Chesapeake Power Boat Symposium

The Effect of Bottom Warp on the Performance of Planing Hulls
Daniel Savitsky, Professor Emeritus, Davidson Laboratory, Stevens Institute of Technology, Hoboken, NJ

The hydrodynamic lift, wetted area and center of pressure of a constant beam, warped bottom planing surface were obtained experimentally for a model having a 3 deg./beam increase of deadrise from 10 deg. at the transom to 30 deg at the stem (typical for the planing area of a warped hull). Towing tank tests of this warped bottom hull were conducted over a wide range of speeds, trim angles and wetted lengths.

An analysis of the data indicated that established planing equations for prismatic hulls are also suitable for this warped hull if the effective deadrise of the warped hull is taken to be that at the mean wetted length of the bottom area. Also, the effective trim angle is not the keel angle relative to the level water surface but is the angle of the ¼ buttock line (at the mean wetted length position) relative to the level water surface.

Published equations for prismatic planing hulls have shown that the longitudinal position of the mean wetted length (relative to the transom) is a known function of the longitudinal position of the center of bottom pressure and the speed coefficient. It is independent of trim angle or deadrise angle. Hence, assuming that the LCG of the craft is located at the longitudinal center of pressure and the thrust moment is small, the mean wetted length is easily determined. Locating this distance on the lines plan of a warped hull identifies the effective deadrise and trim angle of an equivalent prismatic hull to be used with published planing equations. Using these observations, a procedure is provided for estimating the smooth water performance of warped planing hulls. Two examples are provided and show that the analytical results agree with model data obtained at the Davidson Laboratory. Also, a comparison in made with model data obtained at MARIN on tests of a 70 ft. long warped planing hull and show equally good correlation.

If the reference deadrise angle is taken to be that at the transom, it is shown that the use of warp in the planing area deteriorates the planing efficiency of the hull.

Evaluation of High-Speed Craft Designs for Operations in Survival Conditions
Frank DeBord, USCG Surface Forces Logistics Center, Baltimore, MD
Karl Stambaugh, USCG Surface Forces Logistics Center, Baltimore, MD
Chris Barry, USCG Surface Forces Logistics Center, Baltimore, MD
Todd Hiller, USCG Surface Forces Logistics Center, Baltimore, MD
Kirk Torstenson, USCG Surface Forces Logistics Center, Baltimore, MD
Vincent Wickenheiser, USCG Surface Forces Logistics Center, Baltimore, MD
Eric Schmid, USCG Surface Forces Logistics Center, Baltimore, MD 

Designs for high-speed planing craft are typically driven by performance on plane in operating sea conditions.  These conditions govern the principal characteristics, installed power, structural design and design features related to seakeeping and handling.  When these high-speed craft are operated for military, law enforcement or search and rescue missions, performance and safety in severe seas at low speed can become issues and should be considered during design.  This paper discusses the issues related to operations in these survival conditions and provides examples of performance analyses related to the following issues:

For each of these aspects of performance, analysis methodologies are discussed and typical results are provided.  Methods for comparing risks associated with operations in various sea conditions are developed and recommendations are formulated for definition of limiting conditions.  Finally, areas where typical design practices are found to be deficient related to these survival operations are identified and discussed.

A Look at the Impact of Filter Selection on Peak Identification of High Speed Craft Vertical Accelerations
Leigh McCue, Virginia Tech, Department of Aerospace and Ocean Engineering, Blacksburg, VA
Charlie Weil, NSWC Carderock, Combatant Craft Division, Norfolk, VA
Kelly Haupt, NSWC Carderock, Combatant Craft Division, Norfolk, VA
John Zseleczky, United States Naval Academy, Hydromechanics Lab, Annapolis, MD
Don Jacobson, NSWC Carderock, Combatant Craft Division, Norfolk, VA
Michael Riley, The Columbia Group, NSWCCD Det Norfolk, VA
Dr. Tim Coats, NSWC Carderock, Combatant Craft Division, Norfolk, VA

