Deck Load Research Articles

Application of Constrained Multi-Objective Optimization to the Design of Offshore Structure Hulls

Abstract The paper reports on the continuous development of an automated optimization procedure for the design of offshore structure hulls. Advanced parametric design algorithms, numerical analysis of wave-body interaction, and formal multi-objective optimization are integrated into a computer aided design system that produces hull shapes with superior seakeeping qualities. By allowing multiple objectives in the procedure naval architects may pursue concurrent design objectives, e.g., minimizing heave motion while simultaneously maximizing deck load. The system develops a Pareto frontier of the best design alternatives for the user to choose from. Constraints are directly considered within the optimization algorithm, thus eliminating infeasible or unfit designs. The paper summarizes the new developments in the shape generation, illustrates the optimization procedure, and presents results of the multi-objective hull shape optimization.

Design Recommendations for a FRP Bridge Deck Supported on Steel Superstructure

No appropriate provisions from either AASHTO Standard (2002) or AASHTO LRFD (2004) bridge design specifications are available for the design of fiber-reinforced polymer (FRP)-deck-on-steel-superstructure bridges. In this research, a parametric study using the finite-element method (FEM) is conducted to examine 2 design issues concerning the design of FRP-deck-on-steel-superstructure bridges, namely, deck relative deflection and load distribution factor (LDF). Results show that the strip method specified in AASHTO LRFD specification as an approximate method of analysis, can also be applied to FRP decks as a practical method. However, different strip width equations have to be determined by either FEM or experimental methods for different types of FRP decks. In this study, one such equation has been derived for the Strongwell deck. In addition, both FEM results and experimental measurements show that the AASHTO LDF equations for glued laminated timber decks on steel stringers provide good estimations of LDF for FRP-deck-on-steel-superstructure bridges. Finally, it is found that the lever rule can be used as an appropriately conservative design method to predict the LDF of FRP-deck-on-steel-superstructure bridges.

Wave-in-deck loading on fixed steel jacket decks

For quite some years, wave-in-deck loading has been an issue of concern for engineers dealing with the performance of offshore structures. The topic is particularly relevant for reassessment of existing structures located in subsiding areas. One agrees that wave-in-deck loading is of dynamic nature, and that structural analyses should reflect this. There is, however, no general consensus on the size of the load and the shape of the load time history to be used for such analyses. In this paper focus has been on finding realistic load time histories for wave-in-deck loading on jacket platforms in the North Sea. A (normalised) time history shape and a simple expression to calculate a reference load (maximum load) to quantify the time history is presented. The presented ‘recipe’ for time histories is based on experimental data and is supported by results reported in the literature, comprising relevant computer simulations and model experiments of wave-in-deck loads on fixed offshore structures. The recommended load time history is intended for analyses where detailed information on the deck load for a given structure is unavailable, and where a simplified ‘rough-but-reasonable’ estimate can be accepted.

A systematic approach towards the structural behaviour of a lightweight deck–side shell system

Lightweight structures are increasingly used for high-speed ships. This paper presents a systematic approach to analyse the structural behaviour of a lightweight deck–side shell system using high strength steel. An analytical model of the deck–side shell system was first given, which includes the effects of stiffeners for the deck and side shell, the support conditions of the centreline girder (CL-girder), the influence of transverse beams, and the interaction between the side shell and the lightweight deck as parts of problems to the solution. By changing several geometric parameters, the sensitivity of both overall and local stress and deflection for the deck–side shell system was investigated. The different geometric parameters analysed comprise the influence for variation in the thickness of the web for transverse beams, longitudinal stiffeners and the CL-girder, the thickness of lower flange for the transverse beam and, the thickness for the panel. Furthermore, the influence of the lightweight deck and loads from the deck above on the side shell, the effects of the side shell and loads from top deck on the deck, the support conditions for the CL-girder, and the influence of deck loads on the eigenmodes were also analysed. By evaluating the results obtained from FE simulation, the support conditions of the CL-girder, the thickness of the panels and the lower flange of the transverse beams were found to be the most relevant parameters affecting both the stress and the deflection distribution of the structure. The dynamic characteristics of the structure were also analysed. The FE analysis concerning buckling of the structure was present. The results enable naval architects and structural engineers to design new extreme lightweight deck structure more reliable and economical. And some suggestions for future research are also given.

