Section
3 Design
3.1 Minimum blade thickness
3.1.1 For
propellers having a skew angle of 25° or less, as defined in Pt 5, Ch 7, 1.1 Details to be submitted 1.1.4, the minimum blade thickness, T, of the propeller blades at 25 per cent radius for solid
propellers, 35 per cent radius for controllable pitch propellers,
neglecting any increase due to fillets, and at 60 per cent radius,
is to be not less than:
where
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L
|
= |
L
0,25, L
0,35, or L
0,6, as appropriate |
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K |
= |
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G
|
= |
density, in g/cm3, see
Table 7.2.1 Materials for propellers
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U
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= |
allowable stress, in N/mm2 (kgf/mm2) see
Pt 5, Ch 7, 3.1 Minimum blade thickness 3.1.2, Pt 5, Ch 7, 3.1 Minimum blade thickness 3.1.3, Pt 5, Ch 7, 3.1 Minimum blade thickness 3.1.4, and Table 7.2.1 Materials for propellers
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|
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= |
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For aerofoil sections with and without trailing edge washback, E may be taken as
1,0 and 1,25 respectively
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for solid propellers at 25 per cent
radius
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for controllable pitch propellers at 35 per
cent radius
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for all propellers at 60 per cent
radius
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3.1.2 The
fillet radius between the root of a blade and the boss of a propeller
is to be not less than the Rule thickness of the blade or equivalent
at this location. Composite radiused fillets or elliptical fillets
which provide a greater effective radius to the blade are acceptable
and are to be preferred. Where fillet radii of the required size cannot
be provided, the value of
U is to be multiplied by 
where
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r
|
= |
proposed
fillet radius at the root, in mm |
|
T
|
= |
Rule
thickness of the blade at the root, in mm |
Where a propeller has bolted-on blades, consideration is also
to be given to the distribution of stress in the palms of the blades.
In particular, the fillets of recessed bolt holes and the lands between
bolt holes are not to induce stresses which exceed those permitted
at the outer end of the fillet radius between the blade and the palm.
3.1.3 For propellers having skew angles of
greater than 25°, but less than 50°, the mid-chord thickness, T
sk0,6, at the 60 per cent radius is to be not less than:
The mid-chord thickness, T
sk root, at 25 or 35 per cent radius, neglecting any increase due to fillets,
is to be not less than:
where
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θs
|
= |
proposed skew angle as defined in Pt 5, Ch 7, 1.1 Details to be submitted 1.1.4
|
|
T
0,6
|
= |
thickness at 60 per cent radius, calculated by Pt 5, Ch 7, 3.1 Minimum blade thickness 3.1.1, in mm |
|
T
root
|
= |
thickness at 25 per cent radius or 35 per cent radius, calculated by
Pt 5, Ch 7, 3.1 Minimum blade thickness 3.1.1, in mm |
The thicknesses at the remaining radii are to be joined by a fair curve
and the sections are to be of suitable aerofoil section.
3.1.4 Results
of detailed calculations where carried out, are to be submitted.
3.1.5 For
cases where the composition of the propeller material is not specified
in Table 7.2.1 Materials for propellers, or where propellers
of the cast irons and carbon and low alloy steels shown in this Table
are provided with an approved method of cathodic protection, special
consideration will be given to the value of U.
3.1.6 The
value U may be increased by 10 per cent for twin screw
and outboard propellers of triple screw ships.
3.2 Keyless propellers
3.2.1 The
symbols used in Pt 5, Ch 7, 3.2 Keyless propellers 3.2.2 (oil
injection method of fitting) and Pt 5, Ch 7, 3.2 Keyless propellers 3.2.3 (dry fitting cast iron sleeve) are defined as follows:
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d1
|
= |
diameter of the screwshaft cone at the mid-length of the boss
or sleeve, in mm |
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d2
|
= |
outside diameter of the sleeve at its mid- length, in mm |
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d3
|
= |
outside diameter of the boss at its mid-length, in mm |
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di
|
= |
bore diameter of screwshaft, in mm |
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A1
|
= |
contact area of fitting at screwshaft, in mm2
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A2
|
= |
contact area of fitting at outside of sleeve, in mm2
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C
|
= |
0
for turbine installations |
| = |
 |
for oil engine installations
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E1
|
= |
modulus of elasticity of screwshaft material, in N/mm2 (kgf/mm2)
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E2
|
= |
modulus of elasticity of sleeve material, in N/mm2 (kgf/mm2)
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E3
|
= |
modulus of elasticity of propeller material, in N/mm2 (kgf/mm2)
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M
|
= |
propeller
thrust, in N (kgf) |
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T1
|
= |
temperature at time of fitting propeller on shaft,in °C |
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T2
|
= |
temperature at time of fitting sleeve into boss, in °C |
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α1
|
= |
coefficient
of linear expansion of screwshaft material, in mm/mm/°C |
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α2
|
= |
coefficient
of linear expansion of sleeve material, in mm/mm/°C |
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α3
|
= |
coefficient
of linear expansion of propeller material, in mm/mm/°C |
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θ1
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= |
taper of the screwshaft cone, but is not to exceed  on the diameter, i.e. 
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θ2
|
= |
taper
of the outside of the sleeve |
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μ1
|
= |
coefficient
of friction for fitting of boss assembly on shaft |
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|
= |
0,13 for oil injection
method of fitting |
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μ2
|
= |
coefficient
of friction for fitting sleeve into the boss |
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ν1
|
= |
Poisson's
ratio for screwshaft material |
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ν2
|
= |
Poisson's
ratio for sleeve material |
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ν3
|
= |
Poisson's
ratio for propeller material |
Consistent sets of units are to be used in all formulae.
3.2.2 Where it is proposed to fit a keyless propeller by the oil shrink method ,
the pull-up, δ on the screwshaft is to be not less than:
or, where lce Class notation is required, the greater of δT or
δO, where
The yield stress or 0,2 per cent proof stress, σo of the
propeller material is to be not less than:
 N/mm2 (kgf/mm2)
where
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δp
|
= |
proposed pull-up at the fitting temperature |
The start point load, W, to determine the actual pull-up is to be
not less than:
3.2.3 Where a cast iron sleeve is first fitted to the bore of the propeller boss
by an interference fit, the push-up load of the sleeve into the boss,
W2, is to be not less than:
or, where lce Class notation is required, the greater of W2T
or W20
where
The pull-up of the sleeve in the boss at the fitting
temperature is to be in accordance with the following formula:
The push-up load, W1, of the combined boss and sleeve on a
steel screwshaft is to be not less than:
 N(kgf)
or where lce Class notation is required, the greater of W1T
or W10 where
 N(kgf)
The push-up distance of the combined boss and sleeve
on a steel screwshaft is to be in accordance with the following formula:
3.2.4 Where a cast iron sleeve is fitted into the boss by means of Araldite, the
conditions are to satisfy those of Pt 5, Ch 7, 3.2 Keyless propellers 3.2.3 except that the value of W2 is to
be taken as equivalent to:
where
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pA
|
= |
3,5 N/mm2
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(pA
|
= |
0,35 kgf/mm2)
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3.2.5 For
the triple element keyless propeller, the yield stress or 0,2 per
cent proof stress of the propeller material, σo is
to be not less than:
 mm2 (kgf/mm2)
3.2.6 Where
the sleeve is manufactured of material having an elongation in excess
of five per cent, the yield point or 0,2 per cent proof stress of
the sleeve material, σo is to be not less than:
 N/mm2 (kgf/mm2)
or
 N/mm2 (kgf/mm2)
where
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|
= |
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3.2.7 Where
the sleeve is manufactured of material having an elongation not more
than five per cent, the minimum specified ultimate tensile strength σu, based on the ruling section, is to be not less than:
 N/mm2 (kgf/mm2)
or
 N/mm2 (kgf/mm2)
3.2.8 Where
it is proposed to use a sleeve manufactured from a material other
than cast iron, full details are to be submitted for consideration.
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