Embedded Files
A Focus on Reducing Marine Wildlife Entanglements and Promoting Conservation
Project Background
Project Background
In modern lobster fishing, traps sit on the ocean floor and are connected to a surface buoy by a long sink line (rope). The buoy identifies the trap's location, and the rope is then used to pull up the trap to the fisherman's vessel. With a plethora of these traps sitting off the coast of San Diego, the web of ropes between the sea floor and surface ensnares many marine creatures, primarily right whales. Many end up as by-catch, drowned or wounded by the ropes. And the potential for by-catch is extreme. The Port of San Diego has begun pushing for stricter fishing laws, greatly affecting the fishing community and inspiring innovation to protect marine life.
The port authority and fishermen are seeking methods to avoid by-catch by keeping the buoy on the sea floor with the trap until the catch is ready to be collected, thus ensuring marine life will not get entangled. A current methodology to solve this issue involves tying the rope with a low-cost galvanized wire which will release after the wire is fully corroded, but this method's timing is not nearly accurate enough to warrant widespread use. Coastal Monitoring Associates and the team's sponsor, Bart Chadwick, have been looking to develop an effective technology to resolve this issue.
Figure 1: A buoy with the sink line connected to the lobster trap through the water column
Objectives
The objective of this project is to develop a proof of concept for an engineering prototype of a rope-less fishing system that can time-release a buoy for a given amount of time set by the fishermen. Current solutions to this problem are both expensive or inaccurate so this project seeks to address one or both of these issues. In addition, the device would have a limited reset time and would require low amounts of power such that the fishermen can use it for as much of a season as possible before seeking a replacement. Coordination with the lobster fishing community is also important to ensure the product meets their design goals.
Figure 2: Ropeless Trap Idea for Lobster Fishing
Final Design
Figure 3: Internal View of the Finished Device
The buoy deployment system was housed in a PVC tube with a cap on one end and a cam on the other end. To use this device, the CAM is first calibrated to the zero position where the peg can be freely removed. The fishermen then places a magnet near the reed switch to actuate the CAM. Next, the CAM rotates itself to a determined angular position in which the magnet is then pulled away by the fishermen from the switch. The angular position of the CAM corresponds to a set time for the buoy deployment system and will automatically trigger the timing circuit to start. The peg should be locked in place and the CAM begins to rotate back to the zero position over time. Once the set time has passed, the peg is released from the housing cap due to the upward buoyant force created by the buoy.
Performance Results
The system was able to take the required time input, sleep for that amount of time, and then move to a buoy release position in a dry test. The o-ring seals worked at 4.5 kPa but were not tested at the largest expected operating pressure of 1006 kPa for depths of 30.5 meters. Furthermore, as a pressure release valve and seal was not implemented in time, the housing could not be fully sealed and thus the device could not be tested underwater.
During the dry test, electrical current through the batteries while the electrical system was in sleep mode with the motor off were larger than expected, leading to estimates of the system’s battery life at 1.4 days (12V battery for motor) and 5.9 days (AA batteries for arduino), which was much less than the required battery life of 100 days.
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