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.
