VOL.2
WORKSHOP ON DEVELOPMENTS IN
HULL FORM DESIGN
MARIN
22 - 24 OCTOBER 1985
WAGENINGEN, THE NETHERLANDS
PROCEEDINGS
Volume 2
WORKSHOP ON DEVELOPMENTS IN HULL FORM DESIGN
October 22 - 24, 1985 Wageningen, The Netherlands
PROCEEDINGS
VOLUME II
Publication No. 785
Maritime Research Institute Netherlands Wageningen, The Netherlands
SESSION I: LARGE BLOCK HULL FORMS FOR DRY AND LIQUID BULK CARRIERS
Contribution 1,1: Application of Viscous Resistance Theory 11
to Design of Full Ship Forms
by K. Takekuma and T. Nagamatsu (Nagasaki Experimental Tank, MHI)
Contribution 1,2: Hydrodynamic Characteristics of Low Length- 16
Beam, Full Block Ships
by A.M. van Wijngaarden and J. van de Beek (MARIN)
Contribution 1,3: Effect of Principal Dimensions on the 20
Propulsive Performance of Twin-Skeg Hull Forms by K. Yokoo, K. Sato, M. Hirai and S. Ohta (SRC)
Contribution 1,4: Hull Forms for a Lifetime's Economical 26
Operation
by M.G. Osborne (Shell Int. Marine Ltd.)
Contribution 1,5: Hydrodynamic Design of Shallow Draft Twin 30
Screw Full Ship
by K. Takekuma and T. Suzuki (MHI)
Contribution 1,6: Full Forms, Shallow Draft Barge Feeder 37
Vessel
by G.F. Bertaglia, G. Sbrizzai and P. Frandoli (Fincantieri)
Contribution 1,7: Recent Developments of CE85 Method Series 58
by E. Allieri, G.A. Sartori (CETENA) and S. Miranda (Naples University)
Discussion on papers and contributions in Session I 61
SESSION II: HULL FORMS FOR CONTAINER VESSELS, RO-R0 SHIPS AND FERRIES
Contribution 11,1: Applying Resistance Theory and Quadratic 69
Programming Method to Determine Optimal Ship Forms
by Chi-Chao Hsiung (T.U. of Nova Scotia) and Dong Shen-yan (CSSRC)
Contribution 11,2: Interactive Hull Form Design for Minimum 79
Wave Resistance
Contribution 11,3: Effectiveness of the Optimization of 86
Forms of Models of Ships of Modern Architecture by V.M. Pashin, I.O. Mizin, V.S. Shpakov and V.M. Shtumpf (KSRI)
Contribution 11,4: A Prediction Formula of Ship Wave 96
Resistance for Hull Form Design by H. Tagano (SRC)
Contribution 11,5: Model Tests with a Series of Bulbous 105
Bows for Minimizing the Resistance of a Container Ship by S. Kyulevcheliev and T. Tepavicharov (BSHC)
Discussion on papers and contributions in Session II 111
SESSION III: DEVELOPMENTS IN AFT-BODY DESIGN
Contribution The Influence of the Asymmetric 117
Afterbody and the Horizontal Fins of the Rudder Blade on the Propulsive Efficiency
by J.W. Piskorz-Nalecki (Marine Consultants, Poland)
Contribution 111,2: The Simplified Hull Forms Parameter 130
Study of the Buttock Flow Stern by M.K. Hellevaara (TRC, Finland)
Contribution 111,3: Some Latest Developments in Icebreaker 140
Technology
by J. Schwarz (HSVA)
Discussion on papers and contributions in Session III 146
SESSION IV: HIGH-SPEED DISPLACEMENTS SHIPS
Contribution IV,1: Optimization of Hull Form for Seakeeping 155
and Resistance
by D.A. Walden, P.J. Kopp (DTNSRDC) and P. Grundmann (German Federal Office for Military Technology and Procurement)
Contribution 1V,2: Prediction of Resistance and Propulsion 175
Characteristics of High-Speed Displacement Ships by E.J. Stierman (MARIN)
Contribution IV,3; Development of High Speed Craft with 190
Improved Seakeeping Quality by K. Takekuma and K. Kihara (MHI)
Contribution 1V,4: The NRC Hull Form Series - an Update 196
Contribution IV,6: Stern Wedges and Flaps/Destroyer Propulsion 221
by R.K. Burcher (ARE Haslar)
Discussion on papers and contributions in Session IV 226
Session V: ADVANCED MARINE VEHICLES AND PLEASURE CRAFT
Contribution V,1: Resistance Characteristics of Surface 239
Effect Ships
by T. van Terwisga (MARIN)
Contribution V,2: The Hybrid Hydrofoil Catamaran (HYCAT) 246
by D.E. Calkins (University of Washington)
Contribution V,3: Catamaran Design from the View Point of 258
Wave Resistance
by K-S. Min and K-J. Kim (Daewoo)
Contribution V,4: Semi-Planing
Vessels
in a Seaway, 274Comparative Prediction of Operability
by A.M. van Wijngaarden (MARIN) and W. Beukelman (Delft Un. of Technology)
Discussion on papers and contributions in Session V 283
PREFACE
The Workshop on Developments in Hull Form Design, organized by the Maritime
Research Institute Netherlands, has been attended by over 200 participants from 26 countries. In five sessions, different subjects in the field of hull form design have been covered. In each session two or three invited papers and a number of short contributions were presented.
Volume One of the Proceedings includes all invitated papers. Volume Two of the Proceedings includes all contributions and the discussions to both invited papers and contributions.
LARGE BLOCK HULL FORMS FOR DRY AND LIQUID BULK CARRIERS
Abstract
According to the development of viscous resistance formula based on a higher order boundary layer theory, it became possible to study the relationship between hull geometry and viscous pressure resistance component. Char-acteristics of the theory were outlined by use of an example of improvement of full stern form.
1. Introduction
Viscous resistance component is the major part of total resistance of full
ships. In the course of design such
full ships, therefore, much attention is paid to reduction of viscous resistance.
However, the design of hull form with low viscous resistance has been made mostly on experimental basis, because no theoretical and computational means were available for practical use in these decades. For example, the con-ventional thin boundary layer theory, which is drived form the assumption of constant pressure gradient in the direction normal to the body surface and usually the pressure is put equal to that on the body surface in the inviscid flow, can predict only frictional
resistance but not viscous pressure resistance.
From the view-point of designing hull
11
APPLICATION OF VISCOUS RESISTANCE THEORY TO DESIGN OF FULL SHIP FORM
K. TAKEKUMA AND T. NAGAMATSU
MITSUBISHI HEAVY INDUSTRIES, LTD., JAPAN
forms, the prediction of viscous pre-ssure resistance is more important, since the viscous pressure resistance is closely related to the geometrical characteristics of hull form.
In the Nagasaki Experimental Tank, one of the authors developed a higher order boundary layer theory to calculate the ship viscous pressure resistance /1/. In the method, in order to know directly the contribution of local ship form to each component of viscous resistance, the ship viscous resistance is calcu-lated as a sum of frictional and viscous pressure resistance obtained by inte-gratig wall shear stress and pressure over the hull surface respectively. In the present paper, the calculated examples are shown to demonstrate the applicability and usefulness of our method to ship form design.
2. Outline of the calculation method
It has been known empirically that there is close correlation between the stern form and viscous resistance. Therefore, in order to predict ship viscous resist-ance with enough accuracy, the theory for calculating viscous resistance must include the characteristics of the stern flow.
From experimental investigations, it has been found that the stern flow of full form ship is characterized as follows.
at the sides of ship stern due to convergence of streamlines and decrease of body sectional area.
The pressure gradient in the direc-tion normal to the body surface is noticeable (Fig. 1).
The viscous-inviscid interaction becomes significant.
