Applied Mechanics and Materials
ISSN: 1662-7482, Vols. 275-277, pp 2421-2426
doi:10.4028/www.scientific.net/AMM.275-277.2421
© 2013 Trans Tech Publications, Switzerland
Online: 2013-01-11
Ship Form Optimization of 62-Feet Yacht and Analysis of Performance
Shilun Zhao1,a , Chaohe Chen1,b*,Yueqin Liu1,c
1
Naval Architecture and Ocean Engineering R & D Center of Guangdong Province, South
China University of Technology , Guangzhou, 510641, P.R.China
a
[email protected], b*[email protected], [email protected]
* Corresponding author
Keywords: yacht, knuckle lines, hard chine, experienced method, form optimization
Abstract: This paper focus on the ship form optimization of a 62-feet yacht and uses experienced
method based on amount of statistical data to change the width of knuckle lines in order to reduce
the resistance of the hull, including comparison of performance of stability and see keeping.
0 Prefaces
Study for the yacht resistance performance abroad already has a series of model test data and
statistics, including regression formula which are for calculation of the resistance and map like the
TMB 62 series. There are also attempts of computational optimization for resistance. In our country,
it is rare for studying the performance of resistance and making improvement on it. Lacking of
statistics about the yachts we can only design according to the experience abroad. Especially in the
context of rapid development of China's yacht industry, it is meaningful attempt that using statistics
and empirical methods abroad to optimize resistance performance of the yacht.62-feet yacht is the
common product which is the target of the ship form optimization of resistance in this paper.
1 Options for optimization
According to statistical data by Niels E.Sorensen-Viale , properties of a stepless planing hull
like principal dimensions, coefficience of area, longitudinal coordinate of gravity, angle of deadrise
and shape of transverse section have a corresponding value and curve [1]. The ship form
optimization of 62-feet yacht in this paper is changing the shape of knuckle lines properly based on
the experienced method out of statistical data.
Bilge and bottom plane are connected by hard chine which make the water stream flow out
through broadside to reduce wet surface area and the bottom plane become a planing plane.
According to statistical data, the biggest width of high speed stepless planing hull lies in 40%L from
stem[3]. Proportion between width of knuckle lines at transom stern(Bt) and biggest width of
knuckle lines(Bpmax) is in the range of 0.65 to 0.80[4].Oversize of width can increase the resistance
of planing hull [1].
Taking this point into consideration, there is plenty of space for the 62 feet yacht, of which
proportion of Bt and Bpmax is 1 (see Sheet no.1 below),to improve.
Sheet no.1
station
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
(mm)
2134
2134
2134
2134
2134
2134
2134
2134
2117
2079
2003
1850
1665
1395
999
289
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Applied Mechanics and Materials I
The best value for proportion of Bt and Bpmax between 0.65 and 0.80. Now we get the best
half width of Bt is 1663.2mm based on the proportion of 0.80. Restrained by the effective space of
the yacht we just cannot take the best half width of Bt into practice for optimization. Then we
choose 3 value of half width for test which is between the best value 1663.2mm and the original
value 2143mm to calculate the resistance and see performance of stability and seekeeping after
changing the width of knuckle lines.
Three options of optimization , see the sheet no.2, no.3 and no.4 below.
Sheet no.2
station
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
(mm)
2000
2080
2100
2120
2134
2134
2134
2134
2117
2079
2003
1850
1665
1395
999
289
Sheet no.3
station
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
(mm)
1860
1920
2000
2080
2100
2134
2134
2134
2117
2079
2003
1850
1665
1395
999
289
Sheet no.4
station
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
(mm)
1700
1780
1900
1980
2080
2100
2134
2134
2117
2079
2003
1850
1665
1395
999
289
The widths for test of Bt are 2000mm, 1860mm, 1700mm.It is convenient for correcting
corresponding lines at every station when we put the gap into value between 130-160mm for each
test width.
The vertical axe is Bt/Bpmax while the horizontal axe is station number along the yacht and
the chart below represents the curve of every option.
Chart no.1
Applied Mechanics and Materials Vols. 275-277
2423
This paper is using Maxsurf to do the calculation of resistance. The picture below is
comparison of all options for optimization.
Chart no.2
In the perspective of modeling, ship form of option 1 and option 2 have a smooth changing
through the longitude of yacht but not so good for option 3. The reason is too much reduction on the
width of transom stern which leads to the flexible body shape.
2 Analysis of Performance
2.1 Performance of Resistance
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Applied Mechanics and Materials I
Concerning the results from the charts above, every option reduces total resistance. But the
same effect is not happening on friction resistance. The reason is that the wet surface area increases
because of the changing of the width of knuckle lines[2]. However,the residuary resistance and the
total resistance decrease, so the conclusion is that the reduction of residuary resistance contributes
to the reduction of total resistance.
