Model Free Surface Towing Tests of a Submerged Towed Vessel, Technical Report n° C.2609B05CT17-RAP01, TESTS No. 1 - 2

On behalf of the Embassy of Israel, free towing experiments have been carried out at CNR-INSEAN for a Submerged Towed Vehicle model (STV). This report describes the model used in the towing tank tests and presents the measurements of the towing force in calm water, together to the running roll and pitch. The experiments were performed in the 9.5 x 3.5 x 220 m towing tank. The original version of the model showed phenomena of green-water on the deck over the speed of 1.3 m/s. As a consequence a modified bow version was designed and tested, obtaining a speed limit shift of 0.2 m/s before the green-water occurs again. Two lengths of the towing cable were used, 20 and 40 meter long respectively. The resistance measured in free conditions on the modified bow, compared with the results obtained during the Resistance Surface tests, shows a good consistency. The modified bow results in a reduction of predicted full scale towing force of about 14%. As regards the motion, the original vessel tends to assume a negative (bow down) trim, up to -3.5 degrees for the highest speeds tested, while no significative roll angles are measured.