INGENIEUR
SHIP MANOEUVRING TESTS
By Associate Professor Ir . Dr Md Salim Kamil Universiti Kuala Lumpur - Malaysian Institute of Marine Engineering Technology
FEATURE
The common ship manoeuvring tests carried out either by using models or real full scale ships are turning circle , spiral manoeuvre , zig-zag manoeuvre , pull-out manoeuvre and Williamson turn . Other manoeuvring tests — oblique tow , rotating arm and planar motion mechanism tests — are carried out using model ships in a special circular manoeuvring tank or a large towing tank .
Ship manoeuvring tests using models are carried out to predict the manoeuvring characteristics of full size ships in calm waters or waves . These tests are important inputs for the estimation of manoeuvring characteristics of the ships and to ensure that the ship owners ’ requirements and certain statutory body standards or compliance for full scale ships are met . If these requirements or compliance are not fulfilled during the model tests , the hull form and the appendages may have to be redesigned or modification work carried out until the requirements or standards are met .
Full scale manoeuvring tests are carried out on completion of construction and are normally conducted during sea trials . The purpose is to determine the actual manoeuvring characteristics of the full scale ship in real sea environmental conditions and to validate the results predicted through the model tests .
Measuring instrumentation and tracking systems are fitted to the models and manoeuvring tank facilities during the tests . In full scale tests or trials , similar appropriate measuring instrumentation and tracking systems are fitted onboard the ships .
The ship ’ s manoeuvring characteristics serve as guidance to the navigation officer and the captain for steering the ship in open seas , restricted waterways and ports .
TURNING CIRCLE TEST
Turning circle tests are carried to predict and determine the ship ’ s turning characteristics defined below and as shown in Figure 1 :
Approach . The phase from the instant when the ship is approaching at a steady speed until the rudder is deflected .
Advance . The distance travelled in the direction of the ship ’ s course or heading from the instant the rudder is deflected port or starboard until the ship has turned 90 degrees .
Transfer . The distance from the longitudinal centre of gravity of the ship to the line normal to the original ship course or heading when the ship has turned 90 degrees .
Tactical Diameter . The distance normal to the ship heading when the ship has turned 180 degrees .
Steady Turning Radius . The radius when the ship has completed 360 degrees and achieved a steady turn .
Steady Drift Angle . The angle between the line of ship heading and the tangent to the circle .
Steady Heel Angle . The heel angle as the ship has achieved a steady turn .
Model ship turning circle tests are carried out in a special manoeuvring tank . However , a modified turning circle test can be carried out in a rectangular towing tank of a reasonably large size . In this test the model is fitted with the full appendages , a self-propulsion system , tracking and measurement gadgets and appropriate control and monitoring systems . It begins with the model moving straight ahead to achieve a steady speed in the approach phase under its own propulsion system . The rudder is then deflected to a pre-set angle until the model makes a complete steady turn . The position of the model throughout
50 VOL 83 JULY-SEPTEMBER 2020