644 Explanatory notes to the interim standards for ship manoeuvrability

1 The Assembly, at its eighteenth session, adopted resolution A.751(18) - Interim Standards for Ship Manoeuvrability. In adopting the standards, the Assembly recognized the necessity of developing appropriate explanatory notes for the uniform interpretation, application and consistent evaluation of the standards during the interim period. 2 The Maritime Safety Committee, at its sixty-third session (16 to 25 May 1994), approved the Explanatory Notes to the Interim Standards for Ship Manoeuvrability (resolution A.751(18)), set out in the annex to the present circular, as prepared by the Sub-Committee on Ship Design and Equipment at its thirty-seventh session. 3 The Explanatory Notes are intended to provide Administrations with specific guidance so that adequate data may be collected by the Organization on the manoeuvrability of ships. It is the intent of the Maritime Safety Committee to fully evaluate these data with the purpose of reviewing and amending the Standards as necessary. 4 Member Governments are invited to use the Explanatory Notes when applying the Standards contained in resolution A.751(18), and to report the data obtained to the Organization using the form for reporting data contained in appendix 6 of the Explanatory Notes.

1 General principles

1.1 Philosophy and background

The purpose of this section is to provide guidance for the application of the

Interim Standards for Ship Manoeuvrability (resolution A.751(18)) along with the

general philosophy and background for the Standards.

Manoeuvring performance has traditionally received little attention during the

design stages of a commercial ship. A primary reason has been the lack of

manoeuvring performance standards for the ship designer to design to, and for

regulatory authorities to enforce. Consequently some ships have been built with very

poor manoeuvring qualities that have resulted in marine casualties and pollution.

Designers have relied on the shiphandling abilities of human operators to compensate

for any deficiencies in inherent manoeuvring qualities of the hull. The implementation

of manoeuvring standards will ensure that ships are designed to a uniform standard, so

that an undue burden is not imposed on shiphandlers in trying to compensate for

deficiencies in inherent ship manoeuvrability.

IMO has been concerned with the safety implications of ships with poor

manoeuvring characteristics since the meeting of the Sub-Committee on Ship Design

and Equipment (DE) in 1968. MSC/Circ.389 titled "Interim Guidelines for Estimating

Manoeuvring Performance in Ship Design", dated 10 January 1985, encourages the

integration of manoeuvrability requirements into the ship design process through the

collection and systematic evaluation of ship manoeuvring data. Subsequently, the

Assembly, at its fifteenth session in November 1987, adopted resolution A.601(15),

entitled "Provision and Display of Manoeuvring Information on board Ships". This

process culminated at the eighteenth Assembly in November 1993, where "Interim

Standards for Ship Manoeuvrability" were adopted by resolution A.751(18).

The Standards were selected so that they are simple, practical and do not require

a significant increase in trials time or complexity over that in current trials practice.

The Standards are based on the premise that the manoeuvrability of ships can be

adequately judged from the results of typical ship trials manoeuvres. It is intended

that the manoeuvring performance of a ship be designed to comply with the Standards

during the design stage, and that the actual manoeuvring characteristics of the ship be

verified for compliance by trials. Alternatively, the compliance with the Standards can

be demonstrated based on the results of full-scale trials, although the Administration

may require remedial action if the ship is found in substantial disagreement with the

Standards. Upon completion of ship trials, the shipbuilder should examine the validity

of the manoeuvrability prediction methods used during the design stage.

1.2 Manoeuvring characteristics

; Manoeuvring characteristics

 

The "manoeuvring characteristics" addressed by the IMO Interim standards for

ship manoeuvrability are typical measures of performance quality and handling ability

that are of direct nautical interest. Each can be reasonably well predicted at the design

stage and measured or evaluated from simple trial-type manoeuvres.

 

1.2.1 Manoeuvring characteristics: general

 

In the following discussion, the assumption is made that the ship has normal

actuators for the control of forward speed and heading (i.e., a stern propeller and a

stern rudder). However, most of the definitions and conclusions also apply to ships

with other types of control actuators.

In accepted terminology, questions concerning the manoeuvrability of a ship

include the stability of steady-state motion with "fixed controls" as well as the

time-dependent responses that result from the control actions used to maintain or

modify steady motion, make the ship follow a prescribed path or initiate an emergency

manoeuvre, etc. Some of these actions are considered to be especially characteristic of

ship manoeuvring performance and therefore should be required to meet a certain

minimum standard. A ship operator may choose to ask for a higher standard in some

respect, in which case it should be remembered that some requirements may be

mutually incompatible within conventional designs. For similar reasons the formulation

of the IMO Interim standards for ship manoeuvrability has involved certain

compromises.

 

1.2.2 Manoeuvring characteristics: some fundamentals

 

At a given engine output and rudder angle d, the ship may take up a certain

steady motion. In general, this will be a turning motion with constant yaw rate y,

speed V and drift angle b (bow-in). The radius of the turn is then defined by the

following relationship, expressed in consistent units:

R = V / y

This particular ship-rudder angle configuration is said to be "dynamically stable

in a turn of radius R". Thus, a straight course may be viewed as part of a very wide

circle with an infinite radius, corresponding to zero yaw rate.

Most ships, perhaps, are "dynamically stable on a straight course" (usually

referred to as simply "dynamically stable") with the rudder in a neutral position close

to midship. In the case of a single screw ship with a right-handed propeller, this

neutral helm is typically of the order do = -1° (i.e., 1 degrees to starboard). Other

ships which are dynamically unstable, however, can only maintain a straight course by

repeated use of rudder control. While some instability is fully acceptable, large

instabilities should be avoided by suitable design of ship proportions and stern shape.

The motion of the ship is governed mainly by the propeller thrust and the

hydrodynamic and mass forces acting on the hull. During a manoeuvre, the side force

due to the rudder is often small compared to the other lateral forces. However, the

introduced controlling moment is mostly sufficient to balance or overcome the resultant

moment of these other forces. In a steady turn there is complete balance between

all the forces and moments acting on the hull. Some of these forces seeming to

"stabilize" and others to "destabilize" the motion. Thus the damping moment due to

yaw, which always resists the turning, is stabilizing and the moment associated with

the side force due to sway is destabilizing. Any small disturbance of the equilibrium

attitude in the steady turn causes a change of the force and moment balance. If the

ship is dynamically stable in the turn (or on a straight course) the net effect of this

change will strive to restore the original turning (or straight) motion.

The general analytical criterion for dynamic stability may be formulated and

evaluated with the appropriate coefficients of the mathematical model that describes the

ship's motion. The criterion for dynamic stability on a straight course includes only

four "linear stability derivatives" which, together with the centre-of-gravity position,

may be used to express the "dynamic stability lever". This lever denotes the

longitudinal distance from the centre-of-pressure of the side force due to pure sway (or

sideslip) to the position of the resultant side force due to pure turning, including the

mass force, for small deviations from the straight-line motion. If this distance is

positive (in the direction of positive x, i.e. towards the bow) the ship is stable.

Obviously "captive tests" with a ship model in oblique towing and under the rotating

arm will furnish results of immediate interest.

