A COMPARATIVE ANALYSIS of THE RESISTANCE
QUALITIES of a SERIES of
SEfl,DISPLACEF ifi-SPEED MONO-HULL
FORMS
Jacques. B. Hadler and Richard VanHooff, WebbInstitute, Glen Cove New York SUMMARY
This paper presents the results of the still water resistancetests conducted on 6 hi-speed semi-displacement models of widely varying hull geometry at.a common displacement-lengthratio. These results along with selected models from two systematic series comprising 8 more models have been analyzed over a speed range from FN 0.5 to 1.1 to determine some of the factors, particularly thetransom area, that effect the resistance. It was found thatas the speed increases the variation in the model RJW ratio decreases with speed. At the highest speeds the RJW ratio is sensitive
to the wetted.surface but at the lower speeds the hull factors thataffect the residuary resistance dominate.
1. INTRODUCTION Model B is a 5.543-ft stretched version of the US Navy
The hulls of most of the commercial hi-speedcatamarans FFG-7 frigate. The original ship has a length-to-beam and the center hull of trimarans are essentially high ratio of about 8:1 The stretched hull has the same form
c length-to_beam ratio semi-displacement vessels. A except thatthe length-to-beam ratio has been increased to
number of systematic series of hi-speed semi- 14:1. This hull form was developed as the center hull for
'
displacement mono-hulls forms has been published,two trimaran thesis projects at Webb Institute that
i some of which are part of a catamaran or trimaran
series, culminated in the SNAME paper(s).
ci Z
At Webb Institute we have been testing
a growingr-. number of hi-speed semi-displacement models that have
Model c is a 5.0-ft special hi-speed research model
.
hull forms that
fall into the same category. Thewhose planform is wedge shaped with a flat bottom, wall combination constitutes a wide body of experimental sided with a small bilge radius intended to minimize
the
Q) data on the calm water resistance characteristics
of a
angle of entrance and create a wide and flat transom area.variety of hull forms in the hi-speed range considered to °- beFN from 0.5 to 1.10.
Model D is álso a 5.0-ft special hi-speed researchmodel that, is similar to Model C except that the bottom is semi-At Webb Institute the resistance characteristics ofeach circular leading to a cone shaped bottom with
a side of configuration has been determined at a common valúe of the cone on the base line resulting in a large semi-circular the length-displacement ratio, IJV"3. A comparative transom.
analysis ôf the resistance along with the
geometriccharacteristics of the hull, including the sectiònal area
Model E is a 5.15 ft fiberglass model with
a large curves at this displacement, can provide hull form design transom area that has been developed for wateijet andguidance.
catamaran application. This hull form was developed for
use in two catamaran theses projects at Webb Institute.
The first section will describe the experimental work
performed at Webb Institute. The second part will Model F is a 5.66 ft fiberglass model developed at the present selected results from the experiments performed United States Naval Academy-as the center hull for a at the University of Southampton (1) and at the Hyundai trimaran study and used for a thesis project at Webb Maritime Research Institute (2) for direct comparison Institute.
with the experimental results obtained at Webb Institute.
The final section will be a comparative analysis of all of The geometric characteristics of the six models at the
the experimental results with conclusions, tested displacement are contained
in Table
1-1 in
Appendix I along with the sectional areacurves Figure
1-2.1 DESC1W'TION OF MODELS 1.
There were six hi-speed semi-displacement models tested
at Webb Institute at a common length-displacementratio; 2.2 TEST CONDITIONS
three that were developed for student theses and two The model experiments were carried out in the towing special research hull forms. The following provides the tank in the Robinson Model Basin at Webb Institute that genesis of the models and a brief description of 'the has the following characteristics:
models.
Model A is a 5.5-ft fiberglass geosim of model 4796 from Series 64 (3) and has been used as the primary model to evaluate the Robinson Model basin for high speed model resistance testing (4). Since this is a model from a well know series it is used as the basic model for
purposes of comparison.
Length = 93 ft - Effective length 75 ft.