The normal velocity component is not negligibly small.
The turbulence intensities around stern become weaker than that in the thin boundary layer.
Three-dimensional separation appears
Body plan and measuring positions
L=8.00m B/d= 1.600 L/B=10.00 C=0.444 Lwl
11/16:
Measuring positions L=8.00m B/d =2.365 LIB=6.468 CI = 0.571 Lwi L= 8.00m Bid=2.760 L/8=6.00 0=0.802 Lwt.Cargo ship model
Tanker model
Fig. 1 Pressure variation in boundary layer
at stern bilge.
There exists the so-called reversed cross flow.
and so fourth.
These characteristics are out of the assumption of the conventional thin boundary layer. Therefore, taking the
above characteristics from (1) to (5) into account, a higher order boundary layer theory is derived. The details of the higher order theory and calcu-lation procedure are described in Ref. /1/.
Pressure variation in boundary layer
o Measurement Calculation (.1 S.S. 21/7 S.S tt00.1[I 0 50 103 150 0 50 100 150 0.1 S.S. 0.1 11. SS. 0 I 50 100 150 0 50 100 150
WI gley model Till I
5.5. I S.S. 1 11 0 _0.,
...
01r 1, o 0. 62 al{ . o 0 o 1 1 150 IOC ISO 0 50 100 /SO 200
0.1 0 1
0000
...,
1::, 0 [ 0 [ '').... .
. . . . 0 50 100 150 0 50 100 150 200 0.1 0.1 1.: 0 -0.,....,.. ...
(1:11..
1.10 -01[ . 150 0 50 100 150 200 C,mml cI TT -0 2 00 ° -0.3 , - 1 (2) 0 100 200 0 100 200 0 C.,, 0/
C :1)0.1 .° ° -0.3 0 100 200 100 200 coolm1 {ImrniThe viscous resistance of a ship is cal-culated as a sum of frictional
resist-ance R and viscous pressure resist-ance R . According to the physical
vp
properties, RF and R are calcu-vp
lated by surface integral of the shear stress and pressure at hull surface respectively, which are obtained from
the boundary layer calculation. Viscous pressure resistance is divided into three parts as
RR
vpl R Rvp vp2 vp3
vpl represents the pressure resist-ance caused by the pressure variation across the boundary layer and Rvp2 caused by the viscous-inviscid
inter-action. Rvp3 is the pressure
resist-ance at the hull part downstream of the position of numerical breakdown xl3 under the assumption of constancy of pressure difference C - C along
P. Pw
streamlines, where C and C are
po Pw
the pressure coefficients at the hull surface in potential and viscous flows respectively (Fig. 2). Numerical breakdown 04 0 -04 sveomve Assumed constont
Fig. 2 Approximate calculation after
numerical breakdown
3. Calculated results and discussion
Usefulness and applicability of the calculation method may depend on whether the method can predict the favorable direction for hull form improvement or not. In order to examine the capability
(1)
Cp
0
0
13
of the present method, calculations for two tanker models Ship-A and Ship-B, were made and compared with experimental results.
Table 1 Principal dimensions and viscous resistance Note ; Cvcal C C vp F Cvexp Cm( 1 Kexp )
a lima
L1131
Fig. 3 Body plans of two tanker models
The principal dimensions and body plans of Ship-A and Ship-B are shown in Table 1 and Fig. 3. Their fore-bodies are identical and the shape of frameline of their after-bodies are slightly differ-ent. The calculated results agree with
Items Ship-A Ship-B U-form V-form Lpp ( m ) 5.00 5.00 Lpp/B 6.00 6.00 B/D 2.76 2.76 Cb 0.80 0.80 -6 Rn x 10 5.0 5.0 CFO 0.00308 0.00308 Kexp 0.425 0.358 c o m ... m
.
m u , m o C vp 0.00150 0.00097 CF 0.00332 0.00340 K P 0.487 0.313 Kf 0.078 0.104 K 0.565 0.417 Cvcal/Cvexp 1.098 1.043 Ship-A Ship-.the measured ones fairly well as shown
in Table 1. The present method detects
the difference of viscous resistance caused from small difference of framline shapes as well as measurements.
The theoretical calculation, in general, is useful to investigate the detail of the calculated results analytically. The viscous pressure resistance coeffi-cient C ' and sectional mean of
vp
local skin friction coefficientf at each station are shown in Fig. 4. A
small difference of Cf between Ship-A and Ship-B is observed in their after
bodies. This difference may be due to
that the boundary layer thickness and shape factor of Ship-A are larger as a whole, and yield smaller Kf for Ship-A than for Ship-B as shown in Table 1. On the other hand, it is found in Fig. 4 that C ' of Ship-A begins to increase
vp
rapidly at an earlier point on x-axis than that of Ship-B. And the numerical breakdown of Ship-A has occurred earlier
than that of Ship-B.
F.D. 9 8 7 6 5 4 3 2 1 A.P.
Station
Fig. 4 Comparison of viscous
resist-ance components between Ship-B and Ship-C
Fig. 5 shows the girthwise distributions of viscous pressure resistance component calculated at S.S.1. An evidenL differ-ence between Ship-A and Ship-B is
Fig. 5 Girthwise distribution of viscous pressure. resistance component at S.S.1 5.0 Ai3wtpp 2 0 A
8 COE Fl H
IJ
GirthFig. 6 Comparison of girthwise
distri-bution of normal curvature and directional cosine
observed along the girth from position
C to G. Therefore, it can be said that
improvement of this hull part of Ship-B is effective to reduce the viscous pressure resistance. To know the direc-tion of hull form improvement, it is necessary to grasp the correlation between geometrical characteristics of hull form and viscous pressure
resist-ance. The viscous pressure resistance
is obtained by multipling the direc-tional cosine X at the hull surface to
pressure difference (C
-C
), andpo Pw
the normal curvatures K13w and K23w are closely connected to (C - C ),
Po Pw
where C and C are the pressure
Po pw
coefficients at the hull surface in
- Ship-A
Ship -B 0.3 S.S.1 0 Ship-A Ship-B Flat Plate C Vp 0.006 Cf 0.004 C 0.002 0potential and viscous flows
respec-tively. Consequently, directional
cosine R. and normal curvatures,
espe-cially K13w, are important geometrical quantities. The girthwise distributions of 2, and K13w at S.S.1 of both ship
models are compared in Fig. 6. A con-siderable diffierence of K is
13w observed between positions C and E, while x is almost the same magnitude in both models. This implies that larger normal curvature K13w of Ship-A re-sults in larger viscous pressure resist-ance component as shown in Fig. 5.
Another important factor related to viscous pressure resistance is boundary layer thickness. The thicker the boun-dary layer, the more the viscous pre-ssure resistance. The boundary layer thickness may be closely connected to pressure gradient along the streamline and geodesic curvature Knw expressing convergence of the streamlines. Fig. 7
26
Lee
ABC D
EY CH Ii
Fig. 7 Comparison of girthwise
distri-bution of geodesic curvature and boundary layer thickness
shows the comparison of K21w and
boundary layer thickness along frameline at S.S.1 of both ship models. It is
15
found that the boundary layer of Ship-A is thickner as a whole than that of Ship-B and convergence of the
stream-line of Ship-A on the girth from C to G is strong.
As described above, the present calcula-tion method can predict viscous resist-ance of full form ships with reasonable accuracy and inform the relationship between the viscous pressure resistance and local hull form. Therefore, the present method may become a useful tool for design and improvement of hull form.
Reference
1. Nagamatsu, T. Calculation of Ship Viscous Resistance by Integral Method and Its Application, 2nd International Symposium on Ship Viscous Resistance, Goteborg, 1985.
Model series
In this study a number of Wide Beam models was designed. The parameter space covered is shown in Fig. 1.