The value of the dynamic stability lever typically varies from 0.1L (where L is

ship length) for a stable, fine form cargo liner to -0.1L for a full form wide-beam

tanker. It is understood that a change of trim will have a marked effect mainly on

the location of the centre-of-pressure of the side force resulting from sway. This is

easily seen that a ship with a stern trim, a common situation in ballast trial condition,

is likely to be much more stable than it would be on an even draught.

Figure 1 gives an example of the equilibrium yaw-rate/rudder angle relation for a

ship which is inherently dynamically unstable on a straight course. The yaw rate is

shown in the non-dimensional form for turn path curvature discussed above. This

diagram is often referred to as "the spiral loop curve" because it may be obtained

from spiral tests with a ship or model. The dotted part of the curve can only be

obtained from some kind of reverse spiral test. Wherever the slope is positive, which

is indicated by a tangent sloping down to the right in the diagram, the equilibrium

balance is unstable. A ship which is unstable on a straight course will be stable in a

turn despite the rudder being fixed in the midship or neutral position. The curvature

of this stable turn is called "the loop height" and may be obtained from the pull-out

manoeuvre. Loop height, width and slope at the origin may all be regarded as a

measure of the instability.

If motion is not in an equilibrium turn, which is the general case of motion,

there are not only unbalanced damping forces but also hydrodynamic forces associated

with the added inertia in the flow of water around the hull. Therefore, if the rudder

is left in a position the ship will search for a new stable equilibrium, indicated by the

arrows and small circles shown in figure 1. If the rudder is shifted (put over "to the

other side") the direction of the ship on the equilibrium turning curve is reversed and

the original yaw tendency will be checked. By use of early counter-rudder it is fully

possible to control the ship on a straight course with helm angles and yaw rates well

within the loop.

The course-keeping ability or "directional stability" obviously depends on the

performance of the closed loop system including not only the ship and rudder but also

the course error sensor and control system. Therefore, the acceptable amount of

inherent dynamic instability decreases as ship speed increases, covering more ship

lengths in a given period of time. This results because a human helmsman will face

a certain limit of conceptual capacity and response time. This fact is reflected in the

IMO Interim standards for ship manoeuvrability where the criterion for the acceptable

first overshoot in a zig-zag test includes a dependence on the ratio L/V, a factor

characterizing the ship "time constant" and the time history of the process.

In terms of control engineering, the acceptable inherent instability may be

expressed by the "phase margin" available in the open loop. If the rudder is oscillated

with a given amplitude, ship heading also oscillates at the same frequency with a

certain amplitude. Due to the inertia and damping in the ship dynamics and time

delays in the steering engine, this amplitude will be smaller with increasing frequency,

meaning the open loop response will lag further and further behind the rudder input.

At some certain frequency, the "unit gain" frequency, the response to the

counter-rudder is still large enough to check the heading swing before the oscillation

diverges (i.e., the phase lag of the response must then be less than 180 degrees). If a

manual helmsman takes over the heading control, closing the steering process loop, a

further steering lag could result but, in fact, he will be able to anticipate the swing of

the ship and thus introduce a certain "phase advance". Various studies suggest that

this phase advance may be of the order of 10 degrees to 20 degrees. At present

there is no straightforward method available for evaluating the phase margin from

routine trial manoeuvres.

Obviously the course-keeping ability will depend not only upon the

counter-rudder timing but also on how effectively the rudder can produce a yaw

checking moment large enough to prevent excessive heading error amplitudes. The

magnitude of the overshoot angle alone is a poor measure for separating the opposing

effects of instability and rudder effectiveness, additional characteristics should therefore

be observed. So, for instance, "time to reach second execute", which is a measure of

"initial turning ability", is shortened by both large instability and high rudder

effectiveness.

It follows from the above that a large dynamic instability will favour a high

"turning ability" whereas the large yaw damping, which contributes to a stable ship,

will normally be accompanied by a larger turning radius. This is noted by the thin

full-drawn curve for a stable ship included in figure 1.

Hard-over turning ability is mainly an asset when manoeuvring at slow speed in

confined waters. However, a small advance and tactical diameter will be of value in

case emergency collision avoidance manoeuvres at normal service speeds are required.

The "crash-stop" or "crash-astern" manoeuvre is mainly a test of engine

functioning and propeller reversal. The stopping distance is essentially a function of

the ratio of astern power to ship displacement. A test for the stopping distance from

full speed has been included in the Standards in order to allow a comparison with

hard-over turning results in terms of initial speed drop and lateral deviations.

 

1.2.3 Manoeuvring characteristics: selected quality measures

 

The IMO Interim standards for ship manoeuvrability identify six significant qualities for

the evaluation of ship manoeuvring characteristics. Each has been discussed above and

is briefly defined below:

1. Inherent dynamic stability: A ship is dynamically stable on a straight course if it, after a small disturbance, soon will settle on a new straight course without any corrective rudder. The resultant deviation from the original heading will depend on the degree of inherent stability and on the magnitude and duration of the disturbance.
2. Course-keeping ability: The course-keeping quality is a measure of the ability of the steered ship to maintain a straight path in a predetermined course direction without excessive oscillations of rudder or heading. In most cases, reasonable course control is still possible where there exists an inherent dynamic instability of limited magnitude.
3. Initial turning/course-changing ability: The initial turning ability is defined by the change-of-heading response to a moderate helm, in terms of heading deviation per unit distance sailed (the P number) or in terms of the distance covered before realizing a certain heading deviation (such as the "time to second execute" demonstrated when entering the zig-zag manoeuvre).
4. Yaw checking ability: The yaw checking ability of the ship is a measure of the response to counter-rudder applied in a certain state of turning, such as the heading overshoot reached before the yawing tendency has been cancelled by the counter-rudder in a standard zig-zag manoeuvre.
5. Turning ability: Turning ability is the measure of the ability to turn the ship using hard-over rudder. The result being a minimum "advance at 90 degrees change of heading" and "tactical diameter" defined by the "transfer at 180 degrees change of heading". Analysis of the final turning diameter is of additional interest.
6. Stopping ability: Stopping ability is measured by the "track reach" and "time to dead in water" realized in a stop engine-full astern manoeuvre performed after a steady approach at full test speed. Lateral deviations are also of interest, but they are very sensitive to initial conditions and wind disturbances.

1.3 Tests required by the standards

1.3.1 Turning tests

 

A turning circle manoeuvre is to be performed to both starboard and port with

35 degrees rudder angle or the maximum design rudder angle permissible at the test

speed. The rudder angle is executed following a steady approach with zero yaw rate.

The essential information to be obtained from this manoeuvre is tactical diameter,

advance, and transfer (see figure 2).

 

1.3.2 Zig-zag tests

 

A zig-zag test begins by applying a specified amount of rudder angle to an

initially straight approach ("first execute"). The rudder angle is then alternately shifted

to either side after a specified deviation from the ship's original heading is reached

("second execute" and following) (see figure 3).