Freezing and Thawing and Alkali-Aggregate Reaction Weakens Lightweight, Structural Concrete in North Dakota

Abstract The Bureau of Reclamation may replace a transfer deck that is deteriorating in North Dakota. The transfer deck serves as the parking deck and roof for a pumping plant. In late June 2001, portions of the lightweight concrete failed and fell to the pumping plant floor during a storm. The concrete failed along a continuous fracture about 1 cm above the ceiling surface. The fracture penetrated all aggregate particles encountered. Petrographic examination of 15 cores indicated about 18% of the concrete below a waterproofing membrane and 3% of the lower surface of the concrete was damaged by freezing and thawing deterioration and minor alkali-aggregate reaction (AAR). The water saturating the lightweight concrete apparently penetrated the field-manufactured seams in the membrane. Saturated aggregates froze during the winter as the depth of frost penetrated the full thickness of the deck and structural concrete. Evidence indicates that ceiling insulation held water in contact with the lower concrete surface, while freezing and thawing deterioration and AAR caused the concrete to fail. Structural analysis indicates the transfer deck loads be restricted to 40.7 kPa (850 lbsf) unless further deterioration is anticipated or additional damage is observed. The lightweight concrete cannot be repaired and will have to be replaced eventually.

Wave Induced Motions and Deck Loads of Unbraced Semi-Submersibles

Wave Induced Motions and Deck Loads of Unbraced Semi-Submersibles

Roll-on/roll-off semi-trailer models: a comparison of results

A comparison is made of the various mathematical models that have been constructed, over the past 15 years, of a semi-trailer that can be carried on roll-on/roll-off ships, and some results from five of the models developed by the author are given. The purpose of this comparison is to show that even in the absence of reliable experimental evidence, there is such good agreement between the models that the results from each of them can be relied upon. Problems resulting from large lashing loads and deck loads are highlighted, and it is suggested that the present codes which govern the way semi-trailers are secured on board ship need further scrutiny.

Removal of Diaphragms from Three-Span Steel Girder Bridge

This discussion includes commentary on an earlier article in this journal ("Removal of Diaphragms from Three-Span Steel Girder Bridge", Stallings et al., 1999) and the authors' reply. The original article documents the results of a relatively comprehensive bridge deck load distribution research project concerning steel bridges. The author of this commentary contends that unjustified generalizations were made by the original authors. Even though the research reported is somewhat unique in that it appears to recognize some association between steel transverse braces and reinforced concrete deck slabs, the authors fail to qualify their recommendations with respect to removal of diaphragms and crossframes from all other similar bridges. The original authors' reply speaks to these contentions.

Restraint Moments in Precast/Prestressed Concrete Continuous Bridges

To eliminate deck joints and shoulder piers, continuous span (jointless) bridges are becoming an attractive option. Different continuity methods and construction sequences have different time-dependent effects on the behavior of the bridge system. These effects are illustrated in this paper. To achieve a favorable performance of bridges made continuous for deck loads, recommendations for achieving continuity and for desirable construction sequence are presented. A new continuity detail using high strength threaded rods is proposed. Based on a cost comparison with currently available continuity methods and a full-scale NU1100 I-beam experiment, this continuity detail is shown to eliminate the potential for bottom concrete creep restraint cracking at pier locations and to increase the span capacity by as much as 20 percent.

Stiffnesses of Abutments on Piles in Seismic Bridge Analyses

The characterization of bridge-abutment-backfill-pile interaction is an important component in seismic bridge response evaluations. This paper presents a relatively simple and realistic methodology to evaluate the nonlinear translational (longitudinal, and transverse) spring stiffnesses of abutments founded on pile foundation. Many important factors such as the abutment dimensions, nonlinear pile-soil interaction, superstructure loads, and difference in soil behavior under active and passive conditions have been accounted for. Only routinely used soil properties are required in the model. The paper describes a calibration study undertaken to ascertain the predictive capability of the proposed approach using large-scale field tests. A very good agreement exists between the predictions and the large-scale field tests results. Both longitudinal and transverse field tests were utilized in the calibration. This paper also presents the results of a parametric study in which the influence of pile fixity conditions, relative contribution of piles to abutment stiffness, and deck loads were investigated.