For comparison purposes the displacement and the draft were kept
constant
throughout the series. The parent hull was a Nedlloyd product carrier having LID = 5.1 and C, = 0.77.
by A.M. van Wijngaarden and J. van de Beek (MARIN)
Introduction
Draft restrictions are quite frequent in shipping trades. Moreover, the lengths of ships are limited in many harbours. Consequently, the only main
dimension
left to increase the deadweight capacity of ships is that of their beams. Economical evaluations of new designs based on the Wide Beam concept require data on powerconsumption.
Therefore the NationalFoundation
for the Co-ordination of MaritimeResearch (CMO) commissioned an extensive model test program to determine accurately the resistance and powering characteristics of medium block hull forms with a low ratio between length and beam.
L pp/13
FIGURE I: PARAMETER SPACE COVERED BY THE MODEL SERIES
OF WIDE BEAM SHIPS
Variations in L/B ratio and block coefficient
The main dimensions of the parent ship were re-scaled linearly at a
constant
block coefficient of 0.77 for the development of two blunt models in the Wide Beam area. The L/B ratio was reduced in these models from 5.1 to 4.5 and 4.0 respectively. At the same timethe B/T ratio increases sharply. At
constant
displacement, draft and block coefficient an inversely quadratic relationship exists between L/B and B/T through the displacement equation. Subsequently, four models were createdfor the two lower L/B ratios at reduced block coefficients. In a Lackenby transformation procedure CB was
decreased from 0.77 to 0.72 and 0.65 (again at constant displacement and draft).
Restrictions in hull shape variations
The body plans of the seven Wide Beam series models are given in Fig. 2. The aim of this small systematical series was to study the pure effects of L/B and CB variations. Therefore some inevitable restrictions had to be imposed on the
CB =0.77 CB .0.72 CB .0.65 L PP/13 .4.00 MODEL No.3
I.
MODEL No 7model hull forms.
The relative bulb area was kept constant throughout the series and the same absolute dimensions were chosen for the engine gondolas. All models had the same
FIGURE 3 RUDDER, SCREW APERTURE AND PROPELLER FOR THE
WIDE BEAM MODEL SERIES
17
FIGURE 2 BCOY PLANS OF THE WICE BEAM MODEL SERIES
L PP/ 13 .4.50
Y
MODEL No. 5
LPP/E3 :509
MODEL No.2 MODEL No.I
stern contour and the same rudder, screw aperture and propeller (see Fig. 3). The L/B ratio was reduced at a constant sectional area curve.
In the hull form transformation process an attempt was made to maintain
realistic values for the midship
coefficient and the LCD location.
During the tests of the extreme models a
few adverse effects on the local water flow were noticed. If the restrictions imposed on the test series were
abandoned, an improvement of the calm water performance might be reached.
Results from resistance and propulsion tests
A typical resistance test result is shown in Fig. 4. This test was performed for the full loaded condition. The model measurements were extrapolated to full-size results by the three-dimensional
ITTC 1978 method.
A reduction of the length-to-beam ratio at constant block coefficient caused a
considerable resistance increase at higher speeds. When followed by a
reduction of the block coefficient (at constant LIE) this unfavourable effect is largely neutralized.
The same applies in an even larger measure for the powering results as can be seen from Fig. 5.
At relatively low speeds, however, it was concluded that medium block Wide Beam ships do not require a higher propulsive power.
Application in ship design
In this extensive model test program valuable results have been derived for the resistance and powering
characteristics of hull forms in a
100 RT(.(0 CB .077 B 13 14 15 SPEED ( KNOTS)
FIGURE 4: RESISTANCE AS A FUNCTION OF LENGTH-TO- BEAM RATIO (ABOVE) AND BLOCK COEFFICIENT ( BELOW)
100 PD (I 100 50 PD(.10 CB .077 40 L/B.45 51 0 12 L/13x4.0 065 CB .Q72 077
RGURE 5 DELIVERED POWER AS A FUNCTION OF LENGTH-TO-BEAM RATIO (ABOVE) AND BLOCK COEFFICIENT (BELOW:
parameter area where hydrodynamic design data were scarce so far. For a ship falling inside the dimension space covered by this model series, the first shaft power data for preliminary design can be obtained by interpolation. The insights gained on the flow around
the ship and some available details subsequently lead the way to power reduction. This can be accomplished by an optimization of the bulb shape, the location of the LCB and the local aft body geometry. Some preliminary
calculations support the claim that the propulsive performance of these hull
forms can be further improved. 17 16 012 13 14 15 SPEED (KNOTS) 16 17 14 15 SPEED ( KNOTS) 0 12 13 17 16 13 14 15 SPEED ( KNOTS)
In order to enhance the application of these hydrodynamic research results in ship design, it has been proposed to extend the model series in the true full block area (C, = 0.82) with emphasis on low speeds. This extension will enable a powering comparison based on a
L ,
constant /C ratio.
B B
Presumably iso-power curves can be found in this way for the parameter space in Fig. 1.
Feasibility of the Wide Beam concept
Some of our colleagues from the Far East are convinced of the Wide Beam concept for trades between shallow ports. In Fig. 6 a relation between
transportation cost and deadweight for restricted draft vessels is shown. This figure is taken from a recent Mitsubishi advertisement. Significant cost savings are claimed for their Ultra Shallow Draft Vessel when compared with a conventional restricted draft ship. For this USDV concept (dual engine, dual shaft) a minimum L/B ratio of 3.5 and a maximum B/T ratio of 6.5 are stated. The results of this hydrndynamic
research project will serve as input to a complete economical evaluation. The weight and the construction cost
DEADWEIGHT AND TRANSPORTATION COST
FIGURE 6: DEADWEIGHT AND TRANSPORTATION COST FOR THE MITSUBISHI ULTRA SHALLOW DRAFT VESSEL CONCEPT
19
FIGURE 7: REQUIRED FREIGHT RATE AS A FUNCTION OF LIB RATIO AND DESIGN SPEED FOR A SERIES OF RESTRICTED DRAFT PRODUCT CARRIERS
algorithms in this program package will have to be upgraded to match the
accuracy of the fuel cost calculation. Refined expressions are needed for the
impact of variations in the ship's main dimensions on the deadweight and the construction costs. Finally, a Required Freight Rate calculation will yield the answer to the feasibility of Wide Beam ships.
Some preliminary results of an
economical evaluation are shown in Fig. 7. The RFR has been calculated for a series of product carriers under
systematical variation of the L/B ratio,
the block coefficient and the design speed. The draft, the specific cargo weight and the annual output were fixed. The attention of a feasibility study will be focussed on low service speeds. From the model research it was concluded
that Wide Beam ships exhibit only a marginal increase in fuel costs at low speeds. The share of energy costs in the total annual costs decreases at lower speeds. If a significant reduction in construction costs can be demonstrated, the scale can turn in favour of the Wide Beam concept.
.E.t.N.CT OF PRINCIPAL DIMENSIONS ON THE PROPULSIVE
PERFORMANCE OF TWINSK HULL FORMS
by Koichi Yokoo, Kazunori Sato, Minoru Hirai, Satoru Ohta
Introduction
A Twin-Skeg hull form gave better propulsive performance by 5% compared with a conventional form with bossings, in case of the bulk carrier with
L/B = 4.0, B/d = 5.0 and CB = 0.80.1) In this paper is shown the effect of
L/B and B/d on the propulsive performance of twin-skeg hull forms.
Model Ships
The Series is composed of five model ships as shown in Fig.1. M.S.No.R024
is the best form derived from fore and after form series of six
model ships.1) M.S.No.R024 has a bulbous bow of AB/Am = 0.11 and a twin-skeg.The distance between skegs is 30% of ship breadth.
