THE FIFTH CHESAPEAKE POWERBOAT SYMPOSIUM
June 14-15, 2016
St. John's College, Annapolis, Maryland, USA
i
PROGRAM
STEVENS
Iiistiiuic of lechnology
USNA
U N I T E D S T A T E S N A V A L A C A D E M YT H E F I F T H C H E S A P E A K E P O W E R B O A T S Y M P O S I U M
St. John's College, Annapolis Maryland,
14-Jun-2016
Order Time Paper Title Authors Category
7:00
R e g i s t r a t i o n B e g i n s7:30
C o n t i n e n t a l B r e a k f a s t8:00
Opening Remarks Tuesday 14 June 2016
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8:05
J o s e p h G . K o e l b e l , a T r i b u t e to a M o s t U n f o r g e t t a b l e I n d i v i d u a l J o h n P. H o l l i n g s w o r t h Biography2
8:50
A n a l y z i n g a S t a n d a r d Sei'ies of P l a n i n g Boats w i t h Smoothed ParticleHydrodynamics R i c h a r d A l a r s , M i c h a e l MacNicoU Presentation Numerical 3 4 5
9:35
10:20
11:05
A t - A n c h o r W i n d - I n d u c e d Y a w I n s t a b i l i t y of a M o n o h u U M o t o r y a c h tM o t i o n C o n t r o l f o r S m a l l Fast Boats i n F o l l o w i n g Seas
V e r t i c a l Accelerations and Surge on a P l a n i n g H u U
J o n a t h a n Soja, J e f f r e y Bowles
J A . (Lex) K e u n i n g
D a v i d Tauber, Carolyn Judge
Waves, Ride Quality, Impacts Waves, Ride Quality, Impacts Waves, Ride Quahty, Impacts
12:00
Lunch
6
1:00
Wave H e i g h t a n d P l a n i n g H u l l Wave Slams i n Regular Waves C a r o l y n Judge, Alexander Mychalowych, Rachel SlaterWaves, Ride Quahty,
Impacts
7
1:45
H i g h Deadrise Stepped Cambered P l a n i n g H u l l s w i t h H y d r o f o i l s , A Proofof Concept Stefano Brizzolara, C a r o l y n Judge, BUI Beaver Design
8
2:30
FunctionaHty A n d Safety O f S m a l l Passenger C r a f t : Some Lessons Robert G.Latorre, A l b e r t Nazarov Hydrodynamics9
3:15
I n v e s t i g a t i o n o f Factors l e a d i n g to D y n a m i c I n s t a b i l i t i e s i n High-Speed,Shallow D r a f t Boats M i c h a e l M o r a b i t o Hydrodynamics
4:00
Adj ourn
^1
Order Time
T H E F I F T H C H E S A P E A K E P O W E R B O A T S Y M P O S I U M
St. John's College, Annapolis Maryland,
15-Jun-2016
Paper Title
Authors
Category
11 1 2 13
7:00
7:30
8:00
8:05
R e g i s t r a t i o n B e g i n s C o n t i n e n t a l B r e a k f a s tOpening Remarks Wednesday 15 June 2016
On The Hydrodynamics O f T h e Wedge A n d Transonic H u l l s A Comparison of Whole-Body V i b r a t i o n a n d Shock Response Spectra
8:50 Parameters fo r Q u a n t i f y i n g M i t i g a t i o n Characteristics of M a r i n e Shock
Isolation Seats
9:35
Fatigue L i f e Analysis o f t h e US Coast Guard's 47 M o t o r L i f e BoatA l b e r t o Calderon, B r i a n Maskew
Presented by William Hocliberger
M i c h a e l Riley, T i m o t h y Coats, H . C . N e i l Ganey
V i n c e n t Wickenheiser, K a r l S t a m b a u g h Design Waves, Eide Quahty, Impacts Structures
14 10:20 Some Notes on A l u m i n u m SmaU C r a f t Design a n d Construction
15 11:05 State of the A r t i n A l u m i n u m W o r k Boat Design and Construction
12:00 Lunch
Christopher B a r r y
L o u Codega, James Codega, Jason Powers
Presentation Structures Structures 1(3 17 18 1!)
