Chapter 7 : Trials. Ch7. Sea trials / Manoeuvring characteristics of ships IMO Recommendations MSC 137(76) The manoeuvrability of ships can be evaluated

Chapter 7 : TrialsChapter 7 : Trials

Ch7. Sea trials / Manoeuvring characteristics of shipsCh7. Sea trials / Manoeuvring characteristics of ships

IMO Recommendations MSC 137(76)IMO Recommendations MSC 137(76)

• The manoeuvrability of ships can be evaluated from The manoeuvrability of ships can be evaluated from the characteristics of conventional trial manoeuvres.the characteristics of conventional trial manoeuvres.

• Two methods can be used:Two methods can be used:– Scale model tests or computer predictions using Scale model tests or computer predictions using

mathematical models at the design stage / full scale trials mathematical models at the design stage / full scale trials must be conducted to validate these resultsmust be conducted to validate these results

– Full scale trials Full scale trials

• Test speed = at least 90% of full speed = 85% of full Test speed = at least 90% of full speed = 85% of full engine powerengine power


Imo Manoeuvring StandardsImo Manoeuvring Standards• By resolution A.751(18) in 1993 IMO adopted By resolution A.751(18) in 1993 IMO adopted

Manoeuvring StandardsManoeuvring Standards• The standards apply to:The standards apply to:

– All ships of 100m in lenght and overAll ships of 100m in lenght and over– All chemical tankers and gas carriersAll chemical tankers and gas carriers

• They consist of:They consist of:– Turning circles to Port and starboardTurning circles to Port and starboard– Stopping TestStopping Test– Zig-Zag TestZig-Zag Test

Conditions at which the standards applyConditions at which the standards applyIn order to evaluate the performance of a ship, In order to evaluate the performance of a ship,

manoeuvring trials should be conducted to both port manoeuvring trials should be conducted to both port and starboard and at conditions specified below:and starboard and at conditions specified below:

.1 deep, unrestricted water .1 deep, unrestricted water ((> 4xmean draft)> 4xmean draft)

.2 calm environment .2 calm environment (Wind(Wind< 5Bft / Sea< 4)< 5Bft / Sea< 4)

.3 full load (summer load line draught), even keel .3 full load (summer load line draught), even keel conditioncondition

.4 steady approach at the test speed4 steady approach at the test speed(min90% full)(min90% full).


• Manoeuvring performance has traditionally received little Manoeuvring performance has traditionally received little attention attention during the design stagesduring the design stages of a commercial ship. of a commercial ship.

• Consequently some ships have been built with very poor Consequently some ships have been built with very poor manoeuvring qualities, resulting in marine casualties / manoeuvring qualities, resulting in marine casualties / pollution. pollution.

• Designers have relied on shiphandling abilities of human Designers have relied on shiphandling abilities of human operators to compensate for deficiencies in inherent operators to compensate for deficiencies in inherent manoeuvring qualities of the hull. manoeuvring qualities of the hull.

• The implementation of manoeuvring standards will The implementation of manoeuvring standards will ensure that ships are designed to a uniform standard, so ensure that ships are designed to a uniform standard, so that an undue burden is not imposed on shiphandlers in that an undue burden is not imposed on shiphandlers in trying to compensate for deficiencies in inherent ship trying to compensate for deficiencies in inherent ship manoeuvrability.manoeuvrability.

((Extract of IMO MSC/Circ1053)Extract of IMO MSC/Circ1053)


Ch7. Sea trials / PreliminaryCh7. Sea trials / Preliminary

Forces and motions in manoeuvrabilityForces and motions in manoeuvrability

Definition of the Pivot Point: Definition of the Pivot Point: • the point around which the ship rotatesthe point around which the ship rotates• The centre of the hydrodynamic forces acting on the The centre of the hydrodynamic forces acting on the

ship’s hullship’s hull

Position of the Pivot Point:Position of the Pivot Point:• Depends on the shape of the hullDepends on the shape of the hull• With no forward speed: pivot point at midshipWith no forward speed: pivot point at midship• At speed: pivot point shifts forwardAt speed: pivot point shifts forward

