The DVL is part of a package of navigational aids, which Walter Caharija describes as a “sensor fusion”. Ultra-short baseline acoustic positioning (USBL), compass readings, a laser system and the on-board camera all contribute location data. But, in terms of maintaining distance from the cage net, it is the DVL that does the work.
Development in-house makes the DVL “very reliable” for ROVs used in aquaculture
Caharija says the Nortek DVL has done the job well. The team used laser measurements to verify those from the DVL and they confirmed its accuracy.
“We’ve been satisfied with the instrument’s performance. In the early tests we got it to lock on to the net to provide distance and velocity measurement without any major problems, helped by hints from Nortek, and it has proven to be very reliable in measuring distance from the net,” he says.
He is also happy with the level of support provided by Nortek. “Nortek was very helpful in setting up the DVL. We have had good communication with the Nortek team in Oslo, and now in their new Trondheim office. I definitely hope to keep on developing this relationship with future projects,” he says. “Nortek is one of the most innovative companies when it comes to subsea technology, especially the DVL. They do a lot of development in-house that makes the instruments very reliable,” he adds.
Testing an aquaculture ROV in deeper, rougher waters
Artifex and its successor projects are part of a drive with much wider ambitions. They could pave the way for completely unmanned fish farms, with monitoring and repair controlled remotely by personnel based on land, and repairs carried out by ROVs, rather than divers, as is the case now.
The Artifex team also aims to fit the ROV with a robotic arm to carry out net repairs, while the project partners are developing an unmanned surface vessel (USV) to which an ROV could be tethered, along with a drone to assist inspections.
Moving fish farms further offshore is a growing trend as farmers seek to meet growing global demand for fish. So the next step for the researchers is to move away from the relative calm of near-shore fish farms to test the ROV in deeper, rougher waters.