1:00
1:45
The M y s t e r y of Sinkage and T r i m f o r H i g h Performance C r a f t
A n Oblique 2 D + T Approach f o r H y d r o d y n a m i c M o d e l i n g o f Y a w e d P l a n i n g Boats i n C a l m W a t e r
2:30 I n v e s t i g a t i o n O f "Unsteady" M e t h o d For M o d e l C a l m w a t e r Performance
3:15
N e u r a l N e t w o r k p a r a m e t r i c model f o r t r i m a r a n h u l l sA . Steven Toby
Sasan T a v a k o h , Abbas Dashtimanesh, Prasanta Sahoo
Presented by Micliael Morabito
U i h o o n Chung, R a j u D a t i a R i c h a r d Royce Hydrodynamics Numerical Numerical Numerical
4:00
Adjourn
F I F T H C H E S A P E A K E POWERBOAT SYMPOSIUM
14-15 June 2016
St. John's College, Annapolis Maryland, U S A
ABSTRACTS
Joseph G . Koelbel, Jr., a Tribute to a Most Unforgettable Individual
John P. HoUingswortbJoe Koelbel is intemationally recognized for his contributions to high-speed marine vehicles of various types for more than 50 years. Highlights of his career include design of the "experimental PT 810 while at Sparkman and Stephens, work on the hydrofoil boats Denison and PlainvieM', and design of the coastal interdiction craft CPIC. I n addition to this Joe has contributed numerous papers on planing craft design. A n in-depth look at his career and achievements w i l l be shared in honor of his numerous contributions to the marine industry during his lifetime o f bringing science and technology to the naval architecture.
Analyzing a Standard Series of Planing Boats with Smoothed Particle
Hydrodynamics
Richard Akers, Michael MacNicoU
(Presentation)
Naval architects use test results from standard series boat models to predict the running attitude and resistance o f f u l l size boats. A number o f standard series for planing boats exist including Series 62 (Clement, et al., 1963) and Series 65 (Hubble, 1974), the Southampton Series (Taunton, et al., 2010), and the USCG Systematic Series (Kowalyshyn and Metcalf, 2005, Metcalf, et a l , 2005). Unfortunately the range o f applicability o f existing series is limited, especially since small changes in hull forni can result in large changes in resistance and seakeeping performance. Furthermore, the majority o f these tests have been on prismatic hulls or hulls that are not closely related to modern hulls. Designers o f high-speed planing boats need a virtual towing tank, a numerical method o f simulating planing boats that is accurate, computationally efficient, and scalable i n both boat size and in simulation time.
A n alternative to traditional CFD is a technique called Smoothed Particle Hydrodynamics, or SPH. Instead o f modeling the problem with a mesh o f water volumes or water element boundaries, SPH models the problem with a large number o f individual fluid or boundaiy "particles." The authors used an open-source program called "DualSPHysics" (Crespo, 2015) for this work, and the remainder o f this paper w i l l refer to features o f that specific program. The designer specifies the geometiy by using simple geometric constnacts such as boxes, spheres and prisms. Alternatively the designer can import a surface or solid model directly from the design C A D model. In either case model construction is measured in hours. Once the geometiy is specified along with a small set o f simulation commands, a software tool is used to create the equivalent o f a mesh - in reality the space between boundaries is filled with particles with a fixed diameter and with properties that match those o f water. As an SPH analysis proceeds, moving particles simulate the flow o f water, accurately recreating waves, vortices, viscosity and other hydrodynamic effects essential to predicting planing boat motion. SPH has been applied to planing boat analysis in the past (Ghadimi, et al. 2012). This paper extends the technology by demonstrating its usefulness for modeling a complete standard series.
This presentation w i l l describe the progress obtaining results o f a systematic series o f SPH simulations o f the models used in the USCG Systematic Series. Four models were defined in this series, and two different sets o f models were built, one for resistance tests and another for seakeeping tests. C A D models are created for each o f these models. Command scripts are written and a large number o f SPH simulations are run. Simulation results including steady state resistance, trim, draft and wetted surface can be compared with published results for the USCG Series. By modeling a recirculating tank with a wavemaking wedge, DualSPHysics w i l l be used to predict seakeeping results for each o f the models and simulation conditions. This paper w i l l present the results of these analyses, demonstrating the advantages and deficiencies o f the SPH technique.