This study was motivated by the desire to rapidly identify Types Alpha, Bravo, and Charlie slam events as defined in Riley et al, (2010a), in an automated manner. A numerical code was written to identify Alpha, Bravo, and Charlie events using search parameters to find free fall events and longitudinal peaks in the vicinity of a slam. The specific procedure follows the “Standard g” approach (Riley et al, 2010b), which includes filtering of acceleration data. In the process of attempting to optimize selection of search parameters for slam identification, it was found that the choice of filter had a substantial influence on successful characterization. For example, ringing artifacts, Gibbs phenomena, can introduce oscillation into the time history as well as increase the peak value (Wikipedia, 2011). The nature of the Gibbs phenomena makes it of particular relevance when filtering impulse-like signals for which the phenomena is most pronounced. Of specific relevance in this study, these ringing artifacts can induce zero crossings, which may result in false identification of a longitudinal acceleration leading to Type Alpha characterization when the event was indeed a Type Bravo event. The oscillations may also adversely affect the ability to identify freefall robustly. Gibbs phenomena result in a tradeoff with the abruptness of cutoff and ringing artifacts; a wider transition region yields less ringing whereas if an abrupt frequency truncation is desired, ringing is more pronounced (National Instruments, 2003).

The goal of this study is to lend insight into the effects filter selection can have on data analysis and highlight our need to exercise diligent caution in our selection of filter. The information in this study may help provide the basis for thorough justification of filter selection for impulsive events such as slamming, conscious of the implications of Gibbs phenomena and/or other filtering artifacts in the analysis of data. In classing Type Alpha, Bravo, and Charlie events we are looking for physical characteristics, therefore it is of the utmost importance that filter selection not inadvertently introduce what might be mistaken either by the eye or by an algorithm to be a physical result. This paper will provide details of the filtering study conducted along with recommendations for future work.

Static and Dynamic Forces and Wetted Lengths for a Planing Hull Model Forced in Roll
Carolyn Q. Judge, United States Naval Academy, Annapolis, MD

An experimental program at the United States Naval Academy has been designed to investigate the transverse plane stability of planing hulls. An experimental mechanism to force a planing hull model in roll motion was designed and built. The first model tested was a wooden prismatic planing hull with a constant deadrise of 20^o, a beam of 1.47 ft (0.45 m), and a total length of 5 ft (1.52 m). The model was forced in roll while fixed in pitch, heave, sway, yaw and surge. The tests were done at three model speeds and two displacements at three roll amplitudes and four oscillation frequencies. In addition to the dynamic tests, the model was run at the same model speeds and displacements while held fixed in roll at seven heel angles between 0^o and 25^o. For both the dynamic and static roll conditions the heave and sway forces, along with the roll moment, were measured and underwater photography was taken. This paper will explore how the heave and sway forces depend on heel angle and roll amplitude as well as how the wetted lengths (keel and chine) vary between the static and the dynamic roll conditions.

Modeling of Vertical-Plane Motions of Tunnel Hulls
Christopher Chaney, School of Mechanical and Materials Engineering, Washington State University, Pullman, WA
Konstantin I. Matveev, School of Mechanical and Materials Engineering, Washington State University, Pullman, WA

Tunnel hull boats are among the fastest waterborne vehicles capable of achieving speeds up to 150 knots. A tunnel hull configuration consists of a platform and two side hulls. The weight of this craft is supported mainly by hydrodynamic forces on hulls and aerodynamic force on the platform. Utilization of aerodynamic support usually improves the boat lift-drag ratio. However, it also leads to deterioration of stability characteristics. Frequent crashes of high-speed boats, including tunnel hulls, show importance of the stability issues. In this study, a mathematical model is developed for vertical-plane motions of tunnel hulls. Nonlinear formulations of the added-mass strip theory and extreme ground effect theory account for unsteady hydrodynamic and aerodynamic forces, respectively. The influence of the system geometrical and loading parameters on transitions to unstable regimes will be shown. Simulations of unsteady motions, such as responses to wind gusts and behavior in waves, will be also demonstrated. The developed mathematical model can be applied for design of a variety of fast boats with aerodynamic support.

