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Concept & Formula
Concept & Formula
Inputs
Stocks Diameter
Description
Unit
Remarks
S
N
u
3
Ö Q
R
K
s
mm
Upper Stock Diameter
Q
R
Total rudder torque
kN-m
K
s
Material factor for upper stock
-
Q
R
C
R
r
kN-m
C
R
rudder force
kN
r
c(a - A
f
/A)
m
> 0.1c for ahead condition
c
mean breadth of rudder area
m
a
-
Ahead
a
0.66
-
Astern
A
f
Area of rudder blade situated forward
of the centerline of the rudder stock
m
2
C
R
nK
T
AV
2
kN
A
total projected area of ruder
m
2
V
V
d
for the ahead condition but is not to
taken as less than V
min
knots
V
V
a
for the astern condition but is not to
taken as less than 0.5V
d
or 0.5V
min
, whichever is greater
knots
V
d
the design speed with the vessel running
ahead at the maximum continuous rated
shaft rpm and at the summer load line
knots
V
a
maximum astern speed
knots
V
min
(V
a
+ 20)/3
knots
K
T
1.463
-
Ahead
K
T
1.682
-
Ahead behind fixed propeller nozzle
K
T
1.063
-
Astern
K
T
1.2
-
flat sided rudders Astern
K
T
1.222
-
Astern behind fixed propeller nozzle
K
T
1.38
-
Flat sided rudders astern behind
fixed propeller nozzle
A
t
sum of rudder blade area A and the rudder
post or rudder horn area within the
extension of the rudder profile
m
2
n
-
K
(n
y
/Y)
e
-
U
minumum tensile strength of material used
N/mm
2
e
1
for Y £ 235 N/mm
2
e
0.75
for Y > 235 N/mm
2
c
mean breadth of rudder area
m
A
f
Area of rudder blade situated forward
of the centerline of the rudder stock
m
2
A
total projected area of ruder
m
2
V
d
the design speed with the vessel running
ahead at the maximum continuous rated
shaft rpm and at the summer load line
knots
V
a
maximum astern speed
knots
A
t
sum of rudder blade area A and the rudder
post or rudder horn area within the
extension of the rudder profile
m
2
Y
Specified minimum yield strength of the
material, but is not to be taken as greater
than 0.7U or 450 N/mm
2
, whichever is lesser
N/mm
2
n
y
N/mm
2
U
minimum tensile strength of material used
N/mm
2
l
n
distance from center of neck bearing to the
centroid of rudder area
m
Kt
Location of Propeller
Ahead
Ahead behind fixed propeller nozzle
Astern
flat sided rudders Astern
Astern behind fixed propeller nozzle
Flat sided rudders astern behind fixed propeller nozzle
Symbol
Formula Expression/ Definition
Value
Unit
S
N
u
3
Ö Q
R
K
s
mm
Q
R
Total rudder torque
K
s
Material factor for upper stock
-
Q
R
C
R
r
kN-m
r
c(a - A
f
/A)
m
C
R
Design Rudder force nK
T
AV
2
kN
V
V
d
for the ahead condition but is not to
taken as less than V
min
knots
K
T
-
A
t
sum of rudder blade area A and the rudder
post or rudder horn area within the
extension of the rudder profile
m
2
K
(n
y
/Y)
e
-
n
y
N/mm
2
U
minimum tensile strength of material used
N/mm
2
Minimum Required Lower Rudder Stock Diameter
Symbol
Formula Expression/ Definition
Value
Unit
S
1
S
6
Ö 1 + (4/ 3) (M/ Q
R
)
2
mm
S
upper stock required diameter
mm
Q
R
rudder torque
kN-m
M
bending moment at the station of the
rudder stock
M
C
R
l
n
kN-m
C
R
rudder force
kN
l
n
distance from center of neck bearing to the
centroid of rudder area
m
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