Ship
Manoeuverability
IMO requirements to ship
manoeuverability
IMO resolutions
• A.160 (ES.IV) Recommendation on
data concerning manoeuvring
capabilities and stopping distances of
ships.
• A.209(VII) Recommendation on
information to be included in the
manoeuvring booklets.
IMO requirements to ship
manoeuverability
• A.601(15) Provision and display of
manoeuvring information on board
ships, adopted on November, 20 1987
• Appendix 1 – Pilot Card
• Appendix 2 – Wheelhouse poster
• A.751(18) Interim standards for ship
manoeuvrability
• Adopted November, 4 1993, contains
standard manoeuveres and criteria to ship
manoeverability.
Circular letter МSС/Circ.1022.
Explanatory Notes to the interim
standards for ship manoeuvrability
• adopted in 2002.
Annex
Chapter 1 General Principles
Chapter 2 Guidelines for the application of Standards
Chapter 3 Prediction guidance
• Appendix I - Nomenclature
• Appendix II - General view of prediction of manoevering
performance
• Appendix III - Stopping ability of very large ships
• Appendix IV – Additional manoeuvres
• Appendix V – Background and bibliography.
Manoeuvering
characteristics
Yaw Course Course Inherent
Turning Stopping
checking changing keeping dynamic
ability ability
ability ability ability stability
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°
change of heading» and «tactical diameter»
defined by the «transfer at 180° change of
heading». Analysis of the final turning
diameter is of additional interest.
Transfer
ROT=const
Max ROT V90
t90
ch
rea
V180
ck
Tra t180
Advance < 4,5 L
V360
t360
~200°
Y-Axis
V=const
V270
t270
1,5~2 L
V0
t0 = 0 Distance
D<5L
The following should be noted:
• Velocity reduction up to 50%
• Ability to change course by speed alteration
• Necessity to have reserve speed during turning
(ability to change ROT and D with speed)
• Vmin – min steering way
• ROT depends on initial speed V0
VFAH ~ ROTFAH, but
VSAH ~ 25-28% ROTFAH
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.
Definitions
used in
stopping
test
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.
Zig-zag 10°/10° test
Zig-zag 10°/10° test
1. L/V < 10s α1 = 10º;
2. L/V ≥ 30s α1 = 20º;
3. 30s > L/V ≥ 10s α1 = (5º + 0.5 L/V)º;
4. α2 = α1 + 15º
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).
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.
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.
The equilibrium
yaw rate/helm relation
Turning circle
• Added mass of water equals to 5-10% of
displacement at deep water, and increase
up to 40% in case of shallow waters.
Reduction of ship’s speed is faster as
compared with speed of added water mass.
• Tactical turning diameter D slightly
depends on V0 (within ship’s width B), and
for given rudder angle could be taken as
constant, ROT and t depends greatly on V0
d
= 1,8
H
• With draft/depth ratio d/H=1,8 tactical
turning diameter increases up to 40%, and
• with draft/depth ratio of d/H=1,2
(this ratio is recommended by IMO for
shallow water testing) tactical turning
diameter increases up to twice as
compared with deep water.
• Advance depends insignificantly on
initial ship’s speed V0 and is minimum in
case of minimum V0 = 0.
• Turning circle elements depend on
rudder angle δ. For example, for
transport ships, tactical turning diameter
D at δ=10º is twice larger than at δ=30º .
Types of stopping
16 kn 12 kn 6 kn
Type
L Rel. L Rel. L Rel.
With turning
3,5 0,3 3,5 0,5 3,5 1,2
circle
Rudder cycling 6,7 0,6 4,5 0,6 3,5 1,2
Straight course 10,5 1,0 7,5 1,0 3,0 1,0
• Rel. – relative to straight course
Manoeuvering in ice
