Deift University of Technology
II11_J J1e1ft
Faculty of Mechanical Engineering and Marine Technology Ship Hydromechanics LaboratoryExperimental Investigation
into Added Resistance of
Surface Effect Ships
J. Moulijn
eReport 1202-P
September 1999
Presented on the Fifth International Conference
on Fast Sea Transportation, FAST'99,
Seattle,
Washington, USA
FIFTH INTERNATIONAL CONFERENCE
ON FAST SEA TRANSPORTATION
Seattle, Washington USA
CAVEAT
The papers bound in this volume are preprints prepared for presentation at the Fifth International
Conference on FAST Sea Transportation (FAST '99), sponsored by The Society of Naval Architects and
Marine Engineers (SNAME), held August 31-September 2, 1999, at the Bell Harbor International
Conference Center in Seattle, Washington.
For information on obtaining a copy of the FAST '99 conference papers, contact the Service Center at SNAME Headquarters. By mail: 601 Pavonia Avenue, Jersey City, NJ 07036. By telephone, U.S. and Canada: 1-800-798-2188; international: I-201-798-4800. All fax and e-mail inquiries, 1-201-798-4975, c-mail: eromanelli@sname.org.
© Copyright 1999 by The Society of Naval Architects and Marine Engineers
It is understood and agreed that nothing expressed herein is intended or shall be
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Art Anderson Associates www.artanderson.com 206-622-6221 360-479-5605
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Conmarke USA, Inc. www. northwest-maritime.net 425-712-1948 425-712-7087
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HamiltonJet, Inc. www. ham iltonjet. corn 206-784-8400 206-783-7323
HydroComp, Inc. www.hydrocompinc.com 603-868-3344 603-868-3366
International Marine Software Assoc. www.hydrocompinc.com/imsa.htm 603-868-3344 603-868-3366
John Crane - LIPS USA 228-872-5970 228-872-5974
John J. McMullen Associates, Inc www.jjma.com 360-613-2540 253-272-0796
Kelvin Hughes, Ltd. www.kelvinhughes.co.uk 44-181-500-1020 44-181-500-0837 LIPS Jets B.V. www. lips-propulsion. nl 31-416-388483
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NC Machinery Co. www.ncmachinery.com 425-25 1 -5877 425-25 1 -6423
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Thermal Ceramics www.thermalceramics.com 800-245-8008 706-560-4056
Transtar Metals www.transtarmetals .com 425-251-8550 425-251 -4888
_________ Exhibitor Entrance Only 2 ZF Marine 6 Entrance From Freight
>
Elevator RadioHolland International NC Kelvin Hughes Marine Machinery21 20 19 18 Software Association 5 4 3 17 Prime Mover Controls 2 LIPS Jet 16BV
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CDI Marine 15 Group aritim Dynamics 14 ATC Chemicals 13 Lloyds Register 12I
7 8 9n
10 11Geberit HamiltonJet Transtar Derecktor Alaska Metals Shipyards Diesel
Electnc
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I Div. NSWC
Pacific Marine
Detroit
Diesel-Allison SystemsSafety stairs (down) Entrance
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conference
TABLE OF CONTENTS
Session lA
- Materials
Fatigue Assessment of Welded Aluminium Ship Details
Bard Wathne Tveiten and Torgeir Moan
Ultimate Strength of Aluminium Plates under Biaxial Loading
19Odd Halvdan Holt Kristensen and Torgeir Moan
Comparison of Structural Behavior of Wet Deck Panels Made of Different Materials
Under Slamming Loads
35Georgios M. Katsaounis and Mano/is Samuel/des
European Research on Composites in High Speed Vessels
49Brian Hayman and Andreas T. Echtermeyer
Session 2A- Motion Contro!