Two kinds of zig-zag tests are included in the Standards, the 10°/10°and 20°

/20°zig-zag tests. A 10°/10°zig-zag test uses rudder angles of 10°to either side

following a heading deviation of 10° from the original course. A 20°/20°zig-zag

test uses 20°rudder angles coupled with a 20°change of heading from the original

course. The essential information to be obtained from these tests is the overshoot

angles, initial turning time to second execute and the time to check yaw.

 

1.3.3 Stopping tests

 

A full astern stopping test is used to determine the track reach of a ship from

the time an order for full astern is given until the ship is stopped dead in the water

(see figure 4).

 

 

 

 

2 Guidelines for the application of the standards

2.1 Conditions at which the standards apply

2.1.1 General

Compliance with the manoeuvring criteria should be evaluated under the standard

conditions in paragraph 4.2 of the Interim standards for ship manoeuvrability. The

standard conditions provide a uniform and idealized basis against which the inherent

manoeuvring performance of all ships may be assessed.

The Standards cannot be used to evaluate directly manoeuvring performance

under non-standard, but often realistic, conditions. The establishment of

manoeuvrability standards for ships under different operating conditions is a complex

task that deserves attention in the future. Research is currently under way to establish

methods for accurately predicting and assessing manoeuvrability in non-standard

operating conditions.

 

2.1.2 Deep, unrestricted water

Manoeuvrability of a ship is strongly affected by interaction with the bottom of

the waterway, banks and passing vessels. Trials should therefore be conducted

preferably in deep, unconfined but sheltered waters. The water depth should exceed

four times the mean draught of the ship.

2.1.3 Full load and even keel condition

The Standards apply to the full load and even keel condition. The term "fully

loaded" refers to the situation where the ship is loaded to its summer load line draught

(referred to hereafter as "full load draught"). This draught is chosen based on the

general understanding that the poorest manoeuvring performance of a ship occurs at

this draught. The full load draught, however, is not based on hydrodynamic

considerations but rather statutory and classification society requirements for scantlings,

freeboard and stability. The result being that the final full load draught might not be

known or may be changed as a design develops.

Where it is impractical to conduct trials at full load because of ship type, trials

should be conducted as close to full load draught and zero trim as possible. Special

attention should also be given to ensuring that sufficient propeller immersion exists in

the trial condition.

Where trials are conducted in conditions other than full load, manoeuvring

characteristics should be predicted for trial and full load conditions using a reliable

method (i.e. model tests or reliable computer simulation) that ensures satisfactory

extrapolation of trial results to the full load condition. It rests with the designer/owner

to demonstrate compliance at the final full load condition.

 

2.1.4 Metacentric height

The Standards apply to a situation where the ship is loaded to the minimum

metacentric height for which it is designed at the full load draught.

 

2.1.5 Calm environment

Trials should be held in the calmest weather conditions possible. Wind, waves

and current can significantly affect trial results, having a more pronounced effect on

smaller ships. The environmental conditions should be accurately recorded before and

after trials so that corrections may be applied. Specific environmental guidelines are

outlined in 2.2.1.2.1.

 

2.1.6 Steady approach at the test speed

The required test speed is defined in paragraph 3.2.1 of the Interim standards for

ship manoeuvrability.

2.2 Guidance for required trials and validation

2.2.1 Test procedures

2.2.1.1 General

The test procedures given in the following guidelines were established to support

the application of the manoeuvring standards by providing to shipyards and other

institutions standard procedures for the testing trials of new ships, or for later trials

made to supplement data on manoeuvrability. This guidance includes trial procedures

that need to be performed in order to provide sufficient data for assessing ship

manoeuvring behaviour against the defined criteria.

 

2.2.1.2 Test conditions

 

2.2.1.2.1 Environment

Manoeuvring trials should be performed in the calmest possible weather

conditions. The geographical position of the trial is preferably in a deep sea, sheltered

area where accurate positioning fixing is possible. Trials should be conducted in

conditions within the following limits:

1. Deep unrestricted water: more than 4 times the mean draught.
2. Wind: not to exceed Beaufort 5.
3. Wave: not to exceed sea state 4.
4. Current: uniform only.

Correction may need to be applied to the test results following the guidance

contained in 3.4.2.

 

2.2.1.2.2 Loading

The ship should preferably be loaded to the full load draught and even keel,

however, a 5% deviation from that draught may be allowed and trim may deviate

from even keel up to 5% of the full load draught.

Alternatively, the ship may be in a ballast condition with a minimum of trim,

and sufficient propeller immersion.

 

2.2.1.2.3 Ship speed

The test speed is defined in paragraph 3.2.1 of the Interim standards.

 

2.2.1.2.4 Heading

Preferably head to the wind during the approach run.

 

2.2.1.2.5 Engine

Engine control setting to be kept constant during the trial if not otherwise stated

in following procedures.

 

2.2.1.2.6 Approach run

The above-mentioned conditions must be fulfilled for at least two minutes

preceding the test. The ship is running at test speed up wind with minimum rudder

to keep its course.

 

2.2.1.3 Turning circle manoeuvre

Trials shall be made to port and to starboard using maximum rudder angle

without changing engine control setting from the initial speed. The following general

procedure is recommended:

1. The ship is brought to a steady course and speed according to the specific approach condition.
2. The recording of data starts.
3. The manoeuvre is started by ordering the rudder to the maximum rudder angle. Rudder and engine controls are kept constant during the turn.
4. The turn continues until 360°change of heading has been completed. It is, however, recommended that in order to fully assess environmental effects a 720°turn be completed (paragraph 3.4.2 refers).
5. Recording of data is stopped and the manoeuvre is terminated.

2.2.1.4 Zig-zag manoeuvre

The given rudder and change of heading angle for the following procedure is 1

0°. This value can be replaced for alternative or combined zig-zag manoeuvres by

other angles such as 20°for the other required zig-zag test. Trials should be made to

both port and starboard. The following general procedure is recommended:

1. The ship is brought to a steady course and speed according to the specific approach condition.
2. The recording of data starts.
3. The rudder is ordered to 10°to starboard/port.
4. When the heading has changed by 10 degrees off the base course, the rudder is shifted to 10°to port/starboard. The ship's yaw will be checked and a turn in the opposite direction (port/starboard) will begin. The ship will continue in the turn and the original heading will be crossed.
5. When the heading is 10° port/starboard off the base course, the rudder is reversed as before.
6. The procedure is repeated until the ship heading has passed the base course no less than two times.
7. Recording of data is stopped and the manoeuvre is terminated.

2.2.1.5 Stopping test

Full astern is applied and the rudder maintained at midship throughout this test.

The following general procedure is recommended:

1. The ship is brought to a steady course and speed according to the specific approach condition.
2. The recording of data starts.
3. The manoeuvre is started by giving a stop order. The full astern engine order is applied.
4. Data recording stops and the manoeuvre is terminated when the ship is stopped dead in the water.

2.2.2 Recording

For each trial, a summary of the principal manoeuvring information should be

provided in order to assess the behaviour of the ship.

Continuous recording of data should be either manual or automatic using analog

or digital acquisition units. In case of manual recording, a regular sound/light signal

for synchronization is advisable.