Ch7. Sea trials /PreliminaryCh7. Sea trials /Preliminary

The Pivot Point at forward speedThe Pivot Point at forward speed


1. Course keeping ability and dynamic stability1. Course keeping ability and dynamic stability

• Dynamically stable ship moves along a new straight Dynamically stable ship moves along a new straight course without using rudder after a small disturbancecourse without using rudder after a small disturbance

• Dynamically unstable ship performs turning circle Dynamically unstable ship performs turning circle with rudder amidshipwith rudder amidship

• More difficult to handle dynamically unstable ships More difficult to handle dynamically unstable ships

• Infos on course keeping and dynamic stability: Infos on course keeping and dynamic stability: obtained from « Initial turning test »obtained from « Initial turning test »


Dynamic stability:Dynamic stability: dynamically stable ships maintaindynamically stable ships maintainA straight course with zero rudderA straight course with zero rudder

Dynamically unstable ships can only Dynamically unstable ships can only maintain a straight course by repeatedmaintain a straight course by repeated use of rudder controluse of rudder control


Factors determining the Directional stability of vesselsFactors determining the Directional stability of vessels• Increase with the depth of the waterIncrease with the depth of the water• Increase with the lenght of the shipIncrease with the lenght of the ship• Increase with Trim by the sternIncrease with Trim by the stern• Decrease with big blockage factorDecrease with big blockage factor• Decrease for large vessel (ratio L/B)Decrease for large vessel (ratio L/B)• Decrease when cross sectional area fwd larger than Decrease when cross sectional area fwd larger than

cross sectional area after (pivot point moves cross sectional area after (pivot point moves forward)forward)

Ro-Ro ships are directionally unstableRo-Ro ships are directionally unstable

They need more rudder to stop a swing than to start a swingThey need more rudder to stop a swing than to start a swing


Change of trimChange of trim• Ship by the stern has a better course keeping abilityShip by the stern has a better course keeping ability• Ship by the head:Ship by the head:

– Slow to start a swingSlow to start a swing– Difficult to stop a swingDifficult to stop a swing– In shallow water, a ship gets trim byIn shallow water, a ship gets trim by the head and the head and

looses directional stabilitylooses directional stability

3 STANDARD MANOEUVRES3 STANDARD MANOEUVRES

TURNING CIRCLETURNING CIRCLE

Turning circleTurning circle: measure of turning ability of vessel: measure of turning ability of vessel

To determine the turning ability To determine the turning ability

- The measure of the ability of a ship using hard-over rudder- The measure of the ability of a ship using hard-over rudder- The result is a minimum « advance at 90° change of heading » - The result is a minimum « advance at 90° change of heading »

and « tactical diameter » defined by the « transfer at 180° and « tactical diameter » defined by the « transfer at 180° change of heading »change of heading »

- Tactical diameter is usually given as multiplacity of ship lenght- Tactical diameter is usually given as multiplacity of ship lenght

• The advance should not exceed 4.5 ship lengths (L) The advance should not exceed 4.5 ship lengths (L) • the tactical diameter should not exceed 5 lengths the tactical diameter should not exceed 5 lengths • Turning circle to be performed with 35°Rudder angle Turning circle to be performed with 35°Rudder angle


Lenght:196m / beam:25m / 24300DWT / Steamship/ 2 propellers/ 19Knots

StatendamStatendam

Advance: 426mAdvance: 426mTransfer: 99mTransfer: 99mDiameter: 263mDiameter: 263mTact.Dia: 290mTact.Dia: 290m

Advance: 426mAdvance: 426mTransfer: 94mTransfer: 94mDiameter: 258mDiameter: 258mTact.Dia: 292mTact.Dia: 292m

Advance & Transfer 90° Turn

Kick

Advance

Transfer

Shiphandling: Terms

Advance:Advance: the distance traveled in the direction the distance traveled in the direction of the original course by the midship point of a of the original course by the midship point of a ship from the position at which the rudder order ship from the position at which the rudder order is given to the position at which the heading is given to the position at which the heading

has changed 900 from the original course.has changed 900 from the original course.

Final Diameter

Turning Circle

Kick

Tactical Diameter

Shiphandling: Terms

Tactical diameterTactical diameter : : the distance the distance

traveled by the traveled by the midship point of a midship point of a

ship from the ship from the position at which position at which

the rudder order is the rudder order is given to the given to the

position at which position at which the heading has the heading has

changed 1800 fromchanged 1800 fromthe original course. the original course.

