Section 1 Shaft alignment

1.1.1 The Builder is to carry out shaft alignment calculations for all installations and to prepare alignment procedures detailing the proposed alignment method and the alignment checks.

1.2.1 Shaft alignment calculations are to be submitted to LR for approval for the following shafting systems:

1. All geared installations where the screwshaft has a diameter of 300 mm or greater in way of the aftmost bearing.

2. All geared installations with multiple input/single output, regardless of shaft diameter.

3. All direct drive installations which incorporate three or fewer bearings supporting the intermediate and screwshaft aft of the prime mover.

4. Where prime movers in a direct drive installation or shaftline bearings are installed on resilient mountings.

1.2.2 The shaft alignment calculations are to take into account the:

1. thermal displacements of the bearings between cold static and hot dynamic machinery conditions;

2. buoyancy effect of the propeller immersion due to the craft's operating draughts;

3. effect of predicted hull deformations over the range of the craft's operating draughts, where known;

4. gear forces, where appropriate;

5. combinations of engine inputs for multiple input and single output installations;

6. propeller offset thrust effects, where applicable;

7. bearing loading in the horizontal plane, where appropriate; and

8. bearing weardown, where applicable, and its effect on the bearing loads.

1.2.3 The shaft alignment calculations are to state the:

1. expected bearing loads at light and normal ballast, fully loaded and any other draughts deemed to be part of the craft's operating profile, for the machinery in cold and hot, static and dynamic conditions;

2. bearing influence coefficients and the deflection, slope, bending moment and shear force along the shaftline;

3. details of propeller offset thrust effects, where employed in calculation;

4. details of proposed slope-bore of the aftermost sterntube bearing, where applicable;

5. manufacturer's specified limits for bending moment and shear force at the shaft couplings of the gearbox/prime movers;

6. estimated bearing weardown rates for water or grease-lubricated sterntube bearings;

7. origin of findings where the effect of hull deformation has been considered, viz. whether finite element calculations or measured results from sister or similar craft have been used;

8. anticipated thermal rise of prime movers and gearing units between cold static and hot running conditions; and

9. manufacturer's allowable bearing loads.

1.3.1 A shaft alignment procedure is to be submitted for all main propulsion installations detailing, as a minimum, the:

1. expected bearing loads at light and normal ballast, fully loaded and any other draughts deemed to be part of the craft's operating profile, for the machinery in cold and hot, static and dynamic conditions;

2. maximum permissible loads for the proposed bearing designs;

3. design bearing offsets from the straight line;

4. design gaps and sags;

5. location and loads for the temporary shaft supports;

6. expected relative slope of the shaft and the bearing in the aftermost sterntube bearing;

7. details of slope-bore of the aftermost sterntube bearing, where applied;

8. expected shear forces and bending moments at the forward end flange of the shafting system connecting to the gear output shaft or, for direct-drive installations, to the prime mover output flange;

9. proposed bearing load measurement technique and its estimated accuracy;

10. jack correction factors for each bearing where the bearing load is measured using a specified jacking technique;

11. proposed shaft alignment acceptance criteria, including the tolerances; and

12. flexible coupling alignment criteria.

1.4.1 For main propulsion installations, the shafting is to be aligned to give, in all conditions of craft loading and machinery operation, bearing load distribution satisfying the requirements of Pt 13, Ch 4, 1.4 Design and installation criteria 1.4.2.

1.4.2 Design and installation of the shafting is to satisfy the following criteria:

1. The Builder is to position the bearings and construct the bearing seatings to minimise the effects of hull deflections under any of the craft's operating conditions.

2. Relative slope between the propeller shaft and the aftermost sterntube bearing is, in general, not to exceed 3 × 10^-4 rad.

3. Sterntube bearing loads are to satisfy the requirements of Pt 11, Ch 2, 4.16 Sternbushes and sterntube arrangements 4.16.2.

4. Intermediate shaft bearings' loads are not to exceed 80 per cent of the bearing manufacturer's allowable maximum load, for plain journal bearings, based on the bearing projected area.

5. Main gear wheel bearing loads are to be within the gearbox manufacturer's specified limits.

6. Resulting shear forces and bending moments are to meet the equipment manufacturer's specified coupling conditions throughout the shafting system.

7. The manufacturer's radial, axial and angular alignment limits for the flexible couplings are to be maintained.

1.5.1 Where calculations indicate that the system is sensitive to changes in alignment under different service conditions, the optimised shaft alignment is to be verified by measurements during sea trials using an approved strain gauge technique.

1.6.1 Where the shafting system incorporates flexible couplings, the effects of such couplings on the various modes of vibration are to be considered, see Pt 13, Ch 4, 2 Requirements for craft which are not required to comply with the HSC Code.