We shall look at a number of turning circles. The size of a ships turning circle is determined by two factors, helm order and under keel clearance. In this case the helm is at maximum and in deep water. This gives the tightest turning circle.
This is the normal turning characteristic. 15 degrees helm and deep water. Depth of water is more than twice the draught.
This now shows the tightest turn in shallow water.
Finally a standard turn of 15 degrees helm in shallow water gives a larger turning circle.
When we approach the chart we first establish the angle of turn. In this case 45 degrees.
We apply that angle to the required turning circle.
This gives an advance (forward) and transfer (sideways) that we apply to our course line to find the wheel over position.
Transfer is applied first, inside the turn.
Advance is then applied back from the point that the transfer line touches the new course.
Wheel over position is found by taking a right angle to the point where advance ends and marking this on the initial course line.
The actual course steered will be inside the waypoint. If the waypoint is reached then the vessel has overshot the turn.
This gives an idea of large vessel turning circles. This is assuming deep water of 1000m. This has implications for Rule 17b when determining if the other vessel is able to avoid collision by his manoeuvre alone.
