specific findings to the report in this article. We recommend reading the full document and its individual investigation reports directly.

Our purpose is narrower and, for a survey manager, more useful. The report’s structure, with its section tracking recommendations from earlier years, reminds us that investigation findings take time to work through into practice. A recommendation can stay open for many reasons. Its implementation date may not have arrived, it may be addressed to a regulator or another body rather than to industry, or it may be under review. We draw no conclusion about industry performance from the existence of that section. We use it instead as a prompt to examine, in our own analysis, the vessel operations on which offshore survey and metocean campaigns depend. These are routine, weather-sensitive deck and small-craft activities that sit beneath every dataset we deliver.

The causal chain behind recurring vessel-operation failures

Survey vessels do not carry exotic hazards. In our experience, and as commonly described in published marine investigation reports, the accident types that affect survey vessel operations are familiar:

• crew injured in the line of fire during launch and recovery of towed or tethered equipment
• workboats and daughter craft damaged or swamped during deployment or recovery alongside
• persons lost overboard from working decks
• errors made by watchkeepers and operators late in long rotations

None of these is technically novel. In our view, that makes their recurrence an engineering problem: the knowledge exists, and the controls are what fall short.

Our assessment is that one root cause runs through most of these chains. The go/no-go decision for a weather-sensitive operation rests on a limit that was never engineered for that operation. That limit is checked against a forecast whose uncertainty is not accounted for. The people making the call often have ambiguous authority to stop. Four contributing mechanisms turn that latent condition into an incident.

Limits defined in significant wave height alone

In the survey vessel operating manuals and task risk assessments we review, launch and recovery limits are commonly expressed as a single significant wave height, sometimes with a wind speed attached. In our experience, that figure is often inherited from vessel marketing material or from a previous campaign. It is rarely derived from the motion response of the vessel at the overboarding point.

In a Rayleigh-distributed sea, the most probable maximum individual wave over a three-hour period (around 1,000 waves) is roughly 1.9 times Hs. The crew handling a towfish or CTD rosette at the A-frame will meet that wave during any extended operation.

Wave period matters as much as height. A modest Hs carried by swell close to the roll or pitch natural period of a small survey vessel can produce larger motions at the sheave than a higher, shorter wind sea. Wind-against-tide conditions in shelf seas steepen waves well beyond what the forecast Hs suggests.

A limit that ignores peak period and relative heading is only a placeholder, and it holds until the sea state and the vessel’s response combine unfavourably.

Splash-zone dynamics during launch and recovery

The splash zone is where most launch and recovery energy is concentrated. DNV-RP-N103 sets out the governing physics:

• slamming and varying buoyancy as the body crosses the free surface
• vertical motion of the crane or A-frame tip
• the risk of slack wire followed by a snap load when the downward velocity of the crane or A-frame tip exceeds the velocity the payload can follow, or when hydrodynamic forces approach the payload’s submerged weight

Snap loads are the mechanism behind many parted lift lines, damaged terminations and equipment swinging into the deck crew.

For survey equipment, the masses are small compared with construction lifts. This leads teams to treat the operation informally, and that is the error. A side-scan towfish, a magnetometer or a sub-bottom profiler on a soft tow cable is still a pendulum attached to a moving overboarding point. The deckhand steadying it with a tag line is in its swing path.

The same exposure applies to deep-water mooring deployments for long-term current measurement, where anchor, releases and buoyancy are handled in sequence over the stern for extended periods.

Divided authority between bridge and survey party

On a survey vessel the master holds overriding authority under element 5 of the ISM Code. The decision to deploy equipment, however, is usually initiated by the party chief or client representative, who is driven by line plans and data acquisition targets. The marine crew and the survey crew often belong to different employers, run different management systems and report through different chains.

In practice this produces a decision that nobody fully owns. The survey party asks whether conditions permit deployment. The bridge assesses vessel safety but does not always know the equipment’s handling sensitivities. The deck crew, who see the actual motion at the overboarding point, are the least empowered to call a stop.

