Turning - Shiphandling Facts and Rules Flashcards
Turning - constant RPM turning circles at slow vs. full ahead (Rowe)
virtually identical at slow and full ahead but rate of turn faster at higher speed (Rowe pg 27, 29)
Turning - accelerated turn - turning circle diameter
can reduce turning circle diameter by half
Turning - VLCC loss of headway
loses 25-30% of headway for every 90º change in heading
Turning - speed reduction from 12kts for complete round turn
12kts to 2-3kts after completing a round turn
Turning - rudder response at slow speed
ships do respond to rudder at very slow speed if given the chance
Turning - directionally unstable ships
- need more rudder to start a turn and more rudder to stop a turn
- have smaller turning circle
Turning Moment = (Hooyer)
Steering moment + moment of lateral resistance (forward) (Hooyer pg 31)
Turning - Ship down by the head - characteristics
- difficult to steer
- slow to start swing
- hard to stop swing
- smaller turning circle
Turning - ship down by the stern
larger turning circle due to weak lateral resistance at the bow and strong abaft the PP which restricts drift angle (Hooyer pg 31)
Turning - drift angle increases until…
increases until AR (lateral resistance abaft the PP) and transverse rudder force reach a balance (Hooyer pg 121)
Steering Lever =
(Hooyer)
distance from rudder to PP (first class lever) (Hooyer pg 123)
Lateral Resistance Lever =
(Hooyer)
distance from PP to R’ (the center of FR, the lateral resistance forward of the PP)
Diameter of Turning Circle - proportional of…
- directly proportional to steering lever
- inversely proportional to the lateral resistance lever (Hooyer pg 123)
Diameter of Turning Circle - evolution (Hooyer)
- first quarter of turning circle is larger
- as turn continues PP moves aft as FR (LR forward of PP) increases and drift angle increases
- as speed decreases, advance (momentum) decreases (Hooyer pg 125)
