SUSTAINABLE AND GREEN IMPROVEMENTS IN ARMY CORPS HOPPER DREDGES

Transcription

1 SUSTAINABLE AND GREEN IMPROVEMENTS IN ARMY CORPS HOPPER DREDGES Timothy Keyser, P.E. 1 and Greg Lee, P.E. 2, ABSTRACT The U.S. Army Corps of Engineers operates a fleet of four ocean going hopper dredges and one small special purpose hopper dredge. In order to perform their dredging missions, while reducing impacts to the environment, the vessels have required upgrades and modifications to increase their efficiencies, lower their carbon footprints, and minimize pollution to the marine environment. This paper surveys Corps of Engineers efforts to develop and implement sustainable and green improvements and modifications for the hopper dredges. In March 2009, the installation of a Power Management System (PMS) on the Dredge ESSAYONS was completed. After almost two years of service, actual fuel reduction and efficiency results are presented. Additionally, the design and model testing of a retrofit bulbous bow for the Dredge ESSAYONS was recently completed. This paper will present the project results and they indicate a retrofit bulb can be effective and reduce wave generated resistance. Furthermore, a small split-hull hopper dredge, currently under construction, is designed with a water hydraulic split hull actuating system. The water hydraulic system will eliminate accidental pollution from leaks or spills involving traditional hydraulic fluid. The considerations, design and selection of the water hydraulic system are presented. Finally, the Corps is investigating the use of other leading sustainable and environmental technologies on various vessels in our fleet. Initial investigations into hybrid power applications on dredges are presented, along with brief discussions on the use of environmentally friendly lubricants and hydraulic fluids, and a look ahead to complying with stricter environmental regulations and potential applications for sustainable improvements within the Corps fleet. Keywords: Fuel efficiency, power management system, bulbous bow, water hydraulics, hybrid system. INTRODUCTION The Corps has six environmental operating principals that drive management, design, construction and operation activities. The first environmental operating principal is: Strive to achieve Environmental Sustainability. An environment maintained in a healthy, diverse, and sustainable condition is necessary to support life. The Marine Design Center (MDC) of the Corps works to incorporate this principal into all of their projects (new construction, repowering, dredges, barges, survey boats, etc.). The Corps is striving to become more sustainable for the preservation of natural resources, the environment and for future generations. The primary initial focus on the hopper dredge fleet to support sustainability goals has been reducing fuel consumption. With respect to environmental impact, there are numerous regulations in place promulgated by the US Coast Guard (USCG), the US Environmental Protection Agency (EPA), the International Maritime Organization (IMO), etc. that regulate everything from engine exhaust emission limits, to ballast water discharge and management, to the practice of cleaning the weather deck with a fire hose. In this area, the Corps is constantly working to ensure our vessels are in compliance with applicable regulations. In many cases steps have been taken to use advanced technologies/products to exceed the minimum requirements. The MDC is very conscious of potential adverse 1 Senior Naval Architect, U.S. Army Corps of Engineers Marine Design Center, 100 Penn Square East, Room 630 South, Philadelphia, PA 19107, USA, T: (215) , Fax: (215) , timothy.j.keyser@usace.army.mil. 2 Chief, Design Branch, U.S. Army Corps of Engineers Marine Design Center, 100 Penn Square East, Room 630 South, Philadelphia, PA 19107, USA, T: (215) , Fax: (215) , timothy.j.keyser@usace.army.mil. 293