At-Anchor Wind-Induced Yaw Instability of a Monohull Motoryacht
Jonathan Soja, Jeffrey Bowles
There is a delicate balance that must exist between the aerodynamic, hydrodynamic, and mooring forces acting on a floating body restrained by a single anchor (single point mooring). I f t h e balance is not achieved, the floating body w i l l exhibit undesirable motions which have been referred to by the industry as horsing, fishtailing, kiting, and '•sailing about at anchor." Significant work related to the offshore o i l industiy documents these yaw instabilities on single point moorings; however, the knowledge base is not very well disseminated outside o f the offshore sector, especially when considering that vessels o f all types are susceptible to this phenomenon.
When the aerodynamic forces dominate the hydrodynamic and mooring forces, no matter the vessel type or configuration, the potential for the undesirable motions to occur exists. With the increased desire for larger interior volumes on vessels, hull and superstructure windages are trending larger and the aerodynamic forces acting on the vessels are becoming more significant, making the phenomenon a more common occurrence.
This paper provides an introductoiy ovei-view to the phenomenon o f yaw instability o f a vessel on a single point mooring, and documents a technical investigation into the phenomenon. The research program conducted consists o f fiiU-scale sea trials, aerodynamic analysis through computational fluid dynamics, numerical simulations, and physical scale model testing. Results o f t h e research program are presented which demonstrate successful replication and mitigation o f the motions.
Motion Control for Small Fast Boats in Following Seas
J.A. (Lex) Keuning
The behavior o f fast and relatively small ships in large following seas has been a serious concern for the operators for a long time now due to the possible occuiTence o f "broaching". Due to the relatively low encounter frequency o f these fast boats with respect to the large and high following and stern quartering seas an intensive coupling between surge, roll and yaw may occur which may finally lead to a capsize o f the boat. The applied (and necessaiy) rudder control using the conventional rudder layout to prevent the excessive yaw motion may even further aggravate the situation.
In an extensive research project the Delft Shiphydromechanics Laboratoiy o f the Delft University o f Technology has constipated, developed, tested and evaluated the application o f a "bow rudder" to control this situation much better . In conjunction with the conventional rudders (or wateijets) at the stern the application o f such a bow rudder yielded a significant (up to 50%) reduction o f the both the yaw and the roll motion in these conditions. Comparative studies o f models with and without such a "bow rudder" in the towing tank showed no tendency to broaching o f t h e boat with bow rudder at all any more. In a later design evolution this bow rudder has evolved into the development o f a "retractable bow rotor", using the well-known Magnus effect as the l i f t (steering) force generator. This made it possible to retract the rotor when it's application was not asked for and thereby eliminating any possible negative effect on the resistance o f the boat.
The results o f earlier studies w i l l be shown i n this publication together with the obtained results o f various towing tank test campaigns carried out to develop the rotor and also some different design concepts. Based on these tests an actual rotor has been build and placed on board a real ship, a D A M E N Stan Pilot 2205, a pilot boat o f circa 22 meters long and capable o f attaining a maximum speed o f 25 knots. Herewith f u l l scale measurement have been carried out at the North Sea and these results w i l l also be presented here. In addition the results o f tests specially o f interest f o r a typical Pilot Boat operation w i l l be shown.
