Buoys

There are two main classes of buoys: drifting and moored.

As the name implies, drifting buoys are not anchored to the seafloor. They are typically used to study currents and circulation patterns. A drogue is sometimes added to have the surface buoy follow a subsurface current.

Subsurface drifting buoys, aka floats, usually have variable buoyancy engines to descend to a predetermined depth where they follow this current and possibly collect environmental data. The buoyancy engine is programmed to occasionally bring the float to the surface where it can telemeter its data back to shore. Trajectories of individual floats show how the water moves horizontally, and trajectories of groups of floats show how the water is mixed by eddies. This information is important for understanding how water tracers and pollutants are transported by the ocean. The Argos program is a large multinational effort to put thousands of floats in the world’s oceans.

Moored buoys are used for many purposes. Some of the most common uses are:

• Aids to Navigation (ATON) – used to mark hazards to mariners, harbor entrances, and other navigable channels.
• Data Collection Platforms - Moored buoys make excellent platforms for collecting data at one location anywhere in the ocean on time scales ranging from weeks to years. Sensors and instruments can be mounted anywhere from the seafloor on up to masts installed on the top of the mooring float
• Marker Buoys – used to relocate objects on the seafloor
• Ship Moorings – typically used to moor large commercial or military ships when dock space is not available or near shore waters are too shallow. Also used for offshore loading and unloading of tanker ships.

Other special types of buoys are:

Subsurface buoys are used when surface measurements are not required. They also eliminate vandalism which can be a big problem with surface buoys.

Self deployed buoys in which the anchor, line, and sensors are packaged in a compact assembly. Air deployed buoys are dropped from a plane.

Moored buoys come in a wide variety of shapes and sizes. Hulls forms include disk, sphere, cone, boat hull, and spar. The typical moored buoy consists of:

• Tower for mounting antennas, sensors, and solar panels
• Float, usually has a well containing batteries
• Bridle for attaching the mooring ling
• Mooring line to connect the bridle to the anchor
• Anchor

Moored buoys are important to the marine technologist because they make excellent platforms for collecting data anywhere in the ocean on time scales ranging from weeks to years. Sensors and instruments can be mounted anywhere from the seafloor on up to masts installed on the top of the mooring float. Anchors are connected to holding lines with acoustic couplings that are released to recall the instruments. Flotation holds the instruments and their tether line upright in the water column and brings them to the surface on release.

A good engineering discussion on moored buoy design options for an oceanographic buoy can be found in section 8 of the document at http://obslab.whoi.edu/buoy.html

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