Section 3 Construction and design

3.1.1 Specification for materials of gears, shafts, couplings and propeller, giving chemical composition, heat treatment and mechanical properties are to be submitted for approval.

3.1.2 Specification for materials for the stock, etc. are to be submitted for approval.

3.1.3 Where an ice class notation is included in the class of a ship, additional requirements are applicable as detailed in Pt 5, Ch 7 Strengthening for Navigation in Ice and Pt 3, Ch 9, 3 Strengthening for navigation in ice.

3.2.1 For steerable bow thrusters, the maximum transmitted torque, M _T, is to be the greater of:

• Manufacturers rating.
• Calculated maximum torque generated by steering motor.

3.2.2 The tunnel structure and/or container in which the thrust unit is fitted, is to be in compliance withPt 3, Ch 12, 4 Bow and stern thrust unit structure.

3.3.1 These gears are to be considered for the following conditions:

• A design maximum dynamic duty steering torque;
• A static duty (≤10³ load cycles) steering torque to be not less than M _T.

Values for the above should be submitted together with the plans.

3.3.2 The rudderstock diameter is to be not less than:

3.4.1 The hydraulic power operating systems for steering the bow thruster are to be provided with arrangements to maintain the cleanliness of the hydraulic fluid, taking into consideration the type and design of the hydraulic system.

3.4.2 Relief valves are to be fitted to any part of the hydraulic system which can be isolated. The settings of the relief valves are not to exceed the design pressure. The valves are to be of adequate size and so arranged as to avoid an undue rise in pressure above the design pressure.

3.4.3 For flexible hoses, reference is made to Pt 5, Ch 10, 7 Flexible hoses.

3.5.1 Diesel engines intended for driving thrusters are to comply with the applicable requirements of Pt 5, Ch 2 Engines.

3.6.1 The gears are to be in compliance with the applicable requirements of Pt 5, Ch 3 Gearing with application factors intended for auxiliary gears.

3.7.1 The diameter of protected screw shafts is to be not less than that required for a screw shaft as per Pt 5, Ch 4, 3.4 Screw shafts and tube shafts 3.4.2, in which 94 as per the formula, may be substituted by 85. For unprotected shafts, Pt 5, Ch 4, 3.4 Screw shafts and tube shafts 3.4.6 will be applicable.

3.7.2 Torsional vibration characteristics of the shaft system are to be in compliance withPt 5, Ch 6 Shaft Vibration and Alignmentfor bow thrust units exceeding 500 kW power output.

3.7.3 Calculations of the lateral vibration characteristics of shafting systems incorporating cardan shafts are to be submitted in accordance with Pt 5, Ch 6 Shaft Vibration and Alignment.

3.8.1 Propellers intended for manoeuvring as in Pt 5, Ch 1, 5 Propulsion redundancy are to be in compliance with the requirements of Pt 5, Ch 5 Propellers.