A Simplified Approach for Analyzing Rigid Body Accelerations Induced by Wave Impacts in High-Speed Planing Craft
Michael Riley, The Columbia Group, NSWCCD Det Norfolk, VA

This paper presents a simplified approach for analyzing acceleration data recorded in high-speed planing craft in waves. These motions are of interest because a broader awareness and a better understanding of cause and effect physical relationships in high speed wave impacts could be applied in craft design or comparative craft system evaluations to address multiple factors associated with seaworthiness, including hull design loads, stability, component ruggedness, and crew or passenger comfort and safety.

The paper builds on lessons learned from historical analysis methods that transition the randomness of ocean waves and full-scale trials data to useful peak acceleration values. The root- mean-square acceleration value is explained, and a new unambiguous procedure for estimating the average of the 1/Nth highest peak acceleration and the average of the 1/Nth highest change in velocity caused by wave impacts is discussed. Example applications are presented that illustrate how the method can be applied in assessing electronic equipment ruggedness, estimating impact load factors for hull design, evaluating shock mitigation seats, or evaluating parameters that affect ride severity under different operating conditions.

The limitations of the new analysis approaches are summarized, and a new deterministic analysis methodology is presented that characterizes the rigid-body responses of the craft in terms of acceleration, velocity, displacement, and rotation motions during each wave impact event. The results demonstrate that vertical rigid-body acceleration responses in planing hulls vary linearly with impact severity. 

It is envisioned that the new analysis methods presented in this paper could help researchers, designers, engineers, builders, and operators increase their awareness and understanding of the dynamics of high-speed wave impacts in planing hulls.  The increased awareness and understanding could have broad applications for improved standard processes, including structural design, correlation with computational modeling and simulation methodologies, correlation of full-scale and scale-model test data, comparative evaluations of different craft, and development of criteria for improved ruggedness and personnel comfort and safety.

Measurement of Maneuvering Motion and Hydrodynamic Forces of a Planing Craft for Validation of a Maneuvering Motion Simulation in Model Scale
Toru Katayama, Graduate School of Engineering, Osaka Prefecture University, Osaka, Japan
Tsubasa Hashimoto, Graduate School of Engineering, Osaka Prefecture University, Osaka, Japan
Akihiko Matsuda, National Research Institute of Fisheries Engineering, Ibaraki, Japan

In previous study, test data of a real craft are used for validation of a maneuvering motion simulation, but they usually contain some disturbances caused by waves and winds etc.  In this study, in order to take maneuvering motion data without any disturbances for variation of a maneuvering motion simulation, a small radio controlled planing hull model is developed and its maneuvering motion is measured at National Research Institute of Fisheries Engineering.  Motion measurement is carried out with and without waves, to investigate the effects of waves on its motion.  Moreover, maneuvering hydrodynamic forces, thrust force and rudder force are also measured at Osaka Prefecture University, and a maneuvering motion simulation results are compared with measured results to improve its accuracy.

Design, Construction and Testing of the Advanced Composite Riverine Craft
Tony Caiazzo, Materials Sciences Corporation, Horsham, PA
Sid Charbonnet, Seemann Composites, Inc., Gulfport, MS
Lou Codega, Naval Architect, Smithfield, VA 

Seemann Composites, Inc. was awarded a series of contracts that allowed it to research, design, build and test a craft that virtually re-writes how riverine warfare craft are built. While the program was focused on this specific mission, the results of have wide reaching implications for all composite craft.

The initial goal of the Advanced Composite Riverine Craft program was to develop a hull material and construction technique that would have the toughness and damage tolerance of conventional aluminum but would offer the advantages of significant weight reduction and elimination of the permanent deformation inherent in a metal structure.

The team undertook an extensive analysis and materials test program to develop a bottom laminate specification to meet these goals. This laminate was incorporated into a hull bottom concept that was essentially unsupported by secondary structure. A craft was then designed around this bottom specification, with minimal artificial constraints placed on the design. The result was an innovative, fully operational 43-foot long fiber reinforced plastic craft that was powered by twin diesel engines and waterjets and had a top speed of over 45 knots. To conclude the program, the ACRC was impact tested to demonstrate that the original design goals of light structural weight and high damage tolerance were indeed met.