IMCA M 220 addresses this problem for DP operations through activity-specific operating guidelines with defined decision points. Most non-DP survey operations have no equivalent instrument.

Fatigue built into the campaign pattern

Survey campaigns typically run continuous acquisition on 12-on, 12-off watches over long rotations. Marine crew hours of rest are governed by STCW and the Maritime Labour Convention: a minimum of 10 hours in any 24-hour period and 77 hours in any seven-day period. Depending on the flag state’s determination of seafarer status under MLC 2006, survey and technical personnel are often treated as special personnel (SPS Code) or industrial personnel (SOLAS Chapter XV). Their hours are then governed by company policy and are not always recorded with the same discipline.

In our assessment, the highest-risk window is the recovery after a weather standby. Equipment must come back aboard in deteriorating conditions, often at night, by people who have been working through a backlog. The hours-of-rest record for the bridge can be compliant while the survey and deck personnel handling the equipment are not rested.

Why existing controls fail to catch the drift

The controls in a typical survey vessel management system look adequate on paper. They fail in practice for structural reasons.

Risk assessments are frozen at mobilisation. The task risk assessment for launch and recovery is written during mobilisation, often in sheltered water, and referenced thereafter. It rarely records the sea state, period and heading for which its controls were judged adequate. When conditions change, nothing in the document prompts a reassessment. A toolbox talk that repeats the mobilisation assessment adds no new information.

Forecast uncertainty is not applied. DNV-ST-N001 distinguishes the operational limiting criterion (OPLIM) from the forecasted operational criterion (OPWF). OPWF is obtained by multiplying OPLIM by an alpha factor below unity. The alpha factor accounts for forecast uncertainty over the operation reference period, which is the planned operation period plus contingency. The standard treats an operation as weather-restricted when the planned period is under 72 hours and the reference period is under 96 hours.

Marine warranty surveyors apply this framework routinely to construction and installation work. In our experience, survey operations rarely apply it, even though a multi-hour tow followed by recovery is a weather-restricted operation in every engineering sense. When the forecast Hs is compared directly with the limit, the margin the alpha factor provides is lost without anyone noticing.

Observed conditions are not reconciled with the forecast. Many survey vessels carry wave radar, a motion reference unit whose output can be used to estimate sea state if calibrated, or both. They also have access to nearby wave buoys. These data are logged but seldom compared, in real time, with the forecast used for the go decision. A forecast that is under-predicting the sea state is therefore usually first noticed through the deck crew’s discomfort, with the instruments that could have flagged it sitting unused.

Leading indicators are absent. Fleet safety reporting is dominated by lagging indicators such as lost-time and recordable injury rates. A towfish that struck the transom during recovery without injuring anyone is often logged as equipment damage and never enters hazardous occurrence reporting under ISM element 9. The near-miss population that would reveal a degrading limit is therefore filtered out before it reaches anyone who could act on it.

Commercial structure biases the decision. Weather standby treatment differs between day-rate and lump-sum contracts. Where the contractor carries weather risk, the commercial structure itself pushes towards deployment at the margin, whatever the individuals involved intend. A management system that relies on personal judgement to resist structural pressure is relying on the wrong control.

What the open-recommendations record teaches

The MAIB’s practice of reporting the status of open recommendations from earlier years carries a lesson that does not depend on any particular figure in the report. The path from investigation to recommendation, to acceptance by the addressee, to implementation and to closure has several stages, and each one takes time. The report itself gives us no timescales, so we draw our own conclusion: a survey contractor or client gains nothing by waiting for a recommendation to reach its sector through regulation or class before reviewing its own controls.

Two transferable lessons follow for survey and metocean teams; the operational detail is set out in the recommended controls below.

