Ingangsdatum: 17-05-2013
Appendix procedures to maintain the manoeuvrability under
adverse conditions, applicable during phase 0 of the EEDI
implementation
1 Scope
1.1 The procedures as described below are applicable
during Phase 0 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 x (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 Carriers | 0.0687 | 2924.4 |
Tankers | 0.0689 | 3253.0 |
Combination Carriers | see tankers above |
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:
- definition of the required advance speed in head wind and waves,
ensuring course-keeping in all wave and wind directions; and
- 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, V_{s}, is set to the
larger of:
- minimum navigational speed, V_{nav}; or
- minimum course-keeping speed, V_{ck}.
3.5 The minimum navigational speed,
V_{nav}, 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, V_{ck}, 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 V_{ck}_{,
ref}, related to ships with the rudder area
A_{R} equal to 0.9 per cent of the submerged
lateral area corrected for breadth effect, and an adjustment factor
taking into account the actual rudder area:
V_{ck} =
V_{ck, ref} - 10.0 x (A_{R%} -
0.9) | (1) |
where
V_{ck} in knots, is the minimum course-keeping
speed,
V_{ck, ref}_{}in knots, is the
reference course-keeping speed, and
A_{R%} is the
actual rudder area,
A_{R}, as percentage of the
submerged lateral area of the ship corrected for breadth effect,
A_{LS, cor}, calculated as
A_{R%} =
A_{R}/
A_{LS, cor} ·100%. The
submerged lateral area corrected for breadth effect is calculated as
A_{LS, cor} =
L
_{pp}T
_{m}(1.0+25.0(B
_{wl}/L
_{pp})
^{2}),
where L
_{pp} is the length between perpendiculars in m,
B
_{wl} is the water line breadth in m and T
_{m}
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 V_{ck,
ref} for bulk carriers, tankers and combination
carriers is defined, depending on the ratio
A_{FW}/A_{LW} of the frontal
windage area, A_{FW}, to the lateral windage area,
A_{LW}, as follows:
- 9.0 knots for A_{FW}/A_{LW} =
0.1 and below and 4.0 knots for
A_{FW}/A_{LW} = 0.40 and
above; and
- linearly interpolated between 0.1 and 0.4 for intermediate
values of A_{FW}/A_{LW}.
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,
V_{s}, 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
R_{cw}, resistance due to appendages
R_{app}, aerodynamic resistance
R_{air}, and added resistance in waves
R_{aw}, can be provided by the ship's
propulsion system, taking into account the thrust deduction factor
t:
T =
(R_{cw} +
R_{air} + R_{aw}
+ R_{app} ) /(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, Re =
V_{s}L_{pp} / is the
Reynolds number, _{ }is water density in kg/m^{3}, S
is the wetted area of the bare hull in m^{2},
V_{s} is the ship advance speed in m/s,
and is the
kinematic viscosity of water in m^{2}/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 C_{B} is the block coefficient based on
L_{pp}.
3.11 Aerodynamic resistance can be calculated as
_{} where C_{air} is the aerodynamic
resistance coefficient, _{} is the density of air in
kg/m^{3}, A_{F} is the frontal windage
area of the hull and superstructure in m^{2}, and
V_{w rel} is the relative wind speed in m/s,
defined by the adverse conditions in paragraph 1.1 of the interim
guidelines, V_{w}, added to the ship advance speed,
V_{s}. The coefficient C_{air}
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, R_{aw} , 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
V_{s} in m/s, wave frequency _{} in
rad/s, the wave amplitude, _{} in m and the wave spectrum,
_{} in m^{2}s. 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
V_{s} 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 | 0.35 | 0.23 |
3.14 The
required advance coefficient of the propeller is found from the
equation:
| (5) |
where D_{P} is the propeller
diameter, K_{T }(J) is the open water propeller
thrust coefficient, J =
u_{a}In_{p.} and
u_{a} = V_{s }(1-w).
J can be found from the curve of (J)/J^{2}.
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 n, P_{D} in watts, is then defined
from the relation:
| (7) |
where K_{Q}(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
< Q_{max} (n) , where Q_{max} (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:
- torque-speed limitation curve of the engine which is specified
by the engine manufacturer; and
- transmission efficiency _{}which is to be assumed
0.98 for aft engine and 0.97 for midship engine, unless exact
measurements are available.