Vertical Accelerations and Surge on a Planing Hull
David Tauber, Carolyn Judge
High-speed planing craft continue to increase in popularity. These craft experience high accelerations when operating at high speeds, even i n relatively minor wave conditions. In the United States Navy, planing craft often operate at high speeds to accommodate mission needs, such as insertion o f Special Forces into hostile areas. Passenger safety and structural integrity are affected by the accelerations experienced. Seakeeping towing tank tests measuring accelerations are generally motivated by structural design considerations or concern for passenger safety. Traditional seakeeping tests tow the model at constant speed, regardless of oscillating slamming loads, and allow the model to move only in heave and pitch. Typically in a planing hull seakeeping test the model is fixed in surge, i.e. restrained from moving backwards and forwards relative to the towing carriage. By contrast, planing boats operating in open water are propelled by constant thrust and forward speed is known to oscillate slightly with each wave slam. A concern for the accelerations measured i n planing model tests is whether the vertical accelei'ations measured are accurate when the freedom to move in surge is restricted. To produce more accurate acceleration data for planing models, a test was completed at the United States Naval Academy examining the effects o f surge on planing hull wave slam accelerations. These tests were completed i n the 380-foot USNA Hydromechanics Laboratoiy using a model with a 4-foot length. The model was tested at a length-based Froude number o f 1.85 in regular waves with a l.I-second period and a wave height o f 2.4-inches. The testing compared a self-propelled model, which was allowed freedom in surge, to a traditional test. The self-propelled model was outfitted with a motor and propeller that ran on a manual feedback system. Velocit)', drag, pitch, heave, surge, and vertical and longitudinal accelerations were recorded. Statistical analysis o f the acceleration data w i l l be presented. Acceleration time histories o f the impacts with and vvithout freedom in surge vvill be compared. Preliminaiy data shows that using a self-propelled towing apparatus produces an increase in the vertical accelerations. Longitudinal accelerations appear to be smaller using the self-propelled rig than from using the locked-in-surge towing method. Suggestions for future testing, including lessons learned, w i l l also be presented.
Wave Height and Planing Hull Wave Slams in Regular Waves
Carolyn Judge, Alexander Mychalowych, Rachel Slater
High-speed planing boats are subject to repeated slamming impacts. These impacts can cause structural damage and discomfort, or even injuiy, to passengers. The motivation for this research is to determine a relationship between wave height and vertical accelerations o f planing crafts. A series o f towed-scale model experiments was conducted in regular waves to capture a sequence of individual impact events. The experiments were conducted i n a 3 80-foot long, 26-foot wide, and 16-foot deep tow tank at the US Naval Academy. Two model scales o f the same geometry were tested at different Froude numbers and over regular waves with different wave heights. Wave height was varied using two methods. The first method was to keep the wavelength constant and increase the wave height. This produced waves with a larger wave slope, as well as the larger wave height. The second method was to keep the wave slope constant, thus increasing the wavelength along with the wave height. Vertical accelerations were measured at three locations (the LCG, the bow near the FP, and a point between the bow and L C G ) . Each wave encounter was treated as an individual slam event. The acceleration time histories were separated into individual impacts. A l l impacts show a general shape. There is strong agreement in the overall shape o f the impact event. The peak vertical accelerations depend on the ratio o f wave height to boat length squared, the square-root of the wave slope, and the boat speed squared. This paper will explain the methodology for separating impacts in regular waves as well as the scaling relationships for peak acceleration magnitudes and f u l l acceleration impact rime histories.
High Deadrise Stepped Cambered Planing Hulls with Hydrofoils,
A Proof of Concept
Stefano Brizzolara, Carolyn Judge, Bill Beaver
This paper intends to to prove that a properly designed swept back Stepped, Cambered Planing H u l l with Hydrofoils (SCPH2) can reduce the drag o f the conventional reference planing hull by a considerable amount (30 percent in model scale). Taking hull 5631 o f the USCG systematic series as a contemporary deep-V reference planing boat, we design a SCPH2 variant, opportunely using computational fluid dynamic techniques to address the uncertainties approximations o f the Clement's method and then tested in the large basin o f the US Naval Academy Hydromechanics lab. We w i l l show the principal hydrodynamics characteristics o f the new hull typology, comparing the large amount o f infonnation obtained from high-fidelity numerical viscous free surface flow simulations with the data measured from the high quality model tests. The measurement o f the drag in free attitude and the underwater photography confirm the results o f the theoretical design study and the predictions made w i t h the numerical model; at the same time the systematic experimental campaign highlights several areas o f potential further improvement o f the technology which are currently under investigation in a new project sponsored by ONR.
