Detailed Hull Inspection with MicroROVs

When a hull inspection -- such as the two every five years of the outer hull of all sea going vessels required by the American Bureau of Shipping (ABS) -- is needed, the answer is normally an expensive dry dock trip. One of these two inspections can be carried out underwater while the vessel is afloat. Divers can often accomplish the task, but thoroughness and detailed recordkeeping and speed due to an increasing number of ships that need to be inspected is creating new issues. This talk will show how a detailed video record from a low-cost ROV can provide a record of the condition of an entire hull, including all intakes, thrusters, running gear, sea chest, etc. Also discussed will be the list of equipment used, and the conditions that are required.

Before I begin my discussion on Hull Inspection techniques, I think it is important to establish my background and experience. Until I retired in December of 2005, I was the Hazardous Duty Robotic Specialist at NASA Kennedy Space Center. I have been diving for over 40 years, with a concentration on underwater photography/investigation, and have been doing underwater ROV inspections since 2000. To date I have done over 100 different ROV inspection missions. The types of projects include:

•Storage Tank inspections (potable water, rocket fuel)
•Contraband inspections for customs
•Boat fire investigation
•Culvert and Pipeline
•Aquifer
•Dam
•Hull and Pier Inspection
•Offshore Oil Rig Inspection
•Offshore Gas Production Tripod installation
•Many others …

There are many reasons to inspect a hull, and the first thing to establish before planning a hull inspection is the reason(s) for the inspection. You might want to check for structural problems, establish the condition of coating or the running gear. Often it is necessary to check intakes and outflows to insure they are working properly. Most often, however, inspections are required by codes and laws. The American Bureau of Shipping (ABS) & US Coast Guard (USCG) are responsible for vessel inspections under 46 CFR Subpart 71.15, and require two hull inspections every five years. ROVs can be used for Underwater In Lieu of Drydocking (UWILD) surveys, which can take the place of one of the drydock inspections under this requirement.

After the reasons and regulations for a detailed hull inspection have been determined, the next step is to establish whether and how to use an ROV for the inspection. This paper will concentrate on the use of a VideoRay ROV for the task. In order to do this, water and environmental conditions must be established for the inspection. Of course, the inspector will want to find the clearest water and the least current possible for the inspection. When I recently did an inspection of an Offshore Supply Vessel (OSV) for Edison Chouest out of Port Fourchorn, LA, the vessel was moved about 30 miles offshore where the water clarity was very good. ABS regulations in subpart 71.15 establish that at least 80% of the hull be inspected by any alternate means used, this includes 100% of all intakes, outflows and running gear, which the VideoRay under my operation can easily accomplish. Using reference navigation -- that is, measuring visually through the camera image relative distance from a known location to any particular feature that required documentation, I could establish where on the ship the ROV was located and the location of any problem areas.

When considering an ROV for UWILD surveys as opposed to human divers, several factors should be considered -- most of which favor ROVs. Diving with an ROV does not require tagouts of intakes and outflows, nor does it require anywhere near as stringent safety regulations. VideoRays don’t have exposure or other physiological constraints -- they can dive in water of any quality or temperature -- at any depth encountered in hull inspection -- for any amount of time required and in sea state conditions that would preclude divers. In most cases the number of people required for the inspection is much lower. About the only disadvantages is the lack of tactile feedback, and the requirement of a tether that might not be used in the rare case where the diver was using SCUBA.

A few characteristics of the VideoRay equipment I use on hull inspections are important to this task. The VideoRay is very portable -- I check them as airline luggage on almost all my missions, and in the last 50 or so missions I have paid excess luggage fees only once -- despite the lower luggage allotments that have been established by the airlines in the last few years. The VideoRay is easily deployed from any vessel that is designed for more than one person -- the weight of the entire system is generally less than 70 pounds. VideoRays along with video capture devices -- typically laptop computers -- draw less than 500 watts maximum and average 100 watts of electrical power. This means they can be powered by the smallest generators or a tiny inverter and a single 12 volt battery. Nonetheless, the VideoRay has what I believe is the best current handling and tether dragging capabilities in it’s class, with the new “GTO” (Greater Thrust Option) thrusters and VideoRay’s “performance” tether, which is .38 inches in diameter.