On the Robust Design of Motion Regulator for Foil-Catamaran in Irregular Waves
55Key-Pyo Rhee and Sim-Yong Lee
Simulation - An Essential Tool in the Design of Motion Control Systems
73CR. Swanton, A.J. Haywood and B. H. Schaub
Hull Form Considerations in the Design of Low Wake Wash Catamarans
83Stan Stumbo, Ken Fox and Larry Elliot
Predicted vs. Measured Vertical-Plane Dynamics of a Planing Boat
91RIchard Akers, Stephen Hoeckley, Ronald Peterson and Armin W. Troesch
Seakeeping Design of a High-Speed Autonomous Semi-Submersible Vehicle
107P.A. Wilson and DA. Hudson
Session 3A - Propulsion
Pod Propulsion Hydrodynamics
- U.S. Navy Experience
119Gabor Kara fiath and Daniel J. Lyons
Design, Manufacture and Full Scale Trial of High Performance
Surface-Piercing-Propellers
137On the Development of a New Series Propeller for High Speed Craft
151Young-Zehr Kehr
Session lB -Safety
An Unsteady Vortex Lattice Method to Assess Aspects of Safety of Operation for
Hydrofoil Craft
161Frans van Wairee and Tang Seng Gie
Experience Gained by the Application of the Formal Safety Assessment
Approach to
High Speed Craft
173C. Viva/da and R. Giribone
Collision Risk Analysis Tools for HSC
181Jesper Urban,Preben Terndrup Perdersen and Bo Cerup Simonsen
A Possible Application of Reliability Centered Maintenance Principles in the Design,
Construction and Operation of High Speed Vessels
195Richard S. Ploss
Session 2B - Operations
CCDoTT Transportation Automated Measurement System (TrAMS) and Fast Ship
Development at CSULB
207Richard Williams, Tuncer Cebeci and Ken James
A Study on Weather Routing of High Speed Ships
219H. Hagiwara, H. Fukuda, K. Su gai and Y. Kusaka
High Speed Coastal Transport Emergence in the US
231Dr. Robert Latorre and Capt. Robert Foley
Session 3B - Trade-Off Studies
Rational Design Assessment for Classification Purpose-Application to
Hull Design of
Large Monohulls
245Etienne Thiberge
Documentation of HSC Operational Performance and Limitations - The Regulatory
Regime and Practical Application
273Per Werenskiold, Dariusz E. Fathi and Egil Jullumstro
On the Great Trimaran-Catamaran Debate
283Session 4A
- Concepts
The Stepped Hull Hybrid Hydrofoil
299Christopher D. Barry and Bryan Duifty
On Design of a 50 Knot, Payload 1500 Ton Hybrid Ship
315S.!. Yang, Y.G. Kim, C.D. Koh, J. W. Ahn, Y.J. Cho, J. W. Kim and Y.H. Park
The Cost Benefit of Emerging Technologies Using Physics-Based Ship Design
Synthesis
327
David R. Lavis and Brian G. Forstell
Session 5A - Rules
Classification Experience with an 8 Seater WIG Craft
339
K. Fach, U. Petersen and H.J. Reischauer
Trials and Tribulations of a Yacht Builder: The Design, Construction and Testing
of the Sportfishing Yacht "Martena"
351David Rusnak
New Rules for the Classification of Naval Ships
367
N/gel White, David Bignold, Paul James, RIchard Stitson and Fai Cheng
Developments Affecting Classification Requirements for High Speed Craft
385R. Curty, D. Novak, B. Menon and J. F Wu
Det Norske Ventas Requirements for Direct Calculation Methods of High Speed and
Light Craft
399
Oyvínd Pettersen and Karl M. Wik/und
Session 6A - Structural Design
Optimum Structural Design of the High Speed Surface Effect Ships of Composite
Materials
409Chan g Doo Jang and Ho Kyung Kim
Session 4B - Hydrodynamics
Formal Hydrodynamic Optimization of a Fast Monohull on the Basis of Parametric
Hull Design
417Theoretical and Experimental Validation of the Seakeeping Characteristics of
High
Speed Mono- and Multi-Hulled Vessels
429PA. Bailey, DA. Hudson, W.G. Price and P. Temarel
Linear and Non-Linear Numerical Seakeeping Evaluation of a Fast Monohull
Ferry
Compared to Full Scale Measurements
443Zhaohui Wang, Rasmus Folso, Francesca Bon dini and Tommy Pedersen
Deck Diving of High Speed Passenger Catamarans in Following Seas: The Effect of
Cross Deck Structure Configuration
457Martin Hannon, Martin Renilson and Andrew Cooper
Modeling of Vertical Plane Motion of an Air Cavity Ship in Waves
463Konstantin I. Matveev
A Study on Hydrodynamics of Asymmetric Planing Surfaces
471Lixin Xu and Armin W. Troesch
Session 5B - Operations
The Comparison of Conventional and Fast Ferries
483Dr. Ian L. Buxton and bannis S. Togias
Enlarged Ship Concept Applied to a Fully Planing SAR Rigid Inflatable
Life Boat
495Ir. J. van der Ve/de and Ir. Jakob Pinkster
Development and Operation of Hydrofoil Catamaran "Superjet"
511Toshihiko Arii, Kazuya Hatta, Masamichi Sugano and Hideaki Miyata
The Hydrodynamic and Economic Evaluation of the Blohm+Voss Fast
Monohull Design
523Dr. Ing. Gerhard Jensen and Dipl. Ing. Jurgen Engelskirchen
The Economic Challenges of High Speed, Long Range Sea Transportation
537Roger L. Schaffer, P.E.