Body plan and end
profiles of M.S.No.R031 is shown in Fig.2. The slopes of tunnel top lines
of four model ships are kept same as that of M.S.No.R024. And, frame lines
at F.P. are kept similar to those of M.S.No.R024, too. So, AB/Am varies
due to the variation of B/d. Block coefficient etc. are kept similar as
follows.
CB 0.800 - 0.801
CP 0.803 - 0.804
CM 0.996
1CB(% of LPP' fore) 3.45 - 3.55
Principal dimensions of five model ships are shown in Table 1. As shown in this table, drafts of all the model ships were kept constant to use the same model propeller of M.P.No.2004RL (Table 2).
Test Results
Resistance and self-propulsion tests were performed at the full load and ballast conditions. Displacement and trim of the ballast condition are
46ZVFULL and 1.2%Lpp for all the model ships. And, Self-propulsion tests
were performed with inward and outward directions of propeller rotation.
Since the propulsive performance of the models with the inward turning of the propeller was better, only the results of model tests with inward turning are
21
shown in this paper.
DHP curves etc calculated from the test results are shown in Figs. 3 and
4, for L/B series and B/d series, respectively. The displacement of actual
ships are kept constant, as V=
116,700m3
. So, Lpp etc. are different forvariations of L/B and B/d, as shown in Table 3. In this table, principal
dimensions of propellers are shown, too. Ratio of diameter of the propellers
to drafts Dp/d are kept constant to be 0.52. So, number of revolusions of
the propellers are different with variations of L/B and B/d, as shown in
Figs.3 and 4.
Figs.3 and 4 show that variation of DHP due to the variation of L/B is small, but that variation of DHP due to the variation of B/d is comparatively
large. By the condition that the displacement is kept constant, the draft
of the ship with larger breadth-draft ratio decreases, so, the diameter of the ship propeller decreases also and it is difficult to get high propeller efficiency. But, in case of L/B series, variation of diameter of propellers is small comparatively.
4. Merit of Increasing Breadth
Finally, the propulsive performance of a conventional ship with single screw and that of twin skeg-type ships with large breadth and same length and draft as the conventional ship are compared.
Dimensions of above two type ships are shown in Table 4, and
self-propul-sion factors and DHP/V etc. of skeg type ships with larger breadth
anddisplacement are shown in Fig.5. As shown in this figure, DHP/V at Vs = 13 knots is
For conventional single screw ship 0.107
(V=
60,000m3)For twin skeg ships with larger breadth 0.092 - 0.095
(17 = 86,000 - 102,000m3)
Merit of DHP/V by adopting twin skeg type with larger breadth is about 11 -14%.
Reference
1) K. Sato, M. Hirai, S. Ohta and K. Yokoo, Performance of Shallow Draft
Fig.2 Body plan and end profiles
Table 1 Principal dimensions of model ships
M.S,40. R024 R031 R032 R033 R034 Lpp (m) 6.0000 7.2000 4.8000 6.7500 5.2500 B (m) 1.5000 1.8000 1.2000 1.5000 1.5000 d (m) 0.3000 L/B 4.0 4.0 4.0 4.5 3.5 B/d 5.0 6.0 4.0 5.0 5.0 3,5 4 4.5 L/B
Fig.1 L/B and B/d of five model ships
6
B/d 5
B/d Series
23
Table 2 Principal dimensions of MI.P.W.2004RL
Table 3 Principal dimensions of ships and propellers
V..116,700000
L/B series
Diameter 0.1563m
Pitch Ratio 0.750
Expanded Area Ratio 0.469
Number of Blades 4
M.S.NO.
Ship Propeller
Lpp(m) B(m) d(m) Diameter(m) Expanded area ratio Pitch ratio
R034 207.5 59.3 11.86 6.17 0.346 0.705
R024 226.8 56.7 11.34 5.90 0.356 0.707
R033 245.3 54.5 10.90 5.67 0.379 0.709
M.S.NO.
Ship Propeller
Lpp(m) B(m) d(m) Diameter(m) Expanded area ratio Pitch ratio
R032 210.5 52.6 13.15 6.84 0.294 0.776
R024 226.8 56.7 11.34 5.90 0.356 0.707
20000 5,000 20.000 ,15.000 10.000 5.000
/
-
-
500 0 300 7 ---INWARD TURNINGFULL LOAD BALLAST
-120 -.120
2-100 a 100
-80
80-0.7n -10.6 as Caern1-]600 g 400E
VsllcnotS 10 12 14 16 111 13 15 III ii1 1
1 1 1-1-11-1-171-11-711-1-11-7± Gil 0.13 0.15 0.17 Fn 0110 rj FrjErjEHEE11-1-11 0.12 0.14 0.16 Fa 0.12 0.14 0.16 0.18 EnFig.3
DEW etc. curves for L/B series
Cacti
/
./1-,
___,
.., V, (knots) 10 12 14 1 I I E ---116 0.8 0.8-0.7
0.7-0.6
0.6-600
500 120 - 120 100 100 CC -BO z BO 6060-500 2
400-400 3 400 300--7/
Cl/ gath1,
V, (knots) 11 13 15 I 1 I 1 I I R024 0.11 riFrir_rjr_Fir_rjr_Finj
I R031 1 R032 0.13 0.15 0.17 0.19 FnFig.4
DEEP etc. curves for B/d series
s no Va ARKS.11.11225111"IIIIM N
IMIIIMPIIMISIII
MINENII=MINUMIMEIBC=1
117ZIMICIIIMIIMIIIIIIIMM
RIMIMEZIECIIMEMMIERMII
'4.5."°. a/d .A., FULL LOAD BALLAST
8032 4.0 1.09 1.14 8024 5.0 1.13 1.17 R03,
6.0 ----
'115 i ,8 17 1 20.000 13.000 a, 10.000 --, 17 5.000 I 20000 15,000 -7 ---aclm I Q000 ---Vs (knots) 5,000 FULL LOAD I NWARD TURNING BALLAST 160-140
140 15000 0. 10000Sr14 000 E
1 3,000
12.000
2 5
Table 4 Dimensions of two type ships
L pp = 197.3 m THE SAME DIMENSIONS d =l1.34mJ AS CONVENTIONAL
SINGLE SCREW SHIP
Ca =0.80 WITH 7.60000&
CONvENTIONAL HULL FORM WITH SINGLE SCREW.
(7.60,000(0) D H P/7 3 .10
"MO
Tn0-0
Conventional Single Screw Ship Twin Skeg Type
Length 197.3m Breadth 32.9m 48 -- 57m L/B 6.00 4.1 -- 3.5 draft 11.34m B/d 2.90 4.2 -- 5.0 C6 0.815 0.800 Displacement 60,000m3 86,000 -- 102,000m3 cu ,s3 5.0 A ,-., c3/6
--90 80-1.0
3.5--0.9
1, t 1 hUTSQ8
0.4 -
0.7
m 0.3-L.0.2
-0.001 . 45 50 55 60 El (alFig.5 DHP/V etc. of twin skeg
type ships with larger breadth
0.11
0.10
HULL FORMS FOR A LIFETIME'S ECONOMICAL OPERATION
By M.G. Osborne, Chief Naval Architect Shell International Marine Ltd. INTRODUCTION
This short paper describes some of the
potential constraints on the hull form designer and the operational requirements which must be
met if the ship is to operate successfully
under widely differing conditions of service. Comments are concentrated on the areas of bow
and stern design, drawing on the results of
recent model tests. Finally an attempt is made
at predicting future trends in requirements for full form ships, with suggestions on areas for further development.
1. PRACTICAL CONSTRAINTS ON THE HULL FORM
DESIGNER
The principle constraint on tanker trades is that of draught, the U.S. East Coast limit
of 12.2 m (40 ft.) being a popular target for
ships in the 60,000 100,000 dwt range.