Composite Construction for Affordable Limited Production Boats; Not What You Might Think
Christopher D. Barry, USCG Surface Forces Logistics Center, Baltimore, MD

One problem for high performance yachts is to produce a light enough, strong enough structure. This is possible with modern composite construction, but at substantial cost to produce the molds. Thus, composites are difficult for limited or amateur construction. However, the term “composite” means a combination of any two different materials. Prior to advent of fiberglass, “composite construction” meant a combination of wood and metal, generally wood planks and perhaps primary framing over steel or aluminum secondary framing and other heavy structure.

This type of composite construction enjoyed a limited short renaissance in the early 80’s (for high performance sailing yachts), due to the popularity and high performance potential of one-off cold molded wood construction.

Simultaneously, it was hoped that CAD and CNC technology would help to revive wood boatbuilding. The wooden U.S. Navy MSH class in the 80’s implemented considerable CNC construction technology but much of the most involved labor on a wooden craft is on heavy internal structure, which requires six axis cutting, with equipment too expensive for widespread use. Another issue is the difficulty of finding (or laminating) heavy timbers for main structural members such as keels.

The combination of three axis CNC cutting and the use of metal for heavier structure offers solutions to these problems. The major framing is cut out of metal by plasma arc, water jet or laser cutters. The wood shell is made by strip planking, cold molding, or a combination; carvel or lap strake planking, or most appropriate for planing craft, plywood. Especially in the last case, planks or shell “plating” can be CNC cut as well, providing substantial reductions in labor for a one-off or limited production boat compared to either making a mold for a fiberglass boat or for traditional wood construction. This technique is also amenable to sustainable wood resources, and of course, metals are generally from recycled sources and readily recyclable. This process also is easy for amateur builders because the metal and wood can be precut as a kit. This technique provides as good structural performance as any system except the most exotic cored carbon fiber or Kevlar systems at sizes from as small as six or seven meters to 30 meters or so, especially for hard chine, developable plywood hull forms.

The paper examines the structural performance of composite construction; variations of this technique; optimization of structural performance by setting the wood/metal transition; materials, fasteners and adhesives; and specific details, tools and techniques for CAD lofting, design and construction.

Practical Application of Interceptors on a Small Non-Planing Powerboat
Ron Grifka
Todd M. Hiller, U.S. Coast Guard, Baltimore, MD

Ron Grifka purchased a surplus U.S. Coast Guard 26 foot Motor Surf Boat (MSB). The MSB’s performance was compromised due to excessive trim associated with the hull form. With full buttocks forward, rounded stern and rudder placement, adjustable trim tabs were not considered to be a practical option.

Traditionally small powerboats use trim tabs to adjust trim angle. This has worked well, most of the time, for both planning and semi-planing boats. Trim tabs have for the most part been installed at the outboard corners of the transom below the design waterline. This placement is often dictated because outboard motor(s), rudder(s) and configuration of the underwater planing surface would preclude any other location.

Interceptors, wedges and stern flaps have been installed on larger boats and ships and have been for the most part been installed in the middle half or two thirds of the stern avoiding the corners and the associated wake. Interceptors, wedges, stern flaps and combinations of these have been individually designed, tank tested and sea trialed to determine the size and placement of the appendage. There is a body of knowledge with respect to the use of wedges and flaps on ships and larger power boats. There is also a study of these methods on a simple fishing boat comparing interceptors to a wedge.

What is of special interest in this case is the rounded stern of the vessel and the relatively low speed (under 15 knots) of the MSB, both of which are unusual in the application of interceptors. Despite these unusual aspects of this case, the interceptors produced significant favorable reduction in trim resulting in improved dynamic stability, improved fuel economy and increased speed. However, the reduced trim has resulted in a regime of operation of potential bow down dynamic instability at higher speeds, and heavier loads forward.

This paper discusses the design, installation and tests of an interceptor on a 26 foot MSB. Tests were performed and data gathered during this project was shared with the U.S. Coast Guard. The USCG subsequently conducted tests with nearly a full capacity of passengers to verify the improvements and determine the speed/load range of bow own instability.