Session 6B - Speed
The Advantages of Advanced Sandwich Composites Over Traditional
Aluminum
Construction
553Albert W. Horsmon Jr. and Bryant Bernhard
Materials Considerations for High Speed Ships
563Theoretical Studies of Wetdeck Slamming and Comparisons with Fuliscale
Measurements
577Elm Manta Haugen and Odd Faltinsen
Numerical Simulation of Viscous Flow Around Three-Dimensional Wing-in Ground
Eftect with Endplates
593Myung-Soo Shin, Chen-Jun Yang, Seun g-II Yang and Guo-Qiang Wang
Design Data for High Speed Vessels
605T. Karayannis, A.F. Mo/land and Y. Sarac Williams
Session 7A - Concepts
Bathmax 1500 - High Speed Containership Design Optimization and Model
Test Results
619John Avis, Russ Hoffman, Daniel E. McGreer and Jan Si,vio
Developments in Hydrofoil Assistance for Semi-Displacement Catamarans
631G. Migeotte and K.G.Hoppe
Large High Speed Trimaran - Concept Optimization
643lgor Mizin and Eduard Amromin
Large Slender Monohulls for Fast Freight Carriers
657Jan Sirviö and Niklas Ahlgren
Session 8A
- Structural Loads
Fatigue Evaluation for High Speed Light Craft Based on Direct Load Transfer
Procedures
673Tor Skjelby, Magnus Lindgren and Anja C. Kjeldaas
Slamming Studies on High Speed Planing Craft Through Full-Scale Trials and
Simulations
683A. Rosen and K. Garme
Hydro-Elastic Eftects of Bow Flare Slamming on a Fast Monohull
699Geert K. Kapsenberg and Stefano Brizzolara
Global and Slamming Sea Loads Acting on an 86m High Speed Catamaran Ferry
. .709
Paul Steinmann, Karsten Fach and Balji Menon
Global Loads For Structural Design of Large Slender Monohulls
719
Session 9A - Structura! Design
Fatigue and Damage Tolerance Design Philosophies: An Aerospace Perspective with
Applications to High-Speed Marine Vessels
731John Roberts
Approaches in Stress Analysis of High Speed
Craft
745
O/e Andreas Hermundstad and MingKang Wu
Global Structural Analysis of Large Catamarans
757
Svein Er/ing Heggelund, Torgeir Moan and Stig Orna
Ultimate Strength Assessment of Fast Mono Hull Vessels
773Dario Boote, Massimo Figari and Alcide Sculati
Session 7B - Hydrodynamics
From Model Scale to Full Size-Towards an
Understanding of the Scaling of
Resistance of High-Speed Craft
781N.A. Armstrong and C. Eng
Power Prediction for High Speed Catamarans from Analysis of Geosim Tests and
from Numerical Results
789D. Bruzzone, P. Cassella, C. Cop po/a, G. Russo Krauss and /. Zotti
Theoretical and Experimental Investigation of Resistance
of High-Speed Round
Bilge Hull Forms
803Prasanta K. Sahoo, Lawrence J. Doctors and Martin R. Reni/son
Experimental Investigation into the Added Resistance of Surface Effect Ships
. . . 815Joost C. Mouhjn
Exploring Hydrodynamic Enhancements to the Arleigh
Burke (DDG 51)
827Dominic S. Cusan el/h Stuart D. Jessup and Scott Gowing
Session 8B - Propulsion
A Method for Automatic Optimisation of the Intake
Duct Geometry of Marine
Water-jets
843Peixin Hu and Mehrdad Zangeneh
Development of Waterjet Inlets for loo knots
853On Engine Power and Manoeuvring Safety of High Speed Small Crafts
869Michio Ueno, Mitsukiyo Hatate, Teruaki Suzuki, Kazunori Sato and Akihiko Tanigami
A Universal Parametric Model for Waterjet Performance
879
Donald M. MacPherson
Influence of Bounday Layer Ingestion
on Waterjet Performance Parameters at
High Ship Speeds
883Norbert W. H. Bu/ten
Experimental Validation of a Coupled Lifting-Surface/RANS Procedure
for Waterjet
Pump Design and Analysis
893T. E. Taylor and R. W. Kimball
Session 9B - Novel Considerations
Fast Ship Drag Reduction
901Eduard Amromin, Yakov Khodorkovsky and Svetlana Kovinskaya
Resistance Prediction for Fast Displacement Catamarans
915S verre Steen, Hans Jorgen Rambech, Rong Zhao and Knut J. Minsaas
Novel Hydrodynamic Concepts of Fast Vessels with Enhanced
Seakeeping Performance
923
V. M. Pashin, G. G. Filipchenko and G. Trincas
Suggestion of Off Center Line Bow Bulbs and Fundamental Studies
on their Wave
Making Characteristics
937
Kazuo Suzuki, Takumi Yoshida and Risa Kimoto
Local Pressure on Hull Plating Due to Slamming
947
Experimental Investigation into the Added Resistance of
Surface Effect Ships
Joost C. Moulijn1
ABSTRACT
This paper presents an experimental investigation into the added resistance due to waves of
Surface Effect Ships (SES). SESs appear to have a large speed loss when they are sailing in a seaway. This speed loss is probably caused by a very large increase of the resistance due to the
ambient waves. The main goal of this investigation is to find the origin of this large added
resistance. An extensive series of model experiments was carried out at the Ship Hydromechanics Laboratory of Deift University of Technology. Two versions of a model were subjected to three types of experiments: forced oscillation experiments, wave force experiments and experiments where the model was free in heave and pitch. The contribution of the air cushion to the added resistance was measured separately, next to the total added resistance. The difference yields the contribution of the hulls to the added resistance. Furt he rniore the added resistance due to sinkage caused by a drop of the cushion pressure was investigated. The outcome is that the contribution of the hulls to the added resistance is largest. This added resistance of the hulls is mainly caused by
sinkage.
i INTRODUCTION
This paper presents results from a four years research project on motions and added resistance due to waves of Surface Effect Ships (SESs). MARIN and the Royal
Netherlands Navy jointly sponsor this research project.
