Although thickness testing is not required for all UWILDs, the surveyor is very likely to request this data when an area of suspicion is located. The video above shows Deep Trekker's DTG3 equipped with a thickness gauge to perform these measurements.

Importance of Being UWILD Certified

Large vessels are required to be inspected thoroughly every year, as well as have a secondary inspection every three years and half decade by a classification society in order to remain certified to be in operation. Why do these classifications exist? Classifications began as technical assessments for marine insurers in the second half of the 18th century (IACS 2011). What started as a program for insurers to protect their interests developed into a fair assessment by a third party organization with all stakeholders' interests in mind.

The goal of having certified vessels versus suspended or non-certified vessels is to protect owners, employees, insurers and the companies who depend on the ships getting to their destinations. These classification societies know that credibility is the main source of business for them and they have no commercial interest in any side of the shipping industry.

The classification societies that implement these certifications for vessels are ABS, DNV-GL,Bureau Veritas, and Lloyd's Register, among others. ABS has a very comprehensive program that we have summarized below, other classification societies use similar criteria making it relevant to all owners and stakeholders of the shipping and offshore drilling industries. Mobile Offshore Drilling Units (MODUs) have very similar guidelines to vessels as well.

A full, thorough inspection similar to the 5 year inspection is required to become ABS certified. Once classed, ABS uses a Hull Inspection and Maintenance Program to make it easier for vessels to stay certified or become reclassified if a suspension takes place. The program is the most important part of a classification because it ensures long term sustainability of the vessel.

Maritime Inspection

HIMP Program and ABS Certification

The Hull Inspection and Maintenance Program (HIMP) has been developed for ABS classed vessels, vessels given formal certification by American Bureau of Shipping (ABS) to remain certified and safe. In order to enroll in this program, the vessel must be ABS certified, there must be an ABS certified inspector of the hull and the HIMP software must be installed on the vessel's computer (s)(ABS 2015). All previous documentation for the vessel is to be submitted and reviewed by the ABS surveyor.

All inspections, above board and below the surface, are to be completed by the ABS certified inspector from the vessel's company with a ABS employed surveyor in attendance. The surveyor's responsibility is to ensure that all visuals of the vessel's hull, motors, ballast tanks and maintenance equipment are in operating condition. If an area is suspected of needing repair, the vessel can be placed on temporary suspension without losing certification, while a repair is made and reassessed by the inspector and surveyor once again.

The inspections occur annually, with additional focuses in three and five year time periods. These are referred to as Annual, Intermediate and 5 Year Inspection Intervals.

Annual Inspection

The areas of a vessel that must be examined and reported for the surveyor annually are:

  • Any suspect or critical structural locations identified
  • Deck area
  • Structural/Coating Condition of all Ballast Tanks (Including Cargo Tanks, Peak Tanks, etc.)
  • Hatch Covers and Access Hatches with Closing Appliances
  • Deck Equipment, Fittings, Helicopter Landing Pads
  • Piping and Supports
  • Superstructures and deckhouses
  • Shell plating above the waterline
  • Cargo holds, tanks and spaces
  • Voids and cofferdams
  • Pipe ducts and tunnels
  • Longitudinal box girders and cross deck box beams
  • Sea connections and overboard discharges

Intermediate Inspections

The areas of a vessel that must be examined and inspected for the surveyor every 3 years are:

  • All Areas included in the Annual Survey List
  • External Shell Plating below the waterline
  • Internal condition of boundary plating, internal bulkheads, framing, girders
  • Internal condition of all tanks containing bilge or oily water

5 Year Inspections

The areas of a vessel that must be examined and inspected for the surveyor every 5 years are:

  • All Areas included in the Annual and Intermediate Survey List
  • All Tanks including Fresh Water Tanks, Fuel Tanks, Diesel Tanks, Lube Oil Tanks, etc.

Deploy a ROV to perform quick, safe and affordable hull inspections

Inspection Checklist

UWILD or underwater inspections in lieu of divers are critical for maintaining vessels safely and efficiently.

