Casting for data in the open ocean
ABB’s ACS880 drive brings safety and precision to essential marine research
Since 1988, about once a month, a research vessel arrives at a spot in the Pacific Ocean known as Station ALOHA about 60 miles north of the island of Oahu. There, specialized equipment takes water samples and various measurements that become part of one of the longest-running oceanographic studies in the world.
For the last 18 years, this has been the job of the Kilo Moana, a 60-meter research vessel owned by the US Navy and operated by the University of Hawai‘i Marine Center. The ship enables scientists to conduct tests that increase their understanding of the effect of deep ocean currents on marine life and climate change.
One of the key activities for the Kilo Moana when it arrives at Station ALOHA is to carry out conductivity, temperature and dissolved oxygen (CTD) ‘casts’ at depths of up to 5,000 meters. These are conducted using an assembly of sensors along with 24 bottles that collect water samples at various depths.
Altogether, the CTD package weighs in at just under a ton (900kg) and is lowered into the water using a launch and recovery system (LARS) equipped with a crane and powerful winch. Not only must it safely lower the package into the water and back out again, it must keep the instruments at a fixed location relative to the sea floor even as the ship pitches up and down.
In 2019, the UH Marine Center decided to upgrade the LARS to a new design with active heave compensation (AHC). Hawboldt Industries installed an ABB winch drive with unique inbuilt (AHC) software that takes information on wave action from the vessel’s motion reference unit (MRU) and adjusts the winch motors to compensate. The precise adjustments – made hundreds of times per second – keep the package steady even in 15ft waves.
“A winch drive is an integral element in our equipment and the ABB ACS880 drive is unique because it comes with AHC functionality built in as firmware,” says Dylan Wells, General Manager of Hawboldt Industries. “Therefore, we didn’t need to change the system architecture or deal with the cost and complexity of installing an external, third-party AHC control system. With the ABB drive all we needed to do was to connect it to the MRU and switch it on.”
The AHC reduces CTD cast times on the Kilo Moana by around 30 percent and keeps more consistent cable tension, thereby eliminating slack conditions and tension spikes, which can result in major damage requiring replacement of the long cable.
“Taking CTD samples is a primary element for the Kilo Moana with a cost of around $50,000 to run each day at sea,” says Scott Ferguson, University of Hawai‘i Director for Marine Technical Service. “If we can’t work because the sea is too rough, then we face a major loss of revenue. The advantage of our new crane with AHC is that it enables CTD casting to be carried out with safety and precision even when waves are 4 meters high. That’s why our scientists love it, and our deck crew appreciates it because of its reliability and ease of operation.”
The Kilo Moana spends between 200 to 250 days at sea with operations from a few days up to a month. The addition of the ABB winch drive will ensure the ship makes the best use of its time at Station ALOHA and elsewhere, allowing scientists to continue their vital research.