M Ship’s Rapid Empirical Innovation (REI) Open Water Model Test Platform
William Burns, M Ship Company, LLC, San Diego, CA
T.J. Perrotti, M Ship Company, LLC, San Diego, CA
Chris Todter, Keppel Professional Services, San Diego, CA
Daniel Casal, M Ship Company, LLC, San Diego, CA
Johnny Smullen, M Ship Company, LLC, San Diego, CA
John G. Hoyt, Naval Surface Warfare Center, Bethesda, MD

M Ship Co. has developed an innovative Rapid Empirical Innovation (REI) approach to open-water ship model testing with the goal of providing a system targeted towards rapid, low cost ship design. The system is designed to provide test data quality close to that of a towing tank, at a substantially lower cost. It is capable of both smooth water drag and trim measurement as well as rough water drag and motions assessment, comparable to towing tank measurements. After developing, testing, and refining the testing platform, and its systems, a series of arbitrary models (including the classic Series 62 model) of widely varying concepts were designed, produced, and tested using the REI system. This process consisted of an extensive set of smooth water, and rough water tests to characterize the models as well as the testing platform. The final phase of the program was validation, by taking three of the models (including the historically tested Series 62 model) to the NSWCCD David Taylor Model Basin (DTMB) for both smooth and rough water testing so comparisons could be made between the towing tank data (DTMB) and the REI system. All phases of platform development and data quality investigation were successfully completed in 2011.  Our report will summarize M Ship’s testing methodology and comparative results.

Turning Characteristics and Capabilities of High-Speed Monohulls
Jeffrey Bowles, Donald L. Blount & Associates, Chesapeake, VA

The turning characteristics and capabilities of displacement vessels are well understood and documented.  Standards for the maneuvering capability of displacement vessel exist.  However, the same information regarding high speed craft is not so readily available.  Most documents available in the public domain contain information on what high speed craft shouldn’t be able to do, not what they should be able to do.  

This paper examines various aspects of the turning capabilities and characteristics of high speed monohull craft with regard to typical behavior and what type of maneuvering performance should be achievable.  Notional maneuvering criteria are proposed.  The dynamics, characteristics, and relationships of a hard chine monohull in a high speed turn are investigated and summarized. 

The execution of high speed turns on hard chine monohulls can sometimes lead to unexpected responses.  This paper identifies several of the typical symptoms.  The severity of these events will be discussed and their typical causes are discussed.  

On Application of Parametric Method for Design of Planing Craft
Albert Nazarov, Albatross Marine Design Co., Ltd, Chonburi, Thailand

Paper describes features of parametric method based on combined analysis of main dimensions and volumes, weight components, performance and range predictions, seakeeping and construction cost of planing craft. Method is derived from statistics of designs of special, pleasure and small commercial monohull craft with hull length below 30m, developed by Albatross Marine Design. Dimensions of hull are defined form usable areas and essential volumes, with recommendations provided for different architectural types of boats. Equations are proposed for weight groups based on hull dimensions, horsepower, type of propulsion system, level of accommodations and furnishing, required payload, etc. Approaches for preliminary estimate of powering, range, fuel efficiency, ride stability are provided. Method proved to be efficient tool for design analysis, optimization and feasibility check of design requirements. Case studies are presented illustrating application of parametric approach for different designs.

Development of Empirical Equations for Planing Craft Motions in Irregular Waves through Genetic Algorithms
Eric Giesberg, Stevens Institute of Technology, Hoboken, NJ
Raju Datla, Stevens Institute of Technology, Hoboken, NJ

The quick prediction of planing boat performance in irregular waves is useful for quickly verifying concept designs and for seeing the effects of speed, wave height and various geometric parameters on motions. Simple, but fairly accurate for initial design, empirical equations currently only exist for estimating vertical accelerations and added resistance but not for heave and pitch motions. The present paper studies the effect of planing boat parameters, speed and wave height on the resulting motions and accelerations. Genetic algorithms are used in order to help develop an empirical method. Data sets were taken from prismatic model tests by Fridsma(1971) and Brown (1980); and a free software tool, Eureqa, was used to generate several equations for heave, pitch, accelerations at CG and bow. The equations were narrowed down by hand picking and looking at trend graphs, and final equations were selected on the basis of simplicity, accuracy and physical correctness. The accuracy of the newly generated equation was then compared against the existing methods, Fridsma's charts for heave and pitch and Savitsky's empirical equations for accelerations. Additional validation is performed using model results from Coast Guard 47 ft MLB standard series and a few other newer hullforms tested in the Davidson lab.

