Section 3 Assessment for LNMA notation
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Naval Ships, January 2023 - Volume 3 Additional Class Notations - Part 1 Ship Type Capability - Chapter 4 Manoeuvring Assessment - Section 3 Assessment for LNMA notation

Section 3 Assessment for LNMA notation

Parent topic: Chapter 4 Manoeuvring Assessment

3.1 General

3.1.1 The LNMA notation provides a means for a ship’s manoeuvring performance to be specified and defined according to its mission requirements, for example Replenishment at Sea, Mine Warfare, or Amphibious Operations.

3.1.2 In addition to the mission requirements, a ship’s manoeuvring performance is to remain within safe limits and is to also comply with the minimum standards set by the IMO in Resolution MSC.137(76) - Standards for Ship Manoeuvrability - (adopted on 4 December 2002).

3.2 Verification requirements

3.2.1 For assignment of the LNMA notation, a ship’s manoeuvring performance shall be verified at the design stage through simulation and model tests, and is to be validated during sea trials.

3.2.2 The means of assessment (detailed computations, simulations and model tests) are to be proposed by the designer in agreement with the Owner and LR. These are to be undertaken in accordance with an appropriate standard for the manoeuvring abilities defined in Table 4.3.1 Definition of Manoeuvring Abilities and the results submitted to LR for review. Where an appropriate standard does not exist the method proposed is to be submitted to LR for consideration.

3.2.3 Model tests are to be carried out by a recognised facility that is acceptable to LR and a report is to be submitted detailing the test arrangements, schedule of tests, and results, presented in both diagrammatic and tabular form.

3.2.4  LR may, when requested, undertake calculations on behalf of designers and make recommendations with regard to suitability of any required model tests.

3.2.5 Final verification of the assignment of the LNMA notation will be dependent on the results of sea trials, see Vol 3, Pt 1, Ch 4, 4 Verification trials.

3.2.6 The methods of assessment of manoeuvring characteristics in ice or in shallow water, such as squat, are to be agreed between the Owner and the designer.

3.3 Manoeuvring performance criteria

3.3.1 The ship’s manoeuvring performance criteria are to be agreed between the Owner and the designer for the required mission types defined in the ConOps and manoeuvring abilities defined in Table 4.3.1 Definition of Manoeuvring Abilities. at defined speeds and environmental conditions.

3.3.2 As a minimum, the ship shall be controllable to the extent required to perform manoeuvres essential to its safe operation; this requires compliance with the requirements of IMO in Resolution MSC.137(76) - Standards for Ship Manoeuvrability - (adopted on 4 December 2002). However, consideration shall also be given to the effects of enhanced manoeuvring criteria on stability, persons on board, operation of machinery and payload through induced accelerations and high heel angles.

3.3.3 The manoeuvring performance criteria are to be specified for each mission type, environmental condition and manoeuvring ability using the required verification speed. These manoeuvring performance criteria, once determined, are to be justified and documented in a ship-specific report for ease of reference.

3.3.4 The means by which the performance criteria are established may make reference to an appropriate reference standard such as ANEP–70 Vol. I 'Guidance for Naval Surface Ship Mission Oriented Manoeuvring Requirements' .LR may, when requested, assist with regard to specification of performance criteria.

Table 4.3.1 Definition of Manoeuvring Abilities

Ability Unit Description Definition of Criteria Environmental Conditions

(see Note 1)

Minimum Required
Course keeping Ψ [Deg] Accuracy with which the steered ship is able to maintain a predetermined heading without excessive oscillations of steering device or heading. Maximum allowed course deviation (95 per cent probability within at least 100 oscillations of the steering device). Mission sea state Yes
Track Keeping [m] Accuracy and effort with which the steered ship is able to maintain a predetermined, mission defined track without excessive oscillations of steering device. Maximum allowed track deviation (95 per cent probability within at least 100 oscillations of the steering device). Mission sea state Optional
Turning Non-Dimensional (y0180/LPP) Ability to turn the ship using optimum steering angle.
Note (Roll) stability requirements typically include a limitation of the heel angle during steady high-speed turning.
y0180 (ITTC symbol) Tactical diameter [m] Calm Yes
Initial Turning Non-Dimensional ta/(LPP/V0) Ability defined by the change of heading response to a moderate helm ta (ITTC symbol) Initial turning time

[s] Time elapsed from order execute to achieve 20° heading change at setting of propulsion unaltered using 20° steering angle.

