The "rig" is AusOcean's sea surface platform for supporting ocean science in coastal waters. It has been designed to meet the following requirements:
The rig is a custom pontoon design in a light-weight modular construction. The pontoons, braced by steel crossbars, provide a stable and buoyant platform, similar to the bridge deck of a catamaran. Two solar panels span each side of this platform. Projecting vertically from the platform is a highly visible pole, known as the “mast”, which houses the electronics inside. Both the pontoons and the mast are built from low-cost but durable stormwater-grade PVC, and the frame is made from metal (steel and aluminium). The rig's batteries are located in a water-proof compartment just above sea level, contributing to the rig's low centre of gravity and good stability. The rig is further stabilized by a weight suspended below the rig, which in addition to providing the function of a keel, maintains mooring line tension. The pontoons, mast and batteries can be easily disassembled and reassembled.
Traditional, vertically-oriented "pear-shaped" buoys with heavy keels (to provide ballast), provide either limited space and/or poor orientation for solar panels. In contrast, the rig's design affords the maximum horizontal surface area for its size, in turn maximizing the capacity of the rig's solar panels.
The rig incorporates the features of a maritime "special marker", notably a bright-yellow pole (the “mast”) and a yellow-flashing navigation light, which can be seen up to 1.5 nautical miles away. By default, the navigation light flashes 3 times for 1 second, then repeats every 30 seconds, i.e., Fl(3)30. The sequence is controlled by an onboard microcomputer (described below) and is fully configurable however. A surveillance camera is optionally mounted on top for additional security.
The rig's electrical system is 24V DC. Power is generated by two 40W solar panels in series, and energy is stored in two 14Ah 12V batteries also in series, providing 336Wh of energy (14Ah @ 24V). Each rig comes standard with an ESP8266 microcontroller which performs mission-critical functions, such as the navigation light, battery monitoring and power management. Each rig also comes standard with rig-to-shore communications equipment and the standard sensor pack, which includes:
Other sensors may be added upon request, subject to operating within the rig's power budget. We are continually adding support for new sensors.
In addition to having the onboard capabilities described above, rigs are connected to the Internet, and therefore form part of the so-called Internet of Things (IoT). By virtue of being connected, rigs are remotely manageable via AusOcean's NetReceiver cloud service. Note however that the rig's mission-critical functions are not dependent on network connectivity.
The rig's mooring line is connected to two anchor points on the seafloor. Two anchoring methods are possible, depending on the conditions. In Method A, Danforth-style fluke anchors with short lengths of chain are employed. In Method B (preferred), small screw-pile style anchors are employed without chain.
The mooring line has 3 rings (shown below). Two rings (R1, R2) are shackled to eye bolts at each end of the centre bar. A third ring (R3) in the middle is attached to the centre weight (CW). This system permits the rig to travel along the mooring line to absorb wave energy, while maintaining orientation and accommodating changes in depth.
AusOcean has deployed a rig at Windara Reef in the semi-protected waters of Gulf St Vincent, South Australia since January 2018. While this rig has been brought ashore for short periods (for testing, etc.), it has logged over 4 months of continous operation at sea, including several months during the winter storm season experiencing 3-metre seas. Although individual components have failed (and since improved), the overall design and construction has proven to be seaworthy.
Rig design documents are available online here.
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