The Hull

The actual structure of the buoy is surprisingly inconspicuous above the surface. Above the waterline only an unobtrusive spar and exhaust port are visible. Access is provided to the buoy by means of a boat landing deck and a watertight door to an access shaft that leads down into the buoyant equipment chamber.

The buoyant equipment chamber (BEC) housing all the production technology is constructed of tubular carbon steel sections. It lies below the waterline, and is divided by watertight decks that house the following equipment:

Control System

The first deck of the BEC is home to the control equipment and instrumentation for the buoy. Access is provided by means of a central shaft that runs from the boat landing platform above sea level through to deck 4 of the buoy, the last deck accessible to personnel. The buoy control system (BCS) is designed to ensure that all systems are on-line and functioning correctly. The BCS typically uses Allen Bradley ControlLogix PLC equipment configured in a dual redundant architecture interfacing to field input devices and other systems via a Simplex ControlLogix I/O subsystem.

Power Source

The buoy has a number of operating loads that together require around 300kW of power. The buoy is capable of generating enough power to run independently by means of three 85% dual fuel generators. This configuration will allow two generators operating at 60% efficiency to supply the required power output for normal operation. The third, standby generator will automatically cut-in in the event of generator failure and operate in a temporary overload situation to avoid a cascade failure. The generators, together with ancillary equipment such as batteries and cooling systems, are housed on decks 2 and 3 of the buoy.

Process Equipment

The process equipment housed on the buoy is dependent upon the application. The oil production buoy houses 2-3 gas fired thermal heaters for separating the produced oil, the power substation buoy houses a series of transformers and associated switchgear, the grid power generating buoy houses a series of gas turbines etc.

Regardless of the application, the process equipment will be housed on deck 4 of the buoy.

Fuel

In the case of production buoys, under normal operations the buoy generators will run on the produced gas from the well. When such gas is not available a store of enough diesel fuel to run the generators for up to 10 days is available in a storage tank on deck 5 of the buoy.

Communications

The buoy is equipped with a sophisticated communications system to enable communication between the host platform (or shore station) and the buoy. This enables the remote control and status monitoring of the buoy through the BCS. The communications system will typically consist of a UHF radio system, with built-in redundancy for maximum reliability and availability. In more remote areas a satellite system could be utilised. This could also serve as a backup system to the UHF radio in normal operating conditions.

This equipment is housed on deck 1, with the antennas being located within the spar above the water line.
Traditional marine and aeronautical communications systems are installed on the buoy control deck for safety and operational communication with support vessels during operational and maintenance visits. In addition portable radio equipment can be used for communication between persons on board.