Rudder Cycling works on the principle of diverting the fore and aft thrust sideways but not really taking the vessel sideways. Alternately, the similar manoeuvre is done on other side.
Rudder Cycling is found extremely effective in reducing the vessel’s speed in a given period and takes the vessel through minimum distance in original direction. In the Rudder Cycling the heading of the vessel does not change much. A master must be well versed with this procedure as an effective tool to prevent the vessel from running in to danger.
High Frequency Cycling
- Gives a stopping distance of approximately 10 times the ships length.
- Uses the “drag” of the rudder to reduce headway
- Put the rudder hard over and stop the engines. As the vessel starts to swing, put helm hard over the other way.
- Continue to do this cycling until vessel is stopped.
- You may need a short burst of ahead power and corrective helm to bring the vessel back on course.
- This results in minimal deviation of heading and the effectiveness of the manoeuvre is not reduced by shallow water.
- This manoeuvre is not really suitable for use on vessels of full hull form which are deeply laden.
- Most effective on fine form vessels in lightship condition.
Low Frequency Cycling
- Gives a stopping distance of approximately 6 times the vessel length.
- Uses the “drag” of the hull as the vessel turns. Put rudder hard over to port until vessel is 40 degrees off course, then hard to starboard with full astern. This will stop the vessel with small deviation to the port side of her course and close to her original heading. Shallow water will reduce the effectiveness of this manoeuvre.
- It must be remembered that vessels on reciprocal courses will close at their combined speeds and that a ‘safe’ speed to conform with IRPCS should therefore be one at which the vessel can be brought to a standstill in half the range of her visibility.
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
The stopping distances were estimated by computer simulation for a bulk carrier 32 000 DWT
Zig zag
Zig-zag test is the manoeuvre where a known amount of helm is applied alternately to either side when a known heading deviation from the original heading is reached. The 10°/10° zig-zag test is performed by turning the rudder alternately by 10° to either side following a heading deviation of 10° from the original heading in accordance with the following procedure:
- after a steady approach with zero yaw rate, the rudder is put over to 10° to starboard or port (first execute);
- when the heading has changed to 10° off the original heading, the rudder is reversed to 10° to port or starboard (second execute); and
- after the rudder has been turned to port/starboard, the ship will continue turning in the original direction with decreasing turning rate. In response to the rudder, the ship should then turn to port/starboard. When the ship has reached a heading of 10° to port/starboard of the original course the rudder is again reversed to 10° to starboard/port (third execute).
Track reach & Head reach
Stopping ability is measured by the “track reach” and “head reach” realized in a stop engine-full astern manoeuvre performed after a steady approach at the test speed until ahead speed in ship coordinates changes sign (i.e., vessel starts going backward).
- Track Reach is defined as a distance along the vessel’s track that the vessel covers from the moment that the “full astern” command is given until ahead speed changes sign.
- Head Reach is defined as a distance along the direction of the course at the moment when the “full astern” command was given. The distance is measured from the moment when the “full astern” command is given until the vessel is stopped dead in the water.
Track Reach Criterion
The stopping ability of the vessel is judged using a full astern crash stop manoeuvre. Based on IMO requirements the track reach should generally not exceed 15 ship lengths (measured along the path).
However, in the case of low-powered large displacement vessels, this value may be modified, but in no case should exceed 20 ship lengths, subject to special consideration and approval by the Bureau.
Determination of whether a vessel falls into the category of “low powered large displacement vessels” also will be done by the Bureau.
Head Reach Criterion
Head reach criterion in a form of rating is based on statistics of sea trials.
Stopping ability rating only if:
TR < 20L only for low-powered large displacement vessel
TR < 15L in all other cases
where
TR = track reach, in meters
L = vessel length, in meters
