Safety and risk profile
Diving brings unmatched human dexterity, but also the highest intrinsic risk because people are placed directly into a dynamic, impact-prone environment. Industry guidance from The International Association of Oil and Gas Producers (IOGP) frames diving as work where errors can escalate rapidly in an unforgiving environment, necessitating extensive controls and competence management.
ROVs remove personnel from the water column, which is a major safety gain, but their tethers and launch-and-recovery workflows keep deck teams busy in rough conditions; station-keeping in waves is non-trivial and can deteriorate abruptly as wave action and aeration increase. Control research and tank tests highlight the narrow stability margins available for station-keeping under waves and the sensitivity of performance to thruster dynamics and free-surface effects.
Access robots shift the highest-severity hazards from people to equipment. Operators remain in a topside control cabin while the robot attaches directly to the structure, often with dual-point securement and defined retrieval procedures. Because the tool is clamped or tracked onto the member, the inspection head—camera, UT probe, CP contact, or laser/photogrammetry payload—stays where it’s needed even when the sea state is lively.
Weather windows and uptime
The splash zone punishes anything that can’t maintain position and sensor contact across the cresting interface. Divers see their window narrow quickly with visibility, current and vessel motion; aborts and pauses are common as surface conditions change. ROVs handle moderate chop, but aeration may rob thrusters of authority and disrupt sensors.
By contrast, access robots are engineered for tide cycles and rougher seas. Multiple commercial and research systems specify operability in the 3–3.5 m Hs range (and higher for certain heavy crawlers), which converts marginal weather into productive inspection hours. For planning purposes that typically means steadier daily progress and fewer stop-starts across multi-day scopes.
Environmental footprint
For inspection, the dominant environmental lever is not debris handling but vessel days. Both diver and ROV operations usually require a dedicated offshore support vessel (OSV), most often a platform supply vessel (PSV). These vessels are the workhorses of offshore logistics, but they also represent the largest single source of emissions during a splash zone operation.
Academic and industry data show that a PSV typically burns around 9–10 tonnes of marine diesel per day in normal operations. With standard fuel-to-CO₂ conversion factors (~3.1–3.2 tonnes of CO₂ per tonne of fuel), this equates to roughly 28–32 tonnes of CO₂ per vessel-day. Actual figures vary with vessel type, operating speed and idle time, but the order of magnitude is consistent: every extra PSV day adds tens of tonnes of CO₂ to the campaign footprint.
Access robots change that equation. Because they can be deployed directly from the platform with compact topside units, splash zone inspections can be carried out without a support vessel on standby. Cutting even a handful of PSV days saves more emissions than the robot itself consumes in power over an entire program. For operators under increasing pressure to reduce emissions, eliminating support vessel days is the single most effective lever available in splash zone inspection.
Inspection quality
Inspection quality is about stable geometry, good data and repeatability. Near the surface, bubbles from breaking waves scatter light and sound, degrading ROV video and sonar. Access robots avoid this by locking onto the structure and maintaining repeatable stand-off or contact for CVI and NDT.
Many splash zone checks need firm, repeatable contact. Ultrasonic thickness gauging (UT) requires controlled coupling and alignment; NDT specialists emphasise fixturing for consistent probe pressure and angle to achieve accurate readings. Those conditions are difficult for a diver or ROV to maintain at the interface, but they are precisely what a tracked/clamped system provides.
Access robots that attach to structures—using clamps, tracks, or magnetic adhesion—can carry UT, corrosion mapping, and CP payloads around risers, caissons, conductors, and jacket legs in the splash zone. Robotic solutions can be easily integrated with various inspection methods such as ACFM, TOFT, Phased Array, and PEC.
OceanTech can readily deploy such equipment. And because the tool is fixed, the probe or camera maintains stable coupling and stand-off through surge at the air–water interface, enabling repeatable, auditable data from topside deployment.
