Transom sterns are a common characteristic for military, commercial, and recreational vessels. Transom sterns offer ease of construction, greater aft deck area, and reduced resistance at higher speeds. Predicting the resistance for vessels with this type of stern is difficult due to separated flow. Viscous flow solvers have been shown to provide adequate predictions for transom flows, however the time and computational cost of these high-fidelity calculations tend to be extremely high. The separation, and eventual ventilating, are viscous processes, thus potential flow solvers are unable to make these calculations without a priori information on the elevation of the transom flows. This paper provides experimental transom flow data for a 19° deadrise hull. The model used in these experiments was previously used in an effort by Royce and Doherty in 2015. The prior effort relied on video data for visual elevation measurements, while this experiment uses sonic and impedance wave probes for the measurements. The results collected with the impedance wave probes compare favorably to the prior visual measurements. Short comings of sonic wave probes are identified and a recommendation for the use of inexpensive impedance wave probes is made for future experiments.

Structural finite element analysis (FEA) is routinely used in the design of modern ship and offshore structures. The benefits of FEA are apparent when used proficiently, but it can yield incorrect and misleading results when misused. There are certain types of errors in FEA that are unfortunately not that rare, but many of these errors can be avoided if clear and direct advice is provided to the analyst. SNAME Hull Structure Panel (HS3) aims to help analysts recognize the limitations of FEA tools and provide guidance on how to overcome them. A generic semisubmersible model is studied in order to demonstrate the simplification of the real structure in an FEA model, studying beam idealization in ship/offshore structure FEA, along with how to deal with the global and local loading. The effect of modeling geometry discrepancy is identified with numerical examples to illustrate the benefits of the guidelines. When a local model is built and boundary conditions are to be applied, displacement from the global model is often used to transfer the global loads. The difference between a detailed shell local model and the simplified coarse beam/shell global model requires the use of so-called rigid elements, such as RBE2/RBE3 in the commercially-available program ANSYS, which was used in developing these guidelines. Other than displacement, the local model may be analyzed using force boundary conditions obtained directly from the global model beam element internal forces. While the two methods are acceptable in the applications, there are issues with each of the methods. Theoretical formulation is used to show that either of the choices of boundary conditions could be established in order to solve the basic equation. However, a judicious process to deal with the boundary conditions will help analysts determine the best approach. An investigation of the effects of different methods is shown to illustrate the consequences. A summary of guidelines to these particular problems is presented. Future work is also discussed

The presented GD NASSCO research for the National Shipbuilding Research Program (NSRP Research Announcement No. 2018-444) continues the testing and analysis of swage panel specimens with an investigation of the influence of shipboard connection details on swage panel strength characteristics. These connection details are represented by cutouts in the swage panel, either in the form of overhead deck stiffeners or conduit and cable penetrations. A total of twelve specimens, comprising three types of geometries, are tested to failure in either compression or shear at the SDSU Structural Engineering Laboratory. These test data are compared with accompanying finite element analysis results. The results allow for a detailed investigation on the effect of connection details and configurations and a comparison to traditional stiffened panel arrangements. The comparison to non-linear finite element analysis serves to validate the effectiveness of this tool in representing swage panel force capacity and failure mode.

The authors previously discussed (SNAME Transaction 2013) the fallacies of the U.S. Navy modifying an existing "parent" or "legacy" design as opposed to a new "clean sheet of paper" design. We explained that many acquisition executives believe that a so-called "modified repeat" design has fewer technical risks than a new design. Yet, this approach has frequently resulted in significant cost and schedule growth and/or serious technical problems during construction, in-service and during modernization. The authors will describe why traditional design and build margins and Service-Life Allowances (SLAs) for weight/displacement, vertical center of gravity (VCG), electric power, and cooling are necessary but not sufficient because they can still result in ships that are "too little". The authors will stress the need to include and place more emphasis on space and volume and relate these to "just right" design requirements for reducing work content in detail design & construction and in-service modernization. On the other hand, some recent new designs have also experienced unanticipated cost and schedule growth during construction as well as substantial technical problems. The authors will examine some of these new ship designs and highlight the fallacies of over-constraining arrangements through arbitrary size and displacement restrictions – another example of "too little." We will emphasize that displacement is NOT a good indicator of cost – a lesson learned by leading foreign navies years ago. The authors will scrutinize the "too much" syndrome of incorporating unproven technology into a new ship design before it is demonstrated, or at least fully characterized and the ship impact understood. The cascading deleterious effect of including multiple major unproven technologies inevitably results in cost and schedule overruns. Indeed, one entire class of ships has been described as a "failure" due to "too much" new technology going into the design before its time. The authors will also briefly describe the development and use of more physics-based design tools during early stage design. This can reduce the risks of a new clean sheet ship design through early rigorous design space exploration and actual design maturation. The authors are convinced from our experience on over fifty major naval ship designs that much of the unbudgeted and unnecessary growth in the costs to produce naval ships can be attributed to poor design decisions made during early concept design. Achieving the "Goldilocks effect" of "just right" design starts with a mature stable ship design earlier in the design process. This is critical for ensuring successful ship design, acquisition, construction, in-service and modernization outcomes.

