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3.3.2. circulating test equipment.

    The tests were conducted in the Circulating Water Channel (CWC) at the U.S. Coast Guard Academy in New London, Connecticut. This facility is described in reference 5 and provides a f low channel 2 feet deep by 4 feet wide by 12 feet long with a maximum flow velocity of 8 feet/sec. The arrangement of the test set-up is shown in Figure 7. The drogue towline was led from the drogue through an eye located at the end of the rotating arm, and from there it was led to the load cell. The arm was driven by a variable speed electric motor. As the arm rotated the towline received a sinusoidal variation in horizontal velocity. Wave height was simulated by varying the length of the rotating arm, wave length was simulated by adjusting the rotational arm speed, and drift velocity was varied by adjusting the flow rate in the channel.

        A variety of drogue designs were tested including cone drogues with both rigid and flexible hoops, parachute drogues, and a novel design called a series drogue. The series drogue consisted of a large number of flexible cones attached to a line with a weight at the end. The drogue models were made of 0.0015-inch polyethylene material and were heat welded to the proper shape. The elasticity of the towline was simulated by the use of rubber strands of the correct dimensions. Figure 8 shows several of the drogue models.

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