 

2.2.2.1 Ship's particulars

Prior to trials, draughts forward and aft should be read in order to calculate

displacement, longitudinal centre of gravity, draughts and metacentric height. In

addition the geometry, projected areas and steering particulars should be known. The

disposition of the engine, propeller, rudder, thruster and other device characteristics

should be stated with operating condition.

 

2.2.2.2 Environment

The following environmental data should be recorded before each trial:

1. Water depth.
2. Waves: The sea state should be noted. If there is a swell, note period and direction.
3. Current: The trials should be conducted in a well surveyed area and the condition of the current noted from relevant hydrographic data. Correlation shall be made with the tide.
4. Weather: Weather conditions, including visibility, should be observed and noted.

2.2.2.3 Trial related data

The following data as applicable for each test should be measured and recorded

during each test at appropriate intervals of not more than 20 s:

Position

Heading

Speed

Rudder angle and rate of movement

Propeller speed of revolution

Propeller pitch

Wind speed

A time signal should be provided for the synchronization of all recordings.

Specific events should be timed, such as trial starting-point, engine/helm change,

significant changes in any parameter such as crossing ship course, rudder to zero or

engine reversal in operating condition such as ship speed and shaft/propeller direction.

 

2.2.2.4 Presentation of data

The recordings should be analyzed to give plots and values for significant

parameters of the trial. Sample recording forms are given in appendix 6. The

manoeuvring criteria of the Standards should be evaluated from these values. Data

should also be presented as in appendix 2 of resolution A.601(15) for turning and

stopping manoeuvres.

3 Prediction guidance

3.1 General

To be able to assess the manoeuvring performance of a new vessel at the design

stage, it is necessary to predict the vessel's manoeuvring behaviour on the basis of

main dimensions, lines drawings and other relevant information available at the design

stage.

A variety of methods for prediction of manoeuvring behaviour at the design

stage exists, varying in the accuracy of the predicted manoeuvres and the cost of

performing the prediction. In practice most of the predictions at the design stage have

been based on three methods.

The first and simplest method is to base the prediction on experience and

existing data, assuming that the manoeuvring characteristics of the new ship will be

close to those of similar existing ships.

The second method is to base the prediction on results from model tests. At

the time these notes were written, model tests must be considered the most reliable

prediction method. However, it may be said that traditionally the requirements with

regard to accuracy have been somewhat more lenient in this area than in other areas

of ship model testing. The reason for this has simply been the absence of

manoeuvring standards. The feedback of full-scale trial results has generally been less

regular in this area than in the case of speed trials. Consequently the correlation basis

for manoeuvrability is therefore of a somewhat lower standard, particularly for hull

forms that may present a problem with regard to steering and manoeuvring

characteristics. It is expected that this situation will improve very rapidly when it

becomes generally known that a standard for ship manoeuvrability is going to be

introduced. Model tests are described in section 3.2.

The third method is to base the prediction on results from calculation/simulation

using a mathematical model. The numerical values of the characteristic coefficients

appearing in this mathematical model are largely based on the analysis of the results

of so-called captive scale model tests, derived from force measurements on models of

varying forms. It may be said that many of the mathematical models in existence

give reasonably accurate results for conventional not too full hull forms. Such hull

forms seldom present problems with regard to steering and manoeuvring. Applied to

the ships that are poor in the manoeuvrability database, existing mathematical models

seem to achieve a lower level of reliability. In such cases it is recommended that

special captive model tests be performed for the new design. As in the case of model

tests an improvement in reliability is expected for mathematical models in the near

future. Mathematical models are described in section 3.3.

3.2 Model tests

There are two commonly used model test methods available for prediction of

manoeuvring characteristics. One method employs a free-running model moving in

response to specified control input (i.e. helm and propeller); the tests duplicate the

full-scale trial manoeuvres and so provide direct results for the manoeuvring

characteristics. The other method makes use of force measurements on a "captive"

model, forced to move in a particular manner with controls fixed; the analysis of the

measurements provides the coefficients of a mathematical model, which may be used

for the prediction of the ship response to any control input.

 

3.2.1 Manoeuvring test with free-running model

The most direct method of predicting the manoeuvring behaviour of a ship is to

perform representative manoeuvres with a scale model.

To reduce costs by avoiding the manufacture of a special model for manoeuvring

tests, such tests may be carried out with the same model employed for resistance and

self-propulsion tests. Generally it means that a relatively large model will be used for

the manoeuvring tests, which is also favourable with regard to reducing scale effects

of the results.

The large offshore, seakeeping and manoeuvring basins are well suited for

manoeuvring tests with free-running models provided they have the necessary

acquisition and data processing equipment. In many cases, conventional towing tanks

are wide enough to allow the performance of the 10 degrees/10 degrees zig-zag test.

Alternatively, tests with a free-running model can be conducted on a lake. In this

case measuring equipment must be installed and the tests will be dependent on weather

conditions.

Both laboratory and open-air tests with free-running models suffer from scale

effects, even if these effects to a certain extent will be reduced by using a large

model for the tests. Sometimes it has been attempted to compensate for scale effects

by means of an air propeller on board the model. Another improvement is to make

the drive motor of the ship model simulate the characteristics of the main engine of

the ship with regard to propeller loading.

Manoeuvres such as turning circle, zig-zag and spiral tests are carried out with

the free-running model, and the results can be compared directly with the standard of

manoeuvrability.

More recently, efforts have been made at deriving the coefficients of

mathematical models from tests with free-running models. The mathematical model is

then used for predicting the manoeuvring characteristics of the ship. Parameter

identification methods have been used and this procedure has been combined with

oblique towing and propulsion tests to provide some of the coefficients.

 

3.2.2 Manoeuvring tests with captive model

Captive model tests include oblique-towing tests in long narrow tanks as well as

"circling" tests in rotating-arm facilities, but in particular such tests are performed by

the use of a Planar Motion Mechanism (PMM) system capable of producing any kind

of motion by combining static or oscillatory modes of drift and yaw. Generally, it

may be said that captive model tests suffer from scale effects similar to those of the

free-running tests, but corrections are more easily introduced in the analysis of the

results.

In using captive model tests due account of the effect of roll during

manoeuvring should be taken.

The PMM has its origin in devices operating in the vertical plane and used for

submarine testing. The PMM makes it possible to conduct manoeuvring tests in a

conventional long and narrow towing tank. The basic principle is to conduct various

simpler parts of more complex complete manoeuvres. By analysis of the forces

measured on the model the manoeuvring behaviour is broken down into its basic

elements, the hydrodynamic coefficients. The hydrodynamic coefficients are entered

into a computer based mathematical model and the results of the standard manoeuvres

are predicted by means of this mathematical model.

A rotating arm facility consists of a circular basin, spanned by an arm from the

centre to the circumference. The model is mounted on this arm and moved in a

circle, varying the diameter for each test. The hydrodynamic coefficients related to

ship turning as well as to the combination of turning and drift will be determined by

this method. Additional tests often have to be conducted in a towing tank in order to

determine hydrodynamic coefficients related to ship drift. As in the case of the PMM

the manoeuvring characteristics of the ship are then predicted by means of a

mathematical model using the coefficients derived from the measurements as input.

