The Clear Water Towing Tank (CWTT) at the Institute for Marine Dynamics (IMD) measures 200 m long x 12 m wide x 7 m deep with a usable run length of approximately 150 meters. The tank is equipped with an electrically driven (manned) towing carriage capable of speeds up to 10 mis and a hydraulically operated, computer controlled dual-flap wavemaker which can generate regular waves of up to 1.0 min height or irregular waves with significant wave heights of up to 0,3 meters.

The tank when built was not equipped with any form of side beaches. Retro-fitting the facility with traditional-style side beaches would be a major expense. Adjustable-height vertical baffles would also, perhaps, be impractical given the limited amount of space between the underside of the towing carriage and the water surface.

In an effort to improve the efficiency of use of this facility, it was decided to experiment with low cost flexible side beaches in the CWTT. Beaches of this type are described by Enzinger and Johnson (Reference 1). The authors report a marked decrease in tank settling time and a corresponding increase in the testing efficiency of their tanks. One notable difference in the IMD approach is the use of these 'beaches' on both sides of the tank rather than just one as is the case in the Hydromechanics Laboratory of the U.S. Naval Academy. It was logical to assume that having energy absorbing devices on both walls would decrease the settling time even further for a nominal extra expense.

This paper describes the use of the (double) 'course rope' beaches in the CWTT and experiments conducted in calm water and regular waves to determine their effectiveness for this facility.

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