Section 8 Propeller tolerances

8.1.1 This section applies to conventional fixed and controllable pitch propellers, ducted propellers, supercavitating and surface piercing propellers.

8.1.2 All propellers are to have manufacturing tolerances specified on the design drawings.

8.1.3 Adequate records defining the manufactured dimensions of the propeller are to be maintained in order that subsequent compliance with the requirements of this Section can be demonstrated.

8.1.4 The fitting of the propeller to the shaft interface is dealt with separately in Vol 2, Pt 4, Ch 1, 7.3 Interference fit of keyless propellers and Vol 2, Pt 4, Ch 1, 7.4 Keyed propellers pushed up by a hydraulic nut .

8.2.1 As a minimum requirement for all naval surface ship types, with the exception of work boats and very low performance craft having speeds below 10 knots, the Class 1 requirements of the ISO 484/1 or 484/2 specifications are to be applied.

8.2.2 For work boats and very low performance craft having speeds below 10 knots, the Class 2 requirements of the ISO 484/1 or 484/2 specifications may be applied.

8.3.1 After the production processes and assembly, where appropriate, have been completed, the propeller must be statically balanced by an approved method, details of which are to be submitted.

8.3.2 For fixed pitch propellers, the propeller and cone must each be statically balanced according to the requirements of Table 1.8.1 Balancing requirements

Table 1.8.1 Balancing requirements

Propeller rotational speed	Balance criterion
Up to 200 rpm	± 0,225 kgf.m/tonne
200 to 400 rpm	± kgf.m/tonne

8.3.3 For controllable pitch propellers the blades, hubs and fairing cones are to be balanced separately. For propellers having rotational speeds between 200 and 400 rpm, the maximum allowable total imbalance is ±15000/R ² kgf.m/tonne. For propellers having rotational speeds less than 200 rpm, the maximum allowable total imbalance is ±0,375 kgf.m/tonne.

8.3.4 For propeller rotational speeds greater than 400 rpm, special consideration will be given to the balancing method, whether it should incorporate dynamic effect and the balance limits. Dynamic balancing tests may be required for high rotational speed propellers where significant out-of-balance couples can be exerted on the shafting. Such tests are to be agreed between the manufacturer and Owner and advised to LR.

8.4.1 For ships and craft having displacements below 500 tonnes and speeds in excess of 25 knots that require the enhanced assessment of propeller manufacturing tolerances notation AP1, the Class S requirements of the ISO 484/1 or 484/2 specifications are to be applied in addition to Vol 2, Pt 4, Ch 1, 8.4 Enhanced assessment of manufacturing tolerances – Fast ships and craft 8.4.2 to Vol 2, Pt 4, Ch 1, 8.4 Enhanced assessment of manufacturing tolerances – Fast ships and craft 8.4.5.

8.4.2 In addition to the leading edge templates required by Vol 2, Pt 4, Ch 1, 8.4 Enhanced assessment of manufacturing tolerances – Fast ships and craft 8.4.1, radial root fillet templates are to be provided at 0 per cent, 5 per cent, 10 per cent and 20 per cent of the chordal length from the leading edge in the blade roots.

8.4.3 A mid-fillet, in the radial sense, blade leading edge chordal template is to be provided. This template is to define the root fillet geometry from the leading edge to the 20 per cent chordal location from the leading edge and is to be based on the designed back and face surfaces of the propeller blade. The manufactured blade profile is to be demonstrated to lie within a tolerance band of ± 0,5 mm.

8.4.4 The diameter of the propeller boss is to be checked at four equi-distant axial stations along the boss length. These stations are to include the forward and aft faces of the propeller boss. The diameters measured at the four axial stations of the boss must be shown to lie within ± 1 mm from the design value.

8.4.5 If the design incorporates through blade penetrations, two plug templates, one in the radial and the other in the chordal direction, must be provided for each type of penetration so as to define the design penetration to blade surface geometry. The manufactured intersection geometry must be shown to lie within ± 0,5 mm of the design intent. Additionally, the tolerance for the surface finish of the intersection geometry shall be 3 µm Ra.

8.5.1 For ships having noise reduced propellers and requiring the enhanced assessment of propeller manufacturing tolerances notation AP2, the Class S requirements of the ISO 484/1 or 484/2 specifications are to be applied in addition to Vol 2, Pt 4, Ch 1, 8.5 Enhanced assessment of propeller manufacturing tolerances – Noise reduced propellers 8.5.2 to Vol 2, Pt 4, Ch 1, 8.5 Enhanced assessment of propeller manufacturing tolerances – Noise reduced propellers 8.5.5.

8.5.2 The requirements of Table 1.8.2 Manufacturing tolerances are to be satisfactorily achieved.

8.5.3 In order to adequately control the blade shape, the local pitch errors of any two consecutive measurements are not to differ by more than half the local pitch tolerance envelope.

8.5.4 To control the shape of the pressure face of the blade, the algebraic sum of the local pitch errors of any two consecutive measurements is not to exceed 75 per cent of the local pitch tolerance envelope.

8.5.5 To limit chordwise deviations of the suction surface of the blade, local thickness errors are not to differ by more than half the thickness tolerance envelope between any two consecutive measurements.