Channel Turns. Cape Fear River

Transcription

1 A Look at the Channel Turns in the Cape Fear River Revised November 5, 2011 Prepared for Save the Cape, Inc. Southport, North Carolina Contents The Channel in the Cape Fear River...2 Experience...7 Corps of Engineers Standards for Channel Turns The PIANC Design Guide The CH2M Hill, Inc., Cut-through Recommendation Conclusion... 15

2 A Look at the Channel Turns in the Cape Fear River All you gotta do is keep it between the lines -Russell Smith and Kathy Louvin (Recorded by Ricky van Shelton) The channel in the Cape Fear River permits ocean-going vessels to call at the Port of Wilmington, approximately 26 miles upriver from the mouth. The port includes the State Port, operated by the North Carolina State Ports Authority, and several private facilities, some on the property of the State Port. The channel is maintained at a depth of 42 feet, with a width of 400 feet, widened to 500 feet at the lower reaches at the mouth of the river. Because the continental shelf falls off only gradually at the river mouth, the dredged channel extends six and a half miles out to sea. The channel has a sharp turn in the lower reaches near Southport, followed by a reverse turn through the mouth of the river between Fort Caswell on Oak Island and Bald Head Island, describing a large S. That turn has been a problem for the larger ships navigating the river. The North Carolina State Ports Authority, a component of the North Carolina state government, has purchased 600 acres of undeveloped land on the Cape Fear River near Southport, and plans to develop an international container terminal to facilitate the import of goods from Asia in a new generation of very large container ships. The terminal would have an annual capacity of 3,000,000 twentyfoot equivalent units (TEU), larger than any container terminal in the eastern United States except the combined terminals at Port Elizabeth and Port Newark, New Jersey. The new terminal would be called the North Carolina International Terminal (NCIT). The design vessel for the NCIT is a a new generation of container ships (called post-panamax ) are too large to transit the Panama Canal, now or after the capacity increases under construction for opening in 2014: 1260 feet long, 185 feet in beam, and drawing 50 feet. Such vessels would require a channel 52.5 feet deep (plus a two-foot overdredge for maintenance of that depth) and 600 feet wide. Consultants to the North Carolina State Ports Authority, in preparing preliminary plans for the proposed container terminal, concluded that the standards of the US Army Corps of Engineers for channel width and turns cannot be met on a channel following the route of the existing channel because of the confines creating the S-curve at Battery Island. The consultants recommend bypassing the turn with a new channel on a relatively straight route from the proposed terminal site to the mouth of the river. We find that the existing channel turns do not comply with the standards of the Corps of Engineers for the vessels now using the Cape Fear River, cannot be enlarged to accommodate larger vessels, and indeed are unsafe for existing vessels. However, we do not endorse the proposal to create a new channel. The capacity of the Cape Fear River for a deepdraft navigation channel has already been exhausted.

3 The Channel in the Cape Fear River This is the chart of the lower Cape Fear River: The Corps of Engineers maintains the channel at a depth of 42 feet within the river, and at 44 feet south of the mouth to deep water. The width of the channel from Lower Swash northwards is 400 feet. The Battery Island, Southport Channel, and Smith Island Range sections are widened to 500 feet. The inshore channel at the Military Ocean Terminal at Sunny Point, shown at the top of the chart, is maintained at a depth of 32 feet. 2

4 The configuration of this channel follows the natural channel in the Cape Fear River. However, when first measured in Colonial times the depth of the river in the natural channel was three to six feet; the entrance to the river over the bar was ten feet deep. The present depth and dimensions of the channel are the result of this succession of dredging projects: 3

