A light-weight buoy system has been developed for the Navy for precise navigation in coastal waters. The mooring employs a unique method*, whereby a low drag wave rider buoy is tethered under constant tension by a thin cable that is coupled to a spring-powered wave-and-tide compensator reel located in the anchor. Moored in this manner, the buoy is resistive to the vagarious position changes exerted by waves and currents. The buoy provides the waterborne platform for mounting navigation systems.
A description is presented of the mooring system, the method of automatically establishing the mooring, and the hydrodynamic performance of the buoy, and the results of sea tests are summarized.
The program that first generated the need for the Precise Navigation Buoy (PNB) was the Navy's Mine Defense Program. To be completely effective, mine sweeping operations require extremely accurate position location and navigation under a variety of different conditions. Buoys were needed that held their position in depths up to 200 feet, despite tide ranges of 12 feet, currents up to 2 knots, and sea states as high as 5.
Apart from its military application, utilization of the PNB is visualized in other activities such as bottom mapping, surveying and exploration, where the location of participating air and sea vessels must be accurately known, often to within a few feet. In situations where a land fix is impractical, and traditional navigational accuracies are inadequate, location markers must be established within the ocean itself.
This new navigation buoy system, developed by Bunker Ramo for the U.S. Navy, can be deployed from ship or helicopter, whereupon the system will automatically establish a taut wire mooring that will then hold the surface buoy to a tight watch circle- radius irrespective of tide, current, and sea state. In the mine clearance role, the PNB is equipped with a modified Teledyne Raydist T system Raydist is a proprietary radio navigation system designed and built by Teledyne Hastings-Raydist. It permits a vessel or aircraft carrying a Raydist receiver to locate its position within 10 feet at ranges of up to 250 miles from the transmitter. For mine-sweeping operations and for highly precise survey work, the distance from the buoy-mounted transmitter would be normally less than 20 miles. Under these conditions, the navigation system is capable of discriminating to one and a half feet. Other navigation systems ranging from the visual, such as light beacons, to radar transponders, can be considered, with the selection of the device tailored to suit the need.
Prior to this development, the techniques used to achieve a shallow water single tether 'stiff' mooring have consisted, in the main, of using a taut moored streamline sub-float located just beneath the surface influence of waves but capable of supporting antennae through the sea/air interface.