The following checklist outlines what submerged areas and components of a vessel should be inspected in an underwater survey of a ship. Operators are looking for defects, scratches, discolourations, dents and any other imperfections. All information should be recorded in an underwater inspection report.


General hull inspection

First and foremost, the general hull of the vessel should be included in the underwater ship inspection. Structural integrity is of the utmost importance - all defects, discolourations, dents, scratches or any other imperfections should be noted. Sonar add ons also allow operators to spot any small cracks that may not be otherwise visible.


The physical ability of the ship to cut through the water in an efficient manner is imperative for optimal performance and fuel economy. A smooth, well-maintained paint job is a large part of vessel efficiency. ROV inspections not only allow operators to verify the quality of their paint job but provide the team with the information necessary to optimize maintenance schedules.


Hull damage or fouling can not only affect the overall speed and fuel efficiency of a ship, but can also be harmful to the crew, cargo, and has the potential to negatively impact surrounding marine life. Regular ROV inspections allow for the effective monitoring of this growth to determine the best time for a full cleaning.

Hatch covers

The primary objective of hatch covers is to keep water out of the cargo hold and protect cargo from being damaged. Furthermore, hatch covers also act as a barrier to the ocean waters that can damage the internal structure of a ship through corrosion. The covers should be thoroughly inspected for any signs of structural damage.


All ports under the freeboard deck must be checked stringently to ensure watertight integrity. Freeing ports should also be inspected to confirm that there is no corrosion on shutters, pins and hinges to allow for free movement.


Anchors and accompanying chains must be carefully inspected for any sign of wear, damage or weakness. Visual inspection of everything from individual shackles and swivels to the anchor as a whole is imperative for safe operation.


Propellers or props are imperative for safe and effective vessel operation. There are 4 main aspects of props that need to be examined;


ROV pilots should check for any dings, dents or bends in the blades to make sure that the ship can be safely operated.


Prop shafts must be inspected for structural integrity and straightness. Any bends or wobbles in the shaft can create unsteadiness.


Propellor hubs are designed to prevent damage to the rest of the drivetrain by giving way if the prop strikes an object. Hubs need to be consistently inspected to confirm their strength and effectiveness.


Shaft seals need to be carefully inspected to ensure proper working conditions. Damage in the seals can result in improper prop function.

Stearn Bearings

It is important to check that the seal assembly remains intact on any oil-lubricated bearings, as well as verify that the clearance or wear down is within limits on the bearing. Oil-lubricated bearings should include accurate oil-loss records and a check for contamination from sea water. Wood and rubber bearings can be inspected through an opening in the top of the rope guard and a suitable gauge or wedge should be sufficient for clearance inspection.

Rudder Bearings

Condition and clearance of the rudder bearings are important to inspect. More specifically, ensuring that all parts of the pintle and gudgeon assemblies are intact and secure. When access to these structures is deemed impractical, clearance verification can be foregone if the Surveyor is satisfied with the physical condition and securing arrangements of the pintle. The operating history and onboard testing will also be considered before foregoing any structural inspection such as the rudders.

Sea Suctions and Valves

Sea suction openings must be clear and are in good condition. Sea valves and their attachment to sea chests to be examined externally, including expansion pieces in sea water cooling and circulating systems.

Shell plating

This is the majority of the surface area that is to be inspected, though most problems arise underwater wherever a seal is made or where two surfaces join together. The general procedure of inspecting the plating begins with an examination of the plating above the waterline, as well as other exposed portions of appendages (propeller, rudder and rudder bearings). The next step is to follow these portions under the water line.

This is the point where the surveyor does not have direct visualization of the plating and submerged structures. The only way that this inspection is approved is if there is two way communication from the inspector to the surveyor and all parts of the inspection are recorded. The time at which the diver or ROV inspection commences to the end of the inspection must be documented.

Why are UWILD Inspections Useful?

Dry docking is a complicated, expensive, and very time-consuming process. It involves taking the vessel to a designated facility, having it lifted from the water to allow access to the parts of the ship that are typically submerged underwater, and placed in the dry dock for maintenance, repairs, inspections, and other related activities. This process can range from a few days, to several weeks, or even months, depending on the scope of maintenance and repairs required.