5 All of those projects followed the natural course of the river, which includes these turns near the river mouth: 4

6 The Wilmington District of the US Army Corps of Engineers initiated a project called the Wilmington Harbor Deepening project in 2000 to increase the depth of the channel from 38 to 42 feet. The channel was opened at a depth of 42 feet in Certain aspects of the project environmental mitigation and dredging of a turning basin at the Port of Wilmington remain in progress, and are planned for completion in The charts presented above reflect the dimensions and course of the channel resulting from that project. In the 1996 feasibility study leading to that project, the issue of the channel turns arose. The design vessel for that study and engineering analysis was a Panamax vessel the largest vessel then able to transit the Panama Canal with an overall length of 965 feet, beam of 106 feet, and design draft of 39 feet. Such a vessel raised issues of the configuration of the turns in the channel, which follows the natural course of the river. In Appendix D, Engineering and Design, to the Record of Decision released for that project in 1996, the Wilmington District compared the turns to the recently released criteria for channel turns in the Corps of Engineers Engineering Manual : Some of the turns did not fit the new criteria as far as the combinations of turn deflection angle and ratio of turn radius to ship length. It was decided that the authorized turn designs were adequate at this time. The turn widths will be studied during preparation of the plans and specifications as part of the ship simulation model. Although not mentioned, the turn in question is the turn at Battery Island. Moving downriver, this has a 65-degree turn immediately followed by a 30-degree turn, resulting in a 95-degree change of direction for vessels using the channel. This is immediately followed by a reverse turn to pass through the river mouth at Bald Head Island. The Corps of Engineers arranged for tests to be conducted at a private ship simulator, the Raymond T. McKay Simulation Training and Research Center at Dania, Florida, in The facility has a full-size mockup of a ship s bridge, and the ability to simulate response of a vessel in a programmed channel configuration under various conditions of current. Test runs were conducted for a design vessel of 950 feet overall length and 106-foot beam, drawing 38 or 42 feet, in both ebb and flood tides. In all runs, five for each test condition, the vessels left the marked channel. Although in a few runs grounding would have occurred, most runs were without incident because the naturally deep water on the outside of the marked channel provided the necessary space to execute the turn. At the suggestion of the pilots conducting the tests, a widener was added to the apex of the turn between Bald Head Shoal and Smith Island Range. Otherwise, the project proceeded with the original design of the channel configuration. This issue was not addressed in a later report, an Environmental Assessment issued by the Wilmington District in February 2000 for modifications of the alignment of the offshore part of the channel. A composite diagram of the simulation runs conducted with an inbound vessel of 42- foot draft in flood tide is shown on the next page. 5

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8 Experience The S turn has caused difficulty since the larger Panamax vessels began using the river after the channel was opened at the 42-foot depth. The problems with this configuration were addressed in a recent Corps of Engineers report, the Wilmington Harbor Initial Appraisal ( section 216 report ) dated July 2010: This turn is problematic for certain container vessels under specific conditions of wind and tide. These particular vessels are being forced to delay their transit and await favorable tide conditions in order to serve the harbor. These delays are expensive and result in increased transportation costs. Certain vessels are being subject to draft restrictions as a result of this turn (see Attachment 1). Contributing factors influencing safe maneuvering of these ships through the channel include the ship handling characteristics and size, channel configuration, tide conditions, and inbound or outbound transit operation. The handling characteristics of certain companies' container ships are less responsive than other container ships of the same class. Turning these ships is challenging due to the dimensions of the turn and the adjacent channels. Battery Island Channel is 2,589 feet long with a 30 degree, 36 minute turn angle at the southern end and a 65 degree, 3 minute turn angle at the northern end. Given the dimensions of the channel and a combined north and south turning maneuver of95 degree, 39 minute, safely navigating these ships through the Battery Island Channel, and the turns at either end, is an extremely complex maneuver. Strong ebb and flood tidal currents significantly affect ship maneuverability. The most difficult transit of the Battery Island Channel occurs when a ship is inbound with a maximum ebb tide current. These issues have resulted in vessel delays and issues of vessel safety in serving the Port of Wilmington. The river pilots have been obliged to impose draft restrictions on the larger vessels calling at Wilmington. With that precaution, the Cape Fear River pilots have been able to pilot the two Panamax vessels calling at Wilmington each week around that turn. By starting the turn at or outside the outer edge of the channel (and perhaps using bank effects to help start the turn), clipping the inside apex of the turn and finishing the turn at or outside the outer edge, pilots have been able to fit the arc of a turn with a radius of about 3000 feet, about three times the length of a Panamax vessel, into the space available in the river, if not in the marked channel. But not always. The turn is challenging, with no room for error, and there have been groundings. Coast Guard records show three grounding incidents in the Cape Fear River since the channel was opened at the new depth in One grounding, the Lijnbaansgrach in August 2005, occurred at the Battery Island turn. 7

