Date of Award

Spring 2007

Project Type

Thesis

Program or Major

Ocean Engineering

Degree Name

Master of Science

First Advisor

M Robinson Swift

Abstract

Two prototype research feed buoys, designed with a feed capacity of a quarter-ton and one-ton respectively, were designed, modeled, constructed and field-tested to support raising aquaculture finfish in submerged cages at the University of New Hampshire's Open Ocean Aquaculture Demonstration site. These two buoy systems consisted of a surface buoy, moorings to a submerged fish cage mooring, feed dispensing machinery, feed transfer hose and buoy telemetry and control systems. Numerical finite element analysis and physical model scale wave tank testing were performed on both feed buoys. Various mooring concepts were also tested. Both buoys were moored close to the aquaculture cages using compliant mooring members, which allowed motion through tidal, current and storm wave conditions. Feeding mechanisms consisted of feed dispensing equipment and centrifugal pumps to actively force a feed and seawater mixture down to fish in the submerged cages.

The first buoy, with a quarter-ton feed capacity, was battery-powered and recharged by both a wind generator and two solar panels. A control system managed the operation of the feed equipment, and telemetry sent diagnostic and system status information back to shore to the project manager. The quarter-ton feed buoy was deployed to the University's aquaculture site in early December 2002. After correcting initial start-up problems, the buoy operated for many years enabling beneficial, metered and regular feeding to the caged fish. To meet immediate needs of an expanding aquaculture operation, a larger one-ton capacity feed buoy was designed, built and deployed to the aquaculture site within a ten-month period. This buoy had a similar design to the quarter-ton feed buoy, but was scaled larger to hold a greater amount of fish feed. One significant innovation on this buoy was the onboard diesel generator, which was necessary to power industrial feed equipment, as well as to charge the buoy's battery bank. In case of generator failure, the buoy's control system received its own power from an internal battery bank, which was charged from solar panels and/or the generator.

The larger one-ton feed buoy was deployed to the aquaculture site in early December 2003 and, after overcoming the complexity of remotely starting and controlling the diesel generator, the buoy supplied greater amounts of feed to the fish cages than was previously possible. After operating for just one year, the one-ton feed buoy sank during a Nor'easter storm in late December 2004. On examination of the salvaged buoy seven months later, it appears a weld failure in the feed system was the root cause of flooding and the ultimate sinking of the buoy. Despite the unfortunate loss of the one-ton feed buoy, the research discussed in this thesis will likely serve as a basis for developing future commercial aquaculture feeding systems suitable for an open ocean environment.

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