 

3.2.3 Model test condition

The Standards are applicable to the full load condition of the ship. The model

tests should therefore be performed for this condition. For many ships the delivery

trials will be made at a load condition different from full load. It will then be

necessary to assess the full load manoeuvring characteristics of the ship on the basis

of the results of manoeuvring trials performed at a condition different from full load.

To make this assessment as reliable as possible the model tests should also be carried

out for the trial condition, meaning that this condition must be specified at the time of

performing the model tests. The assumption will be that when there is an acceptable

agreement between model test results and ship trial results in the trial condition, the

model test results for the loaded condition will then be a reliable basis for assessing

the manoeuvring characteristics of the ship.

3.3 Mathematical model

A "mathematical model" is a set of equations which can be used to describe the

dynamics of a manoeuvring ship. In this section, the method used to predict the

manoeuvring performance of a ship at full load for comparison with the Standards is

explained.

The following details of the mathematical model are indicated:

1.  when and where to use
2. how to use
3. accuracy level of predicted results

3.3.1 Application of the mathematical model

In general, the manoeuvring performance of the ship must be checked by a sea

trial to determine whether it satisfies the manoeuvring standards or not. The Standards

are regulated in full load condition from the viewpoints of marine safety.

Consequently, it is desired that the sea trial for any ship be carried out in full load

condition. This may be a difficult proposition for ships like a dry cargo ship, for

which the sea trial is usually carried out in ballast or heavy ballast conditions from

the practical point of view.

In such cases, it will be required to predict the manoeuvring performance in full

load condition by means of some method that uses the results of the sea trial. As an

alternative to scale model tests, usually conducted during the ship design phase, a

numerical simulation using a mathematical model is a useful method for predicting ship

manoeuvring performance in full load condition.

 

3.3.2 Prediction method using a mathematical model

There are many types of mathematical models for predicting ship

manoeuvrability, and in general, each one of them has merits and demerits for

application from the point of accuracy. Therefore it would be very difficult to pick

out and select any one method as the best mathematical model. It is a well-known

fact that there are still some problems to be solved, and it is required in the near

future to develop a more accurate method for predicting ship manoeuvrability. But it

may be possible to predict the manoeuvrability for the conventional ship's form with

certain accuracy from the practical point of view using some mathematical models

which have already been published.

3.4 Corrections from non-standard trial conditions

; Corrections from non-standard trial conditions

 

3.4.1 Loading condition

In the case for predicting manoeuvrability of a ship in full load condition using

the mathematical model through the sea trial results in ballast or heavy ballast

condition, the following two methods are used in current practice.

Option 1:

The manoeuvring performance in full load condition can be obtained from the

criteria of measured performance during the sea trial in ballast condition (T) and the

interaction factor between the criteria of manoeuvrability in full load condition and in

a trial condition ( F / B ), that is as given below;

R = T F / B

where, B: the estimated performance in the condition of sea trial based on

the numerical simulation using the mathematical model or on the

model test.

F: the estimated performance in full load condition based on the

numerical simulation using the mathematical model or on the

model test.

T: the measured performance during the sea trial.

R: the performance of the ship in full load condition.

Option 2:

The manoeuvring performance in the condition of sea trial such as ballast or

heavy ballast are predicted by the method shown in appendix 2, and the predicted

results must be checked with the results of the sea trial.

Afterwards it should be confirmed that both results agree well with each other.

The performance in full load condition may be obtained by means of the same method

using the mathematical model.

 

3.4.2 Environmental conditions

Ship manoeuvrability can be significantly affected by the immediate environment

such as wind, waves, and current. Environmental forces can cause reduced

course-keeping stability or complete loss of the ability to maintain a desired course.

They can also cause increased resistance to a ship's forward motion, with consequent

demand for additional power to achieve a given speed.

When the ratio of wind velocity to ship speed is large, wind has an appreciable

effect on ship control. The ship may be unstable in wind from some directions.

Waves can also have significant effect on course-keeping and manoeuvring. It has

been shown that for large wave heights a ship may behave quite erratically and, in

certain situations, can lose course stability.

Ocean current affects manoeuvrability in a manner somewhat different from that

of wind. The effect of current is usually treated by using the relative velocity

between the ship and the water. Local surface current velocities in the open ocean are

generally modest and close to constant in the horizontal plane.

Therefore, trials shall be performed in the calmest weather conditions possible.

In the case that the minimum weather conditions for the criteria requirements are not

applied, the trial results should be corrected.

Generally, it is easy to account for the effect of constant current. The turning

circle test results may be used to measure the magnitude and direction of current.

The ship's track, heading and the elapsed time should be recorded until at least a 72

0° change of heading has been completed. The data obtained after ship's heading

change 180° are used to estimate magnitude and direction of the current. Position

( x 1i , y 1i , t 1i ) and ( x 2i , y 2i , t 2i ) in figure 5 are the positions of the ship measured

after a heading rotation of 360°. By defining the local current velocity V i for any

two corresponding positions as

 

All trajectories obtained from the sea trials should be corrected as follows:

x' ( t) = x ( t) - V ct

where x(t) is the measured position vector and x'(t) is the corrected one of the ship

and x'(t) = x(t) at t=0.

 

 

3.5 Uncertainties

 

3.5.1 Accuracy of model test results

In most cases, the model will turn out to be more stable than the ship due to

scale effects. This problem seems to be less serious when employing a large model.

Consequently, to reduce this effect model scale ratios comparable to that considered

acceptable for resistance and self-propulsion tests should be specified for manoeuvring

tests that use a free-running model. Captive model tests can achieve satisfactory

results with smaller scale models.

While the correlation data currently available are insufficient to give reliable

values for the accuracy of manoeuvring model test results, it is the intent of the

Standards to promote the collection of adequate correlation data during the interim

period.

 

3.5.2 Accuracy of predicted results using the mathematical model

The mathematical model that can be used for the prediction of the manoeuvring

performance depends on the type and amount of prepared data.

If there is no available data, under assumptions that resistance and self-propulsion

factors are known, a set of approximate formulae for estimation of the derivatives and

coefficients in the mathematical model will become necessary to predict the ship's

manoeuvrability.

If there is enough experimental and accumulated data, it is desirable to use a

detailed mathematical model based on this data. In most cases the available data is

not sufficient and a mathematical model can be obtained by a proper combination of

different parts derived from experimental data and those obtained by the estimated

formulae.

 

 

Appendix 1 Nomenclature

A.1.1 Nomenclature and reference systems

 

The manoeuvres of a surface ship may be seen to take place in the x o y o -plane

of a right-handed system of axes Oo ( x o y o z o ) "fixed in space", the z o -axis of

which is pointing downwards in the direction of gravity. For the present discussion

let the origin of this system coincide with the position at time t = 0 of the midship

point O of the ship, and let the x o -axis be pointing in the direction of ship's heading

at the same moment, the y o -axis pointing to starboard. The future orientation of the

ship in this system is given by its heading angle y, its angle of pitch q, and its angle

of roll f. (See figure A1-1.)

In calm conditions with no tide or current ship speed through water (V) equals

the speed over the ground, and the progress along the ship track is equal to the time

integral

V dt .

