Ship Hull Inspections

Deciding Between Close Visual Inspection (CVI) and General Visual Inspection (GVI)

General visual inspection (GVI) and close visual inspection (CVI) are two different types of inspection methods that ship operators can use to identify the potential risks and damages on the hulls of their ships.

Read on to learn more about the differences between general visual inspection and close visual inspection of ship hulls and to decide which ship hull inspection you need.

What is General Visual Inspection?

General visual inspection (GVI) is a simple and fast ship inspection method to detect defects in the surface of ship hulls. General visual inspections (GVI) look at the visible areas of a ship. 

Any defects or issues that can be seen without needing specialized light or magnification will be noted during a GVI survey. The main types of general visual defects that may be detected using GVI include Paint; Boiler tubes, Rust, corrosion, biofouling, Flaking paint on steel surfaces; Loose paint, or other foreign matter on the outside of the vessel.

A general visual inspection is nothing like a final check; instead, it’s just one step in a larger process that has many other criteria to inspect for such as the extent of biofouling, type of biofouling, the extent of corrosion and major damages to the hidden areas of the ship. 

What is a Close Visual Inspection?

A close visual inspection (CVII) is a specialized type of visual inspection that looks at the hidden areas of a ship. Any defects or issues that can only be viewed under magnification are noted during a CVI survey. 

The goal of a CVI inspection is to catch potential issues before they can become visible during a GVI survey. In many cases, CVI is the only way to detect defects like micro-cracks or re-welds that are difficult to see with the naked eye.

Right: An inspection footage of a vessel hull, captured by Sentinus from multiple angles.

Differences Between GVI and CVI

General visual inspection is a quick, cost-effective way to evaluate the surface of a ship’s hull for biofouling. It does not provide detailed information about the extent or type of fouling on different areas of the hull, but it does give operators an indication as to whether there is any biofouling present.

CVI involves a more detailed process than GVI, it is more cost-effective in the long run because it allows operators to target high-risk areas of the ship’s hull before they become heavily infected with biofouling.

A GVI inspection looks at the ship’s visible exterior areas, and a CVI inspection looks at the ship’s hidden exterior areas. A GVI inspection can be done in any condition, but a CVI requires specific visibility standards to be met.

Many times, a shipyard will use a GVI inspection during the day when visibility is optimal and switch to a CVI inspection during the night when visibility is not as good or in bad weather conditions. Both methods use different inspection techniques and standards of visibility to achieve this objective.

When is CVI Used?

A CVI inspection is used on ships that need to be inspected with magnification when viewing the inside of a ship’s hull, or areas that are close to the ship’s hull. 

A CVI inspection is used when viewing a ship’s hull at an angle where a GVI inspection would be obstructed. Following are examples of some structures of the ship that need to be inspected using a close visual inspection technique. 

Right: A 3D model of a vessel hull segment, an example of close visual inspection. 


Hull refers to the bottom of the ship. A CVI is a thorough inspection of the entire ship hull to ensure safe and efficient operation, whether for commercial or recreational use. 

Looking for any defects, damage, or other imperfections that could pose an issue for the ship. By scheduling regular hull inspections ships receive necessary information from their inspection team to make the best decisions regarding cleaning, painting, and maintenance schedules.

3D model of ship hull created from the inspection footage captured by underwater robot Sentinus 

Bow Thrusters

Consistent inspection of the bow thrusters is essential to ensure safe and effective operation in a marine environment. Bow Thrusters help in maneuvering in tight spaces and low-speed operations.

A malfunctioning bow thruster can cause accidents and put the crew and the vessel at risk. This can lead to damage and loss of control for onboard systems moreover, fuel efficiency can be decreased as well.

3D model of bow thrusters created from the inspection footage captured by underwater robot Sentinus 

Sea Chests

The main function of sea chests is to provide an intake pipe from which piping systems can draw raw water. The water is then used for cooling the elements like stern tube oil, exhaust, air conditioner, etc. 

Ideally, for maximum efficiency and ease of operation, sea chests should free be of any internal obstructions. They are inspected to prevent damage to their contents as well as any associated components or equipment. Sea chests can also contain baffles and grating that prevent access to unused water inside the sea chest itself.

3D model of sea chests created from the inspection footage captured by underwater robot Sentinus 

Tool for Close Visual Inspection

General visual inspection can be done with a simple ROV on the other hand, close visual inspection requires a more specific tool that can inspect the crucial hidden parts of the hull. 

Blue Atlas Robotics’ self-operating underwater robot “Sentinus” is an ideal tool that can inspect your ship hull below the waterline. It has all the elements that are needed while performing close visual inspections. 

Technical Requirements for CVI Fulfilled by BAR Robot
Optimal Lighting
Our underwater robot has 14 individual lumen lights onboard for detailed results.
BAR robot stays close to the target Staying close means fewer particles between the cameras and the target, resulting in clear outputs, even in murky water, however, at the same time, it keeps a 20-30 cm safer distance from the target so it does not get bumped into the target.
Visual Clarity
Equipped with eight high-quality cameras. It can capture the footage is crystal clear even when the water conditions are not optimal.
Crucial Points Inspection
Sentinus can perform visual inspection in any orientation.

Click the social media icons below to follow Blue Atlas Robotics’ innovative underwater inspection technologies.