Hull Exams

As a Port Engineer, one of the bigger tasks during a vessels scheduled repair period is the hull exam. Depending on the regulatory or internal company requirements, a hull exam is typically done at least once every 5 years, if not twice in a 5 year period. Why do we do this? It may be fairly obvious why you would want to inspect your hull, one is to find and repair damage, the other is to identify any areas of corrosion that needs to be treated.

But what “has-to” be done versus “should-be” done? This can be a subjective area that is usually determined by experience of the Port Engineer, although some common procedures will help guide the novice through what can be, a very expensive maintenance period.

Most vessels must comply with some form of regulatory maintenance cycles as defined by the likes of the U.S. Coast Guard Certificate of Inspection, Loadline or Classification requirements. Other vessels have internal requirements as set forth by programs like the American Waterway Operators Responsible Carrier Program. In the coming years, all tugs over 26’ in length will become ‘inspected’ vessels per 46CFR, Subchapter M. This means that as part of the scheduled maintenance program for each vessel, along with machinery and drydock activities, a hull exam must be accomplished to ensure the tugs structural integrity is acceptable to continue to operate. A hull exam generally consists of an external exam, an internal exam and ultrasonic gaugings.

External Exams

External exams are just that, a visual examination of the hull, typically done while the vessel is out of the water.Sometimes the external exam is done while the tug is in the water, called an Underwater Inspection in Lieu of Drydocking (UWILD). Normally a UWILD is an acceptable form of externally examining the hull for the interim exam, although the vessel must be drydocked a minimum of once per 5 year period regardless.

During an external exam, the hull is inspected for any visible signs of damage, cracks, holes, scrapes, etc. that can be seen. Regulatory inspectors such as from the USCG or surveyors from the American Bureau of Shipping are typically concerned about the integrity of what’s called the ‘envelope’ of the vessel. This is basically the external surfaces that allow a vessel to stay afloat. Any damage seen externally is typically a prelude to damage that will be found internally, and these cursory inspections key in to suspect areas of concern.

Sea chests and other through hull openings are also examined at this time, again to ensure that the integrity of the hull or envelope is acceptable.

Propellers and shafts, sometimes called running gear, and rudders, thrusters, etc. are also examined during the external exam. Much more detail regarding these inspections will be discussed in forthcoming articles.

Inspectors or surveyors are typically not overly concerned with the underwater hull coatings, only to say that if visible corrosion is found due to lack of or improper application of hull coatings, it is a prelude to potentially other areas of concern. Hull coatings are generally left to the vessel owner to manage, a Port Engineer should rely on his paint manufacturer’s representative to inspect the coatings system and recommend action. More on this topic later.

Internal Exams

Internal exams are also visual examinations of the hull, of course from the inside, and includes inspection of the structural framing adjacent to the hull plating. Most internal exams are considered very labor intensive, as it requires opening up tanks, voids and other spaces not normally accessible. In all internal exams, spaces such as the forepeak, chain locker, engineroom and lazarette (or steering compartment) are entered and visually inspected. Other areas such as ballast tanks or fuel tanks are inspected based on other factors such as the vessel’s age, damage, or if an inspector or surveyor deems these areas to be suspect.

The internal exam is typically where repair items are found, and must be dealt with to the satisfaction of the inspector or surveyor. The internal framing to include longitudinal and transverse frames, gussets and bulkheads are inspected along with the hull plating. Damaged or tripped frames are an indicator of contact damage. Depending on the severity of the damage, these frames must be cropped (cut out) and renewed (replaced). A certain amount of deflection or bend is allowed in the hull plating before needing to be cropped and renewed, though any found damage should be thoroughly examined to verify the extent of the damage.

Corrosion of internal areas is probably the most frequent reason for steel repairs following an internal exam. Framing around access hatches, aft bulkheads of forward compartments and forward bulkheads of aft compartments are normal suspect areas where corrosion is found. Chain lockers and steering compartments are notorious for finding corroded steel, although more and more of the newer tugs are being constructed with coated internal spaces, as owners are seeing the long term benefit of investing in this preventive measure which significantly prolongs the life of a vessel.