This distance may conveniently be expressed by the number of ship lengths sailed, i.e.

by the non-dimensional time

 

Mathematical models of ship dynamics involve expressions for the forces acting

on the hull, usually separated in their components along the axes of a system O(xyz)

moving with the body. The full six-degrees-of-freedom motion of the ship may be

defined by the three components of linear velocities (u,v,w) along the body axes, and

by the three components of angular velocities (p,q,r) around these axes. Again, for the

present discussion it is sufficient to consider the surface ship, moving with forward

velocity u and sway velocity v in the O(xy) plane, and turning with yaw velocity r

around the z-axis normal to that plane. On these assumptions the speed

 

which is also seen to be the non-dimensional measure of the instantaneous curvature of

the path of this ship L

R

.

Many ships will experience a substantial rolling velocity and roll angle during a

turning manoeuvre, and it is understood that the mathematical model used to predict

the manoeuvring characteristics should then include the more stringent expressions as

appropriate. Further information can be found in section 3.2 of the Interim standards

for ship manoeuvrability.

which is also seen to be the non-dimensional measure of the instantaneous curvature of

the path of this ship L / R

.

Many ships will experience a substantial rolling velocity and roll angle during a

turning manoeuvre, and it is understood that the mathematical model used to predict

the manoeuvring characteristics should then include the more stringent expressions as

appropriate. Further information can be found in section 3.2 of the Interim standards

for ship manoeuvrability.

 

 

Appendix 2 General view of prediction of manoeuvring

A mathematical model of the ship manoeuvring motion can be used as one of

the effective methods to check whether a ship satisfies the manoeuvrability standards or

not, by a performance prediction at the

full load condition and from the results of the sea trial in a condition such as ballast.

Existing mathematical models of ship manoeuvring motion are classified into two

types. One of the models is called a 'response model', which expresses a relationship

between input as the control and output as its manoeuvring motion. The other model

is called a 'hydrodynamic force model', which is based on the hydrodynamic forces

that include the mutual interferences. By changing the relevant force derivatives and

interference coefficients composed of a hydrodynamic force model, the manoeuvring

characteristics due to a change in the ship's form or loading condition can be

estimated.

Furthermore, a hydrodynamic force model is helpful for understanding the

relationship between manoeuvring performance and ship form than a response model

from the viewpoint of design. Considering these situations, this Appendix shows the

prediction method using a hydrodynamic force model. Certainly, the kind of

mathematical model suitable for prediction of the performance depends on the kind of

available data. Presently, there are many kinds of mathematical models.

In figure A2-1, the flow chart of prediction method of ship manoeuvring

performance using a hydrodynamic force model is shown. There are in general

various expressions of a hydrodynamic force model in current practice, though their

fundamental ideas based on hydrodynamic considerations have little difference.

Concerning the hydrodynamic force acting on a ship in manoeuvring motion, they are

usually expressed as a polynomial term of motion variables such as the surge, sway

and angular yaw velocities.

The most important and difficult work in performance prediction is to estimate

such derivatives and parameters of these expressions to compose an equation of a ship

manoeuvring motion. These hydrodynamic force coefficients and derivatives may

usually be estimated by the method shown in figure A2-1.

The coefficients and derivatives can be estimated by the model test directly, by

data based on the data accumulated in the past, by theoretical calculation and

semi-empirical formulae based on any of these methods. There is also an example

that uses approximate formulae for estimation derived from a combination of theoretical

calculation and empirical formulae based on the accumulated data. The derivatives

which are coefficients of hydrodynamic forces acting on a ship's hull, propeller and

rudder are estimated from such parameters as ship length, breadth, mean draught, trim

and the block coefficient. Change of derivatives due to a change in the load condition

may be easily estimated from the changes in draught and trim.

As mentioned above, accuracy of manoeuvring performance predicted by a

hydrodynamic force model depends on accuracy of estimated results by hydrodynamic

forces which constitutes the equation of a ship manoeuvring motion. Estimating the

hydrodynamic derivatives and coefficients will be important to raise accuracy as a

whole while keeping consistency of relative accuracy among various hydrodynamic

forces.

A stage in which theoretical calculations can provide all of the necessary

hydrodynamic forces with sufficient accuracy has not yet been reached. Particularly,

non-linear hydrodynamic forces and mutual interferences are difficult to estimate with

sufficient accuracy by pure theoretical calculations. Thus, empirical formulae and

databases are often used, or incorporated into theoretical calculations.

 

Appendix 3 Stopping ability of very large ships

It is stated in the Interim standards for ship manoeuvrability that the track reach

in the full astern stopping test may be modified from 15 ship lengths, at the discretion

of the Administration, where ship size and form make the criterion impracticable. The

following example and information given in tables A3-1, 2 and 3 indicate that the

discretion of the Administration is only likely to be required in the case of large

tankers.

The behaviour of a ship during a stopping manoeuvre is extremely complicated.

However, a fairly simple mathematical model can be used to demonstrate the important

aspects which affect the stopping ability of a ship. For any ship the longest stopping

distance can be assumed to result when the ship travels in a straight line along the

original course, after the astern order is given. In reality the ship will either veer off

to port or starboard and travel along a curved track, resulting in a shorter track reach,

due to increased hull drag.

To calculate the stopping distance on a straight path a number of assumptions

must be made.

1. The resistance of the hull is proportional to the square of the ship speed.
2. The astern thrust is constant throughout the stopping manoeuvre, and equal to the astern thrust generated by the propeller when the ship eventually stops dead in the water.
3. The propeller is reversed as rapidly as possible after the astern order is given.

An expression for the stopping distance along a straight track, in ship lengths,

can be written in the form:

S = A log e ( 1+ B ) + C ,

where:

S : is the stopping distance, in ship lengths.

A : is a coefficient dependent upon the mass of the ship divided by its

resistance coefficient.

R : is a coefficient dependent on the ratio of the ship resistance immediately

before the stopping manoeuvre, to the astern thrust when the ship is dead

in the water.

C : is a coefficient dependent upon the product of the time taken to achieve

the astern thrust and the initial speed of the ship.

The value of the coefficient A is entirely due to the type of ship and the shape

of its hull. Typical values of A are shown in table A3-1.

The value of the coefficient B is controlled by the amount of astern power

which is available from the power plant. With diesel machinery, the astern power

available is usually about 85% of the ahead power, whereas with steam turbine

machinery this figure could be as low as 40%.

 

Table A3-1

Ship Type   Cargo ship Passenger/Car ferry Gas carrier Products tanker VLCC

Coefficient A   5-8  8-9 10-11 12-13 14-16

 

Accordingly the value of the coefficient B is smaller if a large amount of astern

power and hence astern thrust, is available. Typical values of the coefficient B are

given in table A3-2.

 

Table A3-2

Type of Machinery     Diesel Steam turbine

Percentage Power Astern   85% 40%

Coefficient   B     0.6-1.0 1.0-1.5

Log (1+B)       0.5-0.7 0.7-0.9

 

The value of the coefficient C is half the distance travelled, in ship lengths, by

the ship, whilst the engine is reversed and full astern thrust is developed. The value

of C will be larger for smaller ships and typical values are given in table A3-3.

