PART Section 3: Propellers

4
CHAPTER 3 Propulsion and Maneuvering Machinery

SECTION 3 Propellers

1 General

1.1 Application
This section applies to propellers intended for propulsion. It covers fixed pitch and controllable pitch
propellers. Propellers for thrusters used for maneuvering and dynamic positioning are covered in Section
4-3-5. Performance of propellers, in respect to developing the designed output, is to be demonstrated during
sea trials.
Additional requirements for propellers intended for vessels strengthened for navigation in ice are provided
in Part 6.

1.3 Definitions
For purpose of this section, the following definitions apply.
1.3.1 Skew Angle
Skew Angle ( ) of a propeller is the angle measured from ray ‘A’ passing through the tip of blade
at mid-chord line to ray ‘B’ tangent to the mid-chord line on the projected blade outline. See
4-3-3/Figure 1.
1.3.2 Highly Skewed Propeller
A Highly Skewed Propeller is one whose skew angle is more than 25°.
1.3.3 Propeller Rake
1.3.3(a) Rake. Rake is the distance at the blade tip between the generating line and the line
perpendicular to the propeller axis that meets the generating line at the propeller axis. See
4-3-3/Figure 2.
1.3.3(b) Rake angle ( ). Rake Angle of a propeller is the angle measured from the plane perpendicular
to shaft centerline to the tangent to the generating line at a specified radius (0.6 radius for the
purpose of this section). See 4-3-3/Figure 2.
1.3.4 Wide Tipped Blade Propeller
A propeller blade is to be considered as a wide tipped blade if the maximum expanded blade cord
length occurs at or above 0.8R, with R being the distance measured from the centerline of the
propeller hub.

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FIGURE 1 FIGURE 2
Maximum Skew Angle Rake and Rake Angle
C D

skew B Rake
A angle

mid-chord 0.6
line radius
leading
edge

1.5 Plans and Particulars to be Submitted

1.5.1 Fixed Pitch Propeller of Conventional Design
Material
Design characteristics of propeller
Dimensions and tolerances
Propeller plan
Blade thickness calculations
1.5.2 Controllable Pitch Propeller of Conventional Design
As per 4-3-3/1.5.1
Hub and hub to tail shaft flange attachment bolts
Propeller blade flange and bolts
Internal mechanism
Hydraulic piping control system
Instrumentation and alarm system
Strength calculations for internal mechanism
1.5.3 Highly Skewed Propeller and Other Unconventional Designs
In addition to the foregoing, where propeller blade designs are of the types for which the Rules do
not provide simplified blade thickness calculations, such as
highly skewed propellers with 50°;
high skewed propellers made of other than Type 4 materials with 50° 25°;
controllable pitch propellers with 25°;
cycloidal propellers;
propeller load and stress analyses demonstrating adequacy of blade strength are to be submitted.
1.5.4 Keyless Propeller
Where propellers are to be fitted to the shaft without keys, stress calculations for hub stresses and
holding capacity, along with fitting instructions, are to be submitted.

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3 Materials

3.1 Normally Used Propeller Materials

4-3-3/Table 1 shows the properties of materials normally used for propellers. See 2-3-14/3 and Section
2-3-15 for full details of the materials.
Where an alternative material specification is proposed, detailed chemical composition and mechanical
properties are to be submitted for approval (for example, see Section 2-3-14 and Section 2-3-15). The f and
w values of such materials to be used in the equations hereunder will be specially considered upon
submittal of complete material specifications including corrosion fatigue data to 108 cycles.

TABLE 1
Propeller Materials
Elongation, %
Tensile strength Yield strength Gauge Length
Type Material N/mm2 kgf/mm2 lb/in2 N/mm2 kgf/mm2 lb/in2 4d 5d
2 Manganese bronze 450 46 65,000 175 18 25,000 20 18
3 Nickel-manganese 515 53 75,000 220 22.5 32,000 18 16
bronze
4 Nickel-aluminum 590 60 86,000 245 25 36,000 16 15
bronze
5 Manganese-nickel- 630 64 91,000 275 28 40,000 20 18
aluminum bronze
CF-3 Stainless steel 485 49 70,000 205 21 30,000 35 32

3.3 Stud Materials

The material of the studs securing detachable blades to the hub is to be of at least Grade 2 forged steel or
equally satisfactory material; see 2-3-7/7 for specifications of Grade 2 forged steel.