Limits on length overall, and sometimes beam,
can also limit the flexibility of the hull
designer. If there is no limit on beam, there
may be a requirement for significant rise of floor to prevent the bilge touching bottom when the ship is rolling in shallow water or when crossing a bar.
Having established these design
boundaries, the designer can draw up diagrams of parametric relationships which satisfy them,
and proceed to choose his main dimensions.
These will usually be decided on the basis of
minimising building cost, leading to the
adoption of the minimum L/B ratio at which
there is still a reasonable probability of
achieving the required still water trials
performance.
In trying to improve the hull form within these dimensional limits there is little chance
of moving the LCB position. This must be
determined by the achievement of even keel trim in the laden condition with no ballast, and not
by hydrodynamic considerations alone. This
usually results in a position about 3-3.5%
forward of midships.
In some trades there can be a requirement for a specified length of parallel midbody to facilitate berthing arrangements.
When all these essential practical requirements have been satisfied, the scope for hydrodynamic design comes down to selection of the lines for the bow and stern to give the
best performance, usually defined as the best
speed from a specified main engine output over
a measured mile of calm sea. It is with the
design of these two areas that this paper is
mainly concerned.
Laden Condition
If only calm water trials at the loaded draught are considered, it is probable that a cylindrical stem would be the preferred
option, with no bulb. This gives a slightly
lower wetted surface area, and successful
hull forms are claimed to have been developed
using this concept (I), despite the
difficulty of minimising wavebreaking
resistance.
Once the ship enters service and starts
operating in waves, however, it is doubtful
if the cylindrical, or elliptical, bow is the
most efficient. The added resistance due to
waves consists of the two components: Wave reflection resistance Induced ship motions.
Most studies of wave reflection
resistance (e.g. 2,3) show that it is a
function of Sin' 6, where 0 is the average
waterline angle to the centreline of the
ship. A cylindrical bow hull has a high sin' 6 value, making it a comparatively poor
performer as far as wave reflection
resistance is concerned. On the other hand,
the U sections normally associated with the cylindrical bow lead to an easier pitching motion and less motioninduced speed loss.
Attempts to reduce this motion further by the addition of a bulb have not been successful
(4).
Since large tankers do not usually
experience significant speed loss due to
induced motions, reduction of wave reflection resistance is a more important consideration than reduction of pitching, negating to some
extent the smooth water advantages of the
cylindrical bow.
Unfortunately, therefore, reduction of
the added resistance in waves requires a
fining of the entrance angle with a
consequence movement aft of the LCB position. This can be restored by the addition of a
bulb, which has the added advantage of
damping the greater motions due to the
resulting non Usection shapes.
Our current preference for fore end
design of large tankers (i.e. those where
reduction of wave reflection resistance is
more important than reduction of motion
induced resistance) is therefore a half angle
of entrance in the region of 45° at the
loaded draught, with the LCB position
controlled by the addition of a bulb. For
smaller ships, say below about 20,000 tonnes
dwt, reduction of motion may become the
predominant consideration, leading to
different conclusions.
The problem with fitting a bulbous bow is to come up with a design which provides reasonable performance over a wide range of
regulations on provision of segregated ballast,
tankers have ceased to be 'deadweight
carriers', and are now 'capacity carriers',
meaning that they can fill their tanks
virtually regardless of the specific gravity of
the cargo. The laden draught is therefore determined by the specific gravity of the cargo
and no longer by minimum freeboard
requirements. This trend is accentuated in the
new breed of ships designed for a wide range of black or white products (and correspondingly
wide range of specific gravities) and crude
oil. To complicate matters further, several
port authorities around the world use
deadweight as a limiting parameter for access
to certain berths and channels. It is
therefore necessary to limit the ship's
deadweight (and hence draught) when using these
ports. All these factors combine to require a hull that will operate efficiently over a wide
range of draughts. By estimating the
percentage time of its life that a ship will spend at each loaded draught, it is possible to
derive weighting factors to apply to the
performance of a bulb at each draught, thereby
determining the correct bulb for the
anticipated service conditions. Ballast Condition
Although elimination of ballast legs is a top priority for minimising financial losses,
ballast operation still forms a substantial
part of a tanker's trading, and careful
attention needs to be paid to performance in
ballast at the design stage. Shell's practice
in this respect is to require a guarantee on
ballast speed in the contract with the
shipbuilder. This usually takes the form of
specifying the average of laden and ballast
speeds on trials to be about 1/2 knot greater
than the expected speed at design laden
draught. The IMO ballast draughts of
2 + .02 L metres with .015 L trim by the stern
are used purely as a convenient means of
comparison.
Once in service it is unlikely that the ship will operate on the IMO ballast draughts, since recent research by Shell has shown that substantial fuel savings can be made by using lighter ballast draughts, weather permitting.
In good weather, for example, it can be
beneficial to sail at zero forward draught. A
recent cooperative research exercise has
examined potential problems of this type of
operation, such as slamming, vibration, speed
loss in waves and manoeuvrability. It is
therefore essential that the fore end lines are
suitable for operation at light ballast
draughts in fine weather, and also for deeper
draughts in worse weather. In this respect the
cylindrical bow shows good qualities in calm weather, with no significantly poor performance over a wide range of speeds and ballast
draughts. The cylindrical bulb, on the other
hand, whether 'faired' or 'unfaired' shows bumps in the power curve at certain forward
draughts. A 'teardrop' type bulb also shows
similar tendencies.
27
Variation of service speed in ballast is another parameter that must be considered in
the design of the fore end. There is often a
requirement to reduce speed to avoid arriving at a loading berth before cargo is ready, or conversely to increase speed to arrive at the
berth ahead of another vessel. It is
possible to construct a matrix of ballast
operating conditions which might look like:
the figures indicating the approximate percentage of its lifetime the ship operates
in the specified speed and weather
conditions.
To summarise, service conditions require that the fore end design meets the following
criteria:
Good performance over a wide range of forward draughts when laden.
Low added resistance due to wave
reflection in a seaway.
For smaller ships, low added resistance due to motion in a seaway.
Control of LCB position to give near
even keel trim.
Good performance in light ballast
conditions.
Good seakeeping at moderate ballast
conditions.
No performance humps which are speed or draught related.
3. DESIGN OF AFT END LINES
There is no doubt that design of the aft end of full form ships is a critical aspect, and one that is still rich in potential for
improving propulsive performance.
Significant improvements have already been
made in the last few years, and there are
more still to come, but these must not be
achieved at the expense of incurring wake
related problems such as vibration and
cavitation. However, it is worth noting that
there are propulsion appendages available today which can effectively cure vibration
problems. Maybe now is the time to ask
whether these can be added to known 'wake
maker' type hull forms (convex waterlines at the aft end) which give good performance but
suffer from severe vibration. Would such a
combination give us the best of both or not? Speed Full Weather -2 kn -4 kn -6 kn Draught (metres) Good 15 15 15 5 0 Moderate 10 10 10 5 2 m Bad 0 0 5 10
5m
Considerable work is still needed in this area to produce the best match of aft end lines and propulsion appendage.
The present answer to improving propulsive performance at the aft end is to use 'pram' or
'gondola' type designs. The substantial reduction in predicted EHP resulting from model tests of these designs was reported in (5) and similar results have recently been obtained by
us in the development of hulls for for
newbuildings. In our case a reduction in
predicted EHP of 18% in changing to a gondola type aft end was accompanied by a reduction in
hull efficiency of 25%. Nevertheless, the
reduction in wake fraction led to an increased
propeller open water efficiency and a net
reduction in propulsive power of 12%. The
large loss of hull efficiency of these gondola type hulls is of course due to the reduction in wake fraction with no corresponding reduction
in thrust deduction fraction. Further
developments on this type of hull must
therefore find a way of restoring the wake
fraction and reducing the thrust deduction
without significantly increasing the EHP.
