3.1 Fitting of propeller on the propeller shaft

3.1.1 General

1. Screw propeller hubs are to be properly adjusted and fitted on the propeller shaft cone.
2. The forward end of the hole in the hub is to have the edge rounded to a radius of approximately 6 mm.
3. In order to prevent any entry of sea water under the liner and onto the end of the propeller shaft, the arrangement of Fig 4 is generally to be adopted for assembling the liner and propeller boss.
4. The external stuffing gland is to be provided with a seawater resistant rubber ring preferably without joints. The clearance between the liner and the internal air space of the boss is to be as small as possible. The internal air space is to be filled with an appropriate protective material which is insoluble in sea water and non-corrodible or fitted with a rubber ring.
5. All free spaces between the propeller shaft cone, propeller boss, nut and propeller cap are to be filled with a material which is insoluble in sea water and non-corrodible. Arrangements are to be made to allow any air present in these spaces to withdraw at the moment of filling. It is recommended that these spaces be tested under a pressure at least equal to that corresponding to the immersion of the propeller in order to check the tightness obtained after filling.
6. For propeller keys and key area, see Ch 1, Sec 7, [2.5.5].

3.1.2 Shrinkage of keyless propellers
In the case of keyless shrinking of propellers, the following requirements apply:

1. The meaning of the symbols used in the subparagraphs below is as follows:

   A

   :

   100% theoretical contact area between propeller boss and shaft, as read from plans and disregarding oil grooves, in mm2

   dPM

   :

   Diameter of propeller shaft at the mid-point of the taper in the axial direction, in mm

   dH

   :

   Mean outer diameter of propeller hub at the axial position corresponding to dPM, in mm

   K

   :

   K = dH/dPM

   F

   :

   Tangential force at interface, in N

   MT

   :

   Continuous torque transmitted, in N.m; where not indicated, MT may be assumed as indicated in [2.2.1]

   C

   :

   C = 1 for turbines, geared diesel engines, electrical drives and direct-drive reciprocating internal combustion engines with a hydraulic, electromagnetic or high elasticity coupling C = 1,2 for diesel engines having couplings other than those specified above. The Society reserves the right to increase the value of C if the shrinkage needs to absorb an extremely high pulsating torque

   T

   :

   Temperature of hub and propeller shaft material, in °C, assumed for calculation of pull-up length and push-up load

   V

   :

   Ship speed at P power, in knots

   S

   :

   Continuous thrust developed for free running ship, in N

   sF

   :

   Safety factor against friction slip at 35°C

   q

   :

   Half taper of propeller shaft (for instance: taper = 1/15, q =1/30)

   m

   :

   Coefficient of friction between mating surfaces

   p35

   :

   Surface pressure between mating surfaces, in N/mm2, at 35°C

   pT

   :

   Surface pressure, in N/mm2, between mating surfaces at temperature T

   p0

   :

   Surface pressure between mating surfaces, in N/mm2, at 0°C

   pMAX

   :

   Maximum permissible surface pressure, in N/mm2, at 0°C

   d35

   :

   Push-up length, in mm, at 35°C

   dT

   :

   Push-up length, in mm, at temperature T

   dMAX

   :

   Maximum permissible pull-up length, in mm, at 0°C

   WT

   :

   Push-up load, in N, at temperature T

   sID

   :

   Equivalent uni-axial stress in the boss according to the von Mises-Hencky criterion, in N/mm2

   aP

   :

   Coefficient of linear expansion of shaft material, in mm/(mm°C)

   aM

   :

   Coefficient of linear expansion of boss material, in mm/(mm°C)

   EP

   :

   Value of the modulus of elasticity of shaft material, in N/ mm2

   EM

   :

   Value of the modulus of elasticity of boss material, in N/ mm2

   nP

   :

   Poisson's ratio for shaft material

   nM

   :

   Poisson's ratio for boss material

   RS,MIN

   :

   Value of the minimum yield strength (ReH), or 0,2% proof stress (Rp 0,2), of propeller boss material, in N/mm2.

   For other symbols not defined above, see [2.2].
2. The manufacturer is to submit together with the required constructional plans specifications containing all elements necessary for verifying the shrinkage. Tests and checks deemed necessary for verifying the characteristics and integrity of the propeller material are also to be specified.
3. Moreover, the manufacturer is to submit an instruction handbook, in which all operations and any precautions necessary for assembling and disassembling the propeller, as well as the values of all relevant parameters, are to be specified. A copy, endorsed by the Society, is to be kept on board each ship where the propeller is installed.
4. The formulae and other provisions below do not apply to propellers where a sleeve is introduced between shaft and boss or in the case of hollow propeller shafts. In such cases, a direct shrinkage calculation is to be submitted to the Society.
5. The taper of the propeller shaft cone is not to exceed 1/15.
6. Prior to final pull-up, the contact area between the mating surfaces is to be checked and is not to be less than 70% of the theoretical contact area (100%). Non-contact bands extending circumferentially around the boss or over the full length of the boss are not acceptable.
7. After final push-up, the propeller is to be secured by a nut on the propeller shaft. The nut is to be secured to the shaft.
8. The safety factor s_F against friction slip at 35°C is not to be less than 2,8, under the combined action of torque and propeller thrust, based on the maximum continuous power P for which classification is requested at the corresponding speed of rotation N of the propeller, plus pulsating torque due to torsionals.
9. For the oil injection method, the coefficient of friction m is to be 0,13 in the case of bosses made of bronze, brass or steel. For other methods, the coefficient of friction will be considered in each case by the Society.
10. The maximum equivalent uni-axial stress in the boss at 0°C, based on the von Mises-Hencky criterion, is not to exceed 70% of the minimum yield strength (R_eH), or 0,2% proof stress (R_p0,2), of the propeller material, based on the test piece value. For cast iron, the value of the above stress is not to exceed 30% of the nominal tensile strength.
11. For the formulae given below, the material properties indicated in the following items are to be assumed:
    • Modulus of elasticity, in N/mm²:
      Cast and forged steel: E = 206000
      Cast iron: E = 98000
      Type Cu1 and Cu2 brass: E = 108000
      Type Cu3 and Cu4 brass: E = 118000
    • Poisson's ratio:
      Cast and forged steel: n = 0,29
      All copper based alloys: n = 0,33
    • Coefficient of linear expansion in mm/(mm^oC)
      Cast and forged steel and cast iron: a = 12,0 10^-6
      All copper based alloys: a = 17,5 10^-6
12. For shrinkage calculation the formulae in the following items, which are valid for the ahead condition, are to be applied. They will also provide a sufficient margin of safety in the astern condition.
    • Minimum required surface pressure at 35°C:
      
      
      where:
      B = m²-s_F²q²
    • Corresponding minimum pull-up length at 35°C:
      
      
      
    • Minimum pull-up length at temperature T (T<35°C):
      
      
      
    • Corresponding minimum surface pressure at temperature T:
      
      
      
    • Minimum push-up load temperature T:
      
      
      
    • Maximum permissible surface pressure at 0°C:
      
      
      
    • Corresponding maximum permissible pull-up length at 0°C:
      
      
      
    • Tangential force at interface:
      
      
      
    • Continuous thrust developed for free running ship; if the actual value is not given, the value, in N, calculated by one of the following formulae may be considered:
      
      
      

3.1.3 Circulating currents
Means are to be provided to prevent circulating electric currents from developing between the propeller and the hull. A description of the type of protection provided and its maintenance is to be kept on board.