3.5 Material Testing

Materials of propellers cast in one piece and materials of blades, hub, studs and other load-bearing parts of
controllable pitch propellers are to be tested in the presence of a Surveyor. For requirements of material
testing, see 2-3-14/3 and Section 2-3-15 and 2-3-7/7.

5 Design

5.1 Blade Thickness – Fixed Pitch Propeller

Propeller blades of thrusters (as defined in 4-3-5/1.5) and wide-tip blades of ducted propellers are to be in
accordance with the provisions of Section 4-3-5. The thickness of the propeller blades of conventional
design ( 25°) is not to be less than that determined by the following equations:

AH Cs BK
t 0.25 S K1
C n CRN Cn 4C

6. 0
A 1. 0 4.3P0.25
P0.70
2 3
4300wa R D
B
N 100 20

C 1 1.5P0.25 Wf B

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where (units of measures are given in SI (MKS, and US) units respectively):
a = expanded blade area divided by disc area
as = area of expanded cylindrical section at 0.25 radius; mm2 (in2)
Cn = section modulus coefficient at the 0.25 radius. Cn is to be determined by the
following equation:
I0
Cn
U f WT 2

If the calculated Cn value exceeds 0.10, the required thickness is to be computed with
Cn = 0.10.
Cs = section area coefficient at 0.25 radius and is to be determined by the following
equation:
as
Cs
WT
The values of Cs and Cn, computed as stipulated above, are to be indicated on the propeller drawing. If the
Cn value exceeds 0.10, the required thickness is to be computed with Cn = 0.10
For vessels below 61 m (200 ft) in length, the required thickness may be computed with the assumed
values of Cn = 0.10 and Cs = 0.69.
D = propeller diameter; m (ft)
f, w = material constants from the following table:
Material type SI and MKS units US units
(see 4-3-3/3.1) f w f w
2 2.10 8.3 68 0.30
3 2.13 8.0 69 0.29
4 2.62 7.5 85 0.27
5 2.37 7.5 77 0.27
CF-3 2.10 7.75 68 0.28
Note:
The f and w values of materials not covered will be specially considered
upon submittal of complete material specifications including corrosion
fatigue data to 108 cycles.
H = power at rated speed; kW (PS, hp)
I0 = moment of inertia of expanded cylindrical section at 0.25 radius about a straight line
through the center of gravity parallel to the pitch line or to the nose-tail line; mm4 (in4)
K = rake of propeller blade, in mm (in.) (positive for aft rake and negative for forward
rake)
K1 = coefficient as given below

SI MKS US
K1 337 289 13

N = number of blades
P0.25 = pitch at one-quarter radius divided by propeller diameter, corresponding to the design
ahead condition
P0.70 = pitch at seven-tenths radius divided by propeller diameter, corresponding to the
design ahead condition

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R = rpm at rated speed

S = factor, as given below. If greater than 1.025, equate to 1.025.

SI & MKS units US units

1.0 for D 6.1 m 1.0 for D 20 ft
(D 24) (D 79)
for D 6.1 m for D 20 ft
30.1 99

t0.25 = minimum required thickness at the thickest part of the blade section at one quarter
radius; mm (in.)
T = maximum designed thickness of blade section at 0.25 radius from propeller drawing;
mm (in.)
Uf = maximum nominal distance from the moment of inertia axis to points of the face
boundary (tension side) of the section; mm (in.)
W = expanded width of a cylindrical section at 0.25 radius; mm (in.)

5.3 Blade Thickness – Controllable-pitch Propellers

Controllable pitch propeller blades of thrusters (as defined in 4-3-5/1.5) and wide-tip blades of ducted
controllable pitch propellers are to be in accordance with the provisions of Section 4-3-5. The thickness of
the controllable pitch propeller blade of conventional design ( 25°) is not to be less than determined by
the following equation:

AH Cs BK
t 0.35 K2
C n CRN Cn 6.3C

6.0
A 1. 0 3P0.35
P0.70
2 3
4900wa R D
B
N 100 20

C 1 0.6 P0.35 Wf B
where the symbols used in these formulas are the same as those in 4-3-3/5.1, except as modified below:
as = area of expanded cylindrical section at 0.35 radius; mm2 (in2)
Cn = section modulus coefficient at the 0.35 radius and is to be determined by the
following equation:
I0
Cn
U f WT 2

If the calculated Cn value exceeds 0.10, the required thickness is to be computed with
Cn = 0.10.
Cs = section area coefficient at 0.35 radius and is to be determined by the following
equation:
as
Cs
WT
The values of Cs and Cn, computed as stipulated above, are to be indicated on the propeller drawing. If the
Cn value exceeds 0.10, the required thickness is to be computed with Cn = 0.10
For vessels below 61 m (200 ft) in length, the required thickness may be computed with the assumed
values of Cn = 0.10 and Cs = 0.69.