9 Corps of Engineers Standards for Channel Turns The Corps of Engineers Engineering Manual, Hydraulic Design of Deep Draft Navigation Projects, in chapter 8, has this table of recommendations for channel turns: 8

10 Looking at the two turns around Battery Island, we find these discrepancies between the recommended configuration for such vessels and the actual channel: Deflection Configuration Radius Turn Angle Recommended Actual Recommended Actual Southport Channel- Battery I. Channel 30 Apex Angle Battery I. Channel Lower Swash 65 Circle Cutoff 9650 feet 1280 feet 1 The most troublesome of these discrepancies is the radius of the 65 turn between Battery Island Channel and Lower Swash. (Shown on the right.) Instead of the recommended radius of ten times the ship length, the turn has a radius only slightly longer than the length of the design vessel, 965 feet. The Corps of Engineers manual advises that Channel turns should not be designed for turn radius-to-ship length ratios less than 3, because ships cannot hydrodynamically maneuver around a sharper turn. This is consistent with the the standard for maneuverability of the International Maritime Organization (IMO), which requires vessels to have a maximum turning circle with a radius of 2.5 times the ship length, at 35 degrees rudder angle (or the maximum angle, if less). However, the IMO standard relates to open water turns at speed; there are not any standards for the turning circle at reduced speed in shallow water. 1 This is approximate. The turn is not a circle, but a 65 intersection of straight channel sections, with a cutoff of approximately 1000 feet at the inside feet is the radius of a channel arc of the required width that would fit within the part enlarged by the cutoff, connecting the straight sections. 9

11 The dilemma for the Wilmington District of the Corps of Engineers was that a channel conforming to the recommendations and standards for width and turns cannot be fit between the banks of the Cape Fear River. This is demonstrated by the line on this chart, which represents the centerline of a channel conforming to the recommendations for turn radius. (But this line does not have a transition zone between reverse curves a straight section of five times vessel length is recommended by the Corps of Engineers manual.) 10

12 The PIANC Design Guide A working group of the Permanent International Association of Navigation Congresses (PIANC) and the International Association of Ports and Harbors (IAPH) developed and published in 1997 a design guide: Approach Channels, a Guide for Design. This is more comprehensive than the section of the Corps of Engineers manual, taking into account many factors and explaining the rationale in some detail. The Corps is a member of PIANC. The PIANC guidelines offer this advice:! Vessel maneuverability diminishes with channel depth. Although a vessel with good maneuverability may be able to execute a hard-over turn with a radius of two to three times vessel length in deep water, that radius increases to about five times vessel length in a shallow channel with a depth to vessel draft ratio of 1.1 (a depth of 44 feet for a vessel draft of 40 feet).! Designing a channel turn for hard-over turns is inadvisable. Designing for no more than 20 rudder is recommended to provide a margin of safety. For a water depth to draft ratio of 1.1, the recommended radius at 20 rudder angle is 8.5 times vessel length.! Bank interaction, a phenomenon that causes the stern of the vessel to be drawn to the side of a dredged channel and results in instability, must be taken into account in determining channel width. For the design vessel used by the Corps of Engineers for the 1996 study, 965-foot length and 106-foot beam, application of the PIANC guidelines would require a minimum turn radius of 8200 feet, with a width of 500 feet. The channel turn from Battery Island Channel to Lower Swash, with an effective radius of 1000 feet, is far sharper than the recommended radius. Increasing the assumed rudder angle from 20 to 30 (which PIANC does not recommend) would reduce the necessary radius to 6000 feet, still much greater than the actual turn. The CH2M Hill, Inc., Cut-through Recommendation The North Carolina State Ports Authority engaged CH2M Hill, Inc., a respected engineering firm with experience in port projects, to provide preliminary engineering analysis of the proposed North Carolina International Terminal and related infrastructure. In establishing design parameters, the firm selected as the design vessel the latest generation of container ships, such as the Emma Maersk, with a length overall of 1263 feet, a beam of 185 feet, drawing 50 feet of water when fully loaded. In the firm s Conceptual Dredging Study, provided to the State Ports Authority in 2008, channel dimensions of 52.5 foot depth and 600-foot width were determined for the design vessel. The matter of the channel turn was addressed: A recent engineering manual (USACE EM , Hydraulic Design of Deep Draft Navigation Projects, Chapter 8 Channel Width,

