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RUDDER CALCULATION
LOA (m) LBP (m) B(m) D(m) T(m) V (Knots)69.63 61 15.4 6.04 5.07 13
No of Screw 1 Type Spade Rudder
Step 1 RUDDER AREA
a For normal supply vessels the range of rudder area is 3-4 % of (L*T) Taking the rudder area to be 3.5 % of (L*T)
Ar 5.26 m2
b Using DNV Rule
For normal seagoing ships
Where
T - Ships Draught (m)A 8.02 m2 LBP - Ships Length (m)
c Average of Above two areas are taken as a Rudder Area
Ar 7 m2
Step 2 RUDDER GEOMETRY
Area = b * c T = 1.4b+X X = 0.05D-.0055DX 0.26878
b 3.43 m b - SpanC - Chord
c 1.94 m
Aspect Ratio = Span / Chord AR 1.77
Step 3 RUDDER MAXIMUM ANGLE
a αmax = (5/7)*ԃmax Where,αmax - Angle of Attackԃmax - Rudder deflection Angle
αmax 25 deg ԃmax = 33 - 35 for sea-going with conventional rudder
b Rudder Deflection Rate
ԃmin = (24 * V)/L
ԃmin 5.11 deg/sec
A = TL/100 [1+25 (B/L) 2]
A - Rudder area (m2)
Step 4 RUDDER PROFILE
Taper Ratio is taken as 0.5 Taper Ratio = Ct/Cr
C = (Ct + Cr)/2 Cr 2.58 m
Ct 1.29 m
Sweep back angle is taken to be 7 deg (Apporx)
Step 5 LOCATION OF RUDDER TURNING AXIS
a For Tip 0.12217305
BC = b/2 tan 7 BC 0.21054132 m
BD = ct/4 BD 0.32265114 m
AC = EF = C/4 AC = EF 0.48397671 m
AD = AB+BD AD 0.59608653 m
b For Root
IJ = b/2 tan7 IJ 0.21054132 m
JL = Cr/4 JL 0.64530228 m
HI = EF = C/4 HI = EF 0.48397671 m
HL = HI+IJ+JL HL 1.33982031 m
KL = HL-HK KL 0.74373378 m
c Let's take 25% of Area to be at forward part of the rudder Stock
Ar/4 1.65977047 m2
Step 6 RUDDER CONSTRUCTION
a Rudder Stock
Where,
Kr - Rudder coefficient 0.248
1
158.885 mm Xpf = (0.12 * Ar)/6 0.133
ds = 83.3 Kr (FR(V+3)2(AR2XPF
2+N2)1/2)1/3
FR - Rudder profile coefficient
ds
Step 7 RUDDER BEARING
a Zb 198.61 mm
T= 0.2ds T 31.78 mm
b Clearance = 0.001*ds + 1 but not less than 1.5 mm
Clearance 1.2 mm
Step 8 RUDDER SCANTLING
a Plate Thickness
Where, K 1Yw = Vertical spacing between the horizontal web in mm.Xw = horizontal spacing of the vertical web in mmds = the basic stock diameter, mm
Yw 600 mm Xw 900 mm
t 10.93 mm
Depth ZB = 1.25 ds
t= K(0.001Yw+0.61)[4-Yw /Xw](1.45+0.1(ds)1/2)
step 8 Rudder Construction
1 Rudder Stock
ԃs
whereKr=Rudder coefficient = 0.248
V= Service speed =16 Kn
step2Rudder Bearing
Zb= mm
Minimum thickness of the wall for the lower bearing is to be taken as the lesser ofor 100mm
T= mm
minimum7.0N/mm^2given bearing pressure on the projected area of the lowest main bearing for metal
Basic stock diameter ds
ds = 83.3 Kr (FR(V+3)2(AR2XPF
2+N2)1/2)1/3
FR= Rudder profile coefficient =1.0
AR = Rudder area =10.5 m2
XPF = 0.12 AR / YR
YR =Depth of rudder at the center line of stock
Depth ZB = 1.2 ds
0.2ԃ
T= 0.2ds
RUDDER CALCULATION
LOA (m) LBP (m) B(m) D(m) T(m) V (Knots)
322.26 305.4 50.9 25.45 18.97 13
No of Screw 2 Type Spade Rudder
Step 1 RUDDER AREA
a For normal supply vessels the range of rudder area is 3-4 % of (L*T)
Taking the rudder area to be 3.5 % of (L*T)
Ar 98.49 m2
b Using DNV Rule
For normal seagoing ships
Where
T - Ships Draught (m)
A 98.17 m2 LBP - Ships Length (m)
c Average of Above two areas are taken as a Rudder Area
Ar 98 m2
Step 2 RUDDER GEOMETRY
Area = b * c T = 1.4b+X X = 0.05D-.0055D
X 1.132525
b 12.74 m b - Span
C - Chord
c 7.72 m
Aspect Ratio = Span / Chord AR 1.65
Step 3 RUDDER MAXIMUM ANGLE
a αmax = (5/7)*ԃmax Where,
αmax - Angle of Attack
ԃmax - Rudder deflection Angle
αmax 25 deg ԃmax = 33 - 35 for sea-going with conventional rudder
b Rudder Deflection Rate
ԃmin = (24 * V)/L
A = TL/100 [1+25 (B/L) 2]
A - Rudder area (m2)
ԃmin 1.02 deg/sec
Step 4 RUDDER PROFILE
Taper Ratio is taken as 0.5 Taper Ratio = Ct/Cr
C = (Ct + Cr)/2 Cr 10.29 m
Ct 5.14 m
Sweep back angle is taken to be 7 deg (Apporx)
Step 5 LOCATION OF RUDDER TURNING AXIS
a For Tip 0.122173
BC = b/2 tan 7 BC 0.7822023 m
BD = ct/4 BD 1.2862295 m
AC = EF = C/4 AC = EF 1.9293443 m
AD = AB+BD AD 2.4333715 m
b For Root
IJ = b/2 tan7 IJ 0.7822023 m
JL = Cr/4 JL 2.5724591 m
HI = EF = C/4 HI = EF 1.9293443 m
HL = HI+IJ+JL HL 5.2840057 m
KL = HL-HK KL 2.8506342 m
c Let's take 25% of Area to be at forward part of the rudder Stock
Ar/4 24.581879 m2
Step 6 RUDDER CONSTRUCTION
a Rudder Stock ds = 83.3 Kr (FR(V+3)2(AR2XPF
2+N2)1/2)1/3
Where,
Kr - Rudder coefficient 0.248
1
1414.525 mm Xpf = (0.12 * Ar)/6 0.360
Step 7 RUDDER BEARING
a Zb 1768.16 mm
T= 0.2ds T 282.90 mm
b Clearance = 0.001*ds + 1 but not less than 1.5 mm
Clearance 2.4 mm
Step 8 RUDDER SCANTLING
a Plate Thickness
Where,
K 1
Yw = Vertical spacing between the horizontal web in mm.
Xw = horizontal spacing of the vertical web in mm
ds = the basic stock diameter, mm
Yw 600 mm Xw 900 mm
t 21.02 mm
FR - Rudder profile coefficient
ds
Depth ZB = 1.25 ds
t= K(0.001Yw+0.61)[4-Yw /Xw](1.45+0.1(ds)1/2)