A Response Surface for Structural Optimization

Abstract Structural optimization is computationally intensive. Typically, a finite element model must be solved repeatedly during the process. Accordingly, various approximation schemes have been developed to reduce the cost of solves or to eliminate solves entirely during portions of the optimization process. In this paper, a new type of approximation or interpolation function in the form of a global response surface is described. With this function, approximations can be made with a limited amount of calibrating data points. The response surface requires no matrix inversions for coefficient evaluation, and therefore it is relatively efficient and stable. The new response surface is used in conjunction with a modified zero-order Powell search algorithm. The effectiveness of the response surface is evaluated for a reasonably realistic offshore structure application. This planar truss structure is subjected to a deck load, a lateral wave load (considered quasi-static), and member self-weight loads. The objective for this test case was to minimize the structural cost. Nodal coordinates were considered to be the explicit design variables. Response surface results are compared with those obtained by the common optimization algorithms: steepest descent, conjugate directions, and a conventional implementation of Powell’s method. The response surface appears to be effective for the test case considered.

Ocean Scout: Conversion to a Multi-Service Vessel

In today's offshore market some older, smaller, and obsolete semisubmersible drilling rigs are finding a new place in the offshore industry as multi-service vessels capable of an array of tasks. During the spring academic semester at Texas A&M University, College Station, Texas, the ocean engineering senior design class of 22 students, working with industry and faculty advisors, produced a preliminary design for the conversion of the semisubmersible "Ocean Scout" to a multiservice vessel for operation in the Gulf of Mexico. This report explains the major topics of the project addressed by the class which include vessel additions to create a variable deck load of 3000 long tons, a dynamic positioning system capable of stationkeeping in a one-year, nonhurricane storm event, and an economic analysis of the conversion for a five year project life producing a 38 month payback period.

Design of the Compact Semisubmersibles Rockwater Semi 1 and 2

Summary This paper describes the design of two compact semisubmersible vessels usedin the North Sea. The design stages covered range from the initial marketsurvey to the performance evaluation. Introduction In the early 1980's, Smit Intl. considered options for expanding itsoffshore activity beyond its traditional towing, transport, supply, and salvageoperations. Offshore inspection, maintenance, and repair (IMR) andconstruction/installation were determined to be the areas best suited to thecompany's marine background and experience. However, specialized equipment wasneeded to begin these types of operations. Market Evaluation To determine the requirements for vessels to be acquired, Smit Intl.surveyed IMR and medium-sized construction/installation markets worldwide. Thecompany's primary areas of interest were the North Sea, the Mediterranean Sea, the Gulf of Suez, Africa, North and South America, India, and the Middle East. Although many platforms stood in the Gulf of Mexico, this area was notconsidered. Next, the numbers of platforms of interest in each area wereidentified (Table 1). Although it was difficult at that time to figure a totalmaintenance budget, the literature indicated that costs averaged $10billion/year worldwide, including post-startup maintenance and systemsupgrading. Actual estimates for the North Sea were around $2.5 billion. It wasestimated that $500 million would be used for North Sea followup maintenance, $1 billion for underwater maintenance, and $1 billion for general topsidemaintenance and cleaning. Once the sizes and locations of the potential marketswere identified, particular potential markets were identified, particularmarket segments-primarily those of topside and subsea IMR and secondarily thoseof light to medium construction-were evaluated more closely. Subsea IMRincludes activities on completion jackets, pipeline tie-ins, etc., using diversand remotely operated vehicles (ROV's). Topside activities include generalmaintenance and refurbishment, hookup, and accommodation. Also, the markets forplatform installation and removal, construction and equipment replacement, subsea well workovers, and logistics support were evaluated. Most of thepotential work was expected to be in water depths less than 150 m, where 90% ofthe investigated platforms were located. At the time, this market segment wasbeing serviced by monohull diving support vessels (DSV's) for the subsea workand a variety of converted jackups and converted drilling semisubmersibles forthe topside work. A limited number of purpose-built units were being used, butthese were dedicated to oil companies as field support and safety vessels. After this initial market evaluation, Smit Intl. hired Marine Structure Consultants B.V. to design a vessel that would allow the company to enter themarket effectively. Our study evaluated monohulls, jackups, largesemisubmersibles, and compact semisubmersibles. All types of activities(typical day rates, workability in various sea states, flexibility ofoperations, and movements between locations) were considered (see Table 2). After extensive evaluation of all information, a compact semisubmersible designwas chosen. Oil companies were consulted to determine their future service andequipment needs. Their comments greatly affected the final investment. Initial Design Specification To remain cost-effective while outperforming traditional vessels, the newcompact semisubmersibles had to meet the following design criteria:a minimum payload capacity of 1,500 tons (metric), with 750 for deck load;a large net deck area of more than 1,000 m, with a crane capacity of 150 tons anda 30-m reach;utilities to accommodate 110 persons and cabins for 89;positioning achieved with ajoystick dynamic positioning (DP) system; andwire mooring systems (in water depths up to 100 m). The vessels had to beoperable in extreme environments (from the harsh North Sea to the Africancoast, where swell conditions exist). Investment costs had to be competitivewith the monohull day rate of about $10,000/d (1985 price level). JPT P. 460

The Design of Tension Leg Platforms by a Constrained Optimization Method

A method is developed for optimizing the size of a tension leg platform (TLP) and its tethers so as to minimize the weight-based cost of the TLP system subject to various design constraints. The method is intended for preliminary design studies of feasibility and cost sensitivity. Design constraints include minimum tension and maximum tensile stress in the tethers, maximum platform offset under current and waves, and minimum fatigue life of the tethers due to resonant vibration. Other given quantities include deck load, riser pretension, tether properties, and basic results from structural design studies and hydrodynamic analysis or model tests for a specific class of platforms. Example in TLP design studies are presented to illustrate application of the constrained optimization method.

Dynamic Analysis and Fatigue Control of the HYLIGHT Deepwater Platform

Abstract The paper discusses results from a detailed stochastic dynamic fatigue analysis of a new deepwater platform concept designed for North Sea conditions. The platform concept, developed by Norsk Hydro a.s., is a fixed steel structure in a water depth of 335 m and with a deck load capacity of 35000 tonnes. The platform substructure, shown in Fig. 1, is a tripod trusswork design consisting of a central triangle tower connected to three inclined legs at elevation 45 m below the still water level. The fundamental structural natural period is in the range of 4 to 5 s, indicating significant dynamic amplification of the quasi-static wave-induced response, and fatigue will be an important design consideration. Parameters governing the fatigue life of the structure are identified and the fatigue sensitivity to these parameters is investigated. The results indicate that fatigue is important for structural elements in and above the intersection area between the main tower and the inclined legs. Important parameters governing the fatigue life are found to be the damping value, geometric stress effects, dynamic amplification, structural geometry at waterline, wave load modeling and method used for linearization of nonlinear wave forces.

Ice Management In The Labrador Sea

Introduction The Labrador Sea is known as a hostile environment to all forms of marine activities. The region is buffetted by numerous storms every year which bring high winds, severe seastates and superstructure icing. For vessels attempting to navigate through the region the presence of icebergs present a year round hazard and sea ice, present during the winter and spring months, restricts the trafficability of vessels. It is in this environment that the Labrador Group of Companies has undertaken an extensive program of exploratory drilling over the last decade. To date, some 23 wells have been drilled by this consortium, primarily on the offshore banks and the saddles between these banks. To ensure a safe and successful drilling operation, special attention has been given to the environmental constraints and programs have been developed to minimize their effect. In this paper we will present some of the aspects of the iceberg problem and the ice management techniques in place to deal with them. Setting Icebergs are found throughout the region encompassed by the permit acreage within the Labrador Sea. It is difficult to generalize on the presence of icebergs over the entire Labrador Sea region as their presence is variable in time and space. There exists an annual variation which sees the largest numbers of icebergs present in the May and June period, decreasing throughout the summer to a local minimum in October and November and then increasing to a late spring peak. The variability between years, in terms of the total numbers of icebergs recorded, is largely unknown in this region although there are large differences between a light and a heavy iceberg season. Farther south, at the boundary of the Grand Banks, the variation is from a minimum of zero icebergs to a maximum of about four times the mean annual value. The distribution of icebergs within the Labrador Sea shows a decrease in the number of icebergs present with increasing distance from the coastline. Also, at a given point in lime more icebergs will be present in northerly regions than in those farther south. The reduced fluxes with distance offshore and southward along the coast indicate both the deterioration of icebergs and the divergence of icebergs from the surveyed region. A variety of mechanisms, both mechanical and thermal, influence the decay of icebergs in this corridor and their interrelationships are only qualitatively understood. The Equipment On the Labrador Shelf drillships have been used predominantly. Their deck load and cargo capacity permits operation in remote areas with minimum resupply. Dynamically positioned drillships have been preferred due to their ability to move off and back onto a well quickly when threatened by Ice or icebergs. This capability maximizes vessel safety and minimizes costs due to downtime. The dynamic positioning system enables such a drilling unit to maintain position over the wellhead using ship's power alone.

