Figure 1 : Turning Circle Test
the test is tracked and plotted automatically by an optical tracking system .
The test is repeated for different rudder angles and speeds . The measured quantities or parameters in the test include speed , the ship ’ s course or heading , position at any moment , the rudder angle , the wind condition , the current , the wave conditions and any other related parameters as appropriate . The turning circle characteristics are studied for different rudder angles and speeds of the model , and for the actual size ship in varying sea conditions . These characteristics are important for the captain to navigate the ship at sea , in busy and narrow shipping lanes or passages such as ports , straits , restricted passages , rivers and others . Registering the turning circle characteristics of ships may become requirements by relevant statutory bodies or authorities . The turning circle test analysis is carried out to establish the ship ’ s turning circle characteristics as described above and shown in Figure 1 . This can be done by plotting the turning circle based on the data collected or can be plotted automatically during the test by means of optical tracking system with a plotter for the model test . For the full scale test , it can be plotted automatically by means of Differential Global Positioning System complete with a built in plotting capability .
Figure 2 : Curves of Zig-Zag Manoeuvre
ψ - Yaw angle δ - Rudder angle L - Length of ship D - Distance moved O . Y . A - Overshoot Yaw Angle t - Time ( seconds )
Y o
- Distance normal from the original path t 1 - Length of times to deflect the rudder to
20 an angle of 20 ° of the first action t 2 - Length of times to deflect rudder to an
20 angle of 20 ° of the second action t 3 - Length of times to deflect the rudder to
20 an angle of 20 ° of the third action t 4 - Length of times to deflect the rudder to
20 an angle of 20 ° of the fourth action
ZIG-ZAG MANOEUVRING TEST
Zig-zag manoeuvring tests are carried out to evaluate a ship ’ s responses at particular rudder deflections and speeds . The tests are carried out based on the standard procedures in which the models are fitted with full appendages , the necessary motor to provide a self-propulsion system , and a rudder system . The model starts in a straight line in each test run . When a steady speed is achieved the rudder is deflected as quickly as possible to a desired angle ( say 20 ° port ) and the model is allowed to turn and change its course of direction . The length of times required to deflect the rudder to the required angle i . e . 20 ° port and the ship ’ s course at each constant interval are
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