Functionality And Safety Of Small Passenger Craft: Some Lessons
Robert G. Latorre, Albert Nazarov
With waterways traditionally presenting the safest or the only possible route o f travel, boats have been used for transportation for centuries along coastal and inland routes. A t present, their significance has decreased due to development o f other transport types, but transportation by small (i.e. with hull length i H ^ 2 4 m ) watercraft is still in high demanded for tourism and recreational activities in many holiday destinations. For remote resorts such as Maldives, islands o f the Andaman Sea, Gulf o f Thailand or coast o f Vietnam, small water craft ( f i g . l ) are by now the only possible means o f transport. Among the tourist boats are traditional local watercraft that evolved without proper engineering (fig.2). ft is an interesting exercise for any boat designer to look at local boat types as a genesis o f perfectly functional and authentic style that suivives in today's mass production. Unfortunately, the lack o f safety regulation and inspection result in many o f these craft being built and operated under lower safety standards.
Investigation of Factors leading to Dynamic Instabilities in High-Speed,
Shallow Draft Boats
Michael Morabito
This paper summarizes portions o f a multi-year collaborative study on the dynamic stability o f high-speed, shallow-draft recreational boats, in which the author has played a small role. These boats are powered by outboard engines, and sometimes fitted with propeller tunnels to permit raising the outboard to reduce draft. Some o f these boats have been known to exhibit a dynamic instability referred to as "swapping ends" or "spinout," in which the boat enters into a moderate turn and then suddenly completes a 180-degree turn in a f e w seconds, pivoting about a location somewhere near the middle o f the boat. During these incidents, occupants sitting in the boat can be ejected and then struck by the boat. Some other shallow-draft, high-speed boats have also been shown to have limited or intermittent helm control, also leading to passenger ejection. The danger o f intermittent controllability is compounded by the lack o f railings, lifelines, or well-defined seating on these boats to prevent ejection.
Physical explanations are provided to describe some o f the steering problems with these boats. It is shown that, while there are mitigation strategies that apply for some boats, such adding skegs to improve directional stability, it is likely that the root cause o f the problems is the intennittent ventilation o f the outboard engine lower unit, which results in large instantaneous changes i n force, taking operators by surprise. Existing testing protocol, developed by the American Boat and Yacht Council, is discussed, which, i f followed, could allow manufacturers to identify potential problems before boats go into seivice. Some suggestions are also provided on means to keep operators inside the boat, without compromising the mission capabilities o f the boats.
On The Hydrodynamics O f T h e Wedge And Transonic Hulls
Alberto Calderon, Brian Maskew
Papers presented in recent FAST conferences and prior reports by CISD (the US Navy's Center for Innovation in Ship Design) have made available interesting information o f a new hull t}'pe denominated "Wedge". A statement i n the latest such paper presented at FAST 2015 by L . Wang et al (Ref 1) merits special consideration: "Therefore it is extremely important to investigate and
optimize the hydrodynamic performance o f this non-conventional ship because o f its promising features and unknown flow characteristics."
Part I I presents a review o f t h e wave making characteristics o f three vessels: (i) a Transonic Hull (TH) designed by A. Calderon o f Transonic Hull Company (THC), ( i i ) a Transonic Hull imitation denominated Wedge, designed by Navy CISD with a blunt lower bow and lower length/beam ratio, and (iii) the Bulbed Wedge, a modified Wedge with a large bow bulb designed at Davidson Laboratory o f Stevens Institute.
A Comparison of Whole-Body Vibration and Shock Response
Spectra Parameters for Quantifying Mitigation Characteristics of
Marine Shock Isolation Seats
Michael Riley, Timothy Coats, H.C. Neil Ganey
This paper presents an analysis o f t h e applicability o f the vibration dose value ( V D V ) as a perfonnance measure in single-impact laboratoiy testing o f shock isolation seats. Acceleration data for individual wave slam events recorded on a shock isolation seat i n a high-speed craft is used to compare the efficacy of the candidate V D V performance measure with a shock response spectra (SRS) performance measure. SRS and V D V numerical methods are described, computational results are summarized, and conclusions are presented.