Numerical Simulation of Planing Hull Hydrodynamics
Romain Garo, Stevens Institute of Technology, Hoboken, NJ
Raju Datla, Stevens Institute of Technology, Hoboken, NJ
Len Imas, Stevens Institute of Technology, Hoboken, NJ

Planing hull performance in calmwater was modeled numerically using the FineMarine finite volume-based Navier-Stokes solver with a free-surface capturing algorithm and a RANS turbulence model.  The applied free-surface capturing method uses a compressive discretization scheme with interface reconstruction which permits for robust resolution of the density discontinuity between air and water thereby allowing for the study of spray break-up in the context of spray rail design and placement, for example, which is particularly relevant in planing hull hydrodynamics.

A USCG 47 ft motor life boat design was used as the geometry in this study. The results were compared against 1/8th scale model test results, obtained from towing tank studies conducted on the same geometry at the Davidson Laboratory. Figure 1 shows a comparison of the wetted surface between numerical simulation and underwater photographs from the model tests. Figure 2 shows a comparison between numerical simulation and experimental measurements of resistance at 3 different speed-length-ratios, Vk/√L. The ongoing study is currently being extended to the investigation of stepped planing hull hydrodynamics.

Behind the Scenes of Peak Acceleration Measurements
John Zseleczky, U.S. Naval Academy Hydromechanics Lab, Annapolis, MD

Several excellent papers have been written recently regarding methods for analyzing acceleration measurements made on high speed craft (see Refs).  In these papers and most test reports it is assumed that the reader is familiar with the terms and concepts involved in measuring, sampling and recording acceleration values.  The focus is rightly on the more advanced subjects of data analysis and statistics.  The intent of this paper is to flesh out some of the details that are usually not reported about what goes on before analysis.   The information presented here may be considered overly basic by some electronics or computer experts.  But this part of the process is not understood by many naval architects who have a vested interest in the outcome of acceleration measurements and could benefit from an understanding of subtleties that lie beneath the surface.

Electronic sensors, filters and data acquisition equipment for these measurements have changed dramatically over the years and will continue to do so but the end goal remains the same: to obtain repeatable, accurate representations of accelerations experienced on high speed craft.  The seemingly simple goal of obtaining repeatable measurements will be elusive unless the details of the measurement process are understood and well documented. 

The data collected by Fridsma in 1971 is used as a cornerstone for seakeeping predictions of high speed craft.  These test results have served the design community well with many proven hull designs based directly or indirectly on them.  In developing new analysis methods using new capabilities it would be wise to use these data sets as a bench mark to be sure that new measurements are not leading us astray. 

The figure below shows a schematic of the steps involved in obtaining peak acceleration statistics for a high speed craft as the process is likely to be conducted in 2012.  The process is similar for full scale trials and model scale measurements in the laboratory, starting with the physical acceleration of the craft and ending with a statistical representation of the magnitude and quantity of the positive acceleration peaks.  It has become more common to measure accelerations along multiple axes but the measurement process is similar for each.  To avoid duplication, only vertical accelerations in the body axis are discussed.

A Method for Computing Wave-Impact Equivalent Static Accelerations for Use in Planing Craft Hull Design
Michael Riley, The Columbia Group, NSWCCD Det Norfolk, VA

This paper presents preliminary results of an Office of Naval Research grant to investigate the development of simple design tools that support hull design for planing craft. The results include the development a new equation for estimating the equivalent static acceleration, or equivalent static-G (ESG), that characterizes the vertical acceleration response of small craft to wave impacts. The equivalent static acceleration is important because it is used in current procedures for designing craft hull bottom plating, but it has been an elusive parameter often left to the designer to determine whether it is derived from scale-model data, full-scale data, or computer simulations. The paper presents a rationale explanation for what has been referred to in the past as the most difficult and controversial input in the hull design process.

