Monday, January 14, 2013

Surveyor Guide Notes for Rudder, Rudder Stock and Pintle Survey

Rudder Stock and Pintle
The following should be looked for on the rudder stock and pintle:
  • Excessive clearance between sleeve and bush of the rudder stock/pintle beyond the allowable limit specified by the Classification Society.
  • Condition of sleeve. If the sleeve is loose, ingress of water may have caused corrosion.
  • Deep pitting corrosion in the rudder stock and pintle adjacent to the stainless steel sleeve.
  • Slipping of rudder stock cone coupling. For a vertical cone coupling with hydraulic pressure connection, sliding of the rudder stock cone in the cast piece may cause severe surface damages.
  • Where a stainless steel liner/sleeve/cladding for the pintle/rudder stock is fitted into a stainless steel bush, an additional check should be made for crevice corrosion.

What to look for in Drydock

The rudder blade, rudder stock, rudder horn and propeller boss/brackets have to be checked for deformations.

Indications of deformation of rudder stock/rudder horn could be found by excessive clearance.

Possible twisting deformation or slipping of cone connection can be observed by the difference in angle between rudder and tiller.
If bending or twisting deformation is found, the rudder has to be dismounted for further inspection.

Fractures in rudder plating should be looked for at slot welds, welds of removable part to the rudder blade, and welds of the access plate in case of vertical cone coupling between rudder blade and rudder stock and/or pintle.

Such welds may have latent defects due to the limited applicable welding procedure. Serious fractures in rudder plating may cause loss of rudder.

Fractures should be looked for at weld connection between rudder horn, propeller boss and propeller shaft brackets, and stern frame.

Fractures should be looked for at the upper and lower corners in way of the pintle recess in case of semi-spade rudders. Typical fractures are shown in Examples 3 to 5.

Fractures should be looked for at the transition radius between rudder stock and horizontal coupling (palm) plate, and the connection between horizontal coupling plate and rudder blade in case of horizontal coupling. 

Typical fractures are shown in Examples 1 and 2. Fatigue fractures should be looked for at the palm plate itself in case of loosened or lost coupling bolts.

Fractures should be looked for in the rudder plating in way of the internal stiffening structures since (resonant) vibrations of the plating may have occurred.

If the rudder stock is deformed, fractures should be looked for in rudder stock by nondestructive examinations before commencing repair measures, in particular in and around the keyway, if any.

Rudder clearances

Rudder and steering gear arrangements may have different wear criteria depending on the manufacturer. These calibration and running clearance limits should be checked (normally indicated on drawings).
Some points to consider:

Dimension (1) must be substantially greater than jump clearance (4) to protect steering gear from damage in the event of grounding of skeg or rudder.

Dimension (2) should be sufficient to cater for wear in carrier bearing and substantially greater than riding washer clearance (5).

Usually (1) and (2) are of the order 20 mm/25 mm on a small/medium size vessel.
If the riding washer clearance has reduced then the carrier bearing is wearing or the skeg is set up. Check for reduction in steering gear crosshead dimension (2) to verify downward displacement.

Ensure no drydock keel blocks in way of skeg. Always apply the wear limits given by the manufacturer. The following table gives recommended maximum limits of clearances.
Ruder Type
Diameter D (mm) rudder stock/pintle in way of bearing
Maximum clearance (mm)
Type 1, 2, 3 & 5
D < = 50
50 < D < =100
0.02D + 2
100 < D
0.005 + 3.5
(above value not to exceed 7.5 mm maximum)
Types 4 & 6 to 10
(spade and semi spade)
D < =50
50 < D
0.007D + 2.2
(above value not to exceed 6.0 mm maximum)

These limits do not only take into consideration the functioning of the bearing but also the effects of “hammering” and damage to the rudder itself as clearances increase. See manufacturer’s recommendations for special rudder designs or the use of synthetic bearing materials. To avoid jamming and premature failure renewed bearings should have adequate clearance. Special care is required with those synthetic materials which swell. Rudder should always be swung in drydock when possible after repair to check free movement.

Here you have the ABS criteria for rudder pintle clearence:

In general initial clearances should be around 0.050” for a 6” pintle to around 0.70” for a 14” pintle. Far in service acceptable clearance we feel about 1/64" clearance per 1" of diameter of pintle up to 1% of diameter would be acceptable for another two years of service.