Where coating systems, CP and welds converge around appurtenances, access robots can also stage CVI with metrology—photogrammetry or laser line scan—at controlled stand-off, capturing geometry that is otherwise jitter-blurred when the platform is moving relative to the camera. The result is more uniform, auditable data in the very band that drives corrosion risk models. DNV’s risk-based corrosion practice explicitly calls for targeted visuals and photographic records in the splash zone as part of screening; stable, repeatable collection makes those records easier to defend.
Access and reach
Tight geometries—boat landings, conductor guide frames, clamps and anodes—are exactly where free-swimming ROVs pick up tether drag and divers have the least workable time. OceanTech’s access robots clamp or rail-mount to curved members and weld caps, stay engaged across the air–water interface, and are deployed from topsides with small platform crews.
In practice, this is how we execute splash zone inspections: our robots carry CVI/UT/PEC/ACFM payloads from a stable platform, track 360° around braces, and hold position under hydrodynamic loads up to ~3 m Hs once deployed. Recent projects include riser inspections at South Arne completed by a five-person team in ~3 weeks with no divers/ROV vessels, and the ANDWIS autonomous weld-inspection robot (with SINTEF, ConocoPhillips and DNV) that uses 3D vision and closed-loop control to keep the probe steady around nodal welds. These are field-proven methods, not hypotheticals.
Data capture, QA and documentation
A splash zone inspection that cannot be verified is a liability. Divers can and do record helmet-cam footage and notes, but positional repeatability suffers when visibility drops and attention is rightly on safety. ROVs excel at broad visuals, yet position drift and aeration can make image registration unreliable.
By contrast, access robots normally integrate encoders and discrete survey tracks; coupling that with UT, CP contact readings or high-resolution video produces coverage maps, parameter logs and before/after evidence that align well with audit requirements for structural integrity programs.
Cost of operation and logistics
Day rate is only part of the picture. The heavy hitters are weather loss, re-runs for data quality, marine spread requirements and personnel on board (POB). Dive spreads bring substantial equipment and POB; ROVs reduce POB but still need clear deck space and a vessel with launch and recovery. Access robots typically mobilise with a small topside footprint and can be deployed by rope-access or simple rigging, enabling small platform-based teams.
In projects where a free-swimming ROV would otherwise accumulate vessel hours in marginal seas, or where divers would sit on weather standby, robots simply keep working. By doing so, they remove vessel days from the equation entirely, turning marginal weather into productive hours and eliminating the standby fuel burn that dominates both cost and emissions.
Productivity
Divers are fast in short bursts but constrained by exposure limits, decompression and conservative pauses as conditions vary. ROVs are highly efficient for wide-area visuals when the water is calm, but the interface band slows them down most. Once attached, a robot can run long, steady shifts with consistent sensor placement through changing tide and chop. In practice, that steadiness turns into more usable inspection minutes per day and more predictable completion across multi-asset programs.
Some splash zone inspections are simply not safe or viable for divers, and not controllable for free-swimming ROVs, but are routine with access robots. Examples include full-circumference UT thickness sweeps across the air–water interface on risers and caissons, where continuous contact and stable coupling are prerequisites for trustworthy readings; close visual inspections on boat landings and ladders, where confined geometry and impact risk rule out human-in-water work; and high-resolution corrosion mapping around conductor frames and anode clusters.
All three methods will continue to have roles offshore. Divers remain valuable for one-off, intricate interventions where they can work safely in benign conditions. ROVs are excellent for broad visual reconnaissance and subsea scopes away from the aerated interface. But for inspection at the splash zone itself, access robots offer the best combination of safety, uptime, environmental performance and data integrity. They keep people out of the highest-risk band, stay productive through more weather, avoid dedicated support vessels, and deliver the stable, verifiable data sets that integrity management frameworks expect.
OceanTech’s own deployments reflect these advantages: once attached, our systems continue inspection work in significant wave heights up to ~3 m Hs, from topside control, with compact spreads and low POB—an approach that improves safety and markedly reduces the emissions associated with vessel days.