Appendix - Assessment Procedures to Maintain the Manoeuvrability Under Adverse Conditions, Applicable During Phase 0 and Phase 1 of the EEDI Implementation
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Statutory Documents - IMO Publications and Documents - Circulars - Marine Environment Protection Committee - MEPC.1/Circular.850/Rev.2 - 2013 Interim Guidelines for Determining Minimum Propulsion Power to Maintain the Manoeuvrability of Ships in Adverse Conditions... - Appendix - Assessment Procedures to Maintain the Manoeuvrability Under Adverse Conditions, Applicable During Phase 0 and Phase 1 of the EEDI Implementation

Appendix - Assessment Procedures to Maintain the Manoeuvrability Under Adverse Conditions, Applicable During Phase 0 and Phase 1 of the EEDI Implementation

1 Scope

1.1 The procedures as described below are applicable during phase 0 and phase 1 of the EEDI implementation as defined in regulation 21 of MARPOL Annex VI (see also paragraph 0 – Purpose of these interim guidelines).

2 Minimum power lines

2.1 The minimum power line values of total installed MCR, in kW, for different types of ships should be calculated as follows:

  • Minimum Power Line Value = a × (DWT) + b

  • where:

  • DWT is the deadweight of the ship in metric tons;
  • and a and b are the parameters given in table 1 for tankers, bulk carriers and combination carriers.

    Table 1: Parameters a and b for determination of the minimum power line values for the different ship types

    Ship type a b
    Bulk carrier which DWT is less than 145,000 0.0763 3374.3
    Bulk carrier which DWT is 145,000 and over 0.0490 7329.0
    Tanker 0.0652 5960.2
    Combination carrier see tanker above

2.2 The total installed MCR of all main propulsion engines should not be less than the minimum power line value, where MCR is the value specified on the EIAPP Certificate.

3 Simplified assessment

3.1 The simplified assessment procedure is based on the principle that, if the ship has sufficient installed power to move with a certain advance speed in head waves and wind, the ship will also be able to keep course in waves and wind from any other direction. The minimum ship speed of advance in head waves and wind is thus selected depending on ship design, in such a way that the fulfilment of the ship speed of advance requirements means fulfilment of course-keeping requirements. For example, ships with larger rudder areas will be able to keep course even if the engine is less powerful; similarly, ships with a larger lateral windage area will require more power to keep course than ships with a smaller windage area.

3.2 The simplification in this procedure is that only the equation of steady motion in longitudinal direction is considered; the requirements of course-keeping in wind and waves are taken into account indirectly by adjusting the required ship speed of advance in head wind and waves.

3.3 The assessment procedure consists of two steps:

  • .1 definition of the required advance speed in head wind and waves, ensuring course-keeping in all wave and wind directions; and

  • .2 assessment whether the installed power is sufficient to achieve the required advance speed in head wind and waves.

Definition of required ship speed of advance

3.4 The required ship advance speed through the water in head wind and waves, Vs, is set to the larger of:

  • .1 minimum navigational speed, Vnav; or

  • .2 minimum course-keeping speed, Vck.

3.5 The minimum navigational speed, Vnav, facilitates leaving coastal area within a sufficient time before the storm escalates, to reduce navigational risk and risk of excessive motions in waves due to unfavourable heading with respect to wind and waves. The minimum navigational speed is set to 4.0 knots.

3.6 The minimum course-keeping speed in the simplified assessment, Vck, is selected to facilitate course-keeping of the ships in waves and wind from all directions. This speed is defined on the basis of the reference course-keeping speed Vck, ref, related to ships with the rudder area AR equal to 0.9% of the submerged lateral area corrected for breadth effect, and an adjustment factor taking into account the actual rudder area:
  • Vck = Vck, ref - 10.0 × (AR% - 0.9) (1)

where Vck in knots, is the minimum course-keeping speed, Vck, ref in knots, is the reference course-keeping speed, and AR% is the actual rudder area, AR, as percentage of the submerged lateral area of the ship corrected for breadth effect, ALS, cor, calculated as AR% = AR/ALS, cor ・100%. The submerged lateral area corrected for breadth effect is calculated as ALS, cor = LppTm(1.0+25.0(Bwl/Lpp)2), where Lpp is the length between perpendiculars in m, Bwl is the water line breadth in m and Tm is the draft a midship in m. In case of high-lift rudders or other alternative steering devices, the equivalent rudder area to the conventional rudder area is to be used.