The paper deals with the topic of added resistance due to waves. Surface Effect Ships are found to have a large speed loss when they are sailing in a seaway. This speed loss threatens the economical feasibility of sea-going SESs. The speed loss is probably caused by an increase of the resistance due to the ambient waves; the
so-called added resistance due to waves, or briefly
added resistance. The actual speed loss also depends on
the extra resistance due to wind, the calm water
characteristics and the propulsion characteristics of thevessel.
There exist only a surprisingly small amount of literature on the topic of added resistance of SESs.
Faltinsen et al. (1991) presented a comparative study on
the speed loss and operability of a catamaran and an
SES in a seaway. They did not however include the
added resistance due to the air cushion. The outcome of the study is that the SES has a slightly larger speed loss than the catamaran. Ehrenberg (1996) states however that the speed loss of an SES is much smaller than the speed loss of a comparable catamaran. Kapsenberg et
al. (1995) measured a very large added resistance (up to
about two times the calm water resistance). He also
showed that the relation of added resistance with wave
height squared, which holds for conventional ships,
does not hold for an SES.
The added resistance of an SES can be split up into
two components:
The added resistance of the hulls, the increase of
the resistance of the hulls due to ambient waves.
The added resistance of the
air cushion, theincrease of the resistance of the air cushion due to
ambient waves.
T?
There are three mechanisms which cause the added
resistance of SES:
.
Radiation of waves.
This component is alsoexperienced by conventional ships. It is associated with the momentum of the waves that are radiated by the vessel due to the diffraction of the ambient
waves and the motions (and cushion pressure
variations) of the vessel.
Sinkage. When an SES sìils in a seaway the
amount of air leakage under the seals increases.
This results in a decrease of the cushion pressure, and causes the SES to sink deeper into the water
because the buoyancy of the hulls must carry a
larger part of the vessel's weighL The larger draft
of the SES leads to an increase of the resistance.
Momentum of the leakage air. The escape velocity of the air that leaks under the seals is quite high.
The momentum of this leaking air is lost, which
must be compensated by a force. Changes of the
leakage flows due to ambient waves therefore
result in a contribution to the added resistance.
The first two mechanisms contribute to the added
resistance of the air cushion and to the added resistance of the hulls. The last mechanism only contributes to the resistance of the air cushion.
The origin of the added resistance of SESs is not
clear yet. Up to recently, the air cushion was believed to
be responsible for the major contribution to the added resistance of SESs. Computational results in a paper by Moulijn (1998) show however that the added resistance of the air cushion is only small or even negative. This
paper also explains that the added resistance of the hulls
is not likely to be large either, because the hulls are
very slender and only carry a small part of the vessel's weight. Faltinsen et al. (1991) suggested that the large added resistance of SESs is mainly caused by sinkage. Kapsenberg (1993) however showed, by means of an experiment with an increased fan RPM, that an increase of the cushion pressure from 79% to 99% of the design pressure only resulted in an added resistance reduction
of 6%.
This requires new insight into the magnitude and particularly the origin of the added resistance of SES.
The main goal of this paper therefore is to fmd an
answer to the following question: What is the origin of the added resistance of Surface Effect Ships?
In order to answer this question, an extensive series
of model experiments was carried out at the Ship
Hydromechanics Laboratory of Delft University of Technology. Two versions of an SES model were
tested: one version with extremely slender side hulls, and one version with realistic side hulls. Both versions were subjected to forced oscillation experiments and to
wave force experiments in both on-cushion and off-cushion mode. Furthermore the model version with
realistic hulls was also tested in a setup where it was
2
free in heave and pitch (on-cushion mode only). The model with extremely slender hulls could not be tested in this setup because it lacks buoyancy and restoring
capabilities. In the experiments with the model with
extremely slender hulls the effects of the air cushion
were isolated as far as possible.
An attempt was made to measure the added
resistance of the air cushion separately. Subtraction of the added resistance of the air cushion from the totaladded resistance yields the added resistance of the
hulls. These results should indicate which added
resistance component is most important. Furthermore,
the importance of the mechanism of sinkage was
investigated.
The next section presents a description of (both
versions of) the model. Section 3 describes the three
different types of experiments that were carried out. Section 4 goes into the measurement of the added
resistance. Section 5 presents the results
of the
experiments. Finally Section 6 presents conclusions
concerning the origin of the added resistance of Surface
Effect Ships.
2 DESCRIPTION OF THE DUTSES MODEL This section presents a description of the SES model. It
is called DUTSES model. Two versions of the
DUTSES model were tested. One had extremely
slender side-hulls. This version will be referred to as the model with plates. The other version was equipped with
realistic side hulls, and will be referred to as the model
with hulls.
The DUTSES model was partially derived from the
target vessel of the HYDROSES project, a large
collective research project on seakeeping of SESs. TheHYDROSES target vessel was designed as a large
car/passenger ferry by FINCANTIERI. One can find a more elaborate description of the HYDROSES project
in the paper by Kapsenberg et al. (1995).
Figure 1 presents a drawing of the DUTSES model.