While swaged bulkheads have progressively become accepted for non-load bearing locations on U.S. built commercial ships, their widespread application in U.S. shipbuilding practice has been slowed by the lack of specific American Bureau of Shipbuilding (ABS) rules for calculating the capacities of these configurations in load bearing situations. NASSCO has carried out several National Shipyard Research Program (NSRP) projects between 2010 and 2015 to collect a body of data on the strength of swaged bulkheads, including physical testing of full-size specimens, as well as linear and non-linear finite element analyses. The goal of the current Swage Panel SVR Rule Development Project (NSRP Research Announcement 2015-402) is to work towards the implementation of swage technology into commercial vessels built in the US. Currently in the third and final phase, this project furthers the previous work performed studying swage bulkheads. NASSCO has partnered with San Diego State University (SDSU) and ABS to develop swage bulkhead design guidance specific to the commercial use of swage panels in load bearing applications that will be incorporated into the ABS Steel Vessel Rules (SVR). Physical testing to validate the local swage bulkhead non-linear finite element analysis (NLFEA) predictions has been conducted in the structures laboratory at SDSU, including compression and shear load cases. Large scale NLFEA performed using MAESTRO will incorporate swage bulkheads in vessel superstructures under realistic load profiles. This project's outcome will be a proposed rule for the 2020 ABS SVR based on the project's research, with scheduled completion in December 2018.

The modularized design and construction philosophy is a common practice for large onshore and offshore projects due to its opportunity for schedule and cost-savings. Multiple modules are fabricated at different construction yards across the world and then transported to service sites by marine transportation vessels. During transportation, the seafastening system is required to secure modules on transportation vessels. The seafastening system is designed to support the forces imposed on the module by accelerations, motions and deflections of the vessel, and distribute the concentrated forces from the module onto the vessel. The system reliability will depend highly on the forces for which the seafastening is designed. The determination of the forces is typically based on decoupled analysis where the module and vessel are analyzed separately. The resulting forces are usually over-conservative. However, this paper presents a more advanced and accurate approach where interaction FE analysis is utilized to calculate the reaction forces. A light weight seafastening system is designed based on the calculated reaction forces. The system consists of a series of grillage beams with stoppers and wing plates welded to the vessel deck. Additional clips are used to restrain the module uplift. The proposed design allows for an easy and efficient seafastening removal, an optimum use of the vessel capacity and a reduction in fabrication costs. Results from a sample seafastening design are presented.

We construct a multi-fidelity framework for statistical learning and global optimization that is capable of effectively synthesizing low- and high-fidelity simulations towards identifying optimal SWATH hull shapes with superior seakeeping performance. Specifically, we employ multi-fidelity Gaussian process regression and Bayesian optimization to build probabilistic surrogate models and efficiently explore a 35-dimensional design space to optimize hull shapes that minimize wave induced motions and accelerations and satisfy specific requirements in terms of displacement and metacentric height. Our results demonstrate the superior characteristics of this optimization framework in constructing accurate surrogate models and identifying optimal designs with a significant reduction in the computational effort.

When developing the initial weight estimate for a new vessel, the weight engineer or naval architect can produce his or her estimate either by scaling from a known, similar vessel, or by taking the weights of each portion of the vessel from parametric equations or by some combination of these two methods. The preferred source of a parent vessel to scale from or the data from which a parametric equation is derived is the past vessels designed by the naval architect's own firm; however, sometimes the firm may not have suitable designs in its portfolio to base a new design weight estimate upon. This paper seeks to collect as many previously published parametric weight equations for as wide a collection of vessel types as possible in order to provide a convenient reference for the times the naval architect's own data is insufficient to complete a weight estimate. This paper is not intended to be the definitive source of parametric weight equations, rather, the goal is to collect a critical mass of equations across the range of vessel types to start the conversation on the relative merits of the various equations and hopefully elicit new up-to-date equations from others. Ideally discussers will add equations based on their own data in addition to discussing the merits of those collected here. The end goal is the production of a T&R Bulletin, however much additional validation, updating and discussion is required to take the current paper to the point where it could be considered as a draft for such a bulletin.