Breadth= lOft
Water Depth 5 ft
Maximum Carriage Speed =20 ft/sec
The tank is equipped with a single overheadflat-plate rail system with a suspended, lightweight carriage. The model is
attached to the carriage by a heave staff
V
Resistance measurements were made with a 5-lb capacity variable reluctance force block dyriarnometer. The
resistance dynamometer was attached at the LCB of the models. Trim was measured by means of a rotational variable differential transformer (RVDT) mounted on the tow fitting. Sinkage was measured by means of a linear variable differential transformer (LVDT) also mounted on the towing fitting. The electrical signals from the dynarnometer and the differential transformers were transmitted through overhead cables on trolley wires to Validyne signal conditioning equipment and ultimately to the computer, where the signals were analyzed to determine the resistance, trim and heave using a program developed by National Instrument called Lab View.
About 2000 signals are recorded over a 10 second
measuring period and averaged to obtain the speed,
resistance, trim and heave for that run.
Calm water total resistance, running trim and sinkage were carried out for all the models. All tests were carried out over a speed range of 0.20 to 1.10 F. The running
sinkage and trim data are not included in this paper.
Calibration of the dynaznometer and the potentiòmeters was performed prior to and upon completion of testing. The average of the two calibrations was used to convert the measured voltages to resistance in lbs, the heave in
inches and the trim in degrees.
All of the models were fitted with Hama (7) type
triangular turbulence stimulators,
which havé been
shown to be very effective in experimental work at Webb Institute (4 & 6). They were equilateral triangles about 3/4 inches on each side composed of 4 layers of electrical
tape placed four inches behind the stem of the models. 2.3 DISCUSSION OF TEST RESULTS
The resistance measurements were converted into the total resistance coefficient, CT and residuary resistance coefficient, CR using the irrc 1957 correlátion line. The total and residuary resistance coefficient results from the
6 models are presented graphically in Figures 1 and 2.
This group of models present great extremes iñ hull design as shown by the sectional area curves in Figure
1-I and the table of geometric properties Table l-1 in
Appendix I. The test results clearly collect into 3 groupings; Models A, B and F have the lowest resistance over the whole speed range, Model E with a substantially larger transom stern area has significantly higher resistance and not unexpectedly Models C and D with the exaggerated transoms had the highest resistance. The differences are most pronounced in the hump region (FN from 0.3 to 0.5) where the flow is starting to separate at the transom. This implies that the size of the transom is contributing significantly to the resistance. The size of the transom apparently also affects the hump speed, decreasing with increased size. As the speed increases
the resistance coefficients of all of the models decrease and tend to converge. At the highest speeds Models A, B and F still have the lowest resistance coefficients. The difference in total resistance between these widely different models is very small in the region of FN = 1.0
and greater.
Figure 1: Model Total Resistance Coefficient
u laß 10.0 Ro 60 4.0 2.0 8 0.0 0.00 0.20 0.40 0.00 0.00 1.00 1.20
A
c
Figure 2: Residuary Resistance Coefficient
3.1 UN1VERSFY OF SOUTHAMPTON
EXPERIMENTAL RESULTS
The University of Southampton conducted a
comprehensive study on a systematic series of high-speed displacement catatuaran hulls; which was reported in detail by Molland (1). The series consisted of 10 hull configurations in which length-displacement ratio, UV" and breadth-draft ratio, B/T were variéd. The hull forms were derived from the NPL round bilge series (8) and
(9). Each hull configuration was tested
first as a
monohull and then in various cataiaran configurations. Among the 10 hull configurations there were three,Models Sa, Sb arid Sc that were tested at a
length-displacement ratio of 8.5 comparable to the models tested at Webb Institute. The models were 1.6 meters in length also comparable to those tested at Webb Institute. The geometric characteristics of these models are contained
The experimental results of the resistance tests were presented in tabular form as C5 coefficients (Cr- Cfn-rc) over the FN speed range 0.20 to 1.00 comparable to the speed range of the models tested at Webb Institute, thus the residuaiy resistance results are directly comparable. The residuary resistance data for the three models is presented in Figure 3. It is apparent that the effect of BIT ratio is not very pronounced, however model Sb has the lowest residuary resistance over the speed range and also the lowest wetted surface coefficient, thus the lowest
total resistance.
This model will be used for the
comparison with the óther hulls.Figure 3: USH Series Resistance
3.2 HYUNDAI MARITIME RESEARCH
INSTITUTE SERIES
The Hyundai Maritime Research Institute (HMRI) Series
(2) consisted of 60 super-high-speed displacement
monohull models in which the B/T, VB and CB were systematically varied. The variations are tabulated
below:
B/T= 1.2, 2.4 and 3.6
L/B = 10, 15, 20, 25 and 30 CB = 0.4, 0.5, 0.6 and 0.7
The model resistance was measured at six FN, namely
0.3, 0.5, 0.7, 0.9, 1.1 and 1.3.
