Measures and Criteria of Manoeuvrability

Turning Circle

Advance, transfer and tactical diameter
  • Advance – distance until 90° change of heading.
  • Tactical diameter – 180° change of heading.
  • Transfer – 90° change of heading as additional measure of some interest.

The advance, the tactical diameter, and the transfer are given as multiplicity of ship’s length.

IMO standards for Deep water:

  • Tactical diameter must be less than 5L
  • Advance must be less than 4.5L

Effect of Ship’s Size on Turning Performance

Turning performance

Turning characteristics depend on the ship size.

The tactical diameter is not proportional to the displacement of the ship, but relative tactical diameter D/L is equal for ships of different sizes but geometrically similar.

Effect of Wind and Current on Turning Circle

Turning trajectory

Effect of Ship’s Parameters on Turning and Course Keeping

Normally in calm water a fully loaded ship at speed about 5 knots with a rudder hard over (35 deg) will turn round 180 degrees in less than 4 ship’s lengths. With a smaller rudder angle the ship will make larger turning circle and gain more speed.

How ship's parameters affect turning and course keeping

Swept Path

Performing a turning manoeuvre the ship requires some free space. This space is larger than the turning circle, because at each point of the turning circle the ship is positioned at certain angle (drift angle) to the tangent to the path of the centre of gravity (CG).

Swept path

Ways to Stop the Ship

Apart from inertia stopping and crash stop there are also other possibilities to stop the ship, such as:

  • Hard turn
  • Rudder cycling
  • Tactics called Stopping in narrow waterway

The principal reason for introducing the above strategies is desire to shorten the stopping distance by judicious use of the hull and rudder braking forces while maintaining the ship’s controllability .

Rudder cycling procedure

How to stop the ship using rudder cycling

Stopping in narrow waterway

How to stop the ship in narrow waters

Comparison of Different Stopping Procedures

The stopping distances were estimated by computer simulation for a bulk carrier 32 000 DWT