The Naval Postgraduate School (NPS) has begun a project to deploy a seafloor docking station for its REMUS Autonomous Underwater Vehicles (AUVs) in Monterey Bay. Engineers from the NPS Center for Autonomous Vehicle Research (CAVR) and the Department of Oceanography are developing an interface so that the Monterey Inner Shelf Observatory (MISO), located in 16 m deep water 600 meters offshore from NPS, can host a REMUS docking station developed by Woods Hole Oceanographic Institution (WHOI).
Autonomous Underwater Vehicles (AUVs) are free-swimming vehicles used to collect oceanographic data and seafloor imagery. They lack permanent connections, or tethers, to external power sources and the amount of time they can be deployed in an operating area is limited by their battery capacity.
An underwater docking station allows an AUV to periodically recharge its batteries and upload its data to users during a single long-duration mission. Last month, NPS completed several preliminary tasks in preparation for deploying the WHOI dock.
First, NPS tested the beach side of the shore cable supplying power and Ethernet to the MISO cable termination package. Although power to the MISO has been off for over two years, the copper conductors in the shore cable used for electrical power were free of ground faults.
Next, NPS contracted with the Moss Landing Marine Labs (MLML) Science Diving Team to perform a dive operation on October 18, 2012. Two divers set to work cleaning the MISO support frame and uncovering the shore cable from the seafloor. The divers succeeded in cleaning off the bolts securing the cable termination package to the MISO frame, but found that the shore cable was buried too deep in the sediment to recover it using hand tools.
The divers also surveyed the area offshore from the MISO structure in a 50-meter radius to identify a safe location and geometry for the REMUS to approach the docking station. The divers found nothing but flat sand in this area, in agreement with a survey conducted by the Monterey Bay Aquarium Research Institute (MBARI) in 2006.
During a follow-up dive, the MLML science divers used a water jet to successfully excavate 25-meters of shore cable so the termination package could be raised to the surface for inspection. This revealed that one of the bulkhead connectors had failed after several years underwater, and the housing had flooded with seawater. While the original electronics package was badly corroded, the copper conductors and all but one of the fiber optic terminations were fortunately still intact.
After NPS personnel performed repairs, replaced the electronics payload, and re-sealed the housing with a new endcap, a test cable was connected to one of the new bulkhead connectors. From the work boat, NPS verified receipt of power and data at the termination package, successfully connecting to the NPS network with full internet access. This connectivity will be critical for monitoring persistent AUV operations in Monterey Bay via the seafloor docking station.
Finally, the dive team lowered the cable to the seafloor and reattached the termination package to the MISO frame. The next steps for this project include designing a power/data interface to convert the MISO’s 300-volt shore power into a 32- volt, 10-amp power supply capable of charging the REMUS AUV and installing this interface onto the seafloor docking station.
The NPS CAVR looks forward to testing this docking capability in early 2013. This work is supported by Susan LaShomb (PMS485 Maritime Surveillance Systems) and Dr. Tom Drake (ONR).
|Author:||Sean Kragelund, Doug Horner|