Table i presents the main particulars. The side-plates
and side-hulls have the same lateral contours (see
Figure 1). The side-plates were about 12 mm thick. At the bow, keel and stem the plates were rounded. They
were constructed of polyurethane foam, which was
reinforced by glass fiber and polyester. The hulls were constructed by mounting extra polyurethane bodies to the plates. A smooth transition was achieved by means of filler. Figure 2 presents a body plan of the hulls. The
hulls were prismatic from the stem up to
stationnumber iS.
The double deck of
the model was
constructed of plywood.
The bow seal is of the finger-type. It consists of a
row of vertical loops of flexible material, which are
7
50
finger. The bow seal has nine fingers. The stern seal is
of the bag type, a bag of flexible material that is
pressurized at a slightly higher pressure than the air
cushion. The bag is open to the sides, where it is closed
by the side-hulls. Two internal webs restrain the aft side
of the bag, and divide the bag into three lobes. Both
Figure 1: Longitudinal cross section of the DUTSES model
Figure 2: Body plan of the DUTSES model
3
seals were manufactured of spinnaker cloth.
The forces on the seals were measured separately. Therefore the bow seal was mounted to a plate which
was connected to
the model by means of force
transducers. The stern seal was mounted to an air
distribution box that distributes the airflow from the aft fan over the stern seal bag and the air cushion. This box
was also connected to the model by means of force
transducers.
Table 1: Main particulars of the DUTSES model
symbol description unit value L0. Length over all. m 3.200
L, Length at the
perpendiculars.
in 3.000
L. Length of the air cushion. in 3.000
B Beam of the model with plates.
m 0.549
Bh Beam of the model with
hulls.
in 0.739
B0 Beam of the air cushion. m 0.525 D Depth to upper deck. m 0.325
D1 Depth to lower deck. m 0.225
T0 On-cushion draft at m 0.103 Station 0. T20 On-cushion draft at m 0.053 Station 20. V Displacementofthehulls m 0.0168 (on-cushion).
Po Design air cushion excess
pressure.
Pa 300
Ps Design stern seal excess
pressure.
Pa 306
M Mass of the model kg 63
AP FP
aft
leg
Fia
F3oscillator
500The air cushion and the stem seal plenum were
both pressurized by axial fans. The fans were mounted directly to the model. The fore fan pumped air directly into the air cushion. The aft fan pumped air into an air distribution box that distributed the air over the stem
seal and the air cushion. The ducts between the air
distribution box and the stem seal were large. Therefore the volume of the air distribution box can be considered as a part of the seal plenum. A computer controlled the fans, which ensured a very stable fan RPM. The slope
of the static characteristics of the identical fans was
about 0.28 m3/s/kPa. The fans and were kindly on loan
from MARIN.
The air cushion plenum of the DUTSES model was equipped with a diaphragm, a device that reduces the stiffness of this plenum. Kapsenberg et aI. (1995) used
a diaphragm to obtain a correct scaling of the air
cushion dynamics. In the present experiments the aim of the application of a diaphragm is merely to prevent very large pressure amplitudes which might result in a negative cushion excess pressure. One can fmd anelaborate discussion on the scaling of air cushion
dynamics and the diaphragm technique in a report byMoulijn (1998).
3 DESCRIPTION OF THE EXPERIMENTS This section presents descriptions of the three different kinds of experiments to which the DUTSES model was
500
station 10
Figure 3: Experimental setup for the oscillation and wave force experiments
4
fore
leg
F11
F31
subjected: forced oscillation experiments, wave force experiments and experiments where the model was free
in heave and pitch. In all experiments the forward speed was 3.27 mIs (Fn = 0.603).
Figure 3 presents the experimental setup of the
forced oscillation experiments. The oscillator forced the
model to carry out heave or pitch motions in calm water. The model with plates was only tested in
cushion mode. The model with hulls was tested in
on-cushion as well as off-on-cushion mode. During the
experiments the longitudinal and vertical forces in theoscillator legs were measured.
The experimental setup of the wave force tests was
identical to the setup of the forced oscillation
experiments (see Figure 3). The only difference is that
the oscillator is fixed in it's mean position, while the
model was towed in regular head waves. The amplitude of the incident waves was varied from 10 to 40 mm. Both versions of the model were tested in on-cushion and off-cushion mode. During these experiments the
longitudinal and vertical forces in the oscillator legs
were measured again.
Figure 4 presents the experimental setup of the experiments where the model was free in heave and
pitch. These experiments are also called motion
experiments. During these experiments the model was free to carry out heave and pitch motions, while it was
towed in regular head waves. The amplitude of the incident waves was varied from 10 to 40 mm. The
pot. meter
sway and yaw preventer
(front view)
+
964
model was connected to the carriage by means of the
so-called nutcracker; a device which prevents surge,
sway, roll and yaw motions. The nutcracker was
mounted 500 mm iii front of the center of reference (station 10 and 0.35 m above the keel). At the Ship
Hydromechanics Laboratory it is common practice to mount the nutcracker at the center of reference. This was however impossible because of the presence of the diaphragm. The model with hulls was only tested in
on-cushion mode. In off-on-cushion mode the draft of the model was very large. During the experiments the
vertical displacement of the model was measured at the nutcracker and at a point964 mm aft of station 10. The heave and pitch displacements at the center of reference
were derived from these vertical displacements.