These experiences emphasise again the
importance of designing a hull for satisfactory
propulsion performance. It is not enough to
design a form which gives excellent resistance
results, these can easily be accompanied by poor propulsive efficiency.
Model Testing
Although techniques for extrapolating
resistance test results to full scale are well established and relatively straightforward, the
same cannot be said of propulsion testing,
where each testing establishment appears to
have its own technique, based loosely on the
1978 ITTC method. When designing the aft end
lines, we are trying to tune the interaction of hull and propeller, which involves analysis of propulsion factors and a knowledge of any scale
effects on them. Existing extrapolation
methods are probably sufficiently accurate to provide a shipbuilder with a prediction for his
trials performance guarantee. He, in any
event, has a margin built into the contract to
allow for measurement and prediction
inaccuracies before he has to pay a penalty.
But shipowners are seriously looking for
savings of 2 or 3%, which, over the life of a
ship, could be worth abont $1/2 million in net
present value. Can existing extrapolation
techniques really discriminate and predict the
changes to delivered horse power (and fuel
consumption) attributable to small changes in the aft end lines?
4.
There is a temptation to think of hull
design only insofar as it affects ship
performance on trials, but the Owner is
interested in far more than that. Recent
experience on two chartered ships of similar
size and near identical dimensions but
different hulls and bulbous bows has shown one to be vastly better at maintaining speed
in a seaway than the other. Both are
comparatively new ships, built within the
last three years, one at a European yard, the other at a Far Eastern yard.
The message is clear to avoid a
similar disaster in the future seakeeping
performance must be considered during the
hull form design, and tests on added resistance in waves should form part of the
hull form development instead of being
carried out after the hull form has already
been finalised. Shipowners should seriously
consider specifying acceptable limits for
seakeeping criteria to be applied at model
scale as part of their contract with the
builder. In this respect current moves to
establish a rational basis for selecting
these criteria are welcomed.
No doubt there will have to be some
compromise between calm water and heavy
weather performance, and it is up to the
Shipowner to develop the 'service profile'
for which he wishes to have the ship designed
which will contain weighting factors for
various weathers and loading conditions.
Manoeuvring is another characteristic
which is rarely, if ever, considered when
selecting the hull form. Recent moves at
I.M.O. have focussed attention on this issue,
and the day may not be far away when the
Shipbuilder will be asked to guarantee a
manoeuvring performance. The problem is
likely to increase in the future as pressure builds to squeeze the maximum deadweight into the minimum length and draught, thus leading to low L/8 ratios and high B/T ratios, which are bad for both propulsion and manoeuvring
performance. There is a need to develop hull
forms which will overcome these problems. For a tanker, the twin stern design has much
to offer in this respect:
Possibility for improved manoeuvrability with two propellers.
Better propulsive performance for low
L/B ratios.
Smaller diameter propellers, thus
reducing segregated ballast requirement.
Use of lighter ballast draughts with
propellers fully immersed.
Twin sterns do, however, introduce
engineering problems, and it is important
that these are given full consideration at the same time as the hydrodynamic aspects.
5. CONCLUSION
Hull form optimisation is not just a
question of developing a design that gives the
best results in a flat water towing tank.
There are many operational factors that
influence the decision on the 'best' hull, and recent advances in seakeeping and manoeuvring theory must be applied to the early stages of lines development to achieve a hull that is
going to give the minimum life cycle cost. The
day is not far away when shipowners will be specifying their required seakeeping criteria
and possibly other hydrodynamic performance
criteria.
Future commercial demands for maximum
cargo to be carried on minimum draught, coupled with shipbuilders' desires to minimise building costs, will lead to ships with low L/B ratios
and high BIT ratios. Hull form designers must
be fully prepared to meet these challenges. REFERENCES
'Basic Design of an Energy Saving Ship' K. Motozuna and S. Hieda,
SNAME Symposium on Costs and Energy, 1982.
'Effects of Service Conditions on
Propulsive Performance of Ships' H. Tanibayashi.
Scientific and Methodological Seminar of Ship Hydrodynamics, Varna 1983.
'Widerstandserhohung in Kurzen Wellen' K.Y. Lee, Schiffstechnik Bd. 30, 1983.
'Some Effects of Hull Form on Performance
in Head Seas' D.C. Murdey.
'Research and Development on Ships Hull
and Propeller' J.J. Muntjewerf and
M.W.C. Oosterveld, Ship en Werf No.1 1985. 29
Abstract
In order to improve resources transpor-tation economy in the sea routes with shallow water areas, development of a class of shallow draft twin screw tankers having dead weight of 100,000 t at draft of 10 m was made on the basis
of the extensive investigations. Among them hydrodynamic aspects were of pri-mary importance in the course of the
design. They were, proulsive
perfor-mance, manoeuvrability, resistance in waves and seakeeping quality. This paper outlines the investigations made
for development of the shallow draft twin screw tankers from hydrodynamic point of view.
1. Introduction
With development of world economy in these decades, large amount of energy or mineral resources has been transported on various sea routes from production sites to the industrical areas in the world. On the major sea routes where ports and harbours have sufficiently deep water, size of ships had rapidly
become large from 50,000 - 60,000 DWT to about 500,000 - 600,000 DWT within a decade before oil crisis. However, on
the other sea routes having too shallow water areas for operation of large sized
ships, small sized or medium sized ships have been in service with little advan-tages due to mass-transportation by large sized ships. Thus, improvement of
HYDRODYNAMIC DESIGN OF SHALLOW DRAFT TWIN SCREW FULL SHIP
K. TAKEKUMA AND T. SUZUKI
MITSUBISHI HEAVY INDUSTRIES, LTD., JAPAN
resources transportation economy in these sea routes have been one of the serious concerns in the shipping world. To cope with this demand, Mitsubishi Heavy Industries, Ltd. developed some types of the shallow draft full ships having higher sea transportation economy than that of full ships with conventio-nal principal dimensions. Among them, a class of the twin screw tanker was designed having deadweight of about
100,000 t at the designed draft of 10 m, aiming at much improvement of
transpor-tation economy on the sea routes with some restricted water areas. This class of ships is characterized by the twin skeg stern configuration with wide beam, small length/breadth ratio, large
breadth/draft ratio and high block coe-fficient. In the course of the design, technical problems were encountered due to the distinctive feature of the ship's dimension. Among them hydrodynamic aspects were of primary importance to make it for the shallow draft twin screw full ships to be feasible from tech-nical and economical point of view. Those aspects are better propulsive performance in sea ways, proper manoeu-vrability and better seakeeping quality,
low level of vibration excitation. Thus, extensive investigations were conducted into each item of the hydro-dynamic aspects above for development of
the class of the shallow draft twin screw full ships called as Urtla Shallow Draft Vessel ((JSDV).
This paper outlines the design of this class of ships and the investigations made to cope with problems in relation to hydrodynamic aspects.
2. Design of a class of the twin screw tankers with shallow draft
Shipping economy requests a ship to carry the largest amount of oil or re-sources with minimum transportation cost under the restriction specified by the sea routes or harbours. The allowable draft for the water depth of the harbour
is usually one of the most important factors in the course of the design of
ships. To cope with the demand above,
Mitsubishi Heavy Industries, Ltd. deve-loped firstly a class of the single screw medium sized tankers with re-stricted draft, having smaller length/ breadth ratio (L/B=5) and larger
breath/draft ratio (B/d=3.6), when com-pared with those of conventional type of full ships /1/. This class of ships were constructed in the 1970s and commi-ssioned in service with successful im-provement of shipping economy as ex-pected. On the basis of the experiences of these shallow draft ships, improve-ment of shipping economy by increase of cargo carrying capacity under the con-straints of restricted draft has been pursued by extension of the principal dimensions of the full ships to smaller length/breadth ratio, larger breadth/
31 ci 0.90 0.85 0.80 0.75 4 _ 3 -2 ConvemionaISMos
xf3x Dmxd.=23Cx 64'x 16.5"x 10.0'
DW= 105200ton
Fig. 2 Ultra shallow draft tanker
draft ratio and higher block coefficient than those of the preceding single screw shallow draft full ships as shown in
Fig. 1. Twin skeg stern configuration
was adopted to those new type of full ships, taking into account the proper manoeuvrability to be provided for ope-ration in the shallow water areas. On the basis of the above, a class of shallow draft twin screw tanker was developed, having distinctive principal dimensions and configurations as shown in Fig. 2, aiming at having deadweight
ljaao draft
. Single Scraw
Base
- Subject Shin
73NN,
Twin Screw Shallow draftNa.