It is measured in a It is measured in a direction direction

perpendicular to perpendicular to the original the original

heading of the heading of the ship. ship.

CommentsComments• Advance of the ship smaller than the distance ahead Advance of the ship smaller than the distance ahead

with an emergency stop manœuvrewith an emergency stop manœuvre• Request sufficient searoom on the beam (tactical Request sufficient searoom on the beam (tactical

diameter)diameter)• Test are carried out at sea and not in shallow waters: Test are carried out at sea and not in shallow waters:

parameters are bigger in shallow water because parameters are bigger in shallow water because rudder effect decreases in shallow water due to the rudder effect decreases in shallow water due to the reduced waterflowreduced waterflow

• Parameters of the turning circle do not change for Parameters of the turning circle do not change for different speeds of the shipdifferent speeds of the ship


Drift angle and Pivot pointDrift angle and Pivot point•The pivot point (D) is at the intersection of the longitudinalThe pivot point (D) is at the intersection of the longitudinalaxis of the vessel with the radius of the turning circleaxis of the vessel with the radius of the turning circle•The drift angle at the pivot point is zeroThe drift angle at the pivot point is zero•The drift angle at the centre of gravity (G)The drift angle at the centre of gravity (G)


In shallow watersIn shallow waters, the drift angle is smaller : the water, the drift angle is smaller : the waterresistance decreases and the turning circle is largerresistance decreases and the turning circle is larger


Crablike motion of the ship:Crablike motion of the ship:Water resistance reduces the speedWater resistance reduces the speedand the diameter of turning circleand the diameter of turning circle

Forces acting on a ship when Forces acting on a ship when turningturning



The turning circle is affected by the effects of wind and The turning circle is affected by the effects of wind and currentcurrent


Turning characteristics of fullTurning characteristics of fulland slender shipsand slender ships

Comparison of turning characteristics of full and Comparison of turning characteristics of full and slender ships:slender ships:

• Two ships of the same lenght have nearly the same Two ships of the same lenght have nearly the same transfertransfer

• Tactical diameters almost the sameTactical diameters almost the same• Radius of turning circle smaller for tankerRadius of turning circle smaller for tanker• Drift angle much larger for tankerDrift angle much larger for tanker• Pivot point closer to the bow in tankerPivot point closer to the bow in tanker



Water resistance on starboardWater resistance on starboardBeam during turning circleBeam during turning circle

ZIG-ZAG TESTZIG-ZAG TEST

ZIG-ZAG TEST (Kempf)ZIG-ZAG TEST (Kempf)

• Yaw checking abilityYaw checking ability a measure of : a measure of :

– the response to counter-rudder the response to counter-rudder ((Overshoot angle and Overshoot angle and overshoot time)overshoot time)

– Measure of the ability to initiate and check course Measure of the ability to initiate and check course changeschanges

Two tests are includedTwo tests are included: the 10°/10° and 20°/20° tests: the 10°/10° and 20°/20° tests

10°/10° zig-zag test10°/10° zig-zag test: rudder is turned alternately by 10° to : rudder is turned alternately by 10° to either side following a heading deviation of 10° from either side following a heading deviation of 10° from original headingoriginal heading

ZIG-ZAG TEST (Kempf)ZIG-ZAG TEST (Kempf)

10°/10° Zig-Zag Test10°/10° Zig-Zag Test

•after a steady approach, rudder is put over to 10° to starboard after a steady approach, rudder is put over to 10° to starboard (port) ((port) (first executefirst execute))•when heading has changed to 10° off original heading, rudder when heading has changed to 10° off original heading, rudder reversed to 10° to port (starboard) (reversed to 10° to port (starboard) (second executesecond execute) ) • after the rudder has been turned to port/starboard, the ship after the rudder has been turned to port/starboard, the ship continues turning in original direction with decreasing turning rate.continues turning in original direction with decreasing turning rate.• In response to rudder, ship should then turn to port/starboard.In response to rudder, ship should then turn to port/starboard.• When ship has reached a heading of 10° to port/starboard of the When ship has reached a heading of 10° to port/starboard of the original course the rudder is again reversed to 10° to original course the rudder is again reversed to 10° to starboard/port (starboard/port (third executethird execute).).•The first overshoot angle is the additional heading deviation The first overshoot angle is the additional heading deviation experienced in the zig-zag test following second executeexperienced in the zig-zag test following second execute

ZIG-ZAG TEST/ ProcedureZIG-ZAG TEST/ Procedure

The value of the first overshoot angle in the 10°/10° zig-zag The value of the first overshoot angle in the 10°/10° zig-zag test should not exceed:test should not exceed:. 10° if L/V is less than 10 s;. 10° if L/V is less than 10 s;. 20° if L/V is 30 s or more; and. 20° if L/V is 30 s or more; and. (5 + 1/2(L/V)) degrees if L/V is 10 s or more, but less than 30s . (5 + 1/2(L/V)) degrees if L/V is 10 s or more, but less than 30s

where L and V are expressed in m and m/s, respectively.where L and V are expressed in m and m/s, respectively.

The value of the second overshoot angle in the 10°/10° zig-The value of the second overshoot angle in the 10°/10° zig-zag test should not exceed:zag test should not exceed:. 25°, if L/V is less than 10 s;. 25°, if L/V is less than 10 s;. 40°, if L/V is 30 s or more; and. 40°, if L/V is 30 s or more; and. (17.5 + 0.75(L/V))°, if L/V is 10 s or more, but less than 30 s.. (17.5 + 0.75(L/V))°, if L/V is 10 s or more, but less than 30 s.

Recommendations of IMORecommendations of IMO



• The 20°/20° zig-zag test is performed using the same The 20°/20° zig-zag test is performed using the same procedure using 20° rudder angles and 20° change procedure using 20° rudder angles and 20° change of heading, instead of 10° rudder angles and 10° of heading, instead of 10° rudder angles and 10° change of heading, respectively.change of heading, respectively.

• The value of the first overshoot angle in the 20°/20°The value of the first overshoot angle in the 20°/20°

Zig-Zag test should not exceed 25° Zig-Zag test should not exceed 25° Recommendation of IMO MSC 137(76)Recommendation of IMO MSC 137(76)

20°/20° Zig-Zag Test20°/20° Zig-Zag Test

Ship AheadPropeller AsternRudder Amidships

Shiphandling: Single Screw ShipsSTOPPING TESTSTOPPING TEST

• The "crash-stop" or "crash-astern" manoeuvre is The "crash-stop" or "crash-astern" manoeuvre is mainly a test of engine functioning and propeller mainly a test of engine functioning and propeller reversal. The stopping distance is a function of the reversal. The stopping distance is a function of the ratio of astern power to ship displacement.ratio of astern power to ship displacement.

STOPPING TESTSTOPPING TEST

ProcedureProcedure1. ship brought to a steady course and speed1. ship brought to a steady course and speed2. The recording of data starts.2. The recording of data starts.3. The manoeuvre is started by giving a stop order. The 3. The manoeuvre is started by giving a stop order. The full astern engine order is applied with rudder amidship.full astern engine order is applied with rudder amidship.4. Data recording stops and the manoeuvre is 4. Data recording stops and the manoeuvre is terminated when the ship is stopped deadterminated when the ship is stopped dead


Parameters:Parameters:

• track reachtrack reach

• head reachhead reach

• lateral deviationlateral deviation

• time to dead in watertime to dead in water

Measure of the ability to stop while maintaining controlMeasure of the ability to stop while maintaining control

• Full astern stopping test determines the track reach Full astern stopping test determines the track reach of a ship from the time an order for full astern is given of a ship from the time an order for full astern is given until the ship stops in the water.until the ship stops in the water.

• Track reach is the distance along the path described Track reach is the distance along the path described by the midship point of a ship measured from the by the midship point of a ship measured from the position at which an order for full astern is given to the position at which an order for full astern is given to the position at which the ship stops in the waterposition at which the ship stops in the water

• Track reach must not exceed 15 ship’s lenghts Track reach must not exceed 15 ship’s lenghts excepted for very large vessels: maximum 20 Ship’s L.excepted for very large vessels: maximum 20 Ship’s L.


Comparison betweenComparison betweendifferent manœuvresdifferent manœuvresfor stopping a shipfor stopping a ship

• Where standard manoeuvres indicate dynamic Where standard manoeuvres indicate dynamic instability, alternative tests may be conducted to instability, alternative tests may be conducted to define the degree of instability : « define the degree of instability : « Initial turning test » Initial turning test »

• Guidelines for alternative tests such as a « Guidelines for alternative tests such as a « spiral spiral test » or « pull-out manœuvre »test » or « pull-out manœuvre » are included in the are included in the Explanatory notes to the Standards for ship Explanatory notes to the Standards for ship manoeuvrability, referred to in paragraph 6.1 above. ∗manoeuvrability, referred to in paragraph 6.1 above. ∗

• ∗ ∗ Refer to MSC/Circ.1053 on Explanatory notes to the Refer to MSC/Circ.1053 on Explanatory notes to the Standards for ship manoeuvrabilityStandards for ship manoeuvrability

ADDITIONAL TESTS FOR UNSTABLE SHIPSADDITIONAL TESTS FOR UNSTABLE SHIPS

INITIAL TURNING TESTINITIAL TURNING TEST

INITIAL TURNING TESTINITIAL TURNING TEST

Initial Turning abilityInitial Turning ability

• Measure of change of the heading in response to a Measure of change of the heading in response to a moderate helmmoderate helm

• Expressed in :Expressed in : distance covered before course change of 10° when 10° distance covered before course change of 10° when 10°

of rudder is applied (also with 20° rudder angle)of rudder is applied (also with 20° rudder angle)

• Assessed by the « Initial Turning Test »: Assessed by the « Initial Turning Test »: Test to be Test to be performed for unstable ships (IMO Recommandations)performed for unstable ships (IMO Recommandations)

Initial Turning TestInitial Turning Test

• Measure of nonlinear Measure of nonlinear directional stability directional stability

• Ability to control yaw Ability to control yaw motion with small ruddermotion with small rudderanglesangles

With 10° rudder angle With 10° rudder angle to port/starboard, the to port/starboard, the ship should not have ship should not have travelled more than 2.5 travelled more than 2.5 lengths by the time the lengths by the time the heading has changed heading has changed 10° from 10° from original original headingheading

PULL-OUT TESTPULL-OUT TEST

Additional test forAdditional test forships with ships with unsatisfactoryunsatisfactorymanoeuvring manoeuvring standardsstandards

Measure of courseMeasure of coursekeeping ability andkeeping ability anddynamic stability ofdynamic stability ofa shipa ship

PULL-OUT TESTPULL-OUT TEST

1.1. The ship is first made to turn with a certain rate of The ship is first made to turn with a certain rate of turnturn

2.2. The rudder is returned to midship positionThe rudder is returned to midship position

3.3. With a stable ship: rate of turn decays to zeroWith a stable ship: rate of turn decays to zero

4.4. Unstable ship: rate of turn reduces but residual Unstable ship: rate of turn reduces but residual rate of turn will remainrate of turn will remain

SPIRAL TESTSPIRAL TEST


• The Standard Manoeuvres are used to The Standard Manoeuvres are used to evaluateevaluate course-keeping abilitycourse-keeping ability based on the overshoot based on the overshoot angles resulting from the 10°/10° zig-zag manoeuvre. angles resulting from the 10°/10° zig-zag manoeuvre.

• The zig-zag manoeuvre was chosen for reasons of The zig-zag manoeuvre was chosen for reasons of simplicity and expediency in conducting trials. simplicity and expediency in conducting trials.

• However, where more detailed analysis of dynamicHowever, where more detailed analysis of dynamic stability is required some form of stability is required some form of spiral manœuvrespiral manœuvre (direct or reverse) (direct or reverse) should be conducted as anshould be conducted as an additional measure.additional measure.


DIRECT SPIRAL TESTDIRECT SPIRAL TEST

• The direct spiral is a turning circle manoeuvre in The direct spiral is a turning circle manoeuvre in which various steady state yaw rate/rudder angle which various steady state yaw rate/rudder angle values are measured by making incremental rudder values are measured by making incremental rudder changes throughout a circling manoeuvre.changes throughout a circling manoeuvre.

• In the case where dynamic instability is detected In the case where dynamic instability is detected with other trials or is expected, a direct spiral test with other trials or is expected, a direct spiral test can provide more detailed information about the can provide more detailed information about the degree of instability.degree of instability.

• In cases where the ship is dynamically unstable it In cases where the ship is dynamically unstable it will appear that it is still turning steadily in the will appear that it is still turning steadily in the original direction although the rudder is now slightly original direction although the rudder is now slightly

deflected to the opposite sidedeflected to the opposite side.

DIRECT SPIRAL TESTDIRECT SPIRAL TEST

• steady course and speed steady course and speed • recording of data startsrecording of data starts• rudder turned 15 degrees and held until yaw rate rudder turned 15 degrees and held until yaw rate

remains constant for one minuteremains constant for one minute• rudder angle is then decreased in 5 degree rudder angle is then decreased in 5 degree

increments. At each increment the rudder is held increments. At each increment the rudder is held fixed until a steady yaw rate is obtained, measured fixed until a steady yaw rate is obtained, measured and then decreased againand then decreased again

• this is repeated for different rudder angles starting this is repeated for different rudder angles starting from large angles to both port and starboardfrom large angles to both port and starboard

• when a sufficient number of points is defined, data when a sufficient number of points is defined, data recording stops.recording stops.

REVERSE SPIRAL MANOEUVREREVERSE SPIRAL MANOEUVRE

• In the reverse spiral test the ship is steered to obtain In the reverse spiral test the ship is steered to obtain a constant yaw rate, the mean rudder angle required a constant yaw rate, the mean rudder angle required to produce this yaw rate is measured. to produce this yaw rate is measured.

• the yaw rate versus rudder angle plot is created.the yaw rate versus rudder angle plot is created.

RESULT OF SPIRAL TEST FOR STABLE SHIPRESULT OF SPIRAL TEST FOR STABLE SHIP

RESULT OF SPIRAL TEST FOR UNSTABLE SHIPRESULT OF SPIRAL TEST FOR UNSTABLE SHIP

the vessel path follows a growing spiral, and then a the vessel path follows a growing spiral, and then a contracting spiral in the opposite direction.contracting spiral in the opposite direction.

Suppose that:Suppose that:a)a) the first 15° rudder deflection (Sb) causes the vessel the first 15° rudder deflection (Sb) causes the vessel

to turn rightto turn rightb)b) At zero rudder, the yaw rate is still to the right: the At zero rudder, the yaw rate is still to the right: the

vessel has gotten “stuck” here, and will require a vessel has gotten “stuck” here, and will require a negative rudder action to pull out of the turn. negative rudder action to pull out of the turn.

the rudder in this case has to be used excessively the rudder in this case has to be used excessively driving the vessel back and forth. driving the vessel back and forth.

We say that the vessel is unstable, and clearly a poor We say that the vessel is unstable, and clearly a poor design.design.

DIEUDONNE SPIRAL MANOEUVREDIEUDONNE SPIRAL MANOEUVRE

Comments to IMO StandardsComments to IMO Standards

• For deep water and service/design speed onlyFor deep water and service/design speed only• Give no indication of the handling characteristics in Give no indication of the handling characteristics in

wind, waves and currentwind, waves and current• Do not look at manoeuvres normally carried out by Do not look at manoeuvres normally carried out by

most merchant shipsmost merchant ships• Full astern stopping test results in extreme termal Full astern stopping test results in extreme termal

loads on the engineloads on the engine• Criteria derived from databases heavily biased Criteria derived from databases heavily biased

towards (old) tankers and bulk carrierstowards (old) tankers and bulk carriers

Comments to IMO Standards Comments to IMO Standards

• From operational aspects additional requirements From operational aspects additional requirements should be developed:should be developed:– Manoeuvrability in shallow waterManoeuvrability in shallow water– Low speed manoeuvring capabilitiesLow speed manoeuvring capabilities– Maximum tolerable wind forces in harbour Maximum tolerable wind forces in harbour

manoeuvresmanoeuvres– Limited heel angles Limited heel angles – Steering in waves Steering in waves – Steering with special devicesSteering with special devices

Documents

Chapter 7 : Trials. Ch7. Sea trials / Manoeuvring characteristics of ships IMO Recommendations MSC 137(76) The manoeuvrability of ships can be evaluated