2 impacts various systems, equipment, fluids, etc. can have on the environment and strive to minimize risk by eliminating sources where possible and through operational mitigation. The sustainable and environmental technologies sectors are quickly expanding and the MDC capitalizes on opportunities to apply proven technology to improve the sustainability of the Corps fleet, to minimize the environmental footprint and improve our role as environmental stewards. ESSAYONS REPOWERING In 2007 and 2008 the Dredge ESSAYONS underwent a major repowering and overhaul project. The Portland District was experiencing several problems and the repowering was intended to address three main goals as follows: Increase propulsion and bow thruster power to restore as delivered levels of maneuverability to the Essayons, while operating at deeper drafts and greater displacements attained from freeboard reassignment. Replace the original equipment engines with new Tier 2 Emissions Compliant engines. Allow more efficient generator usage by providing for power transfer between the 480 VAC Ship Service and 600 VAC Dredging power systems. Upgrade the original equipment monitoring and automation/control systems. The repowering project for the dredge replaced all of the engines, generators, various automation systems (Integrated Control and Monitoring System ICMS, Propulsion Control System PCS, and modifications to the Dredge Control and Monitoring System DCMS), installation of variable frequency drives for the overside dredge pumps, engine room supply fans, and a new bow thrusters. In addition, the project also included the installation of a Power Management System (PMS), replacement of the 480V and 600V switchgear, and the installation of a stepup/down transformer between the 480V and 600V switchgear. The original configuration of the engines and generators on the ESSAYONS was: Propulsions (Direct Drive) Two (2) EMD E7 (3,600 HP each) 600V Dredge Service Bus (DSB) Diesel Generators Two (2) EMD E7 (3,600 HP each ) 480V Ship s Service Bus (SSB) Diesel Generators Three (3) Caterpillar D399 (1,072 HP each) 480V Emergency Service Bus (ESB) Diesel Generator One (1) 201 HP Detroit Diesel The ship s service loads and bow thruster were powered through the 480V switchgear, and the dredge pumps were powered through the 600V switchgear. The repowered configuration of the engines and generators on the ESSAYONS is now: Propulsions (Direct Drive) Two (2) Caterpillar C (4,640 HP each) 600V Dredge Service Bus (DSB) Diesel Generators Two (2) Caterpillar C (4,640 HP each) 480V Ship s Service Bus (SSB) Diesel Generators Three (3) Caterpillar 3512B (1,476 HP each) 480V Emergency Service Bus (ESB) Diesel Generator One (1) Caterpillar C-18 (624 HP) The new arrangement powers the dredge pumps and the bow thruster through the 600V switchgear, while the ship s service loads remain on the 480V switchgear. The 600V and 480V busses are linked with a bus tie and transformer, so that any generator can power any load. A Power Management System manages generators and loads on both busses. The ship can now operate on basically any configuration of generators and supply all loads. The 480V SSB can supply the 600V DSB through the transformer; and vice versa the 600V DSB can supply the 480V SSB. Figure 1 is the Electrical Single Line diagram. 294

3 Figure 1. ESSAYONS Electrical Single Line Diagram (Ockerman 2008) ESSAYONS Power Management System The PMS is a programmable logic controller (PLC) based system designed and installed by Ockerman Automation Consultants from Anacortes, WA. The system is largely comprised of Siemens equipment and components. All programming was performed by Ockerman Automation Consultants. The system utilizes a dual fiber optic ring bus configuration with backup uninterruptible power supply (UPS) units to add system redundancy and reduce the possibility of losing any equipment due to automation system failure. The purpose of the PMS system is to (Ockerman 2008): Optimize the number of generators connected to the bus relative to fuel efficiency and at the same time provide a sufficient reserve capacity of power based on user defined presets. Provide proportional load sharing in a symmetrical & asymmetrical plant configurations - based on user defined presets. Automatically manage Heavy Consumers (HC s) based on user pre-sets. Automatically control load shedding based on user defined presets Automatically restart of engines to restore power following a Black Out condition based on user defined presets. The PMS system is Mode dependent meaning that the operators select to run the system in Automatic Mode, Semi-Automatic Mode, or Secured Mode. Each of the power systems (i.e. Bus) can be operated together, or independently. The intent of the PMS arrangement is to provide a high level of flexibility and power arrangement/availability options to the operations. The complete system and functional overview of the PMS is outside the scope of this paper. 295