The paper summarizes lessons learned from historical developments including the simplifying assumptions that transitioned complex dynamic loading phenomena into a set of tractable design equations. Newly developed assumptions that align craft rigid body mechanics and structural dynamics are presented as part of the analysis approach, and frequency ranges of interest for the hull structure are discussed. The shock response spectrum for a half-sine acceleration pulse is introduced as a useful tool to demonstrate the equivalent static characteristics of the new ESG parameter.

The paper presents comparisons of the new ESG with accelerations and design limits recommended by the American Bureau of Shipping for high speed craft. Preliminary analyses of full-scale trials data are shown to illustrate the degree of correlation.

It is envisioned that the approach presented in this paper will be subjected to substantial review and assessment within the craft design community, but regardless of the time involved, the intent is to stimulate further discussion, sharing of information, and eventual adaptation and adoption of improved design methods. For example, an interesting aspect of the derivation presented in this paper is the relationship of the ESG to the vertical change in rigid body velocity caused by a wave impact. This relationship is demonstrated using full-scale trials data, and recommendations are presented for further studies to investigate the potential use of the velocity term in future design tool adaptations.

An Experimental Analysis of the Effects of Steps on High Speed Planing Boat
Gregory J. White, Naval Academy Hydromechanics Laboratory, Annapolis, MD
William E. Beaver, Naval Academy Hydromechanics Laboratory, Annapolis, MD

This paper reports on a model testing program conducted in the 380’ towing tank at the Naval Academy Hydromechanics Laboratory (NAHL) exploring the effects of transverse steps on planing boat performance.  The motivation for the testing program was an earlier program carried out by ENS. William Garland, USN, under the supervision of the authors, as a part of his senior independent research course.  The results from ENS. Garland’s testing showed great promise for the military application of steps in planning hulls.  However, anytime a technology is introduced to improve some aspect of performance there always seems to be a penalty paid in some other aspect.  The testing program discussed in this paper intended to answer three questions about the introduction of steps on a typical high-speed:

1.     1.  Can a powering improvement be attained on a typical high-speed military planing boat by introducing steps in the after part of the planing surface?

2.     2.  Does the presence of steps detrimentally impact the ride quality and motions of a typical high-speed military planing boat?

3.     3.  If the answer to #2 is yes, is there a means of combining steps with some other technology to reduce the detrimental impact of the steps.

The model used for this program was a 1/10 scale version of a generic 53 ft high-speed deep-vee planning hull with three longitudinal spray strakes.  The model was made so that two transverse steps could be introduced in the aft part of the planning surface.  Each step could be configure to be from 0 to one inch deep in increments of ¼ in (and in some cases in 1/8 inch increments).  The model was run in both still water and short-crested irregular seas.  A total of 142 separate test runs were conducted at a displacement equal to 44000 lbs for the full scale boat.  A systematic variation of LCG location, speeds, and trim control were used to try to answer the above questions.  Vertical acceleration, running trim, CG rise, and drag data were recorded as well as above water video and underwater photographs.  The short take on the answers to the questions are:

1.     1.  Yes.  But the steps result in dramatically increased running trim.

2.     2.  Yes.  The vertical accelerations in the boat in short-crested seas also increase dramatically, but mostly due to the increased running trim

3.     3.  Yes.  Several approaches are considered and reported on.  The most promising appears to be combining steps with an outdrive and surface piercing propellers

A Detailed Validation of Numerical Flow Analysis (NFA) to Predict the Hydrodynamics of a Deep-V Planing Hull
T. T. O’Shea, SAIC, San Diego, CA
T. C. Fu, Naval Surface Warfare Center, Carderock Division, Bethesda, MD
D. G. Dommermuth, SAIC, San Diego, CA
K. Brucker, SAIC, San Diego, CA
D. C. Wyatt, SAIC, San Diego, CA

Over the past few years much progress has been made in Computational Fluid Dynamics (CFD) in its ability to accurately simulate the hydrodynamics associated with a deep-V monohull planing craft, see (Fu et al, 2010; Broglio & Iafarati, 2010; Fu et al 2011).  This work has focused on predicting the hydrodynamic forces and moments, but also the complex multiphase free-surface flow field generated by a deep-V monohull planing boat at high Froude numbers.  One of these state of the art CFD codes is Numerical Flow Analysis (NFA).  NFA provides turnkey capabilities to model breaking waves around a ship, including both plunging and spilling breaking waves, the formation of spray, and the entrainment of air. NFA uses a Cartesian-grid formulation with immersed body and volume-of-fluid (VOF) methods. Dommermuth, et al (2008) describes the code and recent applications to naval problems.