Calm Yes
Yaw Checking Non-Dimensional tC1/(LPP/V0) Response of a ship to check (stop) a certain rate of turning. tc1 (ITTC symbol) First time to check yaw in 20°/20° zigzag test [s] Time elapsed from order execute to stop yaw. Calm Yes
Turning from rest [s] Accelerating turning from rest using most efficient and available steering and propulsion devices. Time from order execute to turn to 90° from rest (t90). Calm Optional
Stopping Non-Dimensional (sF/LPP) Stop from ahead describes the response of the ship using most efficient and available steering and propulsion devices. sF (ITTC symbol) Distance along track, track reach [m] Calm Yes
Acceleration [m/s2] Acceleration describes the ability to increase the speed either from zero or from a given initial speed to a given target speed. Maximum acceleration during accelerating manoeuvre from zero speed to maximum speed Calm Optional
Astern course keeping Ψ [Deg] Ability to maintain a predetermined heading within reasonable limits when going astern. Maximum allowed course deviation (95 per cent probability within 20 oscillations). Mission sea state Optional
Station keeping [m] and Ψ [deg] Ability to maintain a predetermined position despite environment disturbances in form of current, wind and waves. Station keeping may include the ability to maintain a predetermined heading Maximum allowed position/heading deviation at zero speed (95 per cent probability within at least 30 minutes full scale). Mission sea state Optional
Lateral Transfer [kn] Ability to change position by means of transverse motion at equilibrium angle with zero rate of turn. Minimum required lateral transfer speed. Calm Optional
Standard Deviation of Navigational Error (SDNE) [m] SDNE is a measure of how accurate the ship is able to follow or keep an earth fixed track or position. The ability involves the accuracy of the navigational aids in addition to the ship manoeuvrability capabilities. Standard deviation from predefined earth fixed track or position Mission sea state Optional
Turning at rest [s] The ability to turn at rest with best available propulsion and manoeuvring means. Time from order execute to turn to 90° at rest (t90). Required verification speed is zero knots. Limited position change is allowed Mission sea state Optional
Note 1: Where the required Mission sea state is not able to be achieved during trials the proposed trials conditions and the means of extrapolating to the required sea state are to be agreed between the designer and the Owner.

3.4 Operator guidance

3.4.1 The results of the assessments required by Vol 3, Pt 1, Ch 4, 3.2 Verification requirements together with additional information gained from the verification trials, and trial data for the man overboard manoeuvre, are to be presented in diagrammatic and tabular form and included in a bridge card/poster and a manoeuvring handbook.

3.4.2 The card/poster is to be available in the bridge, and is to contain a clear warning regarding the assumptions or limitations of the information presented. The handbook is to be placed on board and is to contain comprehensive details of the ship’s manoeuvring characteristics.

3.4.3 The format, data and content of the bridge card/poster and the manoeuvring handbook are to meet the requirements of an appropriate standard such as ANEP–79 'Controllability and Safety in a Seaway' or IMO Resolution A.601(15) – Provision and Display of Manoeuvring Information on Board Ships – (Adopted on 19 November 1987), as well as recommended Operator Guidance such as the Manoeuvring Handbook, see e.g. ANEP-70 Vol. II Guidance for the Preparation of Onboard Manoeuvring Information.

3.4.4 For ANEP-77 NATO Naval Ship Code compliance the following information must be included in the Operator Guidance as a minimum:

  • the turning characteristics including initial turning;
  • the stopping and accelerating characteristics
  • the effects of squat and manoeuvring in shallow water;
  • the effects of wind on manoeuvring;
  • the minimum manoeuvring speed; and
  • heel in turn characteristics.

3.4.5 The availability of appropriate Operator Guidance in accordance with the requirements of Vol 3, Pt 1, Ch 4, 3.4 Operator guidanceis to be confirmed by the attending Surveyor.

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