AusOcean Rig Overiew
The "rig" is AusOcean's sea surface platform for supporting ocean science in coastal waters. It has been designed to meet the following requirements:
- low cost
- maritime safety
- flexible support for multiple sensors
Design and Construction
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 (the "centre weight"), 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.
Safety and Security
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.
Electrical and Electronics Systems
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:
- DHT22 combined air temperature/humidity sensor
- DS18B20 sea-surface temperature sensor
- Raspberry Pi Zero based camera (choice of underwater or surface)
Other sensors may be added upon request, subject to operating within the rig's power budget. AusOcean is continually adding support for new sensors.
Management and Operations
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. The preferred anchoring method utilises screw piles shackled to nylon mooring line without the use of 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.
The following diagrams show the horizontal and vertical movement of the rig respectively. For simplicity the extra mooring line that has been absorbed by the centre weight is not shown.
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 periods of time (for testing, etc.), it has logged multiple deployments of several months at sea at one time. During this time the Rig also survived the winter storm season, experiencing 3-metre seas. Although individual components have failed (and since been improved), the overall design and construction has proven to be seaworthy.
Rig design documents are available online here.
Rig #3 at Windara Reef on a calm day.
Rig #3 after 4 months at sea.
Learn more about AusOcean at ausocean.org.