3.7 The reference course-keeping speed Vck, ref for bulk carriers, tankers and combination carriers is defined, depending on the ratio AFW/ALW of the frontal windage area, AFW, to the lateral windage area, ALW, as follows:

  • .1 9.0 knots for AFW/ALW = 0.1 and below and 4.0 knots for AFW/ALW = 0.40 and above; and

  • .2 linearly interpolated between 0.1 and 0.4 for intermediate values of AFW/ALW.

Procedure of assessment of installed power

3.8 The assessment is to be performed in maximum draught conditions at the required ship speed of advance, Vs, defined above. The principle of the assessment is that the required propeller thrust, T in N, defined from the sum of bare hull resistance in calm water Rcw, resistance due to appendages Rapp, aerodynamic resistance Rair, and added resistance in waves Raw, can be provided by the ship's propulsion system, taking into account the thrust deduction factor t:
  • T = (Rcw + Rair + Raw + Rapp) /(1- t) (2)

3.9 The calm-water resistance for bulk carriers, tankers and combination carriers can be calculated neglecting the wave-making resistance as , where k is the form factor, is the frictional resistance coefficient, is the Reynolds number, ρ is water density in kg/m3, S is the wetted area of the bare hull in m2, Vs is the ship advance speed in m/s, and ν is the kinematic viscosity of water in m2/s.

3.10 The form factor k should be obtained from model tests. Where model tests are not available the empirical formula below may be used:
  • (3)

where CB is the block coefficient based on Lpp.

3.11 Aerodynamic resistance can be calculated as, where Cair is the aerodynamic resistance coefficient, ρa is the density of air in kg/m3, AF is the frontal windage area of the hull and superstructure in m2, and Vw rel is the relative wind speed in m/s, defined by the adverse conditions in paragraph 1.1 of the interim guidelines, Vw, added to the ship advance speed, Vs. The coefficient Cair can be obtained from model tests or empirical data. If none of the above is available, the value 1.0 is to be assumed.

3.12 The added resistance in waves, Raw , defined by the adverse conditions and wave spectrum in paragraph 1 of the interim guidelines, is calculated as:
  • (4)

where is the quadratic transfer function of the added resistance, depending on the advance speed Vs in m/s, wave frequency ω in rad/s, the wave amplitude, ζa in m and the wave spectrum, Sζζ in m2s. The quadratic transfer function of the added resistance can be obtained from the added resistance test in regular waves at the required ship advance speed Vs as per ITTC procedures 7.5-02 07-02.1 and 7.5-02 07-02.2, or from equivalent method verified by the Administration.

3.13 The thrust deduction factor t can be obtained either from model tests or empirical formula. Default conservative estimate is t = 0.7w, where w is the wake fraction. Wake fraction w can be obtained from model tests or empirical formula; default conservative estimates are given in table 2.

Table 2: Recommended values for wake fraction w

Block coefficient One propeller Two propellers
0.5 0.14 0.15
0.6 0.23 0.17
0.7 0.29 0.19
0.8 and above 0.55 0.23
     
3.14 The required advance coefficient of the propeller is found from the equation:
  • (5)

where DP is the propeller diameter, KT(J) is the open water propeller thrust coefficient, J = ua/nDP, and ua = Vs (1-w) . J can be found from the curve of KT (J)/J2.

3.15 The required rotation rate of the propeller, n, in revolutions per second, is found from the relation:
  • (6)
3.16 The required delivered power to the propeller at this rotation rate n, PD in watt, is then defined from the relation:
  • (7)

where KQ(J) is the open water propeller torque coefficient curve. Relative rotative efficiency is assumed to be close to 1.0.

3.17 For diesel engines, the available power is limited because of the torque-speed limitation of the engine, Q ≤ Qmax (n), where Qmax(n) is the maximum torque that the engine can deliver at the given propeller rotation rate n. Therefore, the required minimum installed MCR is calculated taking into account:

  • .1 torque-speed limitation curve of the engine which is specified by the engine manufacturer; and

  • .2 transmission efficiency ηs which is to be assumed 0.98 for aft engine and 0.97 for midship engine, unless exact measurements are available.

Parent topic: MEPC.1/Circular.850/Rev.2 - 2013 Interim Guidelines for Determining Minimum Propulsion Power to Maintain the Manoeuvrability of Ships in Adverse Conditions, as Amended (Resolution MEPC.232(65), as Amended by Resolutions MEPC.255(67) and MEPC.262(68)) – (30 August 2017)
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