13 APPENDIX B) was used as the basis for the channel width and channel curves. One-way ship traffic was the design criterion for determining channel width. The existing channel into the Cape Fear River has a dramatic S curve in the first 4 miles inside the inlet. Once a ship passes through Baldhead and Jaybird Shoals, it makes a 45-degree turn to port, immediately followed by a 105-degree turn to starboard around Battery Island, before straightening into the channel reach known as the Lower Swash Channel and heading upriver. This area is known to have a high current state on both the incoming and falling tide. Multiple attempts were made to design a channel that followed the existing course; however, it was found that the standards in Chapter 8 of the manual (USACE, 2006) could not be met without causing obvious impacts at the east end of Caswell Beach or the riverfront at Southport. Another consulting team, TEC Inc. and PF Richardson Associates, engaged to find ways to reduce the cost of the planned container terminal, reached the same conclusion: And: With assistance from Gahagan and Bryant Associates, Inc.(GBA) and references to USACE Channel Width Design Manual, it was concluded that this alignment did not meet USACE design standards and there were no viable modifications that could be performed to meet these standards. According to USACE Engineering Manual EM , reverse turns (Sbends) require a straight segment at least five times the design ship length between successive turns. This is not possible to accomplish within the confinements of the existing waterway In 2011, Moffatt & Nichol revisited the issue in the NCSPA Port Business Case Project prepared for the North Carolina State Ports Authority. Using ship simulation software developed by Maritime Research Institute Netherlands, Moffatt & Nichol tested an existing container ship of the type currently calling at the Port of Wilmington (950 foot length, 106 foot beam) and a future vessel with a capacity of 8000 twenty-foot equivalent units (TEU), 1043 foot length and 140-foot beam. Tests were run inbound and outbound, with and without wind and tide. Moffatt & Nichol reported that The SHIPMA numerical modeling tool indicates that the existing channel alignment at the Battery Island Reach is not satisfactory to safely transit an 8,000 TEU vessel. In the simulation, the larger vessel was obliged to follow a path 264 feet outside of the channel boundary at the apex of the turn. In all cases, the vessels reached or breached the boundaries of the channel. The table below shows the minimum channel width and turn radius the Corps of Engineers manual and the PIANC guidelines would require for the CH2M Hill design vessel, and for the slightly narrower new Panamax vessel that would be able to transit the Panama Canal after the new locks and other improvements are completed, sometime after Such a vessel would also be about 1260 feet in overall length, but the beam would be 160 feet. Design Vessel Channel Width Minimum Turn Radius Corps of Engineers PIANC Corps of Engineers PIANC CH2M Hill design vessel 800 feet 700 feet 12,600 feet 10,700 feet New Panamax ,600 10,700 12

14 This chart shows the path of the centerline of a channel with turns conforming to the Corps of Engineers manual for the design vessel for the planned container terminal. Although it is evident that a conforming turn cannot be fit in the confines of the river, this diagram does not show a transition zone to recover from a turn in one direction before beginning a turn in the opposite direction. The Corps of Engineers manual specifies a straight section of five times vessel length between such turns, in this case 6300 feet. 13

