by Vaughn Entwistle, Managing Editor, International Aquafeed

 

A few years back, I was attending an aquaculture show when I first saw the Electric Subsea Thruster as produced by Danish company Copenhagen Subsea A/S. Unlike typical propellers, this clever design used a ducted, rim-driven impeller.

The design has many advantages. The thruster contains only one moving part: the durable composite rotor. No mechanical parts touch, which reduces the risk of entanglement. The thrusters are very compact and use no internal gearbox, dramatically reducing the need for maintenance. The thrusters use seawater for both lubrication and cooling and are very powerful, while their design makes them very quiet in operation, which is a huge bonus for aquaculture operations where noise greatly stresses fish.

The revolutionary thrusters are currently being used in Remotely Operated Vehicles (ROVs), Autonomous Underwater Vehicles (AUVs) and in manned submersible vehicles.

Pushing cold water to the surface

Now, the company's thrusters are being used in novel new way for aquaculture applications. Instead of propelling a vehicle through the water, the thrusters are being used as highly efficient pumps, which remain fixed in position while propelling a high volume of water.

By creating a flow of water from 30-40 metres of water depth to the surface, the cool, oxygen-rich, and lice-free water will help push any sea lice-contaminated water out of the fish farm.

Pushing warm water to the surface

Similarly, during the winter season, the pumps can help keep fish farms free of ice by providing a constant flow of 'warm' water to the surface, as water at only two-to-three metres depth is warm enough to keep the water's surface free of ice.

Creating horizontal water flow through the fish farm

The pumps can be also used to create a horizontal water flow through the fish cage, which allows fish to exercise in the flow. Moreover, by creating flow in only one part of the fish cage, fish are able to choose when they want to play in the stream and when they want to rest in still water. This not only increases the quality of life for the fish, but also benefits the overall health of fish.

Unique flow capacity

The unique high flow capacity of the thrusters is visualised in the following images (See images 3 and 4). The flow of water through and behind the thruster is visualised of Copenhagen Subsea's two largest models of thruster running at maximum RPM. The changing colouring show the water velocity throughout the water stream.

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