Fatigue Life Analysis of the US Coast Guard's 47 Motor Life Boat
Vincent Wickenheiser, Karl Stambaugh
The Surface Forces Logistics Center's Naval Architecture Section was tasked to review the operational history and conditions o f the US Coast Guard's 47 M L B s and determine i f they w i l l have sufficient remaining hull structural fatigue life to extend their service life to 50 years as part o f a business case analysis. In this process, a fatigue analysis approach was developed to provide guidance to support a feasibility level decision.
Fatigue analysis o f small craft is not common and the Naval Architecture Section developed a relatively quick and easy method for performing the analysis. The analysis utilized regional wave buoy information, operation profiles, operating hours from Coast Guard databases, ABS and Savitsky methods for predicting pressure and slamming loads, and simple finite element models to predict the structural response. A n approach is presented to infer long term loading history using the statistical relationships o f the Rayleigh statistics and operational wave conditions. In this analysis, the boats were categorized into three different operating regions. East Coast, West Coast, and Great Lakes based on differences in wave environment and ftirther subdivided based on a number o f annual operating hours. Results o f the analysis indicate that the 47 M L B s w i l l have a fatigue life o f over 25 years from deliveiy; however, approximately one third o f the 47 M L B s w i l l develop fatigue cracks before 50 years o f seivice based on current utilization rates. Recommendations are provided to evenly distributing the hours o f operation within districts and by home port rotations between different regions on a 10 to 15 year rotation cycle. I f f u l l y implemented by the operators and maintainers, this approach would extend the hull structure seivice life o f all o f the 47 M L B s to 50 years without requiring structural modifications.
Some Notes on Aluminum Small Craft Design and Construction
Christopher Barry
Aluminum is a commonly used material for powerboats, especially military and commercial craft. It is also possibly the most common material for recreational boats under 18 feet or so and is well proven i n this sei-vice, though the design and construction techniques o f these small, light mass-produced craft is different in many respects to that o f larger heavier welded craft.
The advent o f computerized design and cutting has greatly reduced the cost o f aluminum construction such that in certain applications aluminum construction is cost effective on a limited production or custom basis as well as for series production, and that is the reason why aluminum one-off boats are common in commercial sei-vice. I have accumulated a range o f more or less random information on the design and construction of these boats, mainly in the 20-65 foot range, for commercial and military use. None of this information is particularly novel, but it may be useful to other designers. I also have to confess to a substantial degree o f self-plagiarization; much o f t h i s paper is gathered from other papers or articles covering specific topics that I wanted to bring together and correlate.
State ofthe Art in Aluminum Work Boat Design and Construction
Lou Codega, James Codega, Jason Powers
(Presentation)
Many people who are not involved with aluminum work boats think that the industry consists mainly of tiny builders working in poorly equipped shops using outdated techniques. This could not be further from the truth. In this presentation, aimed at those not familiar with this side o f t h e industiy, w e ' l l explore the design and construction processes used by a modern small boat yard. From 3d modeling to N C cut parts to intricate self-jigging assemblies, the methods used i n many small boat yards are veiy similar to those used in sophisticated ship yards. The results are small craft that are not only quite sophisticated and very economical to produce, but are veiy easily customized to exactly suit end-users needs.
The Mystery of Sinkage and Trim for High Performance Craft
A. Steven Toby
For more than a centuiy, displacement ships have been able to exceed "hull speed," the natural speed o f a wave the same length as the ship, or a Froude number based on length o f 0.40. That ability evolved in a time frame
approximately coiTesponding to the American Civil War or slightly afterwards, and featured changes in hull form to reduce the pressure changes that trigger a ship's bow wave, as well as a general elongation o f t h e hull form to reduce the curves flow must follow around the hull. Both these changes reduced the Bernoulli pressure differentials that trigger a ship's wave resistance and form drag.
These same pressure differentials tend to suck the hull down into the water as it approaches hull speed. H u l l form features can affect the running trim angle at these speeds in several ways as well. One might suppose that sinkage and trim, therefore, would be somewhat correlated with ship resistance, and the slender hull f o m s developed for low resistance would therefore sink and trim less, or at least differently. However, this turns out to be incorrect. Because the forces o f resistance on the one hand, and sinkage and trim on the other, are directed at right angles to each other, they are almost independent. This paper illustrates their relationships through analysis o f model tests o f a
An Oblique 2D+T Approach for Hydrodynamic Modeling of
Yawed Planing Boats in Calm Water
Sasan Tavakoli, Abbas Dashtimanesh, Prasanta Sahoo
Determination o f forces acting on planing hulls in maneuvering has been turned into an interesting problem during the last decade. Different methods, based on mathematical or empirical approaches, are elicited in order to compute hydrodynamic forces and moments acting on the boat in different simplified conditions such as steady yawed or heeled conditions. Modeling o f different conditions and combining them with each other may lead to initiate a final simulation model for 6 D 0 F motion o f planing boats i n calm water. These simple modeling approaches, in the other word, can be considered as basics o f a final 6 D 0 F model. Current paper address hydrodynamic modeling o f yawed motion for hard-chine planing boats in calm water.
The current research paper is primarily focused on determination o f horizontal force and yaw moment acting on the boat as is moves forward in steady yawed condition. The derivation approach is based on mathematical formulation of 2D+T theory and added mass variation in longitudinal direction. Virtual mass o f a wedge in horizontal direction is analytically found and then the final force and moments are computed using extension o f sectional forces, acted on wedge section o f t h e boat, over entire wetted length o f the vessel. The precision o f the proposed model is verified by comparing the computational values against previous experimental data o f Brown and Klosienki (1994a, b) and Morabito (2015). A n improvement for the model has been considered to conquer some o f the drawbacks reported by previous researchers. The comparison exhibits an improvement o f the model, the increase in added mass which was previously discussed by Moabito (2015) can be seen. Also it is obseived that in the case that the wetted length o f t h e boat is small, the transom reduction works well and leads to an accurate prediction o f sway force. Finally, it is viewed that the computed yaw moment are in a fair agreement with previous expei-imental data.
Investigation Of "Unsteady" Method For Model Calmwater Performance
Uihoon Chung, Raju Datla
The purpose o f t h i s shidy is to investigate and validate "unsteady" model testing method for calmwater performance evaluation. Model tests for calmwater resistance are typically performed at a set o f discrete constant speed runs where the relevant parameters are measured and averaged over a steady speed data window ofeach run. However, a test matrix can become substantially large when required number o f speeds, loads and hull configurations increase. In this study, an "unsteady" method was investigated where the model was towed accelerating slowly and covering the f u l l speed range o f interest in a single run. The forces due to inertial mass and added mass were subtracted from the measured unsteady resistance data and compared with data from standard calmwater constant speed experiments. Steady constant speed runs were conducted in calmwater over a range o f Froude numbers between 0.08 and 0.55. The "unsteady" tests were conducted in calmwater over the speed range using four different accelerations o f O.I, 0.15, 0.2 and 0.3 ft/s2. Runs were conducted in air at these accelerations to determine inertial forces, and a value o f 0.1 was assumed for surge added mass coefficient. The results showed that the unsteady method compares well with the standard constant speed method.
Neural Network parametric model for trimaran hulls
Richard Royce, Patrick!. Doherty
The location of trimaran side-hulls (amas) plays an important role in the wave-making resistance o f the vessel. Constructive and destructive wave interference occurs between the hulls that either augments or reduces the wave-making resistance o f t h e vessel. In a FAST 2011 paper (Royce et al, 2011) the author presented an Artificial Neural Network ( A N N ) model for trimaran resistance based on numerous tests conducted at Webb Institute's Robinson Model Basin over a two year period. The speed range covers Froude numbers from 0.12 - 0.5. This data is thought to be one o f the most comprehensive sets o f test data on side-hull placement for a single model.
In order to further evaluate the validity o f the trimaran A N N , contour plots of the resistance were developed. The global minimum and maximums were determined for the domain covered by the model at a Froude number o f 0.35. Experiments were then conducted at these two locations to compare with the predictions from the empirical model. The results o f t h e experiments show that the A N N model tends to under-predict the resistance for the best case and over-predicts the worst case. This work demonstrates importance o f the number o f hidden neurons, much like the order of polynomials used in least square regressions.