15 The observations of CH2M Hill, Inc., and TEC/PFRichardson that a conforming channel cannot be fit within the banks of the river at the turn between Southport and Battery Island is quite obviously correct. Even if the existing channel at the intersection of the Battery Island Channel and Lower Swash could be widened to 600 feet by enlarging it on the outside, a full-width channel with a radius of only about 1400 feet could be accommodated, only a fraction of the recommended radius. However, just as in the case of the existing channel, by using the entire width of the widened channel a path 160 feet wide with a radius of 4000 feet can be followed, starting at the outside edge of the straight section leading to the turn, clipping the inside at the apex, and completing the turn at the outside edge of the straight section after the exit. Whether a 1260-foot vessel can turn in a radius of 4000 feet without tugboat assistance is another matter. Such a turn would be much sharper than specified by the Corps manual and the PIANC design guide. There is also the issue, not mentioned by CH2M Hill, Inc., of three Civil War era shipwrecks lying along the side of the channel in this area. All are regarded as being of archeological interest by the North Carolina Department of Cultural Resources. One is the CSS North Carolina, one of two ironclads built in Wilmington. That has already been damaged by dredging operations. As for the riverbank on the outside of Lower Swash, where a conforming turn would have to be cut, that is occupied by the historic district of the City of Southport, which district is on the National Register of Historic Places. That district includes two buildings on the Register, including Fort Johnston, which dates to the Colonial era. CH2M Hill, Inc., consequently recommended a new channel on the east side of Battery Island, by-passing the S-curve. That is shown below (red): This was not a conclusion reached without some concern. The proposed route would be through undisturbed areas with depths measured in single digits. The additional dredging involved would be much more expensive than simply enlarging the existing channel. That portion of the river is part of the John H. Chaffee Coastal Barrier Resource System, a Federal reserve, and the Bald Head Island Natural Area, a State reserve. There would be significant implications for environmental effects from loss of habitat and the increase in tidal amplitude that would result from creating this large, direct path up the river. 14

16 Conclusion The existing channel in the Cape Fear River cannot be widened sufficiently to accommodate larger vessels than now navigate the river. Indeed, the channel is not adequate for those vessels. This is not a healthy situation. In a recent paper presented to the New York Metropolitan Section of the Society of Naval Architects and Marine Engineers, the authors, staff members of the Naval Academy, the Coast Guard, and the Maritime Administration, pointed out that as vessel size has increased, channels have been dredged deeper, but not wider, and maneuverability issues have not been adequately addressed. This is a particular problem with container ships. The authors identified these problems with newer generations of such ships:! Container ships have large windage that can complicate ship controllability in narrow channels as well as during slow speed maneuvering;! Increases in service speeds may also increase the bare steerage speed. Direct-drive diesel ships with high installed power to achieve design service speeds can, in some cases, have a minimum bare steerage speed of about 8 knots quite a high speed in confined waters;! Even the largest container ships usually have single screws, a maneuvering handicap.! There is a trend to smaller rudders. While such rudders may be adequate at service speeds in open water, maneuverability in confined waters at low speed is compromised.! Marine architects are taking advantage of the beam increases that will be possible with the opening of new locks in the Panama Canal to decrease the ratio of vessel length to beam, which improves load capacity without increasing draft. However, decreasing that ratio also decreases directional stability. Although this makes it easier to initiate a turn, it also makes it more difficult to check a turn. Thus while the inadequacies of the channel in the Cape Fear River and the difficulties of maneuvering large container ships so far have been overcome by skillful piloting, this conflict should not be exacerbated by opening this channel to even larger vessels. Groundings are usually only inconvenient, but if the channel is deepened into the rock that lies at the bottom in many places, the risk of hull damage to the deepest draft vessels and consequent spills must be considered. To create access to the site of the proposed North Carolina International Terminal for the post-panamax container ships for which it is intended, a new channel would be required over a different alignment east of the lower reaches of the existing channel. This does not constitute an endorsement of such a new channel. Such a new channel would introduce substantial environmental and economic problems, which may overwhelm any potential benefits from admitting larger ships to the Cape Fear River. There are clear indications that the succession of channel deepening projects over the years has exhausted the capacity of the Cape Fear River for more deepening. The most notable effect is that on beaches of Bald Head Island and Caswell Beach, at the mouth of the river. Those beaches had remained stable and even grown through the centuries, but as the channel in the Cape Fear River was enlarged, the beaches have lost sand and now require regular nourishment by adding sand dredged from the ocean bottom and from the channel. 15

17 Sources CH2M Hill, Inc., Conceptual Dredging Study, North Carolina State Ports Authority (2008). William O. Gray, Jennifer Waters, Alan Blume, and Alexander C. Landsburg, Channel Design and Vessel Maneuverