Section
3 Design
3.1 Minimum blade thickness
3.1.1 For propellers having a skew angle of less than 25° as defined in Pt 5, Ch 5, 1.1 Details to be submitted 1.1.3 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:
|
T
|
= |
|
|
L
|
= |
L
0,25, L
0,35, or L
0,6, as appropriate |
|
K
|
= |
|
|
U
|
= |
allowable stress, in N/mm2
see
Pt 5, Ch 5, 3.1 Minimum blade thickness 3.1.2, Pt 5, Ch 5, 3.1 Minimum blade thickness 3.1.3, Pt 5, Ch 5, 3.1 Minimum blade thickness 3.1.4, and Table 5.2.1 Materials for propellers
|
|
E
|
= |
|
For aerofoil sections with and without trailing edge washback, E may be taken as
1,0 and 1,25 respectively
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 
|
r
|
= |
proposed
fillet radius at the root, in mm |
|
T
|
= |
proposed
fillet radius 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 25° or
greater, but less than 50°, the mid-chord thickness, T
sk0,6, at the 60 per cent radius is to be not less than:
|
T
sk0,6
|
= |
|
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:
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 5.2.1 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 5, 3.2 Keyless propellers 3.2.2 are defined as
follows:
|
d
1
|
= |
diameter of the screw shaft cone at the mid-length of the boss
or sleeve, in mm |
|
d
3
|
= |
outside diameter of the boss at its midlength, in mm. |
|
d
i
|
= |
bore diameter of screw shaft, in mm |
|
P
1
|
= |
|
|
P
10
|
= |
|
|
A
1
|
= |
contact area of fitting at screw shaft, in mm2
|
|
B
3
|
= |
|
|
C
|
= |
0
for turbine installations |
|
|
= |
 for engine installations |
|
E
1
|
= |
modulus of elasticity of screwshaft material, in N/mm2
|
|
E
3
|
= |
modulus of elasticity of propeller material, in N/mm2
|
|
F
1
|
= |
|
|
F
10
|
= |
|
|
M
|
= |
propeller
thrust, in N
|
|
T
1
|
= |
temperature at time of fitting propeller on shaft, in °C |
|
V
1
|
= |
|
|
α1
|
= |
coefficient
of linear expansion of screw shaft material, in mm/mm/°C |
|
α3
|
= |
coefficient
of linear expansion of propeller material, in mm/mm/°C |
|
θ1
|
= |
taper
of the screwshaft cone, but is not to exceed  on the diameter, i.e. θ1 ≤ 
|
|
μ1
|
= |
coefficient
of friction for fitting of boss assembly on shaft |
|
|
= |
0,13 for oil injection
method of fitting |
|
ν1
|
= |
Poisson's
ratio for screw shaft material |
|
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:
|
δT
|
= |
 (p
1
B
3 +
(α3 – α1)(35 – T
1)) mm
|
or, where lce Class notation is required, the greater
of δT or δO, where
|
δO
|
= |
|
The yield stress or 0,2 per cent proof stress, σo of the propeller material is to be not less than:
|
σO
|
= |
 N/mm2
|
|
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:
|
W
|
= |
|
3.3 Keyed propellers pushed up by an hydraulic nut
|