An examination of the Uy"3 ratios of the 20 possible combinations of L/B and CB there were only five that had a VV 1/3 ratios of 8.50 which could be achieved by interpolating between the three values of B/T for each one of these combinations. Quadratic interpolation was
The model resùlts were presented as C = CT - Cfri-rc but based on the dynamic wetted surface rather than the
static. From these data the RJW ratio could be easily
determined for direct comparison with the other data
contained in this paper.
The hull forms were developed analytically and had a large transom area (about 90 % of the maximum area) thus providing further insight to the effect of transom
area upon performance. The geometric hull characteristics are contained in Table 2-2 in Appendix IL
4. ANALYSIS OF COMPARATIVE
RESISTANCE PERFORMANCE
It is customary to present resistance dâta obtained from model tests in the form of CR vs. FN, thus it can then be
easily used to predict the performance of any size
geosim. When comparing the performance of various hull forms this only treats the residuary resistance, which in the higher speed range of these forms, is primarily composed of the wave making and form resistance. In
the hump region there is the additional wave breaking effect or base drag of the transom. The presentation of the resistance in the form of total resistance coefficients, CT is also somewhat limited as one of the independent variables is the wetted surface, which vâries with each model. To overcome this difficulty the resistance-weight ratio, RJW provides a means for comparing the overall model performance as long as the comparisons are made at the same displacement-length ratio. The RJW ratio has been determined for all 14 models at FN of 0.5, 0.7, 0.9 and 1.1 (except for the 3 USH models) for dfrect comparison of their respective pefformance The results have been presented as percent increase or decrease over Model A. The results are presented for each speed in bar graphs, Figures 4 through 7. A bar graph of the wetted
surface coefficient, S/V213 for each model is presented as
percent increase or decrease over Model A in Figure 8
for easy comparison with the RJW data.
The bar graphs show that the R/W ratio of the USH and
HMRI models fall within the same range of values
covered by the Webb models and show the same trends with FN. The variation in the R'W ratio at the high FN, 0.9 to
1.1, among the 14 models is quite small as
compared with the RIW ratio at the lower F. At a FN= 1.1 the variation is less than nine percent if the three
extreme models, C, D and H3 are dropped.
The maguitude of the frictional resistance is a direct functiôn of the wetted surfhce. The bar graph, Figure 8 shows the variation among the 14 models. The variatioñ between the Webb group of models is quite small, 4.0 percent between models D and E, thus the variation in performance between these models is due principally to the residuary resistance. The variation in the HMRJ group is somewhat greater, varying 9.5 percent between model H2 and model H3, thus contributing significantly to the better performance of model H2. The collective results from the 14 models imply that minimizing the wetted surfhce is desirable but that the overall effecton the total resistance is secondary to that of the residuary
resistance.
used to obtain the desired BIT.
tabulated below:
The combinations are
Model CB LIB B/T VV" Hl 0.4 10 2.455 8.50 H2 0.5 10 3.071 8.50 H3 0.5 15 1.360 8.50 H4 0.6 15 1.634 8.50 H5 0.7 15 1.903 8.50
Figure 4: R/W Ratio at FN=O.5 300 25.0 20.0 15.0 L 10.0 5.0 0.0 A B C D E Hl F12 H3 H4 KS Ba 55 Sc -5.0
Figure 5: RJW Ratio at FN=O.7
Figure 6: RJW Ratio at FN=O.9
Figure 7: R/W Ratio at FN=1.1
Figure 8: Wetted Surface as Percent of Model A
The residuary resistance is composed of the form, wave pattern drag and at low speeds, in the hump region and lower, the wave breaking or base drag at the transom. The wave drag has not been measured on the Webb group of models, however it was measured on selected models of the USH senes, specifically model Sb. The
measurements made at the lower speeds on this model,
FN
= 0.5 to 0.7 showed that the wave resistance
coefficient is larger but it is also clear that there is an
additional drag component that is probably due to the size and shape of the transom. Transom size and shape, Kiss (1989) is undoubtedly one of the major contributors to the larger range of variations in resistance between the
models. The magnitude can only be determined by
making wave resistance measurements on these models
similar to those made on model 5b.