 

Table A3-3

Ship Length (metres)   100 200 300

Time to Achieve Astern Thrust (s)   60 60 60

Ship Speed   (Knots)   15 15 15

Coefficient  C     2.3 1.1 0.8

 

If the time taken to achieve the astern thrust is longer then 60 seconds, as

assumed in table A3-3, or if the ship speed is greater than 15 knots, then the values

of the coefficient C will increase pro rata.

 

Although all the values given for the coefficients A, B and C may only be

considered as typical values for illustrative purposes, they indicate that large ships may

have difficulty satisfying the adopted stopping ability criterion of 15 ship lengths.

Consider a steam turbine propelled VLCC of 300 m length, travelling at 15

knots, and assume that it takes 1 minute to develop full-astern thrust in a stopping

manoeuvre. Then from tables A3-1, 2 and 3 we get

A = 16,

B = 1.5, and

 

C= 0.8
Using the formula for stopping distance S, given above, then
S= 16log e ( 1+ 1. 5) + 0. 8 = 15. 5 ship lengths,
which exceeds the stopping ability criterion of 15 ship lengths.
In all cases the value of A is inherent in the shape of the hull and so cannot
be changed unless resistance is significantly increased. The value of B can only be
reduced by incorporating more astern power in the engine, an option which is
unrealistic for a steam turbine powered ship. The value of C would become larger if
more than one minute was taken to reverse the engines, from the astern order to the
time when the full-astern thrust is developed.

 

 

 

Appendix 4 Additional manoeuvres

TER>Appendix 4; Stopping ability of very large ships

 

A.4 Additional methods to assess course keeping ability

The standards note that additional testing may be used to further investigate a

dynamic stability problem identified by the standard trial manoeuvres. This appendix

briefly discusses additional trials that may be used to evaluate a ship's manoeuvring

characteristics.

The standards are used to evaluate course-keeping ability based on the overshoot

angles resulting from the 10°/10°zig-zag manoeuvre. The zig-zag manoeuvre was

chosen for reasons of simplicity and expediency in conducting trials. However, where

more detailed analysis of dynamic stability is required some form of spiral manoeuvre

should be conducted as an additional measure. A direct or reverse spiral manoeuvre

may be conducted, as recommended in MSC/Circ.389. The spiral and pull-out

manoeuvres have historically been recommended by various trial codes as measures that

provide the comprehensive information necessary for reliably evaluating course-keeping

ability. The direct spiral manoeuvre is generally time consuming and weather sensitive.

A relatively new trial, the simplified spiral, can be used to quickly evaluate key points

of the spiral loop curve. DE 35/INF.14 provides a correlation between acceptance

criteria for the spiral loop width versus the overshoot angle in the 10°/10°zig-zag

manoeuvre. Another new trial uses a very small zig-zag manoeuvre to evaluate the

dynamic instability of the vessel.

 

A.4.1 Spiral manoeuvres

A.4.1.1 Direct spiral manoeuvre

The direct spiral manoeuvre is an orderly sequence of turning circle tests to

obtain a steady turning rate versus rudder angle relation (see figure A4-2).

Should there be reasons to expect the ship to be dynamically unstable, or only

marginally stable, a direct spiral test will give additional information. This is a

time-consuming test to perform especially for large and slow ships. A significant

amount of time is needed for the ship to obtain a steady rate of change of heading

after each rudder angle change. Also, the test is very sensitive to weather conditions.

In the case where dynamic instability is detected with other trials or is expected,

a direct spiral test can provide more detailed information about the degree of instability

that exists. While this test can be time consuming and sensitive to weather conditions,

it yields information about the yaw rate/rudder angle relation that cannot be measured

by any other test.

The direct spiral is a turning circle manoeuvre in which various steady state yaw

rate/rudder angle values are measured by making incremental rudder changes throughout

a circling manoeuvre. Adequate time must be allowed for the ship to reach a steady

yaw rate so that false indications of instability are avoided. In cases where the ship is

dynamically unstable it will appear that it is still turning steadily in the original

direction although the rudder is now slightly deflected to the opposite side. At a

certain stage the yaw rate will abruptly change to the other side and the yaw rate

versus rudder angle relation will now be defined by a separate curve. Upon

completion of the test the results will display the characteristic spiral loop as presented

in figure A4-3.

A direct spiral manoeuvre can be conducted using the following general procedure:

1. The ship is brought to a steady course and speed according to the specificinitial condition.
2. The recording of data starts.
3. The rudder is turned about 15° and held until the yaw rate remains constant for approximately one minute.
4. The rudder angle is then decreased in approximately 5° increments. At each increment the rudder is held fixed until a steady yaw rate is obtained, measured and then decreased again.
5. This is repeated for different rudder angles starting from large angles to both port and starboard.
6. When a sufficient number of points is defined, data recording stops.

A.4.1.2 Reverse spiral manoeuvre

The reverse spiral test may provide a more rapid procedure than the direct spiral

test to define the instability loop as well as the unstable branch of the yaw rate

versus rudder angle relationship indicated by the dotted curve as shown in figure A4-2.

In the reverse spiral test the ship is steered to obtain a constant yaw rate, the mean

rudder angle required to produce this yaw rate is measured and the yaw rate versus

rudder angle plot is created. Points on the curve of yaw rate versus rudder angle may

be taken in any order.

This trial requires a properly calibrated rate of turn indicator and an accurate

rudder angle indicator. Accuracy can be improved if continuous recording of rate of

turn and rudder angle is available for the analysis. Alternatively the test may be

performed using a conventional autopilot. If manual steering is used, the instantaneous

rate of turn should be visually displayed to the helmsman.

 

A.4.1.3 Simplified spiral manoeuvre

The simplified spiral reduces the complexity of the spiral manoeuvre. The

simplified spiral consists of three points which can be easily measured at the end of

the turning circle test. The first point is a measurement of the steady state yaw rate

at the maximum rudder angle. To measure the second point, the rudder is returned to

the neutral position and the steady state yaw rate is measured. If the ship returns to

zero yaw rate the ship is stable and the manoeuvre may be terminated. Alternatively,

the third point is reached by placing the rudder in the direction opposite of the

original rudder angle to an angle equal to half the allowable loop width. The

allowable loop width may be defined as:

When the rudder is placed at half the allowable loop width and the ship
continues to turn in the direction opposite to that of the rudder angle, then the ship is
unstable beyond the acceptable limit.

 

A.4.2 Pull-out manoeuvre
After the completion of the turning circle test the rudder is returned to the
midship position and kept there until a steady turning rate is obtained. This test gives
a simple indication of a ship's dynamic stability on a straight course. If the ship is
stable, the rate of turn will decay to zero for turns to both port and starboard. If the
ship is unstable, then the rate of turn will reduce to some residual rate of turn (see
figure A4-1). The residual rates of turn to port and starboard indicate the magnitude
of instability at the neutral rudder angle. Normally, pull-out manoeuvres are performed
in connection with the turning circle, zig-zag, or initial turning tests, but they may be
carried out separately.

