# Presentation: 376464

##  Engineering Challenges and Opportunities in Offshore Aquaculture

- MIT Sea Grant College Program
- Massachusetts Institute of Technology, Cambridge, MA  USA
- Second US-Korea Workshop on Offshore Aquaculture
- Jeju, S. Korea
- 18-19 July 2005

-  **Engineering Challenges and Opportunities in Offshore Aquaculture**

## Motivation

- Sheltered-water technologies bring
- unacceptable risk and high labor costs when used in high-energy locations.
- The scale of operations needed to operate economically offshore will support technology development.

## Topics:

- Mooring systems
- Robotic applications
- Cage design

## Mooring Systems

- Conventional multi-point mooring systems
- have no place offshore.

- Fixing a cage over specific location exacerbates benthic impacts.
- Weather can come from any direction.
- Depth and scope requirements result in excessive “footprint.”

## Anchoring

- Conventional methods of cage anchoring become impractical at depths over 100 meters

## Single Point Moorings

- Lower cost
- Reduced benthic deposition
- Reduced overall cage loads
- Operational advantages

## Deadweight/Drag Embedment

**3.2 m**

**3.2 m**

**45 deg.**

**0.97 m**

- Anchor for GoM OAC S.S. cage

- Omni-directional design
- Concrete with re-bar armature
-  12 tonne

## Robotic Applications in Offshore Aquaculture

- Automated feeding
- Predator control
- Biofouling removal
- Environmental monitoring

## Automated Feeding

- P.E. cone-bottom tank

- Battery/timer box

**30 cu. ft. scuba tank**

- Pneumatic gate valve

- Dispensing tubes

- UNH OOA

- Robofeeder - a 500 lb capacity, cage-mounted system designed for both surface and submerged
- operation.

## Predator Control

- MIT Odyssey II

- WHOI Remus

- Autonomous Underwater Vehicles (AUVs) are commercially available that could be used to deter biological intrusion

- Others are under development

- MIT RoboTuna

## Biofouling Removal

- An autonomous net cleaner powered through a tether from the surface, attaching to the net, and removing biofouling using H.P. water jets or brushes.

- Control:
-   Random (pool cleaner)
-   Intelligent (robotic vacuum)
-   Navigating using net plan (Net Cleaning Spider)

- MIT, Leonard

## Environmental Monitoring

- Water column surveys using an Autonomous Underwater Vehicle (AUV) operating in a long base-line acoustic array, carrying nutrient sensors, conducting an intelligent survey.

## Possible Solutions

- Operational efficiency in the open ocean may favor whole-cage harvesting from smaller cages
- It’s not stocking density, it’s how many fish are between you and the source of clean water.
-   New methods for large-cage servicing
- and partial harvest
- 2.  Smaller cages

- The Cage-size Conundrum

## M/V Cage Tender 

**A purpose-built aquaculture support vessel**

**Goudey, 2001**

## M/V Cage Tender

**Designed for installing, stocking, maintaining, and harvesting ocean cages up to 100’ (30.5 m) in diameter and live fish transport.**** **

**LOA       44 m**

**Beam     40 m**

**Disp.   1,100 T**

**CAGE TENDER**

**Goudey, 2001**

## 100 m2 China/ASA Cage

- Design requirements:
- Full exposure to South China Sea
- 100 m3, fixed volume, surface cage
- Protected feed enclosure for floating pellet
- Site 4 km offshore, 22 m depth
- Self-submergence during storm
- PE construction

## Cage assembly and Deployment at Lingshui Bay 

- Cage assembly and Deployment at Lingshui Bay
- on China's Hainan Island, July 2004

## 100 m2 Corner Weldment

## 6.5 tons per cage in 2004 (65 kg/m3)

- 6.5 tons per cage in 2004 (65 kg/m3)

## The Ultimate Autonomy - Ocean Drifter 

- Manned or autonomous cages capable of low-speed self-propulsion operating in reciprocal or gyre coastal currents or in oceanic circulations.

- How else can we exploit the majority of the EEZ where anchoring is impossible?

## Final Points

- The future lies with the right combination of technologies and species facilitated by a suitable regulatory scheme.
- Systems, species, and the legal framework need to be developed in concert for economic viability to occur.
- Many of the required pieces are in hand.  The integrated system is not, and it must be developed and demonstrated.
- Offshore technology requirements tend to converge, presenting opportunities for international collaboration.
- cgoudey@mit.edu