Although the variation in transom size and shape is quite
great among the Webb models, two
are obviousanomalies and each of the USH and HMRJ group of models had the same size and shaped transom, thus there are a total of 6 variations among the 14 models ranging in a transom area ratio from about 0.177 to greater than 0.8. There appears to be a correlation at a FN = 0.5 between the RJW ratio and the transom area ratio - the
16.0 14.0 12.0 - 10.0 u 8.0 g6.0
J:
...-.-.-..-.--.-.---..-...-I
i
e...
gHi
::
1E
Model 70.0 60.0urn
iiiui
10 ¡E 0.0 -10.0LIi:iiUIii
A B C D E Hl 112 KS KS 115 Ba Sb 5c Model 10.0 80 60 4.0---.---- .
. - .-.... - .... -2.0 -4.0 A C O - F HI FG 114 115 Sa Sb Sc Modellarger the transom area the greater the RJW ratio. This is not altogether true at the higher speeds.
From this work it is clear that more detailed studies of the transom stern area and shape need to be investigated both through measUrements of the total as well as the wave resistance of each configuration particularly as it pertains to the large transom areas required for waterjet
propulsión of these types of hulls.
5. CONCLUSIONS
When these model experiments were initiated it was hoped that it would be pôssible to identify those hull
geometricj characteristics that were most significant in minimizing the still water resistance. Not unexpectedly, this has not been accomplished to the degree hoped, but a number of broad guidelines have emanated from this
work.
1. The residuary and total resistance
coefficients of this wide assortment of hull
forms tend to converge at high speeds. 2. The variation
in the RJW ratio of the
conventional hulls at a FN = 0.9 and greater is less than 15 percent even with a large
variation in transom stem area.
3. The frictional resistance is the largest
component of the resistance at high speeds thus it is desirable to minimize the wetted surface in this speed regime. In the hump speed regime the frictional resistance is secondary and the residuary resistance is
much more significant where other
geometrió parameters than wetted surfuce,
are more important.
4. The B/T ratio does not appear to be too important except for its impact upon the
wetted surface.
This analysis has indicated that further experimental
work would be desirable on these modèls namely:.
Wave resistance measurements to better understand the sources and magnitudes of
the resistance components in the hump
region. (These measurements have just
been initiated at the time of this writing).
Wedges on the stem to determine if it is possible to reduce the trim at higher speeds
and determine the effect on resistance. Trim experiments to determine the minimum trim angle to minimize the resistance at high speeds.
6. ACKNOWLEDGMENTS
The Webb students of the Class of 2004 who
conducted the model experiments in three person teams were:
Abbott, D. Hanson & J. McGrath Allard, C. Brown & M. Fox
R. Hackel, A. Langernian & R Sarraf
J. Kleist, K. Munkenbeck & M. Unger N. Petrakakos, K. Posey & T. Yen
The determination of the hull geometric characteristics, using GHS, by Professor Nèil Gallagher is gratefully acknowledged as well as the assistance of Christopher
Mader in preparing the manuscript for publication.
7. REFERENCES:
MOLLARD, A.F., WELLICOME, J.F.,
COUSER, P.R "Resistance Experiments on a
Systematic Series of High Speed Displacement Catamaran Forms: Variations of Length-Displacement Ratio and Breadth-Draught
Ratio", Transactions of the Royal Institute of Naval Architects, Vol. 137, 1995.
MIN, KEH-SIK & KANG, SEON-HYUNG, "Systematic study on the hull form design and resistance prediction of displacement-type super-high-speed ships" Journal of Marinè Science and Technology Vol. 3 No. 2, SNAJ 1998.
YEH, HUGH Y.H., "Series 64 Resistance Experiments on High-Speed Displacement Forms", Marine Technology, July 1965. HADLER, J.B., GALLAGHER, N.J., VANT-IOOFF, R.W. and the Webb Institute Class of 2002 "Model Resistance Testing in the Robinson Towing Tank at Webb Institute",
Proceedings of the 23rd ATTC.
S. ACKERS, B.B., MICHAEL, T}{AD J., TREDENNICK,O.W., LANDEN, H.C.,
MILLER ifi, E.R, SODOWSKY, J.P. AND
HADLER, LB. "An Investigation of the
Resistance Characteristics of Powered Trimaran Side-Hull Configurations" Transactions
SNAME, Vol., 105, 1997.