1 2 3 4 5 6 7
Breadth/pre,
Fig. 1 Dimensions of medium sized full ships
COO
+
77.77,,,r
of about 100,000 t at design draft of
10.0 m. Conventional type of tankers
with design draft 10 m has usually dead weight of around 30,000 t. This means
that the new type of shallow draft tanker carries around three times more amount of crude oil than a conventional type of single small sized tankers. Extensive investigations have been made
this type of ships to make it feasible, from economical and technical points of
view. Among them, study on hydrodynamic
aspects was of the primary importance, because most of problems was encountered
in their hydrodynamic aspects, namely, propulsive performance, manoeuvring quality, seakeeping quality and so on due to their distinctive principal dimensions and configurations. Thus, a class of twin screw shallow draft tanker (USDV) was successfully developed with
Dead Weight(t)
Same draft
Fig. 3 Transportation economy of USDV
USDV Shallow draft type Conventional type Conventional type
much improved shipping economy than that of the existing small sized tanker with design draft of 10 m as illustrated in
Fig. 3.
3. Investigations into hydrodynamic design
In the course of the design of the shallow draft twin screw ship, problems encountered were raised from its distic-tive feature in principal dimensions and ship form configuration. Less resist-ance in waves and appropriate
manoeuvr-ing quality in shallow water areas were of the primary importance, because of
its wide beam, full ship bow and stern, and large breadth/draft ratio. Twin skeg stern configuration was adopted, aiming at better propulsive performance and appropriate manoeuvrability. Bow
*CC7Ornall'"
11.
10 Opt.rurn co,.
form and stern profile between both skegs were designed mostly, taking into account less resistance in head waves and less wave impact load in the follow-ing waves respectively. Investigations made are summarized in Table 1.
3.1 Propulsive performance
Improvement of propulsive performance was made on the basis of our accumulated Ship form data together with application of hydrodynamic theories within the design constraints. Bow form was
designed to minimize wave-making resist-ance by application of the low speed theory describing the non-linear pro-perties of free surface phenomena around a ship form. Prediction of resistance increase in waves was also made in the design by applying a newly developed theory of resistance increase for full
forms. Locations of skegs and stern
shape were decided to get the flow around propeller as uniform as possible by taking into account the asymmetrical feature of the flow field around a pro-peller due to the confluence of the flows from both outside and inside of the skeg as shown in Fig. 4. In the design of stern profile of the areas between two skegs, consideration was
33
Table 1 List of Investigations
Flow along the ship's bottom (calculated)
Shaft centecb
---a
C-L
a
Fig. 4 Effect of skeg arrangement on
propulsive performance
taken to avoid excessive wave impact load on the hull. Boundary layer theory was applied in the examinations above.
Improvement of the propulsive perfor-mance of the ship's hull was made fur-ther after the examinations on the following items.
Shaft center
BL dMe
a CL Items to be ExaminedPropulsive Performance Principal Dimension, Bow Form
Location of Skegs, Skeg Shape and Stern Slope Manoeuvring Quality Course Keeping and Turning Ability in Deep Water
Manoeuvrability in Shallow Water Bow and Stern Sinkage in Shallow Water Seakeeping Quality Resistance Increase in Waves
Rolling and Racing of Propellers Wave Induced Load
Propeller Low Level of Vibration
3.2 Manoeuvring quality
The shallow draft twin screw ship was developed for service in the sea route with shallow water areas. Reliable operation in the shallow water areas such as harbours, is indispensable item to be examined. Thus, extensive studies on manoeuvring qualities were conducted to make clear the behaviour of the class of the ship in the shallow water areas:
Turning, reverse spiral and pull out manoeuvre test in shallow water, Measurement of bow and bottom sinkage in harbour manoeuvring, Measurement of bottom clearance at the ship sides in rolling in waves,
deep water
Fig. 5 Comparison of turning test
Further, test in shallow water in waves showed that sufficient bottom side
3.0 clearance can be obtained in rolling
under usual sea condition. As the re-sults, it was concluded that the shallow draft twin screw ship can be operated
2.0 safely in shallow water areas, while
some of the aspects are different from conventional single screw full ships.
3.3 Resistance in waves
to
In general, resistance increase in waves is proportional to the square of breadth
/length. Thus, the shallow draft twin
screw full ship with small length/ breadth ratio, large breadth/draft ratio and high block coefficient is subjected to higher level of resistance increase than some existing conventional full
ships. Thus, resistance increase in
waves was examined to make its level to the same order as that of some existing conventional ships (Fig. 7). Effect of bow fullness, water line shape and so
on was examined both by experiments and application of the theory. The results obtained were reflected to the design of the bow form of the ship.
'1Lp°
Fig. 6 Comparison of short turning test
and
Turning ability in stopping condi-tion by use of two propellers.
In the studies above, effect of water depth was examined. Results are shown
in Fig. 5 and Fig. 6. It is found that; Sufficient bottom clearance can be maintained in the slow speed harbour manoeuvring.
Turning ability in shallow water is better than that in deep water. Course keeping ability is considered
to be stable or marginally stable. Good turning ability in stopping condition can be obtained by operat-ing propellers of both sides.
3.0 2.0 1.0
--1 CT Q. CIE b
---c
r'
---__Conventional ship\
Fig. 7 Resistance increase in waves of
some typical bow forms
3.4 Seakeeping quality
Problems due to ship motions in waves are generally classified into
Excessive rolling and acceleration at short rolling period due to high metacenter,
Propeller racing due to large ampli-tude of relative motion at propeller position due to the coupling of lateral and vertical ship motions, and
Deck wettness at both sides of the ship,
Wave induced forces.
Model tests and calculations were made to examine the items above, taking into account the sea routes where the ship is
in service. As the results, it was found that
Amount of rolling angle can be decreased by fitting bilge keels and anti-rolling tank together with appropriate arrangement of ballast tanks.
Propeller racing was confirmed to be avoided.
35
(3) Deckwettness at both sides of the main deck is considered to be almost the same level and frequency as those of existing ships.
Wave induced load on the shallow draft twin screw ship was experimentally examined by use of a segmented model. Bending moments, shearing forces and torsional moments were measured at station No. 7 1/2, 5 and 2 1/2 respec-tively in regular waves as shown in Fig. 8 and compared with those of theoretical calculation. The results were reflected to the structral design
of the ship.
USDV 1 OOKDWT Tanker
vs-14k^
Vertical bending moment at midshio
Fig. 8 Vertical bending moment
at midship
4. Concluding remarks
In order to improve the transportation economy in the sea route with some shallow water areas, a class of the shallow draft tanker with dead weight of 100,000 t at draft of 10 m was deve-loped with twin skeg stern configura-tion, small length/breadth ratio, large breadth/draft ratio and high block coe-fficient. Hydrodynamic aspects were extensively investigated into
0.5
1.0 A/L 1.5better propulsive performance and uniform flow around propellers, proper manoeuvring qualities for reliable operation in shallow water areas,
less resistance in waves for better propulsive performance in service, racing, deck wettness, bottom clear-ance in waves and
wave induced forces on ship hull.
