Damen builds aquaculture support vessel for Norwegian fish farms
Source: Maritime Holland
Author: Bruno Bouckaert
Damen Shipyard Group’s first dedicated newbuild for the aquaculture business started with a small booth on the Aquanor trade fair back in 2013. The group had some concepts it wanted to present, but noted that several of its vessels were actually already in use in the aquaculture industry. Damen’s Multi Cat self-propelled pontoons and standalone pontoons have previously been fitted out for assistance to fish farms, such as delousing.
The aquaculture industry, which is predicted to turn over 200 billion dollars by 2020, was – as it still is – firmly dominated by the Norwegians. Inspired by the potential of this market, Damen set out on an extensive market consultation over the following years, talking with vessel owners and operators to understand their specific needs.
Product Director for Workboats at Damen Lodewijk van Os explains: “When an existing Norwegian customer of Damen Shipyards, Remøy Management, decided to establish a daughter company, Volt Service A.S., to enter the aquaculture business, we proposed a new no-frills concept, the Damen Utility Vessel 4312. They were so enthusiastic about the design that it eventually led to our first order for a dedicated aquaculture support vessel.”
The main task for the new vessel – named Volt Processor – will be the delousing of fish in fish farms. Sea lice are parasites that consume the skin, muscle and fat of the fish, making them vulnerable to infections. The appearance of lice on the fish is a recurrent problem in fish farms and has even contributed to a significant decline in wild salmon. Lice plagues also severely impacted the output of fish farms which has declined as a result.
With Norwegian aquaculture responsible for 8 per cent of the country’s exports, the sea lice have become an economic threat. A new regulation in 2017 has forced fish farms to control the lice problem before output can be increased. Various solutions have been proposed for delousing farmed fish. Until recently this was done by using hydrogen peroxide, but the lice have become resistant to this solution and there are environmental concerns regarding this treatment method. Newly proposed solutions include the introduction of lice-eating fish in the pens, letting the fish swim in freshwater for some time aboard a live fish carrier, mechanically brushing each fish, killing each lice with laser guns and pressure washing each fish.
On Volt Processor, the fish are deloused by letting them pass briefly through a basin with seawater heated at a temperature of 34 degrees Celsius, which make the lice release from the fish. The lice is then collected through a special filtration system on board and delivered for animal feed applications. The main task for Damen was to build a vessel with a large unobstructed working deck, comfortable accommodation and good seakeeping.
To reduce stress impact on the fish (stress can cause a percentage of the fish to die), the freeboard of the working deck was kept as low as possible. This reduces the pumping height for the fish, and also makes working over the side easier for the crew. To ensure good seakeeping and avoid green water on deck when passing from one fjord to the other through the North Sea, the bow has a high forecastle, with Damen’s signature vertical bow. As the power was capped to 750 kW to comply with local regulations, Damen optimised the ship to get maximum efficiency and speed with that available power. A very important consideration was that the vessel should be easily adaptable to other tasks, such as buoy laying, diveand ROV support or other offshore oil, gas or wind operations. This versatility gives it operational value through the winter months when fish farming activity stops for a few months, ensures the vessel of a high resale value and gives it a degree of future-proofing.
Volt Processor was built at Damen Shipyards’ head office in Gorinchem
The vessel has three main operational modes. Free sailing, moored alongside the farms and station keeping. As the energy consumption for each mode is very similar (either propulsion power or power for the deck and delousing equipment) the ship design called for a diesel-electric propulsion installation. Electric power (AC) is generated in three diesel generators of 470 ekW each and one of 139 ekW, managed by a power management system. The need for maneuverability and station-keeping with dynamic positioning favored propulsion with azimuthing thrusters, but conventional thrusters have a high space requirement between the ship’s bottom and the deck, due to the size of the electric motor if vertically mounted.
The Volt Processor has limited height in the hull at the location of the thrusters. Submerging the aft part of the hull deeper would make the hull less efficient and reduce the propeller diameter, increasing resistance and making the propulsion less efficient. Alternatively the electric motors can be placed horizontally, but this results in an extra gear and extra installation- and alignment hours. The solution was found in a new type of thrusters from Veth Propulsion, which were specifically developed for ships with limited space in the aft compartment.
Permanent magnet motors
Eric Veth, managing director of Veth Propulsion: “We developed the Veth Integrated L-drive specifically for these applications. Superyachts for example want a beach club or tender garage in the aft, and they are not too pleased with a huge electric motor sticking through the floor in this area. At the same time, the efficiency and maneuverability of a thruster are very desirable.” The company started the new design for this thruster with a clean slate and worked with Visedo (Finland) to integrate a permanent magnet (PM) motor.
The large-diameter PM is more efficient than a smaller diameter asynchronous motor, especially at partial loads, where it maintains its 96-97 per cent efficiency. Because of the permanent magnets, there is less heat loss. To keep the mounting height limited, the flexible coupling is located in a recess in the lower part of the motor and the tooth rim for steering has been brought to the outside. Due to the large diameter, a single bearing is enough to take up the thrust force in all directions, contrary to the upper and lower bearing on conventional thrusters. In all, the inboard mounting height has been reduced to only 410 millimetres for a 500 kW thruster, and the water cooling system for the motor also leads to less need for ventilation and less noise. Having the motor inboard rather than in the propeller hub allows the thruster to be better optimized hydrodynamically. There is only one angled gear in the thruster, reducing the gear losses.
On Volt Processor, the thruster has a single propeller with a nozzle to improve the bollard pull, but the Integrated L-drive is also available with counter-rotating propellers. Volt Processor is the first ship to be launched with the Integrated L-Drive, but two superyachts are also under construction with the system. Following delivery of the thrusters to Damen they were simply hoisted and thereafter bolted into place.
The ship provides a versatile platform, also usable outside aquaculture season
A specific detail is found in the keel of Volt Processor. Two tubes are welded in at an angle, providing space for a camera facing each thruster. This allows the captain to keep an eye on the thrusters when loose lines or nets are nearby. A frame structure has been built around the thrusters out of square tubing to prevent as much as possible anything from being caught in the propellers. Rudder propellers are a new thing to Norwegian aquaculture, and experience will show whether these precautions were necessary. A further advantage of the electric thrusters is that their precise speed control by variable frequency drives and ability to optimally direct thrust reduces the amount of propeller wash compared to straight shaftlines with rudders. The hydraulic oil used in the deck equipment is biodegradable to reduce the effects of a spill on deck.
The bow thruster was also supplied by Veth and is a conventional tunnel thruster, but it’s driven also by a very compact permanent magnet motor. The vessel has a dynamic positioning system of class DP-1 from Norwegian supplier Kongsberg, allowing joystick maneuvering and station-keeping.
The bow thruster is also driven by a compact permanent-magnet motor
To bring the working deck as close to the waterline as possible, the vessel has a substantial amount of ballast water capacity. A ballast water treatment system is installed to prevent the transfer of invasive species, even though the sailing area will be fairly limited when used in delousing activities. As a late add-on, the owner specified an ozone generator which is fitted in the cargo hold.
The ozone gas is injected into freshwater to disinfect the decks and all working equipment which may come into contact with the fish. To reduce the noise on the working deck, the engine room ventilation passes through a well-insulated void space before going upwards to the working deck.
A number of container fittings on deck allow for the easy mounting of all deck equipment at the start of the aquaculture and delousing season. Another advantage of this modular approach is that the vessel can very easily be adapted to new technology for delousing when this becomes available. A lot of development is going on in this segment. The level of integration was deliberately kept low for this reason, with the vessel mainly supplying electric power, hydraulic oil, sea water, fuel oil and compressed air through penetrations on deck.
There is a void between the tanks and the deck, allowing certain things to be welded onto the deck without damage to tank coatings. The deck gear includes four knuckle boom cranes, two on each side, which are used to handle the hoses and the nets of the fishfarms. Sometimes, the fish are deposited in a different pen, or alternatively a pen is divided in two halves with an additional net. The warm water for the delousing basin is heated with a diesel-fired boiler on deck.
The diesel-electric power plant is efficient both for propulsion and pumping loads
The accommodation has the same standard as applied on Damen’s Offshore Supply Vessels. This includes floors with imitation wood, floor heating and a complete stainless-steel galley. The mess room has been placed on the forecastle deck and has large windows offering panoramic views. All working areas are designed for low maintenance costs, including an abundant use of stainless steel on deck.
A rescue boat is stored behind the deckhouse
Volt Processor is a one-off ship, but the platform is so versatile and offers so many possibilities on a small footprint that it could easily become the first of a series. Other operators are eagerly awaiting the feedback from this first ship. Damen is also looking into other segments of the booming aquaculture market, which has spread far from Norway with amongst others Scotland, Peru, Chili and South-East Asia as hotspots. The shipyard group’s portfolio now also includes live fish carriers, which can be conversion projects based on laid-up platform supply vessels. The company is working on a concept to carry out the fish processing offshore rather than onshore, which is now the case. This would help Damen’s clients to reduce the cost of their operations.
Damen has built vessels for fish-related industries for many years, but there are differences between fishing and aquaculture. The developing nature of the aquaculture business means pragmatic solutions are preferred over tradition. The Volt Processor builds upon the experience of Damen with workboats whilst incorporating the latest thinking in aquaculture to help this business grow. In the fish farming business, ‘seeing is believing’, and therefore Damen expects Volt Processor to lead to repeat orders when she’s been in service for a while.