Steel repairs are considered more art than science, as experience plays a large role in defining what steel needs to be cropped and renewed. Visible damage or corrosion may be obvious, but understanding how much or long a piece to replace, as well as the location of the repair, i.e. adjacent to a seam, takes a good understanding of the properties of steel, rules from regulatory bodies, as well as good marine practice, all of which are typically acquired through experience.

Ultrasonic Gauging

The science part of hull exams come from performing ultrasonic gauging of the vessel’s hull. Ultrasonic gauging, or UT exams are often employed during hull exams as a way to verify the thickness of the hull steel relative to its original thickness. Port Engineers will normally contract this service out to a certified UT vendor who will conduct a thorough survey using specialized equipment. The gaugers are asked to check and document the steel thickness throughout a vessel, particularly along the waterline and across the vessel’s girth belts. For those unfamiliar with this term, a girth belt is the transverse cross section of a boat including the adjacent internal framing. Depending on the age of the vessel, more girth belts are required to be gauged to represent the overall condition of the hull. Gaugers may also be asked to gauge suspect areas for signs of corrosion, such as lower bulkheads in void compartments or bilge ecology spaces.

Port Engineers employ UT gaugers to help in defining the size and scope of steel repairs needing to be accomplished. Gaugers can essentially ‘paint a picture’ of the corroded steel that cannot be seen visually. This is extremely helpful prior to starting any repairs, as there’s nothing worse than continuously cropping out ‘bad’ steel blindly until you get to ‘good’ steel.

One important thing to keep in mind during any steel repairs involving regulatory bodies must be inspected throughout the repair process. This means that the inspector or surveyor must approve the ‘fit-up’ of the new steel (such as needed for plate replacement), prior to production welding. Then, upon completion of the production welding, will inspect and must witness a test to ensure the repair’s watertight integrity. Not to mention, the new steel being used, as well as the welders performing the repair must be certified and verified by the inspector or surveyor. Better to know these kinds of details beforehand, I have seen inspectors make a vessel owner jump through extraordinary hoops to prove that the repair was acceptable.

Lessons Learned

Which leads to lessons learned when dealing with hull exams. While experience is the ultimate learning methodology, a few simple guidelines will ensure that your next hull exam is a successful one.

  1. Prepare. As a good practice, it is always beneficial to prepare as much as possible for the hull exam. Granted, this is only part of the large amount of tasks needing to be managed during a vessel’s downtime, but can also be the most costly in terms of expense and time out of service.

If at all possible, a preliminary survey of the hull should be accomplished prior to the full regulatory inspection or survey. This is critically important not only to identify the size and scope of repairs in advance, but to demonstrate to the inspectors that you are proactively managing the maintenance of the vessel, and finding repairs ahead of time to be dealt with. This goes a long way with most inspectors, where they tend to be a bit more lenient for the balance of the inspection/survey. Use a spray paint or chalk to mark out the steel that you’ve identified as needing to be renewed, and document these findings in a typed report to hand to the inspector upon his arrival.

  1. Be open and honest. This is a general good rule to follow in any instance, but in this case it truly does make things easier in the long run. Attempts to hide needed repairs will always come to haunt you. The old saying applies here: “it is what it is…” so you might as well have a full and complete scope of repairs identified, rather than get caught 4 weeks into the maintenance period and have a whole bunch of additional found repairs that not only delay the vessel from getting back into service, but put you way over the originally projected budget. As a Port Engineer, your professional credibility is at stake should you underestimate the scope of work, and, in my experience, these are often extremely costly mistakes.

  1. Continually Learn. As I’ve stated before, there’s nothing like experience to be the greatest teacher. Unfortunately, we tend to learn the most from bad experiences, and while this may be inevitable, it is critical to understand how mistakes were made and prevent them from occurring again. Hull exams, steel repairs, drydockings, machinery maintenance are all integral to the job of being a Port Engineer. Ask questions, clarify your understanding of the rules and regulations with the inspector or surveyor. Try to get involved in as many maintenance events as possible. Over time, you can acquire the skills and knowledge that will allow you to become a master at the art of Port Engineering.

Should you be looking to take on a project and don’t know where to start, contact us at or call 425.686.8209.

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