4 Emissions & Fuel Reduction Results The results provided are the direct fuel consumption comparisons between pre and post repowering arrangements and operations. Prior to the repowering, the crew of the ESSAYONS has fuel usage records dating back to The records provided average fuel consumption per day based on the dredging location. The crew has maintained the same record for the 2009 and 2010 dredging seasons, with an average fuel consumption per day based on the dredging location. For all recorded dredging locations, the ESSAYONS has experienced fuel savings. When compared to previous dredge operating seasons from 1996 to 2007, daily fuel consumption has been reduced by an average of approximately 18%. When compared to the more recent operating seasons right before the repowering (2004 to 2007), the daily fuel consumption has been reduced by an average of approximately 10%. So, depending on how the data from previous years is grouped and analyzed, fuel consumption has been reduced between 10% and 18% by installing new engines, a flexible power distribution system and by more efficient operation. Analyzing the low end of the recorded fuel savings, a 10% reduction in daily fuel consumption is equivalent to approximately 650 gallons of fuel. The 18% high end of fuel reduction results in 1,150 gallons per day savings. When analyzing the old versus the new ships power plant as a whole on a potential to emit basis (grams per hour), this equates to an overall reduction of approximately 21% in ROG (Reactive Organic Gases), 45% in NOx (Nitrogen Oxides), and 83% in PM (Particulate Matter). The numbers provided are approximate since the operational characteristics of the ships power plant have changed with the repowering, but the reduction percentages are assumed to be on the same level of magnitude as a more detailed analysis. Between the efficiencies in modern engines when compared to the original engines, the difference in overall horsepower, the PMS and the more efficient modes of operation, there is not enough detailed information to make a specific per-engine comparison of the fuel consumption and actual emissions generated. It is clear though, that the new Tier 2 engines and the Power Management System are resulting in significant fuel savings and are helping to improve the sustainability and environmental footprint of the Dredge ESSAYONS. ESSAYONS Original Hull Design ESSAYONS BULBOUS BOW STUDY The dredge ESSAYONS is 350 feet in length, by 68 feet in beam. The original ballasted/transiting operating mean draft was 17-4, and 28-0 full load. The ESSAYONS was designed in the 1970 s, and the as designed hull form did not have a bulbous bow. Bulbous bows are the normal configuration for current technology hopper dredges comparable in size to the ESSAYONS. Model tank testing of the original Essayons hull form was done as part of the design process. The hull was designed for operations in the 10 knot to 14 knot speed range. Increased Operating Draft Recent changes to the original ESSAYONS Load Line assignment allowed the maximum mean draft to increase from 28-0 to As a result the ESSAYONS current operation is at drafts exceeding the original hull resistance optimization draft. Bulb Retrofit Concept & Initial Evaluation: It was thought that a retrofit bow bulb, designed using current best technology techniques, might provide an avenue to offset the added resistance from the draft increase. An initial evaluation of the effectiveness of a bulbous bow on the ESSAYONS was conducted, using Computational Fluid Dynamics (CFD) methods. The CFD investigation was conducted by Friendship Systems GmbH. Friendship Systems was asked to design and fit a bulbous bow so as to improve the hydrodynamic performance of the dredge at the new mean full load draft (29-8 ) and at the mean transit draft (16-10 ) condition at a speed of 14 knots. The bulb configuration reflected a retrofit application, in that it was an add-on shape to the existing bow, with no hull shape changes beyond the area of the bulb. Through the use of CFD, ten significant bulbous bow forms and variations of them were analyzed. All told, 340 bulb designs were 296

5 generated and analyzed (Hochkirch, 2006). Figures 2 and 3 show a comparison of the original hull and the hull with the CFD designed bulbous bow 3. Figure 2. ESSAYONS Panalization, bottom: Baseline, top: OPTBULB Figure 3. ESSAYONS Panalization, right: Baseline, left: OPTBULB 3 Figures 2 through 9 are from Hochkirch (2006) 297

6 Figures 4, 5, 6 and 7 show a comparison of the wave contours and dynamic hull pressures between the original hull form and the hull with the CFD designed bulbous bow. Figure 4. ESSAYONS Comparison of wave contours at Full Load, bottom: Baseline, top: OPTBULB Figure 5. ESSAYONS Comparison of wave contours at Transit Load, bottom: Baseline, top: OPTBULB 298

7 Figure 6. ESSAYONS Comparison of wave contours and dynamic hull pressures at Full Load, left: Baseline, right: OPTBULB Figure 7. ESSAYONS Comparison of wave contours and dynamic hull pressures at Transit Load, left: Baseline, right: OPTBULB 299

8 Figures 8 and 9 represent the various views of the OPTBULB fitted to the original hull form. Figure 8. ESSAYONS OPTBULB, left: Bow View, right: Starboard View Figure 9. ESSAYONS OPTBULB, left: Bottom View, right: Isometric View The CFD design and analysis revealed that around the design speed of 14 knots, significant resistance reductions could be achieved at both draft conditions. At speeds less than 10 knots, the positive effect of the bulbous bow on the wave formation becomes smaller and eventually vanishes. The CFD predicted resistance reduction at the mean full load draft and 14 knots is 16.7%. The CFD predicted resistance reduction at the mean transit draft and 14 knots is 15.6%. 4 Bulb Retrofit Model Test Evaluation: The CFD bulb design compared predicted resistance and Effective Horsepower (EHP) with bulb to the resistance and EHP results from the original design model tests for the original hull (as built). Since the original model tests did not extend to the current ESSAYONS maximum draft, there was no direct comparison possible between the CFD results and the model tests at drafts above the original ESSAYONS Load Line Draft of All of the CFD analysis and results presented in this paper are from Hochkirch (2006). 300

9 In order to validate the CFD bulbous bow design work and resistance predication a new set of towing tank resistance tests was conducted at the US Naval Academy. The goal of the tank tests was to provide a direct comparison of resistances with and without the bulbous bow. The model was constructed with two bow forms, one as per the original hull form, and the second with the retrofit OPTBULB from CFD design work. The bow forms were interchangeable on the main hull form. Figures 10 and 11 show the model with the original bow and with the bulbous bow, respectively (Waters 2007). Figure 10. ESSAYONS Model Original Hull Form Figure 11. ESSAYONS Model Bulbous Bow 301

10 The tank tests were conducted over a speed range between 4 knots and 14 knots, and over a mean draft range of 17-1 to 32-3½. The model test results confirmed that at the higher speeds, the EHP is reduced when comparing the bulb hull form to the original hull form. At the mean full load (29-6¾ draft) and at 14 knots, the EHP for the bulbous bow hull form was reduced 18% when comparing it to the original hull form. However, as was predicted in the CFD work, the EHP at lower speeds can increase when comparing the bulb hull form to the original hull form. The results showed that in most loading conditions, the EHP when comparing the bulb and original hull forms is greater for the bulb hull form at speeds less than 12 knots. Figure 12 shows a ratio comparing the bulb and without bulb hull forms of the EHP versus speed for various loading conditions. 5 Figure 12. ESSAYONS Tank Test Results: EHP Ratio of Vessel with Bulb/without Bulb versus Speed for Various Loading Conditions The test resistance results compared well with the calculated CFD resistances. However, the actual wave pattern from the tank testing was visibly different from the wave Pattern generated with the CFD. Dredge Operating Conditions & Overall Efficiency From a Bulbous Bow The actual resistance improvements in operation from a bow bulb are limited because hopper dredge operation is comprised of 3 usual modes of operation, at differing drafts and speeds. For the Essayons these are as follows: Hopper Empty Transit, 20 foot draft, 10 to 14 knots Hopper Full Transit, 30 foot draft, 10 to 14 knots Dredging, draft ranges from 20 to 30 feet as hopper fills, 4 to 6 knots. The majority of operating time is transiting between dredging sites, and transiting back from the dredge dump location to the dredging location, both with the hopper empty. These operations are typically performed at an approximate 20 foot draft. 5 All of the tank test model results presented in this paper and Figure 12 are from Waters (2007). 302

11 For the Essayons, a bow bulb can reduce resistance at both 20 and 30 foot drafts in the speed range of 12 to 14 knots. However, the bulb will add resistance for transiting at 10 knots and while dredging at 4 to 6 knots, because there is not sufficient speed through the water to generate the bow wave & bulb canceling wave forms. Estimated Costs and Next Steps If this project continues to move forward, a more detailed analysis of the ESSAYONS operating profile will be developed, to provide a better optimization target for the bow bulb. The bulb will be revised for the better target using the CFD procedures used for the initial evaluation as described above. The performance of finalized bulb form will be validated with towing tank testing. A life cycle benefit cost analysis will be performed to determine the potential operational savings versus the retrofit costs. WATER HYDRAULICS ON CORPS SPLIT-HULL COASTAL HOPPER DREDGE Hopper Dredges typically are fitted with extensive hydraulics systems. The environmental issues presented by oil based hydraulics fluids are well known. Many efforts across multiple industries are ongoing to reduce the environmental issues associated with hydraulics system. The Corps is currently constructing a new split-hull shallow draft dredge name the MURDEN which will be operated out of the Wilmington District. The construction of the new vessel is ongoing at Conrad Industries in Morgan City, Louisiana, and the vessel is scheduled for delivery in August Figure 13. Concept Rendering of the Dredge MURDEN The split-hull function of the vessel requires large hydraulic cylinders to open and close the two hulls. The hydraulic cylinders are located below the waterline and as a result any leak of hydraulic oil will be directly into the surrounding waters. In order to eliminate the risk of oil contamination, the Corps utilized a water hydraulics system for the hull opening cylinders. Water Hydraulics Compared to Oil Based Hydraulics Compared to conventional oil based fluid systems, water hydraulics systems are less broadly applicable, for several primary reasons. These are as follows: Corrosion Water as hydraulic fluid will cause corrosion in critical components unless the components are fabricated specifically of non-corrosive materials. 303

12 Lubricity Compared to oil based hydraulic fluids, water has essentially no lubrication properties, especially in high pressure applications. Specially designed pumps, seals and valving components are required for water hydraulics. Heat Water boils (and turns to steam); thus limiting the power that can be transferred by water systems. Water Hydraulics for the Dredge MURDEN The hull opening/closing hydraulic rams & hydraulic system were designed as a water hydraulics system. The hull opening/closing system was a good candidate for water hydraulics for the following reasons: The hydraulic cylinders are large and contain large amounts (300 Gallons) of hydraulic fluid. The leakage risk is therefore large. The cylinders are located below the dredge light waterline. Any leakage from the cylinders will immediately be in sea water. There is reasonable method of leak collection before contamination can occur. The hull opening/closing system operates at low speeds (75 Seconds to open), and relatively low pressures (1,000 PSI). Hull opening & closing are intermittent as opposed to continuous operations. The hull opening/closing system is segregated from the other vessel hydraulics, and has limited pipe run lengths. In summary, the hull opening/closing system is well suited to water hydraulics because pressures are not high, and because the system power, speed and frequency of operation will not generate large amounts of heat. The shortcomings of water hydraulics in the areas of lubricity and heat are minimized in the hull opening/closing system operation. The system was designed by BOC Water Hydraulics, Inc., of Salem, Ohio. The system is comprised of two 16 inch bore, by 86 inch stroke hydraulic cylinders, with a 80 HP hydraulic pump system (two 40 HP pumps, gpm each) and a 300 gallon reservoir. The system operates at 900 PSI nominal pressure, and the cylinders can each develop a maximum of 180,000 pounds of force. The hydraulic fluid will be tap water, with non-toxic anti-freeze. The water hydraulics hull opening/closing hydraulics system was reviewed by the American Bureau of Shipping (ABS) as part of the vessel ABS Class Review. Figures 14 and 15 show the arrangements of the opening/closing cylinders in the split hulls. Figure 16 is a photograph of one of the two hydraulic cylinders. It should be noted that the hydraulic cylinders can be operated using either water or conventional hydraulic oil. Operating experience on this system is not available yet as the MURDEN is not yet completed and in operation. If the system proves out as expected, the use of water hydraulics will be expanded to other hydraulics systems in the Corps floating plant fleet. 304

13 Figure 14. MURDEN: Hull Cylinder Closed Position Figure 15. MURDEN: Hull Cylinder Open Position Figure 16. MURDEN Water Hydraulic Cylinder 305

14 CORPS APPLICATIONS OF OTHER LEADING TECHNOLOGIES In addition to the improvements that Corps has made to our hopper dredge fleet, we have been applying other leading sustainable and environmental technologies throughout the entire fleet. The goal is to be able to incorporate these technologies, where applicable, into the hopper dredge fleet as funding and maintenance/repair periods become available. Plug-In Hybrid Vessel Design The MDC is currently developing a true plug-in diesel-electric/battery hybrid vessel design to replace the DRIFTMASTER, which operates out of New York Harbor. The DRIFTMASTER is a purpose built 100 foot catamaran debris collector that was built in The vessel performs daily patrols within New York Harbor and Long Island Sound to remove debris that are hazards to navigation. The reason MDC selected this design project to apply battery technology is because the operating profile for the vessel is ideal for the existing technology. The DRIFTMASTER operates as a day boat, spending 10 hours per day out working the debris mission, with the remainder of the day dockside. The DRIFTMASTER currently patrols at a ten and twelve knot cruise speed. While performing the drift removal functions, the vessel will operate between zero and three knots. The crew estimates that during a typical day, they are performing these functions, with the low propulsion power demand, for 50% of the time, or five hours. The combination of low propulsion demands during the drift removal operations and the ability to plug-in to shore side commercially generated power made the DRIFTMASTER Replacement design the ideal candidate for the Corps to explore diesel-electric/battery hybrid designs. Catamaran Hull Form The new replacement design is longer than the original vessel at 130 feet. The additional length will provide better hull speed to length ratio for an emergency response speed requirement, and to satisfy modern intact and damage stability requirements. The new hulls were design as asymmetric hulls with flat inboard sides, to reduce resistance and to improve the debris net function. The current speed and resistance predications put the top speed between 16 and 17 knots. Hybrid Power System Overview As an overview, the design of the hybrid system utilizes: Five (5) 550kW Permanent Magnet water cooled generators Two (2) 1,500 HP Propulsion Motors 2,500 kw-hr storage capacity Lithium Battery Banks DC Power Bus with variable RPM generators The 2,500 kw-hr of battery sizing was determined from the following rationale: Normal average power load, including propulsion, over the 10 hour daily debris collection day in New York Harbor is 500 kw per hour. o Therefore, the total daily (for a 10 hour day) power consumption is 5,000 kw-hrs. It was determine that the hulls can carry a total of 60,000 to 70,000 pounds of batteries. o The physical storage requirements, along with the impact on the hydrostatics, were taken into consideration. Selecting Lithium Batteries, which weight range corresponded to a 2,500 kw-hr battery bank. If charged overnight from shore power on the municipal utility grid, the battery power can provide half of the total daily power for the vessel. 306