Structural tests were performed for several padeye shapes where the test specimens were loaded to failure at three angles. Nonlinear finite element analysis was also performed for each of the structural tests and the results from each were used to develop a computer program in Microsoft Excel to determine padeye force capacity for three potential modes of failure: shear, tension, and bending. The output from the Excel program was then compared against another set of structural tests of padeyes. The results show that the program is easy to use with minimal input and provides good overall comparisons to the measured failure loads from the structural tests.

Rarely does marine salvage occur in conditions conducive to obtaining the necessary draft readings to accurately estimate a ground reaction. Obtaining accurate information on the condition of grounded vessels is difficult under the best environmental conditions. The analysis presented here quantifies the uncertainty associated with ground reaction calculations using the propagation of errors methodology. Basic relationships gleaned from classic naval architecture calculations are analyzed to examine the importance of each input and develop a cost/benefit relationship for optimizing each parameter. This study provides a framework for evaluating uncertainty in future salvage cases. Included in this analysis is evaluation of multiple real-world casualty responses from planning to execution. Quantifying the accuracy of information available and the extent to which this information is known provides stakeholders with the ability to create a more well-informed picture of the inherent risks of a given salvage operation. Using the framework described here, actionable recommendations are developed which may be used in the development of plans for responding to future grounding scenarios. In particular, this analysis supports the need for flexibility in salvage plans and emphasizes the value in empowering on-scene leaders to make adjustments in response to new information as it becomes available.

Current guidance for calculating US-flag towing vessel stability date from over 35 years ago. In the intervening time, towing vessel design has evolved to the point that the current guidance may not be conservative. This paper examines those changes and gives examples of how the designs have evolved. Finally, recommendations are given to naval architects calculating towing vessel stability.

Off-axis propeller loads create a significant problem for shaft alignment and bearing performance. As the propeller rotates through a non-uniform ship wake, it generates horizontal and vertical forces and moments that are difficult to support. In extreme cases (such as a high-speed turn), the off-axis loads can become as large as the mean propeller thrust and torque. As the bearing deflects to absorb these forces, and the shaft bends to absorb moments, metal-tometal contact can occur. This paper describes an approach to minimize such problems at the design stage. Computational Fluid Dynamics (CFD) predicts the propeller off-axes forces during a maneuver, and a Fluid/Structures Interaction (FSI) model predicts the resulting shaft stresses and deflections. Bearing forces and moments derive from CFD models of the oil film inside each stern tube bearing. Optimization finds the combination of design parameters that minimize metal-to-metal contact.

The structural components of a typical icebreaker hull grillage section consist of hull plating, main frames, web frames and stringers. The grillage section is the main structure resisting local ice loads during icebreaking and maneuvering operations. As such, the structural integrity of the icebreaker is largely dependent on the design strength of the grillage sections along the length of the vessel. The latest release of the IACS Unified Requirements for Polar Ships specifically pertains to structural design of these local grillage sections. Within the IACS Unified Requirements, prescriptive formulas are used to define the hull plating and main frame strength requirements as a function of stiffening direction, longitudinal/vertical location and operational requirements. The stringer and web frame stability requirements however, are limited to meeting empirical criteria. Limited examples of stringer and web frame prescriptive design strength formulations are available in the literature. These formulations may lead to an overly conservative stringer or web frame section design due to the challenge of representing the grillage section structural component interaction. To properly understand the structural interaction of icebreaker grillage section components, LR has used nonlinear finite element methods to compute the characteristic stiffness curve well into plasticity. The characteristic stiffness curve is considered representative of the effective structural interaction of the section components and has been found to relate directly to the section design methodology (elastic or plastic). This paper presents the development of these stiffness curves; the relationship between stiffness curve characteristics and design methodology; and how stiffness curves may be used for structural design and verification.

The U.S. shale gas boom inspired the marketing demand for a very large containment system (VLEC). Among various kinds of possible cargo containment systems (CCS) for VLEC, the Type-C independent tank is considered to be a reliable, robust design and is a competitive candidate. There are a number of design challenges to design and construct Type-C tanks suitable for VLEC. Thicker plate is generally used, and hence there is more significant tank shrinkage. In addition other factors to be considered includes sloshing, thermal stresses induced by large tank dimensions, and the interaction between tank and hull structure under low temperature conditions. Since the VLEC cargo tank concept design and material selection have been done, the possible maximum thickness of steel plate that may be adopted has been verified. The feasibility of Type-C cargo tank’s application in VLEC project has been researched and verified by various kinds of calculation and analysis, including IGC-based rule check and finite element analysis (FEA), low temperature shrinkage analysis, sloshing analysis, thermal stress analysis, etc. Construction cost and time schedule have also been investigated and compared among three kinds of CCS based on a certain yard case. Some useful conclusions have been presented for VLEC CCS selection.

Ship motions and its hydrodynamic coefficients are solved by three dimensional frequency domain potential theories with a translating and pulsating source distribution method. Furthermore, components of added wave resistance of ships advancing in waves due to the radiation and diffraction waves are obtained respectively. Added wave resistances of Wigley III hull and S175 containership with various forward speeds are carried out and analyzed in frequency domain. The numerical results are validated for the models by comparing them with experimental data. Its percentage of components of the total ship added wave resistance varying with frequency is investigated and discussed. The present method provides a rapid and efficient approach to predict added resistance of different types of ships in waves.

The U.S. Coast Guard’s 154 foot Sentinel Class patrol craft (154WPC), also known as the Fast Response Cutter (FRC), replaces the well known and respected 110 foot Island Class patrol boat (110WPB). Increases in mission and operational capabilities, 110WPB to 154WPC, are discussed and presented showing how increases in length, beam and displacement have had a large impact on seakeeping, habitability, crew fatigue, and operational capability in higher sea states for the 154WPC. Additionally mission capabilities for the 154WPC have been improved via the C4ISR suite and the deployable over-the-horizon cutter boat. The outcome of these capability increases for the 154WPC Sentinel Class is an extended operational duration and coverage of a larger area of responsibility than the 110WPB Island Class that it replaces.

Nitinol, a nickel-titanium shape memory alloy, was analyzed for its feasibility as a linear actuator to be used in a thermal buoyancy engine of an autonomous underwater ocean glider fueled by the temperature gradient of the ocean's thermocline. A nitinol mass suspension apparatus was fabricated to measure the displacement of an array of masses ranging from 0:5kg to 8kg as the wire was transitioned into its heated austenite phase, and then cooled back to its martensite phase, thus representing the expansion and contraction of a buoyancy engine piston under hydrostatic pressure. In validation of nitinol manufacturer Dynalloy; Inc: specifications, the maximum stroke observed in this dead weight bias configuration was 4:25±0:24%, only a 6% difference from the documented 4% stroke.

Series 50 is the largest U.S. planing hull series. Originally developed for semi-planing PT boat type hulls, the tests were conducted in 1940-1941 and consisted of twenty 1m long models tested at nine loading conditions each and a range of speeds for a total of over 2000 test runs. The volumetric Froude numbers tested ranged from 1 to 6. The parent hull of the series has warp, rocker in the buttock lines and a tapered stern, features that are undesirable in very high speed craft, but are often necessary in the design of semi-planing hulls such as motor yachts. Analysis of all of the series data showed that the flow was not fully turbulent on all of the runs, especially conditions with wide beam and short wetted lengths. A thorough re-analysis of the data was undertaken and for runs with suspected transitional flow, the lift, wetted length and trim angle were used to determine resistance, using a modification of methods employed for prismatic planing hulls. Plots are developed showing mean wetted length and residuary resistance to weight ratio as a function of Froude number, allowing the data to be rapidly expanded to any scale ratio. Corrections for aerodynamic resistance, trim flaps and appendages are discussed, and example calculations are provided.

Designed ‘from the ground up’ for high speed, many trade-offs were made within the hullform parameters of this notional 298 m, 36,000 Long Ton, High Speed Sealift (HSS) ship, in an effort to optimize 39-knot performance. Resistance and powering comparisons are drawn between several hullform and propulsor combinations, considered the most applicable to HSS, which include: conventional 2-screw and 4-screw, open-propeller, shaft and strut; waterjet propulsion (axial and mixed-flow jet hulls); hybrid contra-rotating shaft-pod (twin shafts, twin pods) and dual-pods (twin sets of dual pods). This model-scale evaluation established that 39-knots was achievable by several candidate hullform and propulsor variations on this sealift ship, within the anticipated installed power levels.

This paper documents the generation of several seaway load prediction algorithms for catamarans, trimarans, and surface effect ships based on available model and full-scale test data. Froude scaling laws are used for geometrically different ships for each ship and load type using first principles and empirically derived studies. Simple seaway load prediction algorithms are then developed and expressed as functions of ship displacement and various key ship particulars. These global load algorithms are quickly computed, making them suitable for preliminary or concept design studies. In some cases, algorithms were developed from a minimum amount of data, and it is anticipated that as more data is gathered in the future, these algorithms will be further refined. As the ship design progresses, more accurate but time consuming computational analyses and model tests are appropriate.