Whale Sonobuoy Technical Information Sheet
The whale sonobuoy system is designed to allow people on the shore at the Hermanus Old Harbour Museum to listen to the underwater sounds produced by whales in Walker Bay. The underwater sounds produced by the whales travel through the water and are recieved by a hydrophone connected to the sonobuoy. The hydrophone converts the underwater sounds to electrical audio signals in the same manner as a microphone does in air. The audio signals from the hydrophone are transmitted to a shore receiver station by a cable or a radio link. The shore receiver processes the audio signals and presents the whale sounds on a loudspeaker system. The main components of the whale sonobuoy system are as follows:

The Sea-surface buoy
The buoy is conically shaped with a diameter of 3/4m and a length of 4m. The buoy is constructed from reinforced fibreglass and is painted with anti-fouling paint to inhibit marine growth on the underwater surfaces. The buoy is fitted with a 2.5m radio mast and a flag to make the buoy more visble to boats and people on the shore.

The Hydrophone
A hydrophone is the underwater equivalent of a microphone in the air. The hydrophone was constructed to be specially sensitive to the audio frequencies produced by the whales. The hydrophone is a sensitive device and it is enclosed in a stainless steel cage which protects it from mechanical damage. The hydrophone is protected from the effects of long exposure to seawater by a neoprene rubber encapsulation.

The Mooring
The mooring is used to anchor the sonobuoy in position and it was designed to minimise the effects of vibration on the hydrophone. Thick nylon cable connects the sea-surface buoy to a 400kg anchor on the seabed. A sub-surface buoy is used to suspend the hydrophone a constant height above the seabed.

Information supplied by the Old Harbour Museum