Section 3 Rudders

3.1.1 There is no requirement for lowering rudders for examination. However, in the modern type of rudder, it is not always possible to examine the bearings and their bushes thoroughly without lowering and there have been instances where, although no defect was apparent, the necessity for immediate attention was revealed when the bearings were exposed. Where, however, there is evidence that the rudders have been lowered a short time previously, the Surveyor should use his discretion as to whether further examination is necessary.

3.1.2 The Surveyor should ensure that rudder bearing clearances are taken at each dry-docking. Although renewal of bearings or bushes would normally be dealt with at a Special Survey there is no hard and fast rule on this as excessive clearance at any time will necessitate repair. When evidence of excessive slackness is found, the bearings/ carriers should be examined for possible damage.

3.1.3 Where it is proposed to use synthetic resin type compounds such as Chockfast, Belzona, Chesterton polymer, etc. for the repair of rudder pintles and their housings (gudgeons) then, prior to the repair being commenced or agreed, full details are to be forwarded to the LR Naval liaison office. Where there is any doubt of the suitability of a proposed repair, specialist advice should be sought.

3.1.4 The types of rudder and bearings now in service vary considerably, so that only a broad generalisation can be made with respect to maximum allowable clearance prior to repair or renewal. The following guidelines should be borne in mind when applicable:

1. The maximum clearance for synthetic materials should be in accordance with the manufacturer’s recommendations. Alternatively, the maximum clearance for both metallic and synthetic bearings should not exceed 5 + 0,002D mm, where D is the diameter of the stock or pintle over the liner in mm. (There have been instances where rudder bearing clearances have been greater than the permissible limits and Owners have requested consideration be given to deferment of repairs. In all such cases these requests should be referred to the LR Naval liaison office and specialist advice sought.)

2. When the type of rudder and pintle design prevents clearances being taken afloat and the maximum clearance at a dry-docking, although less than 5 + 0,002D, exceeds 4 + 0,002D mm and repairs are not effected, a recommendation should be made that the rudder bearing clearances be specially examined and dealt with as found necessary at the next dry-docking and a suitable entry should be made in the memoranda.

3.1.5 If a rudder or stock has to be removed for repair, special attention should be given to the precise realignment of the unit, so as to minimize the possibility of subsequent wear to pintles or bearings and their bushes:

1. The clearances provided in the various bearings after reassembly require careful consideration and special attention.

2. To avoid jamming and premature failure, renewed bearings should have minimum clearances as given in Table 3.2.6 Double plated rudder construction of the Rules for Naval Ships. Note should be taken of the manufacturer’s recommended clearances, particularly when bush material requires pre-soaking. Final clearances should always be considered in association with any proposed method of lubrication.

3.1.6 Where necessary, rudder types not covered in Figure 3.2.2 Rudder Areas and Figure 3.2.5 Rudder stock horizontal flange palm radius for spade rudders of the Rules for Naval Ships, should be described with a simple drawing when reporting repairs.

3.1.7 All synthetic bearing materials are to be approved by LR before use. LR’s acceptance of synthetic materials for rudder bearings is achieved in stages.

1. LR approval is based on service experience and where a synthetic bearing material is submitted for initial examination, subject to the properties being examined and considered satisfactory, the material will be entered in Group Ia (Provisional Approval) list for a maximum bearing pressure of 5,5 N/mm².

2. Subsequently, after a minimum of five years’ satisfactory service experience, on a significant number of ships (minimum five), which must be classed with LR the manufacturer may apply for the material to be entered in Group II (Final Approval) list for a maximum bearing pressure of 5,5 N/mm².

3. Approval is given in the first instance for a standard maximum bearing pressure of 5,5 N/mm². Higher bearing pressures, with an absolute maximum of 10 N/mm² may be permitted after initial experience at 5,5 N/mm², and will be entered in Group Ib (Provisional Approval) list for a maximum bearing pressure 10 N/mm², with each installation being subject to individual consideration.

4. Final approval for specified pressures up to 10 N/mm² will be considered as indicated in Ch 7, 3.1 General 3.1.7.(b).

5. The lists of approved materials will be made available to Owners, Builders and repairers on request.

3.2.1 Rudders requiring damage repairs should have the alignment of the stock/axle checked by suitable means. If the alignment check indicates that the stock is bent or the damage repairs are extensive, then the rudder should be removed from the ship and the repairs carried out under controlled conditions.

3.2.2 For repairs to forged or cast steel stocks or shafts, see guidance in Ch 15, 9 Cladding by welding.

3.2.3 Damaged areas of rudder plating are to be carefully removed. Fractures have been known to initiate from slot welds at the trailing edge of the rudder, see Figure 7.3.1 Fractures in spade rudders with a welded stock connection. Any damaged internal structure is to be made good by welding and ground smooth prior to replacing plating. Replaced plates to be secured onto backing strips and by slot welds as appropriate, see Figure 7.3.3 Rudder closing details and Vol 1, Pt 3, Ch 3, 2.11 Rudder blade of the Rules for Naval Ships.

3.2.4 Fractures to welding in way of rudder stock are to be ground out completely and checked by means of dye penetrant. Plate edge is to be restored to the original profile by welding and grinding and the closing weld carried out and checked by dye penetrant. For rudders with a welded stock connection, see Figure 7.3.1 Fractures in spade rudders with a welded stock connection and Figure 7.3.2 Rudder repair welds. For rudders with a bolted stock connection, see Figure 7.3.4 Fractures in spade rudders with a bolted stock connection.

3.2.5 Rudders are to be leak tested on completion of repairs.

3.2.6 After repair, internal coatings to be made good in accordance with original specification as far as practicable.

3.3.1 To avoid damage to the steering gear, the rudder lift (the clearance between the tiller and the steering gear) should always be greater than the clearance between the rudder and any fixed anti-jump arrangements on the hull, see Figure 7.3.7 Typical rudder arrangement, locations of stopper.