Case Study
The latest Flyability Elios 3 mounted with Cygnus manual ultrasonic precision thickness meter.
Hull inspections with a UAV offer huge safety, cost and efficiency benefits versus incumbent techniques.
Virtually all commercial maritime vessels must follow IACS rules in order to maintain their vessel class rating and operate. The older a ship is, the more frequent and intensive the inspections become – a major survey is required every 5 years from initial launch with major surveys taking place every 30 months after a ship is over 10 years old. These surveys are a regulatory requirement, critical to the ship being certified as safe to operate. For a Suezmax size vessel over 10 years old the total cost of the maintenance and survey carried out in the shipyard can be $4 to $6 million dollars.
As part of this process, the ship’s hull must be inspected with ultrasonic thickness (UT) measurements to ensure it is structurally sound, as well as visual inspections of target areas. This is focused on the midship area which is under the most pressure when the ship is at sea. These inspections are vital for identifying faults that may not be visible to the human eye or hidden within the ship’s structure. A combination of ultrasonic thickness measurements (UTM) and visual surveys ensures the inspectors can be confident in their results and that the ship inspection is completed according to industry standards.
Ultrasonic A-Scan
Elios 3 with Cygnus meter payload
The process for accessing UT inspection points and taking measurements typically requires many hours of work. For a large cargo oil tank a scaffolding crew as big as 20 people would be required to enter the space and erect scaffolding before a UT inspector can climb the structure and take UT measurements. The scaffolding has an inherent risk for inspectors due to working high up and poses an additional danger to the ship; if a piece is accidentally left behind, it can get sucked into the tank’s pump and break it, which would require the ship to be drydocked for repairs.
A large team of scaffolders will take several days to erect a scaffolding tower like this. Cost of scaffold can run into hundreds of thousands of pounds across the entire vessel.
The inspection process for Cargo tanks within the ship would usually take several days and require special permits for the work at height or in confined spaces. In addition, the ship must be in drydock during the inspection. As drydock is charged by the day, the associated costs with a slower inspection method are much higher. Faster survey methods, such as using a UAV or ROV, present an attractive alternative while still gathering critical data.
Instead of relying on traditional labour-intensive methods, C-Bird used the UT probe with their 2 Elios drones to complete the inspection of the 12 oil tanks. They completed the inspections with the guidance of a class inspector who provided information about what needed to be tested. This drone-based inspection method was much faster than the typical scaffolding approach; once the equipment is onboard the ship, the UT inspection can begin immediately – a huge saving compared to the thousands of hours associated with scaffolding.
C-Bird flew the Elios 3 UT drone around each tank and took measurements in several locations as required by the inspection plan and any additional areas that the class surveyor requested. The UT inspections and visual inspections were both completed within 7 days. At the end of the flights, the pilots cross-checked with the class inspector that the Elios 3’s spot measurements matched the required number and location of measurement points.
The Elios 3 streamlined the visual inspections necessary for this process. The drone enabled the pilots to gather both visual and UT data during the flights, providing a close-up view of the areas being surveyed at the required distance. This made it possible for C-Bird to get the information they needed twice as fast by having one drone focused on visual inspections and the other measuring UT points. This provided results that included a clear visual display of the points of interest and UT spot measurements.
The C-bird team then compiled the data into the format required by the class society and submitted the inspection for review. This was significantly quicker than traditional methods as all the data collection was completed in one go, rather than having to move around scaffolding/adjust a mobile elevation work platform (MEWP).
Following a 2-year program of successful pilot projects, C-Bird and the results they produced using a UAV were certified by the American Bureau of Shipping, one of the top 3 classification societies in the world, as approved recognised service supplier for ESP hull gauging (Enhanced Survey Program). This recognition was the first of its kind, highlighting the value of C-Bird’s achievements with this type of UAV inspection.
Ultrasonic thickness gauging by unmanned aerial vehicle (UAV) include: