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

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

1 Chapter 7 : Trials

2 Ch7. Sea trials / Manoeuvring characteristics of ships IMO Recommendations MSC 137(76) The manoeuvrability of ships can be evaluated from the characteristics of conventional trial manoeuvres.The manoeuvrability of ships can be evaluated from the characteristics of conventional trial manoeuvres. Two methods can be used:Two methods can be used: –Scale model tests or computer predictions using mathematical models at the design stage / full scale trials must be conducted to validate these results –Full scale trials Test speed = at least 90% of full speed = 85% of full engine powerTest speed = at least 90% of full speed = 85% of full engine power

3 Ch7. Sea trials / Manoeuvring characteristics of ships Imo Manoeuvring Standards By resolution A.751(18) in 1993 IMO adopted Manoeuvring StandardsBy resolution A.751(18) in 1993 IMO adopted Manoeuvring Standards The standards apply to:The standards apply to: –All ships of 100m in lenght and over –All chemical tankers and gas carriers They consist of:They consist of: –Turning circles to Port and starboard –Stopping Test –Zig-Zag Test

4 Conditions at which the standards apply In order to evaluate the performance of a ship, manoeuvring trials should be conducted to both port and starboard and at conditions specified below:.1 deep, unrestricted water (> 4xmean draft).2 calm environment (Wind< 5Bft / Sea< 4).3 full load (summer load line draught), even keel condition 4 steady approach at the test speed(min90% full).4 steady approach at the test speed(min90% full). Ch7. Sea trials / Manoeuvring characteristics of ships

5 Manoeuvring performance has traditionally received little attention during the design stages of a commercial ship.Manoeuvring performance has traditionally received little attention during the design stages of a commercial ship. Consequently some ships have been built with very poor manoeuvring qualities, resulting in marine casualties / pollution.Consequently some ships have been built with very poor manoeuvring qualities, resulting in marine casualties / pollution. Designers have relied on shiphandling abilities of human operators to compensate for deficiencies in inherent manoeuvring qualities of the hull.Designers have relied on shiphandling abilities of human operators to compensate for 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.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. (Extract of IMO MSC/Circ1053) (Extract of IMO MSC/Circ1053) Ch7. Sea trials / Manoeuvring characteristics of ships

6 Ch7. Sea trials / Preliminary Forces and motions in manoeuvrability 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 ship’s hullThe centre of the hydrodynamic forces acting on the ship’s hull 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

7 Ch7. Sea trials /Preliminary The Pivot Point at forward speed

8 Ch7. Sea trials / Manoeuvring characteristics of ships 1. Course keeping ability and dynamic stability Dynamically stable ship moves along a new straight course without using rudder after a small disturbanceDynamically stable ship moves along a new straight course without using rudder after a small disturbance Dynamically unstable ship performs turning circle with rudder amidshipDynamically unstable ship performs turning circle with rudder amidship More difficult to handle dynamically unstable ships More difficult to handle dynamically unstable ships Infos on course keeping and dynamic stability: obtained from « Initial turning test »Infos on course keeping and dynamic stability: obtained from « Initial turning test »

9 Ch7. Sea trials / Manoeuvring characteristics of ships Dynamic stability: dynamically stable ships maintain A straight course with zero rudder Dynamically unstable ships can only maintain a straight course by repeated use of rudder control use of rudder control

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11 Ch7. Sea trials / Manoeuvring characteristics of ships Factors 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 cross sectional area after (pivot point moves forward)Decrease when cross sectional area fwd larger than cross sectional area after (pivot point moves forward)

12 Ro-Ro ships are directionally unstable They need more rudder to stop a swing than to start a swing

13 Ch7. Sea trials / Manoeuvring characteristics of ships Change 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 swing –Difficult to stop a swing –In shallow water, a ship gets trim by the head and looses directional stability

14 3 STANDARD MANOEUVRES

15 TURNING CIRCLE Turning circle: measure of turning ability of vessel

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17 To determine the turning ability - The measure of the ability of a ship using hard-over rudder - The result is a minimum « advance at 90° change of heading » and « tactical diameter » defined by the « transfer at 180° change of heading » - 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 lengthsthe tactical diameter should not exceed 5 lengths Turning circle to be performed with 35°Rudder angleTurning circle to be performed with 35°Rudder angle TURNING CIRCLE

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

19 Advance: 426m Transfer: 99m Diameter: 263m Tact.Dia: 290m Advance: 426m Transfer: 94m Diameter: 258m Tact.Dia: 292m

20 Advance: the distance traveled in the direction of the original course by the midship point of a ship from the position at which the rudder order is given to the position at which the heading has changed 900 from the original course.

21 Tactical diameter : the distance traveled by the midship point of a ship from the position at which the rudder order is given to the position at which the heading has changed 1800 from the original course. It is measured in a direction perpendicular to the original heading of the ship.

22 Comments Advance of the ship smaller than the distance ahead with an emergency stop manœuvreAdvance of the ship smaller than the distance ahead with an emergency stop manœuvre Request sufficient searoom on the beam (tactical diameter)Request sufficient searoom on the beam (tactical diameter) Test are carried out at sea and not in shallow waters: parameters are bigger in shallow water because rudder effect decreases in shallow water due to the reduced waterflowTest are carried out at sea and not in shallow waters: parameters are bigger in shallow water because rudder effect decreases in shallow water due to the reduced waterflow Parameters of the turning circle do not change for different speeds of the shipParameters of the turning circle do not change for different speeds of the ship TURNING CIRCLE

23 Drift angle and Pivot point The pivot point (D) is at the intersection of the longitudinalThe pivot point (D) is at the intersection of the longitudinal axis 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) TURNING CIRCLE

24 In shallow waters, the drift angle is smaller : the water resistance decreases and the turning circle is larger TURNING CIRCLE

25 Crablike motion of the ship: Water resistance reduces the speed and the diameter of turning circle

26 Forces acting on a ship when turning TURNING CIRCLE

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28 The turning circle is affected by the effects of wind and current TURNING CIRCLE

29 Turning characteristics of full and slender ships

30 Comparison of turning characteristics of full and slender ships: Two ships of the same lenght have nearly the same transferTwo ships of the same lenght have nearly the same transfer 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 TURNING CIRCLE

31 Water resistance on starboard Beam during turning circle

32 ZIG-ZAG TEST

33 ZIG-ZAG TEST (Kempf) Yaw checking ability a measure of :Yaw checking ability a measure of : –the response to counter-rudder (Overshoot angle and overshoot time) –Measure of the ability to initiate and check course changes Two tests are included: the 10°/10° and 20°/20° tests 10°/10° zig-zag test: rudder is turned alternately by 10° to either side following a heading deviation of 10° from original heading

34 ZIG-ZAG TEST (Kempf) ZIG-ZAG TEST (Kempf) 10°/10° Zig-Zag Test

35 after a steady approach, rudder is put over to 10° to starboard (port) (first execute)after a steady approach, rudder is put over to 10° to starboard (port) (first execute) when heading has changed to 10° off original heading, rudder reversed to 10° to port (starboard) (second execute)when heading has changed to 10° off original heading, rudder reversed to 10° to port (starboard) (second execute) after the rudder has been turned to port/starboard, the ship continues turning in original direction with decreasing turning rate. after the rudder has been turned to port/starboard, the ship 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 original course the rudder is again reversed to 10° to starboard/port (third execute). When ship has reached a heading of 10° to port/starboard of the original course the rudder is again reversed to 10° to starboard/port (third execute). The first overshoot angle is the additional heading deviation experienced in the zig-zag test following second executeThe first overshoot angle is the additional heading deviation experienced in the zig-zag test following second execute ZIG-ZAG TEST/ Procedure

36 The value of the first overshoot angle in the 10°/10° zig-zag test should not exceed:. 10° if L/V is less than 10 s;. 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 where L and V are expressed in m and m/s, respectively. The value of the second overshoot angle in the 10°/10° zig- zag test should not exceed:. 25°, if L/V is less than 10 s;. 40°, if L/V is 30 s or more; and. ( (L/V))°, if L/V is 10 s or more, but less than 30 s. Recommendations of IMO

37 ZIG-ZAG TEST

38 The 20°/20° zig-zag test is performed using the same procedure using 20° rudder angles and 20° change of heading, instead of 10° rudder angles and 10° change of heading, respectively.The 20°/20° zig-zag test is performed using the same procedure using 20° rudder angles and 20° change of heading, instead of 10° rudder angles and 10° 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° Recommendation of IMO MSC 137(76) Zig-Zag test should not exceed 25° Recommendation of IMO MSC 137(76)

39 20°/20° Zig-Zag Test

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42 STOPPING TEST

43 The "crash-stop" or "crash-astern" manoeuvre is mainly a test of engine functioning and propeller reversal. The stopping distance is a function of the ratio of astern power to ship displacement.The "crash-stop" or "crash-astern" manoeuvre is mainly a test of engine functioning and propeller reversal. The stopping distance is a function of the ratio of astern power to ship displacement. STOPPING TEST Procedure 1. ship brought to a steady course and speed 2. The recording of data starts. 3. The manoeuvre is started by giving a stop order. The full astern engine order is applied with rudder amidship. 4. Data recording stops and the manoeuvre is terminated when the ship is stopped dead

44 STOPPING TEST Parameters: track reach track reach head reach head reach lateral deviation lateral deviation time to dead in water time to dead in water

45 Measure of the ability to stop while maintaining control Full astern stopping test determines the track reach of a ship from the time an order for full astern is given until the ship stops in the water. Full astern stopping test determines the track reach of a ship from the time an order for full astern is given until the ship stops in the water. Track reach is the distance along the path described 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 the ship stops in the water Track reach is the distance along the path described 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 the ship stops in the water Track reach must not exceed 15 ship’s lenghts excepted for very large vessels: maximum 20 Ship’s L. Track reach must not exceed 15 ship’s lenghts excepted for very large vessels: maximum 20 Ship’s L. STOPPING TEST

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47 Comparison between different manœuvres for stopping a ship

48 Where standard manoeuvres indicate dynamic instability, alternative tests may be conducted to define the degree of instability : « Initial turning test »Where standard manoeuvres indicate dynamic instability, alternative tests may be conducted to define the degree of instability : « Initial turning test » Guidelines for alternative tests such as a « spiral test » or « pull-out manœuvre » are included in the Explanatory notes to the Standards for ship manoeuvrability, referred to in paragraph 6.1 above. ∗Guidelines for alternative tests such as a « spiral test » or « pull-out manœuvre » are included in the Explanatory notes to the Standards for ship manoeuvrability, referred to in paragraph 6.1 above. ∗ ∗ Refer to MSC/Circ.1053 on Explanatory notes to the Standards for ship manoeuvrability ∗ Refer to MSC/Circ.1053 on Explanatory notes to the Standards for ship manoeuvrability ADDITIONAL TESTS FOR UNSTABLE SHIPS

49 INITIAL TURNING TEST

50 Initial Turning ability Measure of change of the heading in response to a moderate helmMeasure of change of the heading in response to a moderate helm Expressed in :Expressed in : distance covered before course change of 10° when 10° of rudder is applied (also with 20° rudder angle) distance covered before course change of 10° when 10° of rudder is applied (also with 20° rudder angle) Assessed by the « Initial Turning Test »: Test to be performed for unstable ships (IMO Recommandations)Assessed by the « Initial Turning Test »: Test to be performed for unstable ships (IMO Recommandations)

51 Initial Turning Test Measure of nonlinear Measure of nonlinear directional stability Ability to control yaw Ability to control yaw motion with small rudder angles With 10° rudder angle to port/starboard, the ship should not have travelled more than 2.5 lengths by the time the heading has changed 10° from original heading

52 PULL-OUT TEST Additional test for ships with unsatisfactorymanoeuvringstandards Measure of course keeping ability and dynamic stability of a ship

53 PULL-OUT TEST 1.The ship is first made to turn with a certain rate of turn 2.The rudder is returned to midship position 3.With a stable ship: rate of turn decays to zero 4.Unstable ship: rate of turn reduces but residual rate of turn will remain

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55 SPIRAL TEST

56 The Standard Manoeuvres are used to evaluateThe Standard Manoeuvres are used to evaluate course-keeping ability based on the overshoot course-keeping ability 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 ofThe 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 spiral manœuvre stability is required some form of spiral manœuvre (direct or reverse) should be conducted as an (direct or reverse) should be conducted as an additional measure. additional measure.

57 SPIRAL TEST

58 DIRECT SPIRAL 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.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. 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.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. 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 sideIn 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.

59 DIRECT SPIRAL TEST steady course and speedsteady course and speed recording of data startsrecording of data starts rudder turned 15 degrees and held until yaw rate remains constant for one minuterudder turned 15 degrees and held until yaw rate remains constant for one minute rudder angle is then decreased in 5 degree increments. At each increment the rudder is held fixed until a steady yaw rate is obtained, measured and then decreased againrudder angle is then decreased in 5 degree increments. At each increment the rudder is held fixed until a steady yaw rate is obtained, measured and then decreased again this is repeated for different rudder angles starting from large angles to both port and starboardthis is repeated for different rudder angles starting from large angles to both port and starboard when a sufficient number of points is defined, data recording stops.when a sufficient number of points is defined, data recording stops.

60 REVERSE SPIRAL MANOEUVRE 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.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. the yaw rate versus rudder angle plot is created.the yaw rate versus rudder angle plot is created.

61 RESULT OF SPIRAL TEST FOR STABLE SHIP

62 RESULT OF SPIRAL TEST FOR UNSTABLE SHIP

63 the vessel path follows a growing spiral, and then a contracting spiral in the opposite direction. Suppose that: a)the first 15° rudder deflection (Sb) causes the vessel to turn right b)At zero rudder, the yaw rate is still to the right: the vessel has gotten “stuck” here, and will require a negative rudder action to pull out of the turn. the rudder in this case has to be used excessively driving the vessel back and forth. the rudder in this case has to be used excessively driving the vessel back and forth. We say that the vessel is unstable, and clearly a poor design. DIEUDONNE SPIRAL MANOEUVRE

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65 Comments 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 wind, waves and currentGive no indication of the handling characteristics in wind, waves and current Do not look at manoeuvres normally carried out by most merchant shipsDo not look at manoeuvres normally carried out by most merchant ships Full astern stopping test results in extreme termal loads on the engineFull astern stopping test results in extreme termal loads on the engine Criteria derived from databases heavily biased towards (old) tankers and bulk carriersCriteria derived from databases heavily biased towards (old) tankers and bulk carriers

66 Comments to IMO Standards From operational aspects additional requirements should be developed:From operational aspects additional requirements should be developed: –Manoeuvrability in shallow water –Low speed manoeuvring capabilities –Maximum tolerable wind forces in harbour manoeuvres –Limited heel angles –Steering in waves –Steering with special devices

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