- Laws of Fiji

9.14

9-14

Propeller and intermediate shafting

9.14.1 Shaft material

9.14.1.1Shafts shall be manufactured from material having the following minimum required mechanical properties—
- (a)Utility tensils strength (UTS) – 410 MPa
- (b)Yeild Point – 230 MPa
- (c)Elongation-Bronze: 25%, carbon Steel: 23%, Monel: 20%, Stainless steel 17%.
9.14.1.2Where the shaft material is other than the materials specified in subparagraph 9.14.1.1 (c) above, the chemical composition and mechanical properties, including the corrosion fatigue strength in seawater, shall be equivalent.
NOTES:
- (1)Subparagraph 9.14.2, 9.14.3, 9.14.4 and 9.14.5 are based upon the materials having the above values of elongation and a user-specified value of Ultimate Tensile Strength (UTS). Assumptions for shaft material characteristics that are incorrect can invalidate the factors of safety inherent in these paragraphs.
- (2)The material characteristics of a particular shaft material can be determined by referring to the manufacturer’s material data certificates, heat stamp identification details and other relevant test documentation. Such documentation is especially important where—
  - (a)any doubt exists as to the performance characteristics of the material;
  - (a)it is proposed to use carbon manganese steel having a specified UTS of greater than 510 MPa; or
  - (a)it is proposed to use a material having a UTS greater than 618 MPa.

9.14.2 Reference shaft diameter

The reference shaft diameter for use in subparagraph 9.14.3 to 9.14.5 shall be determined by the following formula—

Where—

d _r = reference shaft diameter, in millimetres
a = 1.108 for ships of Classes 3A, 3B and 1.053 for ships of Classes 3D and 3E
k = 89 for propulsion through reduction gears or flexible couplings
P = the maximum brake power (in kilowatts) that the engine will transmit, irrespective of the length of time nominated by the engine manufacturer for which the engine may be run at that power
N = shaft revolutions per minute

NOTES:

(1)Many of the formulae for shafting and shafting components contained within subparagraph 9.14, 9.15, 9.16 and 9.19 are based on minimum required rather than as fitted diameters in order to provide minimum scantlings. Designing to the minimum scantlings may limit flexibility with regard to future modifications to the ship. In particular, this will be of concern if the ship is to be refitted with machinery of increased power.
(2)Values of coefficient k for direct-drive, in-line internal combustion engines may be obtained from the table below.

No of cylinders	2 S.C. k	4 S.C. k
1 and 2	114	109
3	107	109
4	102	109
5	99	105
6	96.5	102
7	95	101
8	93	99
9	90	98
10	90	94
11 and more	90	90

9.14.3 Solid propeller shaft size

Refer to figure 5.

The diameter of the solid propeller shaft shall not be less than that determined by the following formula—

Where—

d _p = minimum diameter of propeller shaft, in millimetres
d _r = reference diameter of shaft, in millimetres, calculated in accordance with subparagraph 9.14.2
D = propeller diameter, in millimetres
K = 144 for shafts protected against corrosion (see subparagraph 9.14.9)
f _p =material factor for propeller shaft, determined in accordance with the following formula:

Where—

UTS _shaft = ultimate tensile strength of the propeller shaft material, in megapascals (MPa).

NOTE:

Certain high-tensile materials used for propeller shafting exhibit rapid deterioration in warm sea conditions, necessitating frequent withdrawal for inspection and possible replacement. Care should be taken to ensure that the shafting material chosen is suitable for the intended or likely area of operation.

9.14.4 Allowable reduction in propeller shaft diameter

The diameter of the part of the propeller shaft forward of the stern gland may be reduced from that calculated in subparagraph 9.14.3, provided that such reduction is as gradual as possible, and the diameter of the reduced part is calculated in accordance with the following formula—

d_rp = 1.14 d_rf_p

Where—

d _rp = inimum allowable diameter of reduced part of shaft, in millimetres
d _r = reference diameter of shaft in millimetres, calculated in accordance with subparagraph 9.14.2
f _p = the material factor used for calculating d _rp (see subparagraph 9.14.3).

9.14.5 Solid Intermediate shaft size

The diameter of solid intermediate shafting shall not be less than that determined by the following formula—

d_i = d_rf_i

Where—

d _i = minimum diameter of intermediate shaft in millimetres
d _r = reference diameter of shaft in millimetres, calculated in accordance with subparagraph 9.14.2
f _i = material factor for intermediate shaft, determined in accordance with the following formula—

Figure 5 — Typical propeller shaft, stern tube, stern bearing and gland

Where—

UTS _shaft = ultimate tensile strength of the intermediate shaft material, in megapascals (MPa).

9.14.6 Hollow shafting

Shafting may be hollow provided that it is of equivalent strength to a solid shaft. The required outside diameter of the shaft can be calculated from the following formula—

Where—

d ₁ = required outside diameter of hollow shaft, in millimetres
d _s = required diameter of solid shaft, in millimetres
y = a nominated ratio of d2/d1,

where—

d2 = the inside diameter of the hollow shaft.

9.14.7 Shaft support

Shafts shall be adequately supported. The maximum allowable distance between shaft supports shall be determined in accordance with the following formula—

S = 0.142 ₃ d_f ²

Where—

S = maximum allowable distance between centres of shaft supports, in metres
df = diameter of shaft fitted, in millimetres.

The forward-most bearing should be located at least 12 shaft diameters from the engine gearbox or thrust block flange.

9.14.8 Propeller Shaft Overhang

The overhang of the propeller shaft between the forward face of the propeller boss and the after face of the adjoining shaft bearing should not be more than the actual propeller shaft diameter. Where an overhang exceeds this, the bending stress due to the additional overhang shall be taken into account when calculating the required shaft diameter.

9.14.9 Protection of Propeller Shaft

Where exposure to water may corrode propeller shafts, they shall either be protected by a continuous, water–resistant liner complying with subparagraph 9.14.10 [see Figure 5(b)], or the shaft shall run in an oil-lubricated stern tube with a sealing gland at the aft end. Protective coatings may be applied in lieu of a liner on those parts of the propeller shaft that are visible when the craft is slipped.

9.14.10 Liners

Liners, where fitted, shall be of bronze or stainless steel. Liners shall be shrunk on to the shaft. Securing pins shall not be used. The thickness of liners fitted in way of the bearings shall not be less than that calculated in accordance with the following formula—

Where—

t = thickness of the liner, in millimetres
d _f = fitted diameter of the shaft within the liner, in millimetres
f = material factor, as follows—
(a) 230 for bronze
(b) 120 for stainless steel

The thickness of a continuous liner between bearings shall not be less than 0.75t

9.14.11 Propeller shaft tapers

9.14.11.1Propeller shafts shall be tapered to provide an accurate fit in the propeller boss, with particular attention given to the fit at the large end of the taper. The taper shall be between the limits of one in 12 and one in 16 on the diameter, except on shafts less than 50mm diameter, where a taper as steep as one in 10 on the diameter may be used.
9.14.11.2The contact area between the mating surfaces prior to final pull-up shall be at least 70%.
9.14.11.3The roughness of the mating surfaces should not exceed 3.5m, and the forward edge at the bore of the boss should be well rounded.
NOTE:
A taper of 1:12 on the diameter has been found to provide a good compromise between being shallow enough to ensure the propeller will remain secured on the taper, and being steep enough to facilitate removal of the propeller from the shaft.