Section 2 Performance
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Ships, July 2022 - Part 5 Main and Auxiliary Machinery - Chapter 20 Azimuth Thrusters - Section 2 Performance

Section 2 Performance

Parent topic: Chapter 20 Azimuth Thrusters

2.1 General

2.1.1 The arrangement of azimuth thrusters is to be such that the ship can be satisfactorily manoeuvred to a declared performance capability. The operating conditions covered are to include the following:
  1. Maximum continuous shaft power/speed to the propeller in the ahead condition at the declared steering angles and conditions.
  2. Manoeuvring speeds of the propeller shaft and/or reversing mechanism in the ahead and astern direction at the declared steering angles and sea conditions.
  3. The stopping manoeuvre described in Pt 5, Ch 1, 5.2 Sea trials 5.2.2.
  4. Astern running conditions for the ship.

2.1.2 The requirements of Pt 5, Ch 19 Steering Systems are to be complied with where applicable.

2.1.3 Where more than one azimuth thruster is fitted, Pt 5, Ch 19, 2.1 General 2.1.2 is considered to be met when:
  1. Each azimuth thruster fulfils the requirements for main steering gear (see Pt 5, Ch 20, 2.1 General 2.1.4); and
  2. Each azimuth thruster is provided with the ability to position and lock the azimuth thruster in a neutral position after a failure of its own power unit(s) and actuator(s). These arrangements are to be of sufficient strength to hold the azimuth thruster in position at the ship's manoeuvring speed to be taken as not less than 7 knots. Instructions displayed at the locking mechanism’s operating position are to include a directive to inform the bridge of any limitation in ship's speed required as a result of the securing mechanism being activated.
2.1.4 The main steering gear is to be:
  1. Of adequate strength and capable of changing direction of the azimuth thruster from one side to the other in accordance with the declared steering angle limits at an average turning speed of not less than 2,3 deg/s with the ship running ahead at maximum ahead service speed which shall be demonstrated in accordance with Pt 5, Ch 9, 8 Testing and trials; and
  2. Operated by power; and
  3. So designed that they will not be damaged at maximum astern speed; this design requirement need not be proved by trials at maximum astern speed and declared steering angle limits.

2.1.5 The auxiliary steering gear is to be:

  1. Capable of being brought speedily into action in an emergency; and

  2. Of adequate strength and capable of changing the direction of the ship’s azimuth thrusters from one side to the other in accordance with the declared steering angle limits at an average turning speed of not less than 0,5 deg/s, with the ship running ahead at one half of the maximum ahead service speed or 7 knots, whichever is the greater; and

  3. Operated by power for ships having propulsion power of more than 2500 kW per thruster unit and for all ships, where it is necessary to meet the requirements of Pt 5, Ch 20, 2.1 General 2.1.5.(b).

2.1.6 In addition to the requirements in Pt 5, Ch 20, 1.1 Application 1.1.1, for ships fitted with a single steerable azimuth thruster, where the main steering gear comprises two or more identical power units and two or more identical steering actuators, auxiliary steering gear need not be fitted provided that the steering gear:

  1. In passenger ships capable of satisfying the requirements in Pt 5, Ch 20, 2.1 General 2.1.4.(a) while any one of the power units is out of operation;
  2. In cargo ships capable of satisfying the requirements in Pt 5, Ch 20, 2.1 General 2.1.4.(a) while operating with all power units; and
  3. Is arranged so that after a single failure in its piping system or in one of the power units, steering capability can be maintained or speedily regained.
2.1.7 For ships fitted with more than one steerable azimuth thruster, where each main steering system comprises two or more identical steering actuating systems, auxiliary steering gear need not be fitted provided that each steering gear:
  1. In passenger ships is capable of satisfying the requirements in Pt 5, Ch 20, 2.1 General 2.1.4.(a) while any one of the power units is out of operation;
  2. In cargo ships is capable of satisfying the requirements in Pt 5, Ch 20, 2.1 General 2.1.4.(a) while operating with all power units; and
  3. Is arranged so that after a single failure in its piping or in one of the steering actuating systems, steering capability can be maintained or speedily regained (e.g. by the possibility of positioning the failed steering system in a neutral position in an emergency, if needed). Consideration will be given to alternative arrangements providing equivalence can be demonstrated.

The above capacity requirements apply regardless of whether the steering systems are arranged with shared or dedicated power units.

2.1.8 The steering gear for azimuth thrusters used for dynamic positioning applications with an associated class notation, is to be capable of a turning speed of not less than 9 deg/s.

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