A.4.3 Very small zig-zag manoeuvre
The shortcomings of the spiral and 10°/10°zig-zag manoeuvres may be
overcome by a variation of the zig-zag manoeuvre that quite closely approximates the
behaviour of a ship being steered to maintain a straight course. This zig-zag is
referred to as a Very Small Zig Zag (VSZZ), which can be expressed using the usual
nomenclature, as 0°/5°zig-zag, where y is 0° and d is 5°.
VSZZs characterized by 0°/5°are believed to be the most useful type, for the
following two reasons.

1. A human helmsman can conduct VSZZs by evaluating the instant at which to
   move the wheel while sighting over the bow, which he can do more
   accurately than by watching a conventional compass.
2. A conventional autopilot could be used to conduct VSZZs by setting a large
   proportional gain and the differential gain to zero.

There is a small but essential difference between 0°/5°VSZZs and more
conventional similar zig-zags, such as 1°/5° zig-zag. A 0°/5° zig-zag must be
initialized with a non-zero rate-of-turn. In reality, this happens naturally in the case of
inherently unstable ships.
A VSZZ consists of a larger number of cycles than a conventional zig-zag,
perhaps 20 overshoots or so, rather than the conventional two or three, and interest
focuses on the value of the overshoot in long term. The minimum criterion for
course-keeping is expressed in terms of the limit-cycle overshoot angle for 0 degrees/5
degrees VSZZs, and is a function of length to speed ratio.

 

 

 

 

Appendix 5 Backgrond and bibliography

A.5.1 Background data
MSC/Circ.389 invited Member Governments to submit ship manoeuvrability data
for use in ship design and for establishing manoeuvrability standards. In response,
ship trials data and other manoeuvring information were submitted to the DE
Sub-Committee by Member Governments. The data, along with other available
information, were incorporated into a ship manoeuvring database to facilitate analysis
for establishing the manoeuvring standards. The Working Group on Manoeuvrability
considered collation papers submitted by the correspondence group (DE 35/4/3, DE
34/4/3) and submissions by Canada (DE 31/3/3), China (DE 35/4/1), Finland (DE
31/INF.2, DE 31/INF.3), Germany (DE/317, DE/316, DE 33/7, DE 26/6), Italy (DE
32/INF.2), Japan (DE 35/INF.14, DE 34/INF.2, DE 33/INF.8, DE/308, DE/329,
DE/323, DE XXII/8/3, DE 28/4/1, DE 32/INF.5, DE 30/4, DE 30/INF.10, DE
29/INF.3, DE 29/INF.4, DE 33/4), the Netherlands (DE 31/3), Norway (DE 35/4/4, DE
34/4/2), Poland (DE/270, DE 27/5/3), Sweden (DE 34/4/4), the USSR (DE/294,
DE/326), the United Kingdom (DE XI/10, DE 32/4, DE 31/INF.5, DE/59, DE 33/4/1),
the United States (DE 34/4/1, DE/300, DE/319, DE/307, DE/314, DE XX/6/1, DE
25/5/1, DE 31/3/1, DE 31/3/2) and reports of the Working Group on Manoeuvrability
(DE 35/WP.4, DE 34/4, DE 34/WP.7, DE XXIV/5 and DE 25/5, DE 25/WP.6). Other
sources of data and information that were also examined in establishing the
manoeuvring Standards are included under "References for Background Data".

A.5.2 Bibliography

1. "Technical Basis for Manoeuvring Performance Standards", December 1981, U.S.
   Coast Guard.
2. "Development and Application of an Enhanced Ship Manoeuvring Database",
   October 1989, U.S. Coast Guard.
3. Norrbin, N.H., "Shiphandling Standards - Capabilities and Requirements",
   International Conference on Ship Manoeuvring, Tokyo, June 1990.
4. Asinovsky, V., "Review and Analysis of Ship Manoeuvrability Criteria", Naval
   Engineers Journal, American Society of Naval Engineers, May 1989.
5. Clarke, D., "Assessment of Manoeuvring Performance", Ship Manoeuvrability -
   Prediction and Achievement, RINA Symposium April/May 1987.
6. Trials Data on Stopping Performance submitted by France to the IMO
   Correspondence Group on Manoeuvrability, dated 14 October 1991.
7. "Design and Verification for Adequate Ship Manoeuvrability", Transactions of the
   Society of Naval Architects and Marine Engineers, New York, 1983.
8. "Guide for Sea Trials", Society of Naval Architects and Marine Engineers, June
   1990.
9. NORSK STANDARD: Testing of new ships (NS 2780), August 1985.
10. IMO - Resolution A.601(15): Provision and display of manoeuvring information
    on board ships - 19 November 1987.
11. Shipbuilding Research Institute (IRCN): Etablissement d'un code d'essais de
    vitesse et de manoeuvrabilite - 8 Novembre 1989.
12. CETENA: Manoeuvrability of full-scale ships - Polish-Italian Seminar on ship
    research - GDANSK - January 1977.
13. IMO - Circular 389 - Interim guidelines for estimating manoeuvring
    performance in ship design.
14. BSRA: Code of procedure for steering and manoeuvring trials -1972.
15. ITTC 1975: Manoeuvring Trial Code.
16. Ankudinov, V., "Simulation Analysis of Ship Motion in Waves", Proc. of
    International Workshop on Ship and Platform Motion, UC Berkeley, 1993.
17. Nobukawa, T., et al., "Studies on Manoeuvrability Standards from the viewpoint
    of Marine Pilots", MARSIM & ICSM 90, June 1990.
18. Koyama, T. and Kose, Kuniji, "Recent Studies and Proposals of the
    Manoeuvrability Standards", MARSIM & ICSM 90, June 1990.

Appendix 6 Form for reporting manoeuvring data to IMO form

Notes:

1. Reference no. assigned by the Administration for internal use.
2. Ship type such as container ship, tanker, gas carrier, ro-ro ship, passenger ship, car carrier, bulk carrier, etc.
3. Rudder type such as full spade, semi-spade, high lift, etc.
4. Propeller type such as fixed pitch, controllable pitch, with/without nozzle, etc.
5. Engine type such as diesel, steam turbine, gas turbine, diesel-electric, etc.
6. IMO criteria for 10 degrees/10 degrees zig-zag test vary with L/V. Refer to paragraphs 4.3.3.1 and 4.3.3.2 of the Interim Standards for Ship Manoeuvrability (IMO Assembly resolution A.751(18), annex).

 

• Informatietype: Internationaal
• Documentsoort: Circulaire niet in wetten.nl
• Toegangsrechten: Extern
• Identificatie: PUC_1729_14
• Versie: 1
• Datum beschikbaarheid: 04-09-2006
• Geldigheid van: 12-07-1996
• Wijzigingsdatum: 24-11-2016
• Titel: 644 Explanatory notes to the interim standards for ship manoeuvrability
• Organisatie: International Maritime Organization (IMO)
• Taal: Nederlands
• Onderwerp: Veiligheid / Safety
• Hoofdtaak: Koopvaardij / Merchant Shipping
• Thema: Zeevaart / Seagoing ships / Information / IMO Instruments (Informative) / Circulars (Informative) / MSC Circulars (Informative) / 0600 until 0699