Furthermore the longitudinal force (resistance) was
measured at the nutcracker.
4 THE ADDED RESISTANCE MEASUREMENT This section describes how the added resistance and the two added resistance components (the added resistance of the air cushion and the added resistance of the hulls) were measured. It also describes how the mechanism of sinkage was investigated.
It is not common practice to measure the added resistance during oscillation and wave force tests,
because it cannot be used in the prediction of the added resistance of a free sailing vessel. The added resistance
is a higher order quantity, or at least a non-linear
quantity. This implies that the added resistance of a free500
station 10
Figure 4: Experimental setup for the motion experiments
nut-C7
5
sailing vessel does not simply follow from a superposition of a forced oscillation experiment and a wave force experiment. The main goal of the present
experiments is however to get more insight into the
origin of the added resistance of Surface Effect Ships, and not to predict the added resistance of some (full-scale) vessel. In this respect experiments with the
model with extremely slender side-hulls were carried
out. This model lacks buoyancy and restoring
capabilities, and could therefore not be tested in a setup
where the model is free in heave and pitch. We chose to
subject this model and the model with realistic side-hulls to wave force and forced oscillation experiments. Furthermore we also subjected the model with realistic side-hulls to experiments where the model was free in
heave and pitch.
Now this section presents how the total added
resistance and the added resistance components were
measured. The total added resistance follows from:
R = R(in waves) R(in calm water)
It is difficult to obtain an accurate measurement of the added resistance because it follows from the difference of two large quantities.
The full
resistance of the air cushion wasdetermined from the seal forces, the cushion excess
pressure and the pitch angle:
R"
Fib F, +pA
sinO-(F3b +F3 +p,A4cosO)ì
where Fib and F3b are the longitudinal and vertical bow
seal forces, F1. and F3, are the longitudinal and vertical stem seal forces, Ad is the deck area, ç is the cushion
20 15 10
5
o
excess pressure, O is the calm water trim angle and i is
the (small) pitch displacement. The overlining denotes that the time-averaged value should be used. Now the
added resistance of the air cushion follows from: R
= R '(in waves ) - R
(in calni waterSubsequently the added resistance of the hulls follows
from:
R> = R R'4
where RßW is the total added resistance. Furthermore the added resistance of the hulls also followed from the
off-cushion experiments. These experiments do of course
not include the interaction of the hulls with
thehydrodynamic effects of the air cushion.
In the scope of the investigation of the mechanism of sinkage, some calm water tests with a reduced fan
RPM were carried Out. From the results we derived
linear relations of the resistance (R), the resistance of
the air cushion (R) and the resistance of the hulls
(R) with the cushion excess pressure (Pc). These
relations were used to calculate the added resistance
due to sinkage for the experiments in waves by
substituting the measured mean cushion pressure. hi thecaptive experiments the model was restrained, so no
sinkage occurred in these experiments. Therefore the
investigation of the added resistance due to sinkage was restricted to the motion experiments in waves.
5 PRESENTATION AND DISCUSSION OF THE
RESULTS
This section presents and discusses the results of the
experiments. First it discuses the magnitude of the
added resistance. Then it goes into the relation of the
added resistance with the wave amplitude.
Subsequently this section treats the different added resistance components, and goes into the question weather the added resistance mainly acts on the air
6
cushion or on the hulls. Thereafter it presents the results
of the investigation of the mechanism of sinkage.
Finally it presents a general discussion of the results.
5.1 The Magnitude of the Added Resistance
Figure 5 presents a comparison of the added resistance as it was measured in the wave force experiments with
the model with plates (Series 1.1), the wave force
experiments with the model with hulls (Series 2.1), and
the motion experiments (Series 2.7). The figure
presents the added resistance (on model scale) as a fimction of LI2, the cushion length divided by the
wavelength. It presents results for several wave amplitudes.
The by far largest added resistance was measured
during the experiments were the model was free in
heave and pitch
(Series 2.7). The largest valuesoccurred in long waves, when the model carried out
severe pitch motions, In the wave force tests the added resistance is much smaller. The added resistance that was measured in the oscillation experiments was only
small (up to about 2 N).
The measured added resistance is much smaller
than the added resistance that was measured by
Kapsenberg et al. (1995) at MARIN. They measured added resistance values up to two times the calm water resistance. In the present experiments the largest added
resistance was about half the calm water resistance.
5.2 The Relation of the Added Resistance with the
Wave Amplitude
Figure 6 presents the added resistance divided by the wave height (left) and the added resistance divided by
the wave height squared (right). The results clearly
show that the relation of the added resistance is neither
linear nor quadratic. For conventional ships this relation
is quadratic. For SESs it is somewhere between linear and quadratic. Probably some part is linear while the
other is quadratic. Series 1.1 + Series 2.1 X * Series 2.7
*
**
X*
*****
xxx+++
+XX+***L
I + I t A = 10 [mm] A = 20 [mm] A =30 [mm] A = 40 [mml 230
230
230
2 3 L/2L [-]600 E
z
o ca 200- 400-o X X X*
X + X + + + o 3From the off-cushion wave force experiments it
appeared that the relation of the added resistance of the hulls with wave height was also not quadratic. This is remarkable because in off-cushion mode the model was expected to behave as a regular catamaran.