1. Treat recurrence as evidence of a design deficiency. An accident type that reappears across operators and years points to a control that is badly specified. Retraining the individuals involved will not fix it. Re-engineer the limit, the decision point or the equipment handling arrangement.
2. Vessel selection is a metocean decision. Survey vessels are often selected on day rate, transit time and equipment fit, with operability treated as a secondary consideration. On exposed sites that ordering is backwards, a point we develop in our discussion of matching survey vessel and campaign plan to a site’s metocean exposure. A smaller vessel working at the edge of its limits generates both the weather downtime and the incident exposure.

Breaking the chain: controls we recommend

The following controls are specific and auditable. A survey manager can test each of them within a single campaign.

1. Define launch and recovery limits as an Hs–Tp matrix per operation. For each deployable system, record allowable Hs in peak-period bands, for example in 2-second bins across the expected swell range, and for head, beam and quartering seas. Derive the values from the vessel’s motion response at the overboarding point where RAOs are available. Otherwise base them on documented trial deployments in measured conditions. Replace every single-value Hs limit in the operations manual with this matrix before the next mobilisation.
2. Apply an alpha factor to every weather-restricted survey operation. Calculate the reference period as planned deployment, acquisition and recovery time plus contingency. Set OPWF from OPLIM using the alpha factor tables in DNV-ST-N001, at a forecast and monitoring level the campaign can actually demonstrate. Record OPLIM, the alpha factor and OPWF on the daily operations plan, so the margin is visible to the bridge and the survey party.
3. Reconcile observed with forecast sea state every three hours. During any operation with equipment in the water, compare measured Hs and Tp from wave radar or the nearest buoy, supplemented by MRU-derived motion estimates where calibrated, against the forecast for that period. If observed Hs exceeds forecast by more than 20 per cent (our recommended trigger, not a DNV-ST-N001 value), or observed Tp moves into a band not cleared in the limit matrix, recover the equipment and re-plan. Log every reconciliation.
4. Issue a survey operating guideline modelled on IMCA M 220. Adapt the activity-specific operating guideline format to non-DP survey activities. Define green, advisory and stop criteria for each operation, and name who holds the stop decision at each level. Give the deck supervisor explicit, documented authority to halt a recovery. Have the master, party chief and client representative sign the guideline at mobilisation.
5. Engineer the splash zone so that nobody needs to handle the payload. Review every launch and recovery arrangement against DNV-RP-N103 snap-load criteria and the lifting principles in IMCA M 187. Fit docking heads or latching cradles where towed bodies currently rely on tag lines. Mark line-of-fire exclusion zones on deck to support the Line of Fire rule in the IOGP Life-Saving Rules (IOGP Report 459). Use the absence of hands on a swinging payload as an audit criterion.
6. Record hours of rest for everyone who works the deck. Extend the STCW and MLC recording discipline to survey and technical personnel engaged in deck operations. Set a rule that nobody who has had less than 10 hours of rest in the preceding 24 hours, or less than 77 hours in the preceding seven days, participates in a launch or recovery. Audit compliance weekly, with particular attention to post-standby recoveries.
7. Lower the reporting threshold and track leading indicators. Classify any uncontrolled contact between deployed equipment and the hull, any unplanned slack-wire event and any recovery aborted for motion as a hazardous occurrence under ISM element 9. Track the rate of these events per hundred deployments, alongside the proportion of operations started within OPWF rather than OPLIM.
8. Map the MAIB recommendations to your own system within 30 days. Take the recommendations issued in 2025 and the open recommendations from previous years as listed in the annual report. Screen each for relevance to your vessels, workboats and deck operations. Assign an owner and a closure date to every relevant item, and review progress at the next management review required under ISO 9001 and ISO 45001.
9. Write weather risk allocation into the contract. Survey clients should state, in the scope of work, that deployment decisions are governed by the agreed OPWF and limit matrix. Schedule and payment terms must not penalise a contractor for observing them. Removing the commercial incentive to deploy at the margin is a control in its own right.

None of these measures needs new technology; established equipment and methods are enough. What they demand is that the limits and decisions governing routine survey deck work are engineered and verified to the same standard we already expect of construction and installation operations.

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Based on: MAIB Annual Report 2025 published