Section 4 Design and construction

4.1.1 The arrangement of all types of thrusters is to be such that the craft can be manoeuvred in accordance with the design specifications.

4.1.2 The requirements associated with the structural and watertight integrity and the installation arrangement are to be in accordance with Pt 3, Ch 3 Control Systems.

4.1.3 In addition to the requirements of this Section reference is to be made to:

1. Main transmission gearing (Pt 11, Ch 1 Gearing).

2. Main transmission shafting (Pt 11, Ch 2 Shafting Systems).

3. Propeller (Pt 12, Ch 1 Propellers).

4. Torsional vibration (Pt 13, Ch 1 Torsional Vibration).

5. Lateral vibration for shafting systems which include cardan shafts (Pt 13, Ch 3 Lateral Vibration).

4.2.1 The following requirements are to be complied with:

1. The azimuthing mechanism is to be capable of a maximum rotational speed of not less than 1,5 rev/min.

2. Gearing for the azimuthing mechanism is to be designed to a recognised National Standard. The design is to consider both static (< 10³ cycles) and dynamic loading conditions.

3. Under dynamic operating conditions, the gear is to be considered for

   1. design maximum dynamic duty steering torque,

   2. variable loading, where applicable. A spectrum (duty) factor may be used. The load spectrum value is to be derived using load measurements of similar units, where possible.

4. Under a static duty (< 10³ load cycles) steering torque, which should be not less than M _T, as defined in Pt 12, Ch 3, 4.3 Azimuth thrusters with a nozzle 4.3.1.

5. The following minimum factor of safety values are to be achieved:

   Surface Stress S _Hmin = 1,0.

   Bending Stress S _Fmin = 1,5.

6. For hydraulic pressure retaining parts and load bearing components, see also Pt 14 Steering Systems.

4.3.1 Where the propeller is contained within a nozzle, the equivalent rudder stock diameter in way of tiller, used in Table 1.4.1 Connection of tiller to stock in Pt 14, Ch 1 is to be determined as follows:

The corresponding maximum turning moment, M _T, is to be determined as follows:

4.3.2 In addition to the requirements of Pt 3 General Requirements and Constructional Arrangements the scantlings of the nozzle stock or steering tube are to be such that the section modulus Z against transverse bending at any section x-x is not less than:

4.3.3 The scantlings of nozzle connections or struts will be specially considered. In the case of certain high powered craft, direct calculation may be required.

4.3.4 Where the propeller is not contained in a nozzle, the scantlings in way of the tiller will be subject to special consideration.