4.2 Mid-Bay Straight Reach Testing

　

 The measured rudder positions. heading deviation from the channel heading, and the distance from the channel centerline are presented below in Figures 8 and 9 for New Amity and for SKS Trinity,respectiverly. Figure 10 shows that both ships followed similar paths near the center of the navigation channel. The inbound New Amity used up to 25 degrees of port and starboard rudder to keep the ship on the port side of the channel within 65 ft (20 m) of the channel centerline. The heading deviated from the channel heading by less than 1 degree. The port bank changed just below channel markers 59-60 and became steeper. Above markers 61-62, less than 5 degrees of rudder were required to maintain course and gradually work the ship to the channel center. The SKS Trinity maintained its position within 70 ft (21 m) on the inbound port side of the channel with rudder angles less than 10 degrees with heading deviations from the channel heading of less than 2 degrees to channel markers 65-66. At this point,the ship moved to the starboard side of the channel about 20 ft (6 m) off the centerline and required 15-20 degrees of rudder to maintain this course.

　

　

　

　

 Simulations Using Recorded Rudder Position and RPM; The recorded rudder positions and RPM settings for the New Amity were used to control the simulation model in this section. The bank conditions were modeled without a multiplier (i.e., used forces and moments measured in towing tank tests and developed into a theoretical algorithm) and with the bank moment at three times the theoretical magnitude. The ship meandered within the channel more than the prototype measurements show. A portion of the ship track line is shown in Figure 11.

　

 Figures 12 and 13 show the rudder positions (since the RPM was unchanged it was not plotted), ship heading deviations from the navigation channel heading, and the distance off the navigation channel centerline for the Base and 500-ft channel models. The bank moment was modeled at three times theoretical; modeling with the theoretical banks resulted in the ship leaving the channel The pattern is different from the measured ship behavior. If the forces and moments are being modeled correctly and the ship model is accurate, it would be expected that the ship behavior would be accurately reproduced.If the model behavior begins to deviate, then the pattern of forces and moments will not align with the ship controls and the ship could be expected to deviate more and more from the measured performance.