1/64" = 0.015625" = 0.397 m/m

Pintle diameter
Acceptable for 2.5 – 3 years

3/32 = 0.0937
7/64 = 0.109
1/8 = 0.125
9/64 = 0.140
5.32 = 0.156
11/64 = 0.171
3/16 = 0.187
13/64 = 0.203
7/32 = 0.218

The above applies to semi-balanced or balanced rudder with lignum-vitae or laminated-phenolic-resin gudgeon bushings


Bent rudder stocks

Bent rudder stocks without any fractures may be repaired, depending on the size of the deformation, either by heating or by cold straightening in an approved workshop according to an approved procedure. Repair proposal should be submitted.

Bent rudder stocks with fractures may be repaired, depending on the nature and extent. If a welding repair is considered acceptable, the fractures are to be removed by machining/grinding and the welding is to be based on an approved welding procedure together with post weld heat treatment as required. Repair proposal should be submitted.

Fractures at rudder stock/horizontal coupling plate

This can only be accepted on a case by case basis. Some types of fractures may require a different solution to local grinding and welding. Repair proposal should be submitted.
Rudder stock and pintle repairs by welding

Repairs by welding may be accepted provided the weld material chemical composition is suitable for welding. Repair proposal to be submitted.
The welding procedures are to be identified as a function of the carbon equivalent (Ceq).

Following is guidance through the repair process:
  • Removal of the wasted area by machining and/or grinding, and NDE carried out
  • Build-up welding by automatic spiral welding according to an approved welding procedure.
  • Extension of build-up welding over the area of large bending moments (shafts) according to the sketch below.

  • Sufficient number of weld layers to compensate removed material, at least one layer in excess (heat treatment of the remaining layer).
  • Transition at the end of the build-up welding according to the following sketch.

  • Post weld heat treatment if required in special cases (never for stainless steel cladding on ordinary steel)
  • Final machining, at least two layers of welding material have to remain on the rudder stock (See the above sketch)
  • NDE to be carried out.

Twisted rudder stocks

If the rudder stock is twisted due to excessive forces such as contact or grounding and has no additional damage (fractures, significant bending etc.), the stock may be reused.

Consideration will be given on a case by case basis.

The Surveyor should seek advice before accepting any repair.
Normally the keyway, if any, has to be milled in a new position.

The following table, giving criteria in relation to the degree of twisting, is for guidance only.

(1) For A < L/D
Stock acceptable for further service without any heat treatment subject to stock being free of cracks or other defects.

For small angles of twist a “stepped” or larger key may be considered as an alternative to a new keyway. Proposal is to be submitted.

(2) For L/D < A < 5L/D:
The stock is to be stress relieved. Proposal is to be submitted[1].

(3) For A > 5L/D
Stock is to be fully annealed or normalized. Proposal is to be submitted.

A = Angle of twist in degrees.
L = Length of the stock over which the twist appears uniform.
d = diameter of twisted portion of stock.

Stainless cladding of rudder stocks and pintle
This may be accepted depending on the weldability.
Proposal is to be submitted.

Rudder plates

Fractures in welding seams can be gouged out and re-welded with proper root penetration. If vibration may be the possible cause an alternative repair may have to be considered.
Fractures in the lower and/or upper corners of the pintle recess of semi-spade rudders that do not propagate into vertical or horizontal stiffening structures may be repaired by gouging out and welding. For longer fractures internal structure should be checked, and repair proposal should be submitted.
As a guide, the preheating temperature can be obtained from the diagram below using the plate thickness and carbon equivalent of the thicker structure.
For fractures at the connection between plating and cast pieces an adequate preheating is necessary. The preheating temperature is to be determined taking into account the following parameters:
  • Chemical composition (carbon equivalent Ceq)
  • Thickness of the structure
  • Hydrogen content in the welding consumables
  • Heat input
As a guide, the preheating temperature can be obtained from the diagram below using the plate thickness and carbon equivalent of the thicker structure.
All welding repairs are to be carried out using qualified/approved welding procedures.
Abrasion of bush and sleeve

The abrasion (wear down) rate depends on the features of the ship such as frequency of maneuvering. 

However, if excessive clearance is found within a short period, e.g. 5 years, alignment of the rudder arrangement and the matching of the materials for sleeve and bush should be examined together with the replacement of the bush.

Bearing materials
Manufacturers’ recommendations should be followed for any work on the bearing material. Replacement synthetic bearing material should be type approved by the Administration or Class Society.

[1] Submitted to technical office