Once out of the water, keel blocks are set into position, and lines are used to support the boat. This transition from the water to setting the vessel on the blocks is the most dangerous part of the process. If not supported properly, the vessel can tip, potentially causing extensive and costly damage, and even injury to workers.

Prior to dry docking, the ship must also be prepared by the crew, which involves removing equipment, cargo, and stores to reduce weight and ensure the safety of personnel and the ship during the process.

Once maintenance and repairs are completed, the ship must go through testing and certification to ensure compliance with safety regulations and class society requirements. This can involve sea trials, testing of equipment, and certification checks.

The frequency in which dry docking is required depends largely on the type of vessel, its operational profile, and regulatory requirements. For commercial vessels, such as container ships, bulk carriers, and oil tankers, dry docking is performed approximately every 2 to 5 years, depending on the ship's age, its trading patterns, and the classification society's rules.

For naval vessels, such as warships and submarines, dry docking is scheduled for maintenance, repairs, and equipment upgrades every 5 to 10 years, depending on the navy and the specific vessel class, but can be more frequent if the vessel has sustained damage or requires extensive modifications.

For pleasure crafts such as small recreational boats and yachts, dry docking is typically performed every 3 to 7 years.

Though the inspections are of the entire vessel, the tricky part for owners is the inspection of the hull and the interior of the liquid filled tanks because they are submerged. The hull of the ship is crucial to maintain to get the longest life cycle out of the ship. However, inspecting said hull is difficult. In the past, dry-docking has been performed to ensure thorough inspection of the hull. This process is extremely time consuming and expensive to perform.

Classification societies then began allowing Underwater Inspections in lieu of Dry Docking (UWILD). These UWILDs are the most scrutinized by the surveyor because the inspector is the only one with direct access to the hull in these situations. These have been performed by ABS certified divers traditionally. This method is still costly and places humans under the hull of a ship with no direct access out of the water. This is a dangerous scenario and is avoidable with the use of a ROV.

Underwater Inspection in Lieu of Dry-Docking (UWILD) with ROVs

ROVs or remotely operated vehicles provide operators with a safe, convenient, cost-effective and efficient way of conducting regular inspections.

Operated via a handheld LCD screen controller, Deep Trekker ROVs empower users to take control of their underwater assets. Quick to deploy and battery operated, Deep Trekker vehicles allow for quick, easy and accurate UWILD operations. By using an ROV, human divers do not have to enter dangerous waters to conduct a routine inspection. Furthermore, the straightforward operation of Deep Trekker vehicles requires minimal personnel to get the job done quickly - allowing teams to save time and money.

SAAM Towage cover

The modular design of Deep Trekker ROVs allow users to conveniently add tools for enhancing inspections.Sonar options provide clear pictures for accurate inspections regardless of water turbidity. Using the Cygnus thickness gauge integration, operators can evaluate the thickness of ship hull’s and compartments to determine structural integrity. Finally, the laser scaler adds value by helping users estimate the size of any cracks, dents or defects.

Yearly inspections of the entire vessel, including the hull and prop are a key part of the passing or failing of necessary surveys. This process has in the past meant a full dry dock of the vessel or an UWILD (Underwater Inspection in Lieu of Drydocking) - both expensive and time consuming options. To assist in this costly and regulated process, surveyors may accept historical time stamped data, like that created by Deep Trekker ROVs, as part of the evaluation process.

The other "forgotten" advantage of having a ROV on staff instead of hiring a diver to perform the inspection is that you are able to have a inspection rehearsal or a quick inspection before the official, supervised one. The advantage of this is that if a problem is found or a possible area of contention with the surveyor, a solution could be implemented beforehand without having to pay for a diver twice. If a problem is not found until the surveyor is in attendance, this could result in a classification suspension or removal, which costs the vessels' owner tremendous amounts of money and time to get their unit back up and running.

As always, our team of experts is here to answer any questions you may have. If you’re ready to take the leap and get a vehicle of your own you can get your own customized quote today.

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