Constant Radius Turn

Constant Radius Turn

Assuming, a vessel has to make a turn as per the path from A to B.

Total course change is θ Degrees, Vessel speed is V in knots, Turn of radius is R in miles.

Distance AB= (Rxθ)/  57.3 miles 

Time taken (T) to cover AB = (Rxθ) /  (57.3 x V)

Therefore Rate of turn, θT = (57.3x V) / (R)               (Degree/hour)

Rate of turn (Degree/minute) = (57.3x V) / (Rx60) 

Rate of turn θ ≈ V / R  (Degree/minute)     (where ≈ means is approx. equal to)

Therefore to execute a turn of constant radius, relationship between V and ROT can be established.


Example 1

For having a Turn of radius (R) = 1 mile, with vessel speed = 12 knots

ROT =V/R

ROT= 12/1

ROT = 12 Degree/ Min

So execution of a constant turn of radius =1 mile can be done by ensuring the ROT is kept equal to the log speed of the vessel during the turn.


Example 2

For having a Turn of radius (R) = 2 mile, with vessel speed = 12 knots

ROT =V/R

ROT= 12/2

ROT = 6 Degree/ Min

So execution of a constant turn of radius =2 mile can be done by ensuring the ROT = 6 Degree/ Min.

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