HADLER, J.B, GALLAGHER, N.J. AND
VANHOOFF, RW.," Módel Resistance Testing
In The Robinson Model Basin at Webb Institute" New York Metropolitan Section SNAME, 18 March 2003.
HAMA, F.R, LONG, J.D. & HEGARTY, J.C.
"On Transition from Laminar to Turbulent Flow", Technical Note BN-81, AFOSR - TN-56-381, AD 95817.
INSEL, M. AND MOLLAND, A.F. "An
investigation into the resistance components of high speed displacement catamarans."
Transaction of the Royal Institution of Naval Architects, Vol. 134, 1992.
BAILEY, D. "The NPL high speed round bilge displacement hull series", Maritime Technology Monograph No. 4. Royal Institution of Naval Architects, 1976.
KISS, T.K. AND COMPTON, RH. "The
Effects of Transom Geometry on the Resistance
of Large Surface Combatants", Transactions
r
\
4 8 10 12
Stations
14 18 18 20
Figure 1-1: Sectional Area Curves
Table l-l: Model Geometric Characteristics
-Geometric characteristics of Models- Webb
Model A B C D E F Dièiionà1quntitjes -LWL, m 1.678 1.730 1519 L524 1.563 1.725 Beam,mm 145.5 1216 158.0 152.8 116.8 113.1 Draft, mm - 71.9 74.9 493 58.9 56.9 73.8 Volume, cm'3 7659 7836 5751 5754 6223 8325 WS,cmA2 2945 2964 2477 2485 2513 3164 At, cm"2 30.6 12.8 76.7 66.8 44.5 20.4 Disp, kg 7.64 7.82 5.74
5i4
6.21 8.34 VzAnglèEntrance 5.21 6.14 2.98 2.98 7.84 5.69 Non-Dimensioml qüáñtitiés -L/B 11.53 14.00 9.62 9.98 13.38 15.27 B/T 2.03 1.65 3.21 2.59 Z05 1.533 LWL/vol(1/3) 8.512 8.110 8.479 8.505 8.498 8.51 S/vòl(2/3) 7579 7.513 7.716 7.738: 7.427 7.703 At/Amax 0.419 0.177. 1.000 1.000 0.792 0.267 Cb 0.436 0.489 0.487 0.419 0.598 0.58 Cp 0.624 0.624 0.494 0.565 0.707 0.63 1 Cm 0.699 0.784 0.986 0:742 0.846 0.923 0.730 0.753 0.500 0.840 0.805 Cvp 0.597 0.649 0.973 0.7 1:2 0.721 LCB % aft amidship 6.59 1.72 16.83 14.70 9.64 3.90 LOE % aft amidship 9.62 5.81 16.67 16.50 7.14 7:38APPENDIX I Hull Characteristics of Webb Models
1.0 0.9 0.8 0.7
B\
-0.6-A
-c
---D
--'E
-
-F
\,F
r
APPENDIX II HùlI Characteristics of Selected USH and HMRI MOdéls
Tablé 2-1: USH Model Characteristics
Table 22: HMRI Model Characteristics
Geometric characteristics of Models-USH
Model Sb 5e Dimensional quantitièi LWL, m 1.600 1.600 1.600 Beäm,mm 125.0 145.5 161.6 Draft, mm 83.3 72.7 64.6 Volume,cmA3 6631 6695 6665 TS,cmA2 2820 2760 2770 At, cthA2 Thsp, kg 6.62 6.68 6.65 Nón-Dimensiónal quantities L/B 12.80 11.00 9.90 BIT 1.50 2.00 2.50 LWL/vól(l/3) 8510 8.500 8.490 SIvol(2/3) 7989 7.770 7.821 At1Amax 0.534 0.534 0.534 Ch 0.397 0.397 0.397 Ó.693 0.693 0.693 cm 0.565 0.565 0.565 cw 0.759 0.759 0.759 Cvp 0.523 0.523 0.523 LB % aft arnidship 6.40 6.40 6.40 LCF%áftamidship
Geometlic chÉacteriátics of Models . HMRI
-Model Hl H2 H3 H4 H5 Dimensional quantitiès LWL,m 1.600 1.600 1.600 1.600 1.600 Beam, mm 160.0 160.0 106.7 106.7 106.7 Draft, mm 65.18 52.09 78.41 65.26 56.06 Volùtne,cthA3 6675 6668 6691 6683 6698 WS,cmA2 2782 2647 2916 2760 2708