This paper describes and documents a recent effort to validate NFA for the prediction of hydrodynamic forces and moments associated with a deep-V planing craft.  This detailed validation effort was composed of three parts.  The first part focuses on assessing NFA’s ability to predict pressures on the surface of a 10 degree deadrise wedge during impact with an undisturbed free surface. Detailed comparisons to pressure gauges have been performed for two different drop heights, 6 and 10 inches. The second part examines NFA’s ability to match experiments performed on constant deadrise planing hulls. Fridsma (1969) details several cases for simple steady forward speed for a prismatic hullform. Specifically a deadrise angle of 20 degrees at five speed-length ratios: 2.0, 3.0, 4.0, 5.0 and 6.0 knots/ft^1/2 were simulated.  The center of gravity was also varied to broaden the parameter space and investigate porpoising stability. In addition NFA will be compared to the parametric equations presented in Savistsky (1964) for sinkage and trim, resistance, and porpoising stability.  The final part of the validation study focused on assessing how well NFA was able to accurately model the complex multiphase flow associated with high Froude number flows, specifically the wave breaking and spray sheet. 

Figure 1 shows a qualitative comparison of a model test visualization and typical NFA result at steady forward speed in calm water. The Froude number is 1.96, which is 40 knots, full scale.  The numerical simulation uses 24x9x6=1296 subdomains, and each subdomain has 1536x576x374=339,738,624 grid points. The spray sheet is captured and much of the spray generation at the chine has the same distribution as the experiments. 

Overall these three validation studies provide a detailed assessment on the current capabilities of NFA to predict the hydrodynamics of a deep-V planing hull.

Optimized design of a SAR boat for the Royal Netherlands Lifeboat Institution
J. A. Keuning, Delft University of Technology, the Netherlands

The Royal Netherlands Lifeboat Institution exploits a fleet of lifeboats around the North Sea coast of the Netherlands. The majority of this fleet consists of aluminum RIB’s. The largest vessels from this fleet are from the so-called “Arie Visser” class with a length of around 18.5 meters and a speed of 35 knots. These are all weather boats and self-righting. The Lifeboat Institution plans to replace the 10 boats in this class in the next 10 years.

Based on the requirements of the Royal Netherlands Lifeboat Institution a design group, composed by the Delft University of Technology, De Vries Lentsch Yacht Design and the High Speed Craft Department of DAMEN Shipyards developed two new designs: one a modest adaptation of the existing boats, subsequently named the Evolutionary design and one based on the successful AXE Bow Concept, subsequently named the Revolutionary design. The emphasis in the new designs was on improved operability of the SAR boats in their typical working environment, i.e. the North Sea with its harsh conditions.

To assess the differences in performances of these designs in calm water and in waves an extensive test program has been carried out with three designs: i.e. the existing design and the two new designs.

First, these have been tested for resistance sinkage and trim in calm water. Also, the maneuverability of the ships have been compared.

In addition, their behavior with high forward speeds in head waves with various significant wave heights and spectral shapes has been tested. Special attention has also been paid on the added resistance in waves.

In particular their behavior in high stern quartering, following and beam seas has been compared with free running models in the Ship Motions Basin (SMB) of MARIN institute in Wageningen to be able to compare a possible tendency for broaching behavior in high seas. These free running models have also been used for side-by-side measurements on open water to be able to get more severe wave conditions than possible to achieve in the towing tanks at this scale. Finally, a special test procedure has been developed to test the models in extremely high head and following waves.

Extensive full-scale measurements on the existing boats of the “Arie Visser” class have also been carried out. This has been done to validate the experiments and calculations and to derive (new) criteria for the “comfortable” and safe operation of these ships in normal and more extreme working conditions.

The results of this research project will be summarized and presented in the paper.