Determination of the engineering properties of the coode island silts using a self boring pressuremeter : Hughes, J M O; Ervin, M C; Holden, J C Proc 3rd Australia-New Zealand Conference on Geomechanics, Wellington, 12–16 May 1980, V1, P249–254. Publ Wellington: New Zealand Institution of Engineers, 1980

The eastern approaches of Melbourne's West Gate Bridge are being constructed as an elevated freeway some 2 km long. For the most part this freeway is being supported on large diameter cast in situ reinforced concrete piles. These piles range in diameter from 1.1 to 1.5 m and are socketed into Silurian mudstone and sandstone. These piles are generally in excess of 40 m in length The upper 30 m to 35 m is in alluvial deposits ranging from dense gravels to soft silty clays. The upper 10 m to 20 m of these deposits are in the so-called Coode Island Silts, which are in fact predominantly soft to firm silty clays. These piles must resist the heavy vertical loads from the dead and live loads of the freeway structures as well as lateral loads imposed by thermal stresses in the bridge deck and substantial construction loads resulting from the prestressing of the deck. The vertical loads are all assumed to be carried in the mudstone. The method of analysis of these pile sockets is described by Williams (1980). The in situ strength and moduli, required for this analysis, have been determined by pressuremeter testing. A significant portion of this testing has been carried out using a high pressure pressuremeter described by Hughes and Ervin (1980).

Design, Fabrication, and Installation of the Ninian Field Southern Platform

In an effort to eliminate problems previously experienced in fabrication and installation of large steel structures, emphasis for the Ninian field southern platform was placed on designing for those factors as well as for functional and long-term loadings. This paper describes design and innovative features of the structure. Introduction Chevron's Ninian field southern platform is noteworthy for its rapid planning, design, fabrication, and extremely successful installation, all of which justified the conceptual philosophy adopted early in the design stage. The aim was to build on past experience and to provide simplicity and refinement within the limits of available technology, consistent with a summer 1977 installation of a platform capable of supporting the heaviest deck load yet proposed for a piled steel structure. These goals, together with severe functional and environmental criteria, resulted in a number of interesting features.This paper describes the process leading to the selection of a self-floating steel tower and outlines the manner in which considerations of fabrication, transportation, and installation influenced the configuration of structure and piles. Selection of Platform Type, Factors Influencing Configuration It was believed that the success of the proposed program would rely as much on designing for fabrication and installation requirements as on structural analysis and design. In the overall development cost, the effect of saving structural steel weight by virtue of exhaustive analytical work is insignificant; on the other hand, time spent on designing for fabrication and installation can result in significant cost savings. Description of Tower The Ninian field southern platform is a four-leg, piled, steel-tower structure supporting modular production and drilling facilities (Fig. 1). It is a self-floating unit with an integral ballasting system designed for remote-controlled operation.The deck comprises two levels of modules, 65 × 68 m in plan, providing three main levels, with a nominal production capacity of providing three main levels, with a nominal production capacity of 150,000 BOPD. Maximum anticipated deck load is 26 000 t, including two drill rigs. Slots are provided for 42 conductors.Typical dimensions are 75 × 75 m center to center of the legs at the mudline, tapering to 55 × 55 m at the top of the module support skid beams. Overall height from mudline to skid beams is 168.5 m.The tower is supported by 32 skirt piles, 1825 mm OD with walls 63 mm thick, arranged in clusters of eight at each leg in a 12.2-m diameter circular pattern.Storage is provided in the upper parts of the 9.2-m diameter flotation legs for 20,000 bbl of diesel fuel and 10,000 bbl of drilling water. JPT P. 1366