Another benefit of the VideoRay equipment is the low weight and size of the submersible. Since it only weighs about 8 pounds in air, it is very difficult for it to injure or affect a ship’s hull or running gear. Since it is so small, it can enter confined spaces through small access hatches -- such as entering a bow or stern thruster tunnel. VideoRays are hydrodynamic in a forward direction only, an important distinction from traditional, larger “open frame” ROVs. However, its wide angle lens on the front camera makes the kind of lateral inspections that are required for hull inspection easy and efficient in a horizontal direction. Inspections in a vertical direction are slower, since the vertical thruster is much slower than the horizontals -- something to take into account when planning the inspection. The camera takes excellent, detailed video -- clients often comment that it is better than other underwater video they’ve seen. The rear camera allows the operator to back out of confined spaces easily, or it can be used for checking the tether if it gets caught on something. VideoRay has an option for a side facing camera, but I don’t see that as beneficial. Some ROVs have lateral thrusters, but in my experience that option -- which isn’t available on the VideoRay -- would be of little use and probably increase drag and decrease the speed and performance of the unit. VideoRay sells a hull inspection positioning system which I have used; this is good if you’re working in very restricted visibility and/or need to verify 100% coverage of the hull, but it is not needed for UWILD inspections in my opinion.

When selecting equipment to use in the harsh offshore environment, it is important to investigate reliability and maintenance techniques. Some of the aspects of the VideoRay design that I appreciate are the ease with which I can inspect the seals on the thrusters for wear. Since the seal cartridges are exposed for inspection, I can monitor their condition and plan for replacement. When they do need to be replaced, this can be done in a few minutes using only a wrench to remove the props. Similarly, light bulbs are of a common type I can buy at a local hardware store, and the light domes spin off without tools. Main camera domes are a bit harder to replace, but no big deal as long as you know how to keep the O-ring seals clean. All of the tools and spare parts you’ll commonly need come with the unit.

After you have established that the inspection can be done in conditions which are within the capability range of the equipment and the operator, you need to agree with the owner and/or the regulatory agency inspectors on coverage, coverage verification, level of detail, deliverable media (videotape, DVD, still pictures, etc.), and analysis if any. When these parameters are established, the inspection is scheduled and planned. As mentioned above, the location for the inspection should have water visibility as good as possible and current as low as possible. Often this means the ship is drifting offshore, in which case relative current is nill but wind can be a factor. To minimize the effect of wind on floating tether or the submersible on the surface, you can operate on the lee side of the vessel, turning it 180 degrees in the middle of the inspection if necessary

I often find I can inspect a 240 foot ship deploying the VideoRay only two times and operating from only one location. However, the operating location needs to be one where the operator is comfortable -- a chair and table are easily arranged in most cases when operating on a vessel so long as this is worked in advance. If operating off of the deck, protection from rain, wind, and especially sun is important. VideoRay provides a small, lightweight sunshade for their control box which I have found effective. If the tether operator is not within earshot, some kind of handheld radio is critical.

A general outline of the process of hull inspection with a VideoRay:

•Enter water at amidships
•Follow hull to bow just below waterline
•Continue along bottom of hull from bow to stern
•Overall observation of hull condition
•Check key areas such as bow thruster, sea chest & keel coolers, etc.
•Close observation of running gear
•Re-look any areas inspectors requests

In conclusion, VideoRays can perform in-water hull inspections to ABS/USCG standards. In my experience, they are faster than human divers, given setup time and the fact that a tag-out is not needed. This kind of inspection allows for immediate feedback from vessel owners/engineers & inspectors. A major advantage to using an ROV for the U/W survey is the 60 month hull credit inspection versus the 36 month hull credit inspection possible using divers.