Underwater Inspection

Underwater inspection is the control and documentation of the condition of structures, vessels and installations below the waterline. In shallow water it is traditionally done by divers; at greater depths and for frequent, documented control, remotely operated vehicles (ROVs) are increasingly used. The goal is always the same: to reveal damage, wear and corrosion early enough to act on it – before small faults become large and costly.

SeaSpection is the Norwegian distributor of MarineNav Oceanus ROV systems and supplies the equipment that makes modern underwater inspection fast, safe and documentable – with training, service and technical support. In this article we look at what underwater inspection is, which methods exist, and when you should choose which.

What is underwater inspection?

Underwater inspection covers everything from routine visual control to the detection of cracks, corrosion and hidden damage. Major damage is easily seen on video, while fine cracks and early corrosion require specialised methods such as magnetic particle, ultrasound or electromagnetic testing. The purpose is to reveal weaknesses before they develop – and to document the condition to the owner, authority, class society or insurer.

The need exists in most industries with something underwater: ships and offshore installations, quays and bridges, fish farms, hydropower plants and municipal infrastructure. What they have in common is that inspections must be both thorough and verifiable – and that the cost of an undetected fault is often far greater than the cost of inspecting regularly.

Methods of underwater inspection

Diver inspection

Divers provide physical access and tactile control, and are often the first choice in shallow water and where the task requires manual intervention – for example simple repair or cleaning in connection with the inspection. The drawback is cost, logistics and safety risk, which limits how often you can inspect.

ROV inspection (remotely operated)

An ROV is a remotely operated underwater vehicle with a camera, lights and sensors, controlled from the surface. It provides fast, safe and repeatable inspection without putting people in the water, and is particularly suited to frequent control and to depths where diving is costly or impractical. How ROV inspection works in practice, and how to choose the right model, is described in our guide to ROV inspection.

Specialised control (NDT)

To detect cracks and wall thickness, non-destructive testing is used underwater: ultrasound thickness measurement, CP measurement of cathodic protection and other methods. Several of these can be mounted on an ROV as a sensor payload, so that visual control and measurement are done in the same operation.

Which method for which task?

The choice is driven by depth, task and how often you must inspect:

• Shallow water + manual task: a diver is often practical.
• Deep water, frequent control, documentation: an ROV lowers the threshold to inspect often, and gives time-stamped video every time.
• Detecting cracks/wall thickness: specialised NDT, often as a sensor on an ROV.

In practice the methods are combined – and more and more routine control is moving from diving to ROV because it is faster and cheaper over time. A common model is to use an ROV for regular monitoring and reserve diving for the tasks that genuinely require hands underwater.

Applications

Underwater inspection is used across industries, and for several of them we have dedicated in-depth articles:

• Hull and propeller – control without taking the vessel out of service.
• Pipelines and subsea structure – regular control of pipelines and structures offshore and subsea.
• Aquaculture – daily control of net, pen and fish welfare in aquaculture.
• Quays, bridges and breakwaters – condition control of structures in and above water.
• Power plants and dams – intakes and underwater parts that are hard to reach.

ROV as the modern method – and the equipment behind it

Where underwater inspection once meant booking a dive, today you can own the capability yourself. A professional ROV system differs from a simple underwater drone with a topside control station (daylight-readable screen, industrial computer, physical joystick), Position Hold via DVL for stable inspection in current, USBL positioning for verifiable documentation, and sensors such as a thickness gauge, CP probe and sonar.

The MarineNav Oceanus ranges from the compact Mini to Pro and Ultimate (up to 500 m depth with an upgrade), so the system can be adapted to everything from shallow quay control to deep subsea inspection. You will find a full comparison in the overview of our ROV models.

Documentation and regulations

Underwater inspection is documentation-heavy. Time-stamped video and measurement data can be attached to reporting, used in maintenance planning and shared with the owner, class society, authority or insurer. Which framework applies depends on the sector – for example class-society rules (such as DNV) for vessels and NORSOK standards offshore. These are used as neutral background; approval itself rests with the relevant body.

Why regular underwater inspection pays off

The cost of an undetected fault – a leak, a crack or corrosion left to develop – is almost always greater than the cost of inspecting regularly. With your own ROV the threshold for inspecting becomes low, so deviations are caught early and can be remedied in a planned way rather than as an emergency. Over time this gives better control of the condition, safer operations and a solid basis for the maintenance budget. The combination of frequent control and good documentation also makes it easier to show the owner, authority or insurer that the installation is followed up systematically.

Frequently asked questions

What is underwater inspection?

The control and documentation of the condition of structures, vessels and installations below the waterline – from visual control to the detection of cracks and corrosion.

Diver or ROV – which should we choose?

A diver suits shallow water and manual tasks; an ROV suits frequent, documented control and depths where diving is costly. Often they are combined.

Can an ROV measure cracks and wall thickness?

Yes, with specialised sensors (e.g. thickness gauge and CP probe) mounted as a payload.

How deep can you inspect with an ROV?

The MarineNav Oceanus operates to 400 m as standard; the Ultimate can be upgraded to 500 m.

How often should you inspect?

It depends on the industry, regulations and risk. The advantage of owning an ROV is that frequent inspection becomes practical and affordable, so deviations are caught early rather than at the next scheduled dive.

Request a quote

Are you considering bringing underwater inspection in-house? We provide a professional assessment based on tasks, depth and conditions, and help you choose the right ROV solution. We respond within one working day. Request a quote.