15 Generator Use In addition to providing up to half of the daily power for the vessel, the hybrid system also maximizes efficient use of the diesel-electric generators because the batteries can provide a buffer from its energy storage if spike loads that exceed the power available from the generators on-line occur. The power available from the battery bank allows the minimum number of generators on-line to match the load, which maximizes the fuel efficiency of the generators. The improved load match between the generators and the ship load is expected to improve fuel efficiency by between 2% and 5%. DC Power Bus & Variable RPM Generators The DC Power bus eliminates the need to synchronize generators to match frequency. Further, the DC power bus also allows the generators to run at variable speed. The variable generator speed allows each generator engine to be programmed to run at the most fuel efficient RPM for any load applied. The buffering capability from the batteries will also provide support over the time required for generator RPM increases in response to larger loads. Life-Cycle Cost Analysis The Plug-In capability, charged over night from the municipal power grid, provides an approximate 40% savings in diesel fuel consumption and emissions for a typical 10 hour debris collection day. For the life cycle cost analysis, the following parameters were used: Battery Life 10 years Engine Life 15 years Annual Increase in Fuel and Off-Peak Electrical Costs 5% Additional Construction Costs for Battery Bank System over Conventional Diesel-Electric: $6,000,000 Using the parameters above, the life cycle costs analysis after 30 years shows a positive return of approximately $1,000,000 from installing the hybrid system. Although the specific figures for reduced emissions have not been calculated, while the vessel is operating off of the batteries and the generators off-line, the emissions production can eliminated, thus contributing to the overall emissions reduction for the vessel s operation. Potential Broader Applications for Hybrid Power Systems The hybrid system as described above incorporates features that can provide broader shipboard applications. These are generally as follows: Permanent Magnet Motors Permanent magnet motors and generators (alternators) are considerably smaller and lighter than conventional induction motor and alternator types. Size and weight are normally two of the most important differences between diesel-electric power systems, and conventional geared diesel with generators systems, with diesel-electric being larger and heavier. The permanent magnet equipment makes a considerable improvement in the comparison between dieselelectric and conventional systems. Battery Banks Large battery banks for use in the plug in hybrid mode are limited in use to vessel operations that can support pier side battery charging times, and large kw power grid charging power. This is uncommon in typical work boat service. 307

16 However, a considerably smaller battery bank can provide a generator buffer capability to absorb spike loads for the short time period required to start another generator. This provides the capability to run a diesel-electric system very efficiently, with only sufficient generators on line to match power demand. Generator loading does not need to be limited to a partial percentage to provide capacity for load spikes. The battery bank takes the load spike while the next generator starts and comes on line. DC Power Bus The DC power bus requires multiple generators on line to share load, but does not require frequency synchronization. DC power bus can also accommodate (DC) battery power. The DC bus provides the system functionality to utilize the battery bank capability described above. Variable Speed Generators The DC power bus does not require generators to synchronize frequencies. Therefore, a generator working with a DC power bus can operate at varying RPM. This allows the generator engine control to match the most efficient engine operating point to the load demand on the generator. For partial generator loads, the fuel savings from variable speed, as compared to constant rated speed operation can be 10% or more. These technologies can be evaluated for specific work vessel types on a case by case basis. Some or all of them may be viable for specific vessel designs. Any of them can provide improvements in efficiency and sustainability over conventional power systems. Environmentally Friendly Lubricants and Hydraulic Fluids As mentioned earlier in this paper, the hazards of lubricants and hydraulic fluids in the environment are well known. For many applications, providing a water hydraulic system is not feasible due to the pressures and temperatures that the system requires. During the design and construction of new vessels, spill containments are placed to minimize the possibility of an accidental discharge. In some instances, the ability to contain an accidental discharge is not practical. In order to minimize the impact to the environment in these circumstances, the Corps is moving away from petroleum-based fluids and lubricants and selecting environmentally friendly fluids and lubricants. The terms Environmentally Friendly and Biodegradable with respect to lubricants and hydraulic fluids are buzz words in the industry today. There are numerous products available that claim to be environmentally friendly, inherently biodegradable, non-sheen, etc. The MDC has evaluated US and international standards with respect to various environmentally related characteristics/criteria for hydraulic fluids and is currently working to develop comprehensive requirements for Environmentally Friendly Hydraulic Fluids. Based on our currently knowledge, we are considering the following fluid characteristics when considering if a fluid is Environmentally Friendly : Biodegradability Eco-Toxicity Generation of Sheen Biodegradability For all intents and purposes, all petroleum based fluids are inherently biodegradable. What that means is that over an infinite period of time, the fluid will complete break down and biodegrade. The concern with an inherently biodegradable fluid is that the period of time to completely biodegrade may be 30 days, 6 months, 60 years, etc. The fluid characteristic that MDC will require is that the fluid be Readily Biodegradable. Currently MDC is evaluating two reference documents that have different criteria for the Readily Biodegradable classification. Considering the method outline in OECD 301 F, a fluid is Readily Biodegradable if 70% of the dissolve organic compounds (DOC) are removed after 28 days. Other tests (OECD 301 A, B, C, & D) will be considered as well. When considering the method outlined in ASTM D (2006), 80% loss of starting material is required in 21 days to be considered a Pw-C fluid, or the highest grade for primary biodegradation. In addition, the standard 308

17 contains Ultimate Biodegradation tests, which require the percent of CO 2 and O 2 remaining after 28 days to be 60% and 67% respectively for the fluid to be considered Pw1. When using the ASTM criteria, MDC will be looking for both the Pw1 and Pw-C designations. At this time, MDC will consider a fluid that satisfies either the OECD or the ASTM criteria as Readily Biodegradable. A fluid that is only inherently biodegradable does not meet the intent of an environmentally friendly fluid. Eco-Toxicity Toxicity of a fluid is usually expressed in the following terms (Totten 1999): LCXX: The lethal concentration to cause the death of XX% of the test organisms. ECXX: The effect concentration for some environmental effect such as growth or deformity to occur in XX% of the test organism. The US Fish and Wildlife Service Aquatic Toxicity Classification Scale, found in Research Information Bulletin 84-78, is provided in Table 2. MDC will consider a fluid to be environmentally friendly if they receive a LC/ EC 50 Practically nontoxic ( > mg/l or ppm) or Relatively harmless ( > 1000 mg/l or ppm) classification for aquatic invertebrates, fish and micro-organism. In addition, the fluid can not contain any hazardous compounds or heavy metals. Generation of Sheen Table 2. U.S. Fish and Wildlife Service Aquatic Toxicity Classification Scale Classification LC50 (mg/l or ppm) Super Toxic >0.01 Extremely Toxic Highly Toxic > Moderately Toxic > Slightly Toxic > Practically Nontoxic > Relatively Harmless >1000 Fluids used in the off-shore oil and gas exploration and extraction industry are required to comply with 40 CFR 435, Subpart A, Appendix 1 Static Sheen Test. Part 1 of the Appendix, Scope and Application states: This method is to be used as a compliance test for the no discharge of free oil requirement for discharges of drilling fluids, drill cuttings, produced sand, and well treatment, completion and workover fluids. Free oil refers to any oil contained in a waste stream that when discharged will cause a film or sheen upon or a discoloration of the surface of the receiving water. The observation/test requirements in part 8.6 of the Appendix state: Detection of a silvery or metallic sheen or gloss, increased reflectivity, visual color, iridescence, or an oil slick on the water surface of the test container surface shall constitute a demonstration of free oil. 309

18 In addition, part 8.6 also states: If an oil sheen or slick occurs on less than one-half of the surface area after the sample is introduced to the test container, observations will continue for up to 1 hour. If the sheen or slick increases in size and covers greater than one-half of the surface area of the test container during the observation period, the discharge of the material shall cease. If the sheen or slick does not increase in size to cover greater than one-half of the test container surface area after one hour of observation, discharge may continue and additional sampling is not required. If a sheen or slick occurs on greater than one-half of the surface area of the test container after the test material is introduced, discharge of the tested material shall cease. The permittee may retest the material causing the sheen or slick. If subsequent tests do not result in a sheen or slick covering greater than onehalf of the surface area of the test container, discharge may continue. Although there is no federal or state requirement for hydraulic oil on a hopper dredge, or other Corps vessel, to pass the 40 CFR 435 Static Sheen Test, the MDC is using this criteria as one of the three components for a fluid to be considered environmentally friendly. Current Corps Applications In July 2010, Conrad Industries delivered the Floating Crane MIKE HENDRICKS to the Little Rock District. The 260 foot long by 84 foot wide by 12 foot deep floating crane is outfitted with 11 hydraulic winches. Seven of those winches are located on the main deck, exposed to the weather and located near the sides or ends of the barge. The MDC required the hydraulic system to use an environmentally friendly hydraulic fluid that satisfied the three main criteria above. A polyalkylene glycol (PAG) based fluid was installed in the main hydraulic section. Based on information provided by the manufacturer, the PAG fluid provided achieved 72% biodegradation using the OECD 301 F method, is LC/EC50 classified as Practically Nontoxic for Daphnid (freshwater) and Mysid Shrimp (saltwater), and it passes the 40 CFR 435 Static Sheen Test. One additional positive characteristic of the selected PAG fluid is that it is Factory Mutual (FM) Fire Retardant Classification Approved. Despite the positive environmental properties, the PAG fluid does have other properties that must be taken into consideration. The PAG fluid is not compatible with some seals used inside hydraulic systems. It is imperative that the system manufacturer verifies the types of seals in a system and that they are compatible with the PAG fluid. Along the same lines, the solubility of PAG fluids with other oils is very low. For most other types of oils, the PAG fluid is insoluble. If a hydraulic system is shop tested with a standard mineral oil based hydraulic fluid, it is difficult and time consuming to repeatedly flush the system. Finally, one of the largest disadvantages of the PAG fluid is the cost compared to a traditional mineral oil. The initial fill cost for the PAG fluid installed the Floating Crane was between two and three times greater than a traditional mineral oil. At this time, the MDC does not have enough operational data on the performance, maintenance, and other feedback on the PAG fluid to report in this paper. However it appears as if this fluid s performance, hydraulically and environmentally, is very positive. Hence, the MDC is also installing other types of environmentally friendly hydraulic fluids on several vessels currently under construction. Pending the successful in-service use of the PAG fluid and other environmentally friendly fluids, the MDC will be looking for other opportunities, new builds and overhauls, to increase their use throughout the Corps fleet. Environmental Look Ahead Marine environmental regulations are becoming more comprehensive and stricter each year. Recently North America became an IMO - Emission Control Zone (ECA). Tier 3 and Tier 4 engine emission requirement deadlines are fast approaching. The US Environmental Protection Agency (EPA) National Pollutant Discharge Elimination System (NPDES) Vessel General Permit (VGP) is due to expire in 2 years, with potential new requirements to follow. Ballast water discharge regulations are quickly evolving and will soon become even more of a factor in vessel design and daily operations. Along with the Corps environmental guidelines and stewardship 310