On the basis of investigatons above, design of this class of ships has been made in these several years. It has
been confirmed that the shallow draft twin screw full ship is feasible and the results were reflected to the design of a full scale twin screw ships with shallow draft built in MHI.
Reference
1. Ono, M., Takekuma, K. and Kawaguchi, N., The Design of Tankers for
Restricted-Draft Service, Proc. SNAME 10th STAR Symposium, Norfolk, 1985.
37
FULL FORMS, SHALLOW DRAFT
BARGE FEEDER VESSEL
G.F. Bertaglia, G. Sbrizzai, P. Frandoli
1) INTRODUCTION
The open dock type barge feeders Nicolay Markin and Anatoliy
Zheleznyakov built and recently delivered by Fincantieri at
Marghera shipyard (Venice) are diesel powered twin screw vessels.
The main characteristics and general arrangement are shown
respectively in table 1 and fig.l.
The vessels were built according to the rules of the Register of
Shipping of the USSR for the notation KM * L4 A2 intended for
unlimited navigation in tropical and temperate latitudes.
Endurance is 7000 nautical miles; fresh water store tank capacity
45 days.
The propulsion plant consists of two controllable pitch propellers
each driven by two diesel engines through a reduction gear.
The main engines are two 8 and two 12 cylinder GMT 230 medium speed
type suitable for service with marine fuel oil having a viscosity
up to 1500 redwood sec.
Electric power is generated by two shaft driven generators each
rated 680 kW and one diesel generator rated 380 kW.
The main engines and other machinery are remote controlled from the
wheelhouse.
Two big ballast pumps each with a capacity of 2000 cubic metres per
hour allow flooding and deballasting of the vessel for loading and
unloading operations.
The vessels are dock type with an open cargo hold, double side
(wing superstructures) from stern up to the deckhouse, which is
situated forward, with most of the accommodation arranged under the upper deck.
An hydraulically operated stern door prevents sea water entering
The vessels are also equipped with an electrically powered bow
thruster of 900 HP.
The ships are designed to carry 6 barges of the D-M type, loaded
with a single tier of 20' containers on the hatch covers. Facility
is also provided for conveying 12 LASH type barges. The barges are
arranged in the hold in a single tier two rows abreast.
TABLE 1
MAIN CHARACTERISTICS
Length overall 157.75 m
Length between perpendiculars 140.00 m
Moulded breadth 29.00 m
Moulded depth to upper deck 14.85 m
Moulded depth to main deck 5.30 m
Mean draught on a summer load line (from Base Line) 4.30 m
Flooding draught (from Base Line) 9.30 m Capacity of cargo hold: DM barges (or 12 LASH Barges) 6 Nr
Speed at draught of 4.30 m and main engine output of abt.
4580 B.H.P. - 90% HER and 10% sea margin - at trial condition : 12.6 kn
2) DESIGN OF THE VESSEL
The intended purpose of the vessel was the most important factor in
determining the main dimensions and the hull form.
The relevant design aspects taken into account included:
speed
deadweight and type of cargo
loading and unloading system
comfort in the accommodation
water entry in the dock
good manoeuvrability in restricted water
good wake field to limit hull pressure pulses.
Selection of the main characteristics came from considerations and
investigations briefly described hereafter.
Max submersion draught
39
Generally this kind of ship is designed with one of two basic
alternatives i.e. with wet or dry hold. The first alternative
involves higher freeboard due to the large openings on the side,
while the second, requiring no water entry in the hold, allows a
lower freeboard.
Because of the low value of the max submersion draught (9.3 m) due
to the fact that the loading and unloading operation has to be
carried out in relatively shallow water, the second alternative was
Tests were conducted to check the effectiveness of the height of
the side walls and the shape of the stern door in preventing entry
of water into the hold in severe sea states (Beaufort 10).
These tests were performed in the seakeeping laboratories of
N.S.M.B.
Draught
Barge loading and unloading is carried out by lowering the ship
to the submersion draught, at which the depth of water in the hold
is about 4.0 m to provide for the entry of barges with a draft of
3.3 m at a wave height up to 1.0 m.
Taking into account the max allowed submersion draught and the free
board, a design draught of 4.3 m was selected.
Beam
This dimension was calculated to allow pairing of D-M barges with
necessary clearance and room for the fenders on the side walls.
Having fulfilled the geometric criteria much attention was directed
towards control of stability to guarantee safety of the ship in
flooded condition during loading and unloading operations.
To comply with the U.S.S.R. Register rules regarding operation in
unrestricted areas of navigation, it was necessary to consider the
particular case of a hold completely flooded with water up to the
level of the stern door top in both fully loaded and ballast
41
In this peculiar case the determination of the static stability
moments as a function of heeling angle, required very complex
calculation. For verification, model tests were performed in the
N.S.M.B. laboratories. The results from theoretical calculation and
empirical experiment were in good agreement.
Length
Was determined to be as short as possible taking into consideration
the length of three barges, 38.25 m each, placed end to end, plus
room for the deckhouse and the fore mooring layout.
Block coefficient
As a result of the analysis, taking into consideration the
afore-said main dimensions, the contractual deadweight, the lightship
weight and the low speed length ratio a block coefficient of about
0.80 was obtained.
Centre of gravity
The centre of gravity of the ship has been put relatively aft since
the barges are carried in the central and after part of the ship.
This means that the position of the longitudinal centre of buoyancy
The choice of the main hull characteristics led to unusual main
dimension ratios (i.e. L/B 4.83 BIT 6.74) which were not
generally experienced in vessels designed and built by Fincantieri.
For these reasons particular care was devoted in investigating the
hydrodynamic problems connected with this new construction.
3) HULL FORM : DESIGN AND OPTIMIZATION
In choosing the most suitable hull form many alternatives were
taken into consideration.
The most important decision was the selection of a twin screw
vessel mainly due to the shallow draught and maoeuvrability,
especially in restricted water. Another important reason for
subdividing the power between two shafts was the limited height of
the engine room due to the depth of main deck 5,3 m.
Afterbody design
The high beam/draught ratio, the low length/beam ratio, the full
forms and the after position of the centre of buoyancy, led us to
consider a twin skeg afterbody as a possible solution. In fact,
published literature data and Fincantieri experimental research on
a twin skeg Ro/Ro Vessel showed such afterbory to have higher
propulsive efficiency than conventional twin screw vessel.
On the other hand a twin skeg afterbody involves a higher
re-sistance due to higher wetted surface and to vorticity coming from
the skegs. It was also anticipated that there would be vibrational
43
Due to the relatively low speed of the vessel and thus the high
contribution of viscous resistance, it was considered that the
inc-reased propulsive efficiency could have been counteracted by an
increased resistance.
In addition, it suited us to have a wakefield as homogeneous as
possible because of the adoption of a C.P. propeller.
Taking into account all these problems, it was decided to adopt an
unusual shape of afterbody with lateral swelling between the
propeller disk and the shell side to allow good water feeding to
the propeller and at the same time enough volume to shift afterward
the centre of buoyancy.
Great care was devoted in drawing the central buttocks lines
together with those in the lateral swelling area and above the
propeller axes.
For the first two a smoothly rising line involving low resistance
was chosen; on the contrary for the latter a convex line was
selected to guarantee a constant feeding of water to the propeller
(fig.1 a).
Forebody design
Due to this unusually high beam/draft ratio a spoon bow type was
first considered because of its effectiveness in obtaining a
buttock flow configuration. However this solution commonly used in
river or lake barges was not very suitable for an ocean-going
ves-sel because of increased resistance and slamming loads in rough
seas.
This consideration led to the choice of V shaped forebody in order
to achieve good seaworthiness.