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I0 = moment of inertia of expanded cylindrical section at 0.35 radius about a straight line
through the center of gravity parallel to the pitch line or to the nose-tail line; mm4 (in4)
K2 = coefficient as given below

SI MKS US
K2 271 232 10.4
P0.35 = pitch at 0.35 radius divided by D
T = maximum designed thickness of blade section at 0.35 radius from propeller drawing;
mm (in.)
t0.35 = required minimum thickness of the thickest part of the blade section at 0.35 radius;
mm (in.)
W = expanded width of a cylindrical section at 0.35 radius; mm (in.)

5.5 Blade Thickness – Highly Skewed Fixed-pitch Propellers

5.5.1 Propeller Blades with Skew Angle ; where 25°< 50°
The provisions of 4-3-3/5.5.1 are applicable to fixed pitch propellers having a skew angle over 25°
but not exceeding 50°, and made of Type 4 material only. For propellers of other materials, see 4-
3-3/5.5.2. Where the skew angle is greater than 50°, see 4-3-3/5.5.3.
5.5.1(a) Blade thickness at 0.25 radius. The maximum thickness at 0.25 radius is to be not less
than the thickness required in 4-3-3/5.1 for fixed pitch-propellers multiplied by the factor m as
given below:

m 1 0.0065 25

5.5.1(b) Blade thickness at 0.6 radius. The maximum thickness of the blade section at 0.6 radius
is to be not less than that obtained from the following equations:
0.5
2C 0.9 HD
t 0.6 K3 1 C 0.9 1
C 0.6 RP0.6Y

25 2
1 0.16 P0.9 100

where
C0.6 = expanded chord length at the 0.6 radius divided by propeller diameter
C0.9 = expanded chord length at the 0.9 radius divided by propeller diameter
K3 = coefficient as given below:

SI MKS US
K3 12.6 6.58 1.19
P0.6 = pitch at the 0.6 radius divided by propeller diameter
P0.9 = pitch at the 0.9 radius divided by propeller diameter
t0.6 = required thickness of the blade section at 0.6 radius; mm (in.)
Y = minimum specified yield strength of type 4 propeller material; N/mm2
(kgf/mm2, psi). See 4-3-3/Table 1.
= skew angle in degrees (see 4-3-3/1.3.1)
= rake angle in degrees [see 4-3-3/1.3.3(b)] at 0.6 radius, positive for aft rake
H, D, and R are as defined in 4-3-3/5.1.

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5.5.1(c) Blade thickness between 0.6 and 0.9 radii. The maximum thickness at any radius
between 0.6 and 0.9 radii is to be not less than that obtained from the following equation:
tx = 3.3D + 2.5(1 – x)(t0.6 – 3.3D) mm; or
tx = 0.04D + 2.5(1 – x)(t0.6 – 0.04D) in.
where:
tx = required minimum thickness of the thickest part of the blade section at radius
ratio x.
t0.6 = thickness of blade section at the 0.6 radius, as required by 4-3-3/5.5.1(b)

x = ratio of the radius under consideration to D/2; 0.6 < x 0.9

5.5.1(d) Trailing edge thickness at 0.9 radius. The edge thickness at 0.9 radius measured at 5%
of chord length from the trailing edge is to be not less than 30% of the maximum blade thickness
required by 4-3-3/5.5.1(c) above at that radius.

5.5.2 Propeller of Other Than Type 4 Materials with Skew Angle ; where 25°< 50°
Propellers made of materials other than Type 4 and with skew angle 25°< 50° are subject to
special consideration. Design analyses, as indicated in 4-3-3/5.7, are to be submitted.

5.5.3 Propeller Blades with Skew Angle > 50°

Propellers with the maximum skew angle exceeding 50° will be subject to special consideration.
Design analyses, as indicated in 4-3-3/5.7, are to be submitted.