19 responsibilities, these new requirements are just a few of the items that will drive the design of new vessel, the overhauls and repowerings of existing vessels, and the daily operations of our fleet. As we approach each new project and design, new design and retrofit, we are striving to achieve the following with respect to sustainable and environmental principals: Look to apply sustainable technologies (i.e. alternate power systems, reduced fuel consumption, reuse of engine exhaust heat, reuse of grey water, optimize hull forms, etc.) Look to reduce our impact on the environment (i.e. promote the use of recycled materials, reduce vessel wake formation, reduce noise generation, clean emissions, etc.) Design the systems with the most up-to-date proven technologies Design the systems to eliminate (or minimize) accidental discharges Maximize onboard storage of fluids (grey water, sewage, bilge, etc.) and minimize the necessity for overboard discharges Design automation, where practical, into the systems to reduce human error Ensure the vessels can easily be modified in the future to incorporate new technology (i.e. SCR exhaust systems, ballast water treatment systems, updated control and monitoring systems, etc.) Each new project that the Corps and MDC undertake allows us to reduce our environmental footprint and increase the sustainability of the fleet. CONCLUSIONS Given the opportunities, the Corps and MDC are looking for innovative ways to make sustainable and green improvements in Corps hopper dredges and throughout the fleet. The MDC has applied proven technologies throughout our projects to achieve positive sustainable and green results. Based on the board range of projects and features described in this paper, it is clear that our focus is not in one particular area, but in all areas of vessel design, construction, equipment, outfitting, monitoring and operation that can result in potential sustainable and green improvements. The opportunities for sustainable and green improvements are vast. The Corps and MDC have been successful with the projects undertaken and have seen documented fuel savings on the Dredge ESSAYONS. The CFD and tank test work reveal that with some additional design iterations, the ESSAYONS can achieve even more potential fuel savings with a bulbous bow. As the hybrid systems advance, the MDC is enthusiastic about use for fuel and emission savings. Although it is difficult to quantify and predict cost savings number, we are expecting the hydraulic fluids improvements to be successful as well. In the near future, the MDC will begin studying other potential sustainable and green improvement for the hopper dredges and the rest of the fleet to include, but not limited to: Engine exhaust gas heat recirculation Exhaust gas after treatment Reuse of grey water Environmentally friendly submerged motor transformer fluids Further utilization of CFD to optimize hull forms, appendages, propellers, design speed, etc. Developing specifications and cost analysis tools to promote the use of recycled materials Improve dredging efficiencies We are living in an exciting time where there is the opportunity to make a positive impact on the environment on each project that is initiated. The Corps will continue to look for ways to improve the sustainable and green features in the fleet and be environmental stewards and leaders. 311

20 REFERENCES ASTM (2006). Standard Classification of Hydraulic Fluids for Environmental Impact. ASTM D Federal Register (2011). Static Sheen Test. 40 CFR 435 Subpart A, Appendix 1. Hochkirch, K. (2006). Bulbous Bow Fitting and Hydrodynamic Optimization of the Hopper Dredge ESSAYONS. Friendship Systems GmbH. Ockerman, J. (2008). Dredge Essayons Power Management System Technical Documentation - Rev E. Ockerman Engineering. OECD (1992) Guideline for Testing of Chemicals, OECD 301. Totten, G.E. (1999). Handbook of Hydraulic Fluid Technology. Taylor & Francis, Inc. Waters, J.K (2007). Model test Results of the U.S. Army Corps Dredge ESSAYONS: With and Without Proposed Bulb Design. Department of Naval Architecture and Ocean Engineering, United States Naval Academy. U.S. Fish and Wildlife Service (1984). Research Information Bulletin CITATION Keyser, T. and Lee, G. Sustainable and green improvements in Army Corps hopper dredges, Proceedings of the Western Dredging Association (WEDA XXXI) Technical Conference and Texas A&M University (TAMU 42) Dredging Seminar, Nashville, Tennessee, June 5-8,