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Although drones with multiple propellers on the same plane are currently the most widespread design, research is taking place into alternative arrangements with tilt rotors and propellers in a tetrahedral configuration. Meanwhile, significant progress has been seen in autonomous operations using higher precision positioning, and considerable advances in machine image recognition and processing.


Typically equipped with a compact camera for photography or recording video and Wi-Fi for data transmission, these easy-to-control, lightweight machines have rapidly grown in popularity. Apart from the consumer hobbyist market, and use for product delivery by online retailers, drones have attracted interest from across industry: they are ideal for collecting images from high or otherwise inaccessible or dangerous locations. They can be utilized for a range of aerial photography, inspections and surveying, and security applications, and have proved invaluable in planning rescues and emergency response.


In the maritime industry, efforts are underway to use drones for inspections and surveys. In fact, discussions on Remote Inspection Techniques (RIT) are already well- advanced at the International Association of Classification Societies (IACS), which published revised guidelines on remote inspection techniques in June 2016. The revisions of the associated IACS Unified Requirements are complete and will take effect in January 2019.


Deploying drones on ships presents some significant challenges. The drone may not function properly in the cargo hold or ballast tank due to being in an enclosed space surrounded by magnetic material which may interfere with some of its sensors – particularly GPS and magnetic compass – that are tightly linked to flight stability. Dark environments can also make it difficult for operators to fly drones safely.


Last September, ClassNK designated ‘survey technology innovation’ as one of four focus areas listed in its new R&D Roadmap, with drones identified as a key technology. The society has been verifying drone performance, with test flights conducted in a variety of enclosed spaces of the sort found on ships.


ASSESSING BASIC PERFORMANCE


A basic performance verification test was devised to demonstrate maneuvering (take-off and landing, forward/reverse and lateral flight, reverse flight with 180-degree yaw) and to assess the capabilities of camera and sensors. The camera performance was tested with a Landolt ring chart – the kind of chart opticians use to test eyes – to evaluate definition of different line thicknesses from 0.1mm to 5mm, and a QR code. Differences in results were observed when the subject drone, a Phantom 3 Standard from DJI, was operating with and without GPS signal. Maneuverability tests in the vicinity of a powered-off crane to assess antimagnetic performance were also carried out.


The outdoor maneuvering test took place in windy conditions, which significantly influenced the results. While fixed-point hovering was easier when using GPS, the gain was large causing the drone to over-compensate in its movements. In non-GPS mode, the gain was small and smooth maneuvering was possible, but wind-thrust had a more marked effect on the drone.


In GPS mode, the drone immediately begins hovering when the operator removes his finger from the controller, whereas in non-GPS mode, inertial force continues to move it until a counter input is given. Consequently, non- GPS mode gives a manual feel to maneuvering and it is possible that operators will find the drone easier to control. When the wind subsided in the trial, stable flight was possible regardless of GPS availability.


The Report • March 2019 • Issue 87 | 33


Indoors with no wind, stable flight was possible both with and without GPS. Since these results were obtained with a low-cost drone, it is conceivable that higher-end drones equipped with ultrasonic sensors and other advanced features will be even more stable.


Many images photographed with the camera were extremely clear. However, because this model lacked an optical zoom, enlarged images were often indistinct. Image sharpness distinctly improved when the drone was flown closer in to its target. In survey applications, optical zoom would be an essential requirement. Camera specification and artificial lighting will also need to be considered if photography in dark environments is deemed necessary.


The tests in the material storage yard with a crane threw up some interesting results. The drone initially failed to take-off, with the system displaying a ‘compass abnormality’ error message. However, when launched from a more magnetically benign location, the drone was able to approach the crane without the issue. This suggests performance in the presence of magnetic structures must be carefully evaluated before a drone is deployed to carry out inspection work.


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