5.7 Blades of Unusual Design

Propellers of unusual design, such as those indicated in 4-3-3/5.5.2 and 4-3-3/5.5.3, controllable pitch
propeller of skewed design ( 25°), skewed propeller ( 25°) with wide-tip blades, cycloidal propellers,
etc., are subject to special consideration based on submittal of propeller load and stress analyses. The
analyses are to include, but be not limited to the following:
Description of method to determine blade loading
Description of method selected for stress analysis
Ahead condition is to be based on propulsion machinery’s maximum rating and full ahead speed
Astern condition is to be based on the maximum available astern power of the propulsion machinery
(the astern power of the main propelling machinery is to be capable of 70% of the ahead rpm
corresponding to the maximum continuous ahead power, as required in 4-1-1/7.5); and is to include
crash astern operation
Fatigue assessment
Allowable stress and fatigue criteria

5.9 Blade-root Fillets

Fillets at the root of the blades are not to be considered in the determination of blade thickness.

5.10 Built-up Blades

The required blade section is not to be reduced in order to provide clearance for nuts. The face of the
flange is to bear on that of the hub in all cases, but the clearance of the spigot in its counterbore or the edge
of the flange in the recess is to be kept to a minimum.

5.11 Strengthening for Navigation in Ice

For vessels to be assigned with Ice Class notations, propellers are to be designed in accordance with
Section 6-1-3, 6-1-5/51 or 6-1-6/27.

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5.13 Controllable Pitch Propellers – Pitch Actuation System

5.13.1 Blade Flange and Mechanisms
The strength of the propeller blade flange and pitch changing mechanism of controllable-pitch
propellers subjected to the forces from propulsion torque is to be at least 1.5 times that of the
blade at design pitch conditions.
5.13.2 Stud Bolt Area
The sectional area of the stud bolts at the bottom of the thread, s, is to be determined by the
following equations:

SI units MKS units US units

2
s 0.056Wkft 0.35 0.0018Wkft 02.35
mm2 in2
rn rn
k 621 63.3 90,000
U 207 U 21.1 U 30,000
where
s = area of one stud at bottom of thread
n = number of studs on driving side of blade
r = radius of pitch circle of the studs; mm (in.)
k = material correction factor for stud materials better than ABS Gr. 2 forged steel
U = ultimate tensile strength of the stud material; N/mm2 (kgf/mm2, psi)
See 4-3-3/5.1 for f and 4-3-3/5.3 for W and t0.35.

5.13.3 Blade Pitch Control

5.13.3(a) Bridge control. Where the navigation bridge is provided with direct control of propulsion
machinery, it is to be fitted with means to control the pitch of the propeller.
5.13.3(b) Duplication of power unit. At least two hydraulic power pump units for the pitch
actuating system are to be provided and arranged so that the transfer between pump units can be
readily effected. For propulsion machinery spaces intended for unattended operation (ACCU or
ABCU notation), automatic start of the standby pump unit is to be provided.
The emergency pitch actuating system [as required by 4-3-3/5.13.3(c)iii)] may be accepted as one
of the required hydraulic power pump units, provided it is no less effective.
5.13.3(c) Emergency provisions. To safeguard the propulsion and maneuvering capability of the
vessel in the event of any single failure in either the remote pitch control system or the pitch
actuating system external to the propeller shaft and oil transfer device (also known as oil
distribution box), the following are to be provided:
i) Manual control of pitch at or near the pitch-actuating control valve (usually the directional
valve or similar).
ii) The pitch is to remain in the last ordered position until the emergency pitch actuating
system is brought into operation.
iii) An emergency pitch actuating system. This system is to be independent of the normal
system up to the oil transfer device, provided with its own oil reservoir and able to change
the pitch from full ahead to full astern.
iv) Where at least two (2) independent propulsion systems are fitted on the vessel each one
provided with its own pitch control system, and with one propulsion system temporarily
out of service (until the emergency pitch control is connected), the vessel can manoeuver
and maintain a speed of 7 knots or one-half of the design speed whichever is the lesser,
the requirements as per 4-3-3/5.13.3(c)iii) need not be applied, provided the system
details are clearly indicated in the operating manuals.

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5.13.3(d) Integral oil systems. Where the pitch actuating hydraulic system is integral with the
reduction gear lubricating oil system and/or clutch hydraulic system, the piping is to be arranged
such that any failure in the pitch actuating system will not leave the other system(s) non-operational.
5.13.3(e) Provisions for testing. Means are to be provided in the pitch actuating system to
simulate system behavior in the event of loss of system pressure. Hydraulic pump units driven by
main propulsion machinery are to be fitted with a suitable by-pass for this purpose.
5.13.3(f) Multiple propellers. For vessels fitted with more than one controllable pitch propeller,
each of which is independent of the other, only one emergency pitch actuating system [as required
by 4-3-3/5.13.3(c)iii)] need be fitted, provided it is arranged such that it can be used to provide
emergency pitch-changing for all propellers.
5.13.3(g) Hydraulic piping. Hydraulic piping is to meet the requirements of 4-6-7/3.
5.13.4 Instrumentation
All controllable pitch propeller systems are to be provided with instrumentation as provided
below:
5.13.4(a) Pitch indicators. A pitch indicator is to be fitted on the navigation bridge. In addition,
each station capable of controlling the propeller pitch is to be fitted with a pitch indicator.
5.13.4(b) Monitoring. Individual visual and audible alarms are to be provided at the engine room
control station to indicate hydraulic oil low pressure and high temperature and hydraulic tank low
level. A high hydraulic oil pressure alarm is to be fitted, if required by the proposed system design
and, if fitted, is to be set below the relief valve setting.
For vessels assigned with ACC or ACCU notations, see 4-9-2/Table 2 and 4-9-5/Table 1 for
monitoring on the navigation bridge and in the centralized control station, respectively.

5.15 Propeller Fitting

5.15.1 Keyed Fitting
For shape of the keyway in the shaft and size of the key, see 4-3-2/5.7, 4-3-2/Figure 2 and 4-3-2/5.11.
5.15.2 Keyless Fitting
5.15.2(a) Design criteria. The factor of safety against slip of the propeller hub on the tail shaft
taper at 35°C (95°F) is to be at least 2.8 under the action of maximum continuous ahead rated
torque plus torque due to torsional vibrations. See 6-1-5/51.7 for propellers requiring ice strengthening.
For oil injection method of fit, the coefficient of friction is to be taken no greater than 0.13 for
bronze/steel propeller hubs on steel shafts. The maximum equivalent uniaxial stress (von Mises-
Hencky criteria) in the hub at 0°C (32°F) is not to exceed 70% of the minimum specified yield
stress or 0.2% proof stress of the propeller material.
Stress calculations and fitting instructions are to be submitted (see 4-3-3/1.5.4) and are to include
at least the following:
Theoretical contact surface area
The maximum permissible pull-up length at 0°C (32°F) as limited by the maximum permissible
uniaxial stress specified above
The minimum pull-up length and contact pressure at 35°C (95°F) to attain a safety factor against
slip of 2.8
The proposed pull-up length and contact pressure at fitting temperature
The rated propeller ahead thrust

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5.15.2(b) Nomenclature. The symbols used are defined as follows.

A = 100% of contact surface area between propeller hub and shaft taper (i.e.,
A = DsL); mm2 (in2). Oil grooves may be ignored. The propeller hub forward
and aft counterbore lengths ( 1 and 2 in 4-3-3/Figure 3) and the forward and
aft inner edge radii (r1 and r2 in 4-3-3/Figure 3), if any, are to be excluded.
B = dimensionless constant based on , and S
c = coefficient, dependent on the type of propulsion drive: 1.0 for drives such as
turbine, geared diesel, electric, and direct diesel with elastic coupling; and
1.2 for direct diesel drive. This value may have to be increased for cases
where extremely high pulsating torque is expected in service.
Db = mean outer diameter of propeller hub corresponding to Ds; mm (in.) Db is to
be calculated as the mean of Dbm, Dbf and Dba, outer diameters of hub
corresponding to Ds, the forward point of contact and the aft point of contact,
respectively, see 4-3-3/Figure 3.
Dba Dbm Dbf
Db =
3
Dbm = mean outer diameter of propeller boss, in mm (in.), at the axial position
corresponding to Ds, see 4-3-3/Figure 3.
Ds = diameter of shaft at mid-point of the taper in axial direction; mm (in.), taking
into account the exclusion of forward and aft counterbore length and the
forward and aft edge radii, see 4-3-3/Figure 3.

FIGURE 3
Theoretical Contact Surface Between Hub and Shaft

1 2

r2
r1

Dba Ds Dbm Dbf

EQ EQ

Eb = modulus of elasticity of hub material, see 4-3-3/Table 2

Es = modulus of elasticity of shaft material, see 4-3-3/Table 2
Fv = shear force at propeller/shaft interface; N (kgf, lbf)
H = power at rated speed; kW (PS, hp)
K = ratio of Db to Ds, see 4-3-3/Figure 3.
L = contact length, in mm (in.), see 4-3-3/Figure 3
P = mean propeller pitch; mm, (in.)

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Pmin = minimum required mating surface pressure at 35°C (95°F); N/mm2

(kgf/mm2, psi)
Pt = minimum required mating surface pressure at temperature t; N/mm2
(kgf/mm2, psi)
Pmax = maximum permissible mating surface pressure at 0°C; N/mm2 (kgf/mm2, psi)
Q = rated torque corresponding to H and R; N-mm (kgf-mm, lbf-in)
R = rpm at rated speed
S = factor of safety against slippage at 35°C (95vF)
T = rated propeller thrust; N (kgf, lbf)
tref = 35°C (95°F)
v = vessel speed at rated power; knots (knots)

b = coefficient of linear expansion of propeller hub material; mm/mm°C

(in/in°F); see 4-3-3/Table 2

s = coefficient of linear expansion of shaft material; mm/mm°C (in/in°F); see

4-3-3/Table 2

min = minimum pull-up length at 35°C (95°F); mm (in.)

t = minimum pull-up length at temperature t; mm (in.)

max = maximum permissible pull-up length at 0°C (32°F); mm (in.)

= half taper of shaft; e.g. if taper =1/15, = 1/30

y = yield stress or 0.2% proof stress of propeller material; N/mm2 (kgf/mm2, psi)

= coefficient of friction between mating surfaces; to be taken as 0.13 for fitting

methods using oil injection and hubs of bronze of steel

b = Poisson’s ration of hub material, see 4-3-3/Table 2

s = Poisson’s ratio of shaft material, see 4-3-3/Table 2

TABLE 2
Material Constants
Modulus of Elasticity Poisson’s Coefficient of Expansion
Material N/mm2 kgf/mm2 psi Ratio mm/mm°C in/in°F
Cast and forged steel 20.6 104 2.1 104 29.8 106 0.29 12.0 10 6 6.67 10 6

Bronzes, Types 2 & 3 10.8 104 1.1 104 15.6 106 0.33 17.5 10 6 9.72 10 6

Bronzes, Types 4 & 5 11.8 10 4

1.2 10 4
17.1 10 6 0.33 17.5 10 6
9.72 10 6

5.15.2(c) Equations. The taper on the tail shaft cone is not to exceed 1/15. Although the equations
given below are for ahead operation, they may be considered to provide an adequate safety margin
for astern operation also.
The minimum mating surface pressure at 35°C (95°F), Pmin, is to be:

2
ST 2 Fv
Pmin = S B N/mm2 (kgf/mm2, psi)
AB T

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The rated propeller thrust, T, submitted by the designer is to be used in these calculations. In the
event that this is not submitted, one of the equations in 4-3-3/Table 3 may be used, subject to
whichever yields the larger value of Pmin.

TABLE 3
Estimated Propeller Thrust, T
SI units (N) MKS units (kgf) US units (lbf)
H H H
1762 or 132 or 295 or
v v v
H H H
57.4 10 6 4.3 10 6 0.38 10 6
PR PR PR

The shear force at interface, Fv, is given by

2cQ
Fv N (kgf, lbf);
Ds
Constant B is given by:
2
B= – S2 2

The corresponding [i.e., at 35°C (95°F)] minimum pull-up length, min, is:

Ds 1 K 2 1 1
min = Pmin b 1 s mm (in.);
2 Eb K 2 1 Es

Db
K
Ds

The minimum pull-up length, t, at temperature, t, where t < 35°C (95°F), is:

Ds
t = min + ( b – s)(tref – t) mm (in.)
2
The corresponding minimum surface pressure, Pt, is:

t
Pt = Pmin N/mm2 (kgf/mm2, psi)
min

The maximum permissible mating surface pressure, Pmax, at 0°C (32°F) is:
2
0.7 y (K 1)
Pmax N/mm2 (kgf/mm2, psi)
4
3K 1
and the corresponding maximum permissible pull-up length, max, is:

Pmax
max min mm (in.)
Pmin

ABS RULES FOR BUILDING AND CLASSING MARINE VESSELS . 2018 307