Evaluation of Semisubmersible Drilling Vessels

Evaluation of motion characteristics, structural integrity, and stability of semisubmersible drilling vessels can be done in several ways. Computer programs for predicting semisubmersible motions and for evaluating semisubmersible stability have been developed. Methods for calculating the range of heave values in regular and irregular waves, and for analyzing stresses in irregular seas are presented. Introduction This paper describes methods for evaluating and comparing motion characteristics, structural integrity, and stability of semisubmersible drilling vessels. A computer program for predicting semisubmersible motion is presented, along with evidence of its validity. The range of heave values calculated for nine different rig designs is shown for both regular and irregular waves. A method for analyzing stresses in irregular seas and a computer program for evaluating semisubmersible stability is described. Design Considerations Any semisubmersible drilling vessel is necessarily a compromise between many design considerations. Not everyone will agree on the best compromise among conflicting requirements, as evidenced by the fact that semisubmersibles presently under construction or built since 1972 have at least 16 significantly different designs. What are some of these design considerations? A major operating consideration is that the vessel have minimum motion in waves to provide a good drilling platform. Another consideration is mobility, since platform. Another consideration is mobility, since semisubmersible drilling vessels are used primarily for exploratory drilling. Factors influencing mobility are the vessel's over-all towing resistance and whether the vessel is self-propelled or assisted by propulsion. Other design considerations include load-carrying capacity, maximum deck load, and storage capacities. These items influence the operating flexibility of the vessel and the frequency with which it must be resupplied. Some rigs have had ease of fabrication and reduced steel weight as major design goals. These two goals are part of what must always be a major design consideration - cost, since there is a limit to how much an operator can pay for a rig. No design is acceptable, however, unless it meets minimum safety requirements. Two of these requirements are adequate structural integrity and adequate vessel stability. (Stability here refers to the vessel's ability to resist capsizing caused by overturning moments such as those from wind forces.) Evaluation of motions, structural integrity, and stability of semisubmersibles will be discussed. Other design considerations are mentioned because they are interrelated with these; but it is beyond the scope of this paper to discuss them in detail. Motions The motion characteristics of a semisubmersible vessel can be evaluated in three ways:observe the motions of a prototype in the field,conduct model tests in a wave tank, andpredict analytically the motion characteristics with a computer. All three should be and have been used, but the third method has definite advantages in time, cost, and flexibility. An added benefit of using a computer to calculate motions is that the dynamic forces in the structure are also calculated and can be used in the structural evaluation of the vessel. JPT P. 422

A Vessel for Offshore Construction In Heavy Seas

A new generation of construction equipment an evolving for offshore work in heavy seas. The progenitor of the line is Choctaw, the world's first column-stabilized construction barge. She is capable of sustaining operations in seas up to 16 feet and of maintaining her station in unrestricted oceans. Foreword Increased worldwide demand for oil and oil products, together with political uncertainties in some of the major oil producing areas, is accelerating the search for oil offshore and extending its boundaries to deeper and rougher waters. Offshore oil production necessitates the construction of platforms and production facilities, as well as underwater storage and pipelines. A great many construction barges have been built to fill this need. Until June, 1969, all construction barges had conventional box-shaped hulls, a feature that limited their operations to seas not exceeding 5 ft. Because of the excessive motion in high seas, these barges had to be towed away to sheltered waters whenever a storm was forecast. In June, 1969, the construction barge Choctaw was christened. Choctaw represented an important turning point in the industry in that she is the first column-stabilized construction barge and is capable of sustaining operations in seas up to 16 ft and maintaining her station in unrestricted oceans. The design principles used in the vessel are discussed in detail in Ref. 2. To restate the basic design philosophy, the designers recognized that a construction barge is seldom called upon to use her maximum crane capacity. For this reason, Choctaw was designed to operate in two different drafts. In the low draft, the crane can handle up to 800 tons at 90-ft outreach, and in the high draft, the crane can handle 150 tons at 110 ft with full deck load and no ballast compensation. On several occasions the vessel was called upon to perform lifts heavier than 150 tons while in the high-draft condition. These exercises were carried out by maintaining the list angle to a minimum through transfer of ballast. Lifts of this type necessitate that careful planning and exacting calculations be carried out by the barge engineers. The crane was designed to sustain a dynamic load produced by roll motion of 5 degrees in 9 seconds double produced by roll motion of 5 degrees in 9 seconds double amplitude (for all but the 800-ton load condition). The force produced by a 50-knot wind was superimposed on the dynamic loading. The crane was designed to sustain a 3 degrees barge list when lifting 800 tons. The vessel was designed to operate in adverse climates: in temperatures ranging from -35 degrees to + 120 degrees F. Both design and construction were closely monitored and approved by Lloyd's Register and the U.S. Coast Guard.