5.3 The Added Resistance Components
Figure 7, Figure 8 and Figure 9 subsequently present
the total added resistance, the added resistance of the air
cushion and the added resistance of the hulls. The
figures present results of the wave force tests with the model with plates (Series 1.1) and the wave force tests with the model with hulls (Series 2.1).
First this paragraph compares the results of the model with plates with the results of the model with
hulls. The total added resistance of the model with hulls
is larger than the total added resistance of the model
with plates (Figure 7). The difference is however not very large. The added resistance of the air cushion of the model with plates does not significantly differ from
the added resistance of the air cushion of the model
with hulls (Figure 8). Apparently the interaction of the hulls and the air cushion is not very important for the added resistance. This also subscribes the accuracy of
the measurement of the added resistance of the air
cushion. Furthermore the model with hulls has a larger added resistance of the hulls than the model with plates
(Figure 9). It is however remarkable that the model with
plates does have a significant added resistance of the
hulls. This was also found in the off-cushion wave force
tests. Added resistance is generally considered to be of
potential flow origin, i.e. the added resistance is associated with the momentmn of radiated waves which are caused by diffraction of the incident waves and by
the motions of the vessel. The plates can hardly
generate any waves (at least in head and following
seas). Therefore the added resistance of the plates was expected to be negligible. 7 30000-o 16 20000-a) o-o 10000-O X X
*
X++
o X + I I + o 3Figure 6: The added resistance divided by the wave height (left) and the added resistance divided by the wave height squared (motion experiments)
This paragraph compares the added resistance of the air cushion with the added resistance of the hulls. Figure 8 and Figure 9 show that, in the case of wave
force tests, the added resistance of the air cushion and
the added resistance of the hulls are about of equal
importance. The results of the oscillation experiments
lead to the same conclusion. In the pitch oscillation
tests the added resistance of the air cushion is negative. This is due to a considerable drop of the cushion excess
pressure, which is caused by the large amount of air
leakage under the seals.
Figure 10, Figure 1 1 and Figure 12 respectively present the total added resistance, the added resistance of the air cushion and the added resistance of the hulls as they were measured during the motion experiments.
It must be noted that in the motion experiments the
added resistance was not measured as accurately as in the captive experiments. This was due to a less accurate measurement of the bow seal force. In advance of each
test run the model floated in rest at a large draft (p. = O). The bow seal was therefore soaked during each test run.
The wet bow seal was probably sticking to the side
hulls, therewith affecting the actually measured bow seal force. This sticking is not likely to reproduce very well. It occurred in the test in waves as well as in the
calm water tests. It is however not expected that the sticking phenomenon affects the magnitude of the
added resistance of the air cushion. It only causes the somewhat scattering behavior of the added resistance of
the air cushion.
The added resistance of the hulls is, in the case of
motion experiments, much larger than the added
resistance of the air cushion (please compare Figure 11 and Figure 12). The added resistance of the air cushion is only small, and in most cases it is even negative. It can therefore be concluded that, when the model is free in heave and pitch, the contribution of the hulls to the
A=10 mm + A =10 mm + A=20 mm X A = 20 mm X A=30 mm X A = 30 mm
*
A=40 mm o A =40 mm o 40000 +8 6 4 2 0 4 2 O -2 6 4 2 O 2 8 Serìes 1.1 Series 2.1 X x + + J X X X X X X+ + + X + J i X + X ++ i X Series 1.1 + Series 2.1 < + X X
f
+ XXXXX XxX.<
++++++++
X*
X + *X X + + X X I I I I I i t I-i
I J Series 1.1 Series 2.1 -4-x X XXx+ XXxx
X XX X XXX + +XX++X+
++++
+ ++ + I I I I I I I t I I I t A = 10 [mm] A = 20 [mm] A = 30 [mm] A = 40 [mm] 230
230
230
2 3 L/X [-1Figure 9: Total added resistance (wave force experiments)
A= 10[mm] A = 20 [mm] A = 30 [mm] A = 40 [mm]
o 2
30
230
1 230
2 3LIX [-]
Figure 7: Added resistance of the air cushion (wave force experiments)
A = 10 [mm] A = 20 [mm] A = 30 [mm] A 40 [mm]
o 2
30
230
230
2 3L/X [-]
added resistance is much more important than the and wave force experiments are only applicable to a
contribution of the air cushion. situation that only exists in a laboratory.
5.4 The Mechanism of Sinkage
Figure 13, Figure 14 and Figure 15 respectively present
the total added resistance due to sinkage, the added resistance of the air cushion due to sinkage and the
added resistance of the hulls due to sirikage. The
mechanism of sinkage contributes to both the added
resistance of the hulls and the added resistance of the air cushion. The contribution to the added resistance of the hulls is large, while the contribution to the added
resistance of the air cushion is small and negative.
Actually, the cushion pressure drop causes a decrease of the wave making resistance of the air cushion. The sinkage, which is a consequence of the pressure drop, causes an increase of the wave making resistance of the
hulls and an increase of the viscous resistance of the
hulls.
A comparison of Figure 10 and Figure 14 leads to
the conclusion
that the mechanism of sinkage
is responsible for a large part of the total added resistance.When Figure 12 and Figure 15 are compared it appears
that sinkage is the main reason for the large added
resistance of the hulls (in the motion experiments). The added resistance of the hulls due to sinkage is almost as large as the full added resistance of the hulls. Therefore
the mechanism of sinkage is very important for the
added resistance of Surface Effect Ships.
5.5 Discussion
The oscillation and wave force experiments led to a
conclusion that is quite different from the conclusion
that was drawn from the motion experiments. In the
first case the conclusion was that the added resistance of the air cushion and the added resistance of the hulls
are of equal
importance. In the latter case theconclusion was that the added resistance of the hulls is large, while the added resistance of the air cushion is of minor importance.
The difference can be explained by the fact that no
sinkage occurred in the oscillation and wave force
experiments. Sinkage appeared to be very important for the added resistance of the hulls. In the oscillation and
wave force experiments the (mean) position of the
model was fixed. The model was not allowed to sink
into the water. Therefore the added resistance of the
hulls due to sinkage was zero, which results in a much smaller added resistance of the hulls and also a much smaller total added resistance.
The experiments where the model was free in heave and pitch are the most representative for the
problem of a real SES sailing in a seaway. Therefore
the conclusions of these experiments are the main
conclusions concerning the origin of the added
resistance of SESs. The conclusions of the oscillation
9
6 CONCLUSIONS
From the results of the experiments the following
conclusions concerning the origin of the added resistance of Surface Effect Ships can be drawn:
The hulls give the major contribution to the added
resistance of Surface Effect Ships. The contribution
of the air cushion is small, and in most cases it is
even negative.
The mechanism of sinkage is very importanL The
greatest part of the large added resistance of the
hulls is caused by sinkage.
ACKNOWLEDGEMENT
I would like to thank the Royal Netherlands navy and
MARIN for their financial support of my Ph.D.-project.
MARIN is also acknowledged for providing a lot of
equipment that was used in the experiments.
REFERENCES
RD. Ehrenberg. Das Verhalten von Luft kissen-.
katamaranen (SES) im Seegang. PhD thesis, Institut fur
Schiffbau der Universität Hamburg, 1996.
O.M. Faltinsen, J.B. Helmers, K.J. Minsaas, and
R. Zao. Speed Loss and Operability of Catamarans and SES in a Seaway. In First International Conference on
Fast Sea Transportation (FAST 91). Trondheim, Norway, 1991.
U.K. Kapsenberg. Seakeeping Behaviour of a SES in
Different Wave Directions. In Second International Conference on Fast Sea Transportation (FAST 93).
Yokohama, Japan, 1993.
G.K. Kapsenberg and P. Blume. Model Tests for a
Large Surface Effect Ship at Different Scale Ratios. In
Third International Conference on Fast Sea
Transportation (FAST 95). Lübeck-Travemünde, Germany, 1995.
J.C. Moulijn. Added Resistance of Surface Effect
Ships. In Proceedings of the Thirteenth International
Workshop on Water Waves and Floating Bodies.
20 15 10 5 o 10 5 o -5 -10 20 15 10 5 o 10 L/. [-]
Figure 10: Total added resistance (motion experiments)
A = 10 [mm] A= 20 [mm] A = 30 [mm] A = 40 [mm] + + + I I t + +
+++++
I I I + + I + +++++++++++
++++++++
I + + + I++LI
I + +++ I I I ++t++++++t
4: ++++++++
I I I + + + I++++
I I + + + I + A = 10 [mm] A = 20 [mm] A = 30 [mm] A = 40 [mm] o 230
230
230
2 3 LIX [-]Figure 11: Added resistance of the air cushion (motion experiments)
A = 10 [mm] A = 20 [mm] A = 30 [mm] A = 40 [mm]
2
30
230
230
2 3L/X [-]
Figure 12: Added resistance of the hulls (motion experiments)
2 3
20 15 10 5 o lo 5 O -5 10 20 15
lo
5 o 11 + + + I I + ++++++
I I I + + + ++++++++++++
++++++++
+++++
+++
+ + + + I I I_I_
I I I I I I I + + + I I + + + I ++ + + I I + 4-I + + A= 10[mm] A = 20 [mm] A = 30 [mm] A = 40 [mm] 13°
230
230
2 3Figure 13: Total added resistance due to sinkage
A = 10 [mm] A = 20 [mm] A = 30 [mm] A = 40 [mm]
o 2
30
230
230
2 3LIA [-]
Figure 14: Added resistance of the air cushion due to sinkage
A = 10 [mm] A = 20 [mm] A = 30 [mm] A = 40 [mm]
2
30
30
230
2 3LIA [-]
J.C. Moulijn. Scaling
of Air
Cushion Dynamics. Technical Report 1151. Deift university of Technology,Ship Hydromechanics Laboratory, 1999.
