The 3 metre hull used by AXYS Technologies Inc. (AXYS) was originally designed at the Woods Hole Oceanographic Institute in the USA as an experimental deep sea and coastal meteorological and oceanographic data acquisition and telemetry platform. The US National Data Buoy Center (NDBC) adopted the design and re-engineered it to meet their specific requirements. The buoy is assembled from three main components: the Hull, the Superstructure, and the Substructure, which are bolted together. This design allows the buoy to be easily dismantled for transportation on land or by ship. The Hull and Superstructure are painted yellow in accordance with international standards.

The buoy hull is discus-shaped, which allows it to move with the waves and therefore to provide accurate measurements of wave height, period, and direction. It is made of non-magnetic marine grade 5086 aluminium with six completely sealed watertight compartments surrounding a central compartment which houses the electronics, the wave sensor, and the batteries. With this design, the central compartment is protected from damage. Sacrificial zinc anodes that preferentially corrode are bolted to the buoy to mitigate corrosion.

The central instrument compartment has a hatch with a rubber seal. The buoy has a rugged rubber bumper around the perimeter to withstand impacts with vessels and wharves. There are three large lifting eyes for lifting and maneuvering, and the flat deck makes boarding and servicing at sea easy and safe. It has a service life of at least 20 years, and is easy to maintain and to modify for adding other features in the future.

The superstructure is manufactured of marine grade aluminium (6061-TS) and has a tripod design with cross bracing that adds strength and allows sensors, antennas, solar panels, the light, and navigation aids to be easily attached (Figure 9). A ladder is built into one of the legs. Cables are run inside conduit from the electronics compartment to the top of the superstructure.

The design of the superstructure and the stability of the hull allow meteorological sensors to be safely replaced at sea without having to lift the buoy out of the water and onto a vessel. Therefore, a small vessel can be used for payload and sensor maintenance tasks.

The substructure is manufactured of mild steel and is an inverted tripod bolted to the bottom of the hull. It is electrically isolated from the aluminium hull with nylon washers and spacers. The mooring is shackled to a mooring eye at the bottom of the tripod and isolated from the mooring with a Thordon™ bushing. Very high quality 2-part epoxy paint and zinc anodes bolted to the substructure protect the it from corrosion. The substructure is modular and can be broken down for ease of transportation.

Some of the advantages of adopting the 3 metre hull design are:

• A long and proven track record in deployments worldwide
• Easy to modify in the future to accommodate changes in technology and new sensors
• Easy to service
• Very long serviceable life
• Can be transported by truck
• Extremely rugged