2.2 Performance of Stability
The angle of entrance of 62 feet yacht is 54º, so the calculation stop at the angle of 60º. From
the sheet no.6 we can conclude that the performance of stability is not affected due to the changing
of lines. The shape narrows gradually to the stern which results in the reduction of volume. The
block coefficient decreases, although it differs little we still figure out that the longitude of gravity
moves towards stem slightly. We do not need to bear sacrifice on performance of stability in the
condition that performance of resistance improves.
Applied Mechanics and Materials Vols. 275-277
2425
2.3 Performance of Seekeeping
Sheet no.5
Bretschneider
7.047s
V=10kn
Heave
original
Option 1
Option 2
Option 3
2m
Following
0deg
oblique
45deg
Portbeam
90deg
unit
RMS
Sig amp
RMS
Sig amp
RMS
Sig amp
m
0.382
0.763
0.398
0.795
0.446
0.891
Roll
deg
0
0
6.71
13.42
14.71
29.43
Pitch
deg
2.95
5.9
2.84
5.67
2.07
4.13
Heave
m
0.382
0.764
0.398
0.796
0.446
0.891
Roll
deg
0
0
6.7
13.4
14.68
29.36
Pitch
deg
2.94
5.89
2.83
5.65
2.07
4.13
Heave
m
0.382
0.764
0.398
0.796
0.445
0.891
Roll
deg
0
0
6.7
13.4
14.61
29.22
Pitch
deg
2.93
5.86
2.83
5.66
2.07
4.15
Heave
m
0.382
0.764
0.398
0.796
0.446
0.891
Roll
deg
0
0
6.73
13.46
14.54
29.07
Pitch
deg
2.88
5.76
2.81
5.63
2.08
4.15
We calculate value of the motion response respectively in direction of following seas, oblique
seas and port beam seas on a low speed of 10kn using the 1 parameter Bretschneider spectra, of
which the significant amplitude of wave is 2m according to the division of sailing area. The heave
and roll and pitch motion response of three option still differs little to the original yacht. What we
concerning at first is that it might bring additional load to the strength of the yacht body , with the
increasing motion responses. But now we know that there is no need to worry about that problem
according to the calculation.
3 Comparison
See the chart below .Here we take a 24 feet yacht into comparison on the curve of Bt/Bpmax.
Chart no.3
Both two yachts have a trend on the changing width of knuckle lines. Bt/Bpmax of the original
yacht and 24 feet yacht is 1 and Bpmax of 24 feet yacht lies near the stern. In this regard we can
take a similar optimization on 24 feet yacht. Because the optimization of 62 feet yacht is giving us a
reasonable practice.
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Applied Mechanics and Materials I
4 Conclusion
Proven by the analysis of the three options of optimization , changing the width of knuckle
lines on transom stern according to the experienced method does not give any consequences on the
performance of stability and seekeeping and this changing remain the properties of most aspects of
the original 62 feet yacht.
Taking the used space into consideration, option 1 got a 2.1% reduction of total resistance
while the option 2 got 5.9%.Giving a 8.7% reduction of total resistance ,option 3 performs the
best ,but it costs the used space and is not satisfactory on body shape. So above all, option 2 is a
reasonable choice for this optimization.
Besides, on the comparison with 24 feet yacht we can see that there is possibility of improving
the performance of resistance on different size of yacht, which have a similar trend on width
changing of knuckle lines, using the experienced method .In this paper we give a reasonable
practice.
Using experienced method based on statistical data , this paper presents an example for
improving the performance of resistance. On one hand it proves the feasibility of experienced
method, on the other hand it also tells us that it can be more efficient if we are improving the design
with parameterization method. This paper can be a practical example for improvement of similar
kind of yacht.
References
[1] Niels E.Sorensen-Viale.the design and tank testing of planing hulls.High-speed Surface
Craft,May/June,1985:30-34
[2] Siu C.Fung.Resistance predictions and parametric studies for high-speed displacement
hulls.Naval Engineers Journal,March 1987
[3] D.Radojcic.A statistical method for calculation of resisitance of the stepless planing
hulls.International Shipbuilding Progress,1984,31(364)
[4] Minhu Zhu.the design of stepless planing hulls. Technology and Economy Information of Ship
Bulldings Industry , 2004.12
[5] Minhu Zhu.the hydrodynamic calculation of planing hulls. Technology and Economy
Information of Ship Bulldings Industry , 2005.2
Applied Mechanics and Materials I
10.4028/www.scientific.net/AMM.275-277
Ship Form Optimization of 62-Feet Yacht and Analysis of Performance
10.4028/www.scientific.net/AMM.275-277.2421