Fishermen's News - The Advocate for the Commercial Fisherman

By Paul Ivy 

Portable RSW Refrigeration System for the F/V Wizard

Wizard SRW

 


Captain Keith Colburn was looking for help with the refrigeration on the F/V Wizard and turned to Teknotherm Refrigeration of Seattle for a solution. The 155-foot Wizard is well known from the Discovery Channel series Deadliest Catch.

Refrigeration is vital on most fishing vessels. The Wizard, like many boats, serves double duty throughout the year. In the summer she serves as a tender, transporting salmon caught by other vessels working for the Trident Seafoods Company. In the fall she turns into a crabber and has one of the best records of any boat working out of Dutch Harbor.

These two very different duties put a unique stress on the ship's refrigeration system. While tending, the Wizard needs an efficient refrigerated seawater (RSW) system, but when crabbing she needs little more than a clear deck for all the crab pots, as the holds are filled with non-refrigerated water. So Keith got together with the engineers at Teknotherm to design a unique refrigeration system: two complete RSW systems inside a cargo shipping container.

Designed for simplicity, the container can simply be lifted onto the deck by a crane and secured. Water, power, and control wiring are hooked up to make it operational. Putting the refrigeration system topside frees up precious space below deck. When the ship changes from fishing to crabbing, the container will be removed, allowing the full deck space for crab pots. The system weighs approximately 26,000 lbs., so removing it from the ship in the fall also saves on fuel.

A new 24-foot cargo container was retrofitted with a man door on the side, lighting, and electrical outlets, as well as various penetrations for water, electrical, and ventilation. A steel I-beam runs the length of the space to support a wheeled trolley for moving heavy equipment inside, because there is no way to use a forklift in the tight quarters. Doors and soft patches (access hatches) allow access to all sides of each piece of equipment for servicing.

The refrigerant will be ammonia. With the increasingly broad bans on so many refrigerants, ammonia will be one of the few left standing several years from now. Because it is an excellent refrigerant, is not ozone-depleting, and does not contribute to global warming, ammonia was an obvious choice. It is more efficient than most other refrigerants, which means a quicker chill-down time. Both ammonia and its matching oil are far less expensive than other options as well. There are sensors that alert operators in the unlikely event of a leak, and a ventilation system to evacuate the container if needed. Since ammonia is lighter than air, as soon as it is sucked outside it will dissipate.

This unit consists of two 85 ton refrigerated seawater systems using Bitzer open-drive screw compressors and 100-HP motors. It uses proprietary TeknoLogic automation and controls for ease of use. As long as the boat has an internet connection, engineers and technicians can see exactly what is going on with every part of the system and diagnose problems from anywhere in the world. Compressor usage, refrigerant flow, liquid levels, water temperature and more can be monitored and adjusted. A touch-screen panel allows for monitoring and control from the bridge; no need to enter the container to perform many routine functions.

These two systems operating together will chill 4,000 cubic feet of seawater from 60°F to 32°F in slightly less than 4 hours. The nominal capacity of each system is more than 85 tons of refrigeration capacity at a suction temperature of 23°F (-5°C). This is determined by the capacity of the compressor for this system. During "pull-down" conditions with entering water temperature of 60°F (15°C) and a suction temperature of 41°F (5°C), this capacity is quite a bit more at 127 tons of refrigeration. Teknotherm's RSW systems are designed to operate fully loaded until the water temperature reaches the set point.

The design is symmetrical. A chiller, condenser, and high-pressure receiver are secured to each side of the container. Oil separators plus compressors and motors are at one end while controls are at the other. The condensers use titanium tubes with water on the tube side. All the equipment is fully piped, meaning all connections are made to the flanged connectors on the exterior.

The finished refrigeration plant includes the two Bitzer/OSKA8551-K screw compressors with100-HP, 3500-RPM motors. Photo by Paul Ivy.

Building this system inside the shipping container was quite a challenge. Although the main pieces of equipment were fabricated in the shop, they had to be assembled inside the container. Tight quarters meant that only a few welders could be inside at one time. As the system came together the space got even tighter. The finished system is an impressive piece of engineering, fabrication, and controls.

One other interesting feature of this powerful system: it produces enough chilled water that Keith can sell the surplus to other, smaller vessels. This helps them preserve their catch better and is another source of revenue for the Wizard.

This flexible refrigeration system is a beautiful solution for the vessel's seasonal refrigeration needs. With the increased value and marketability of properly chilled fish, plus the fuel saving and extra space during crabbing season, as well as the chilled water sales, this system will pay for itself in just a few years.

Paul Ivy is Sales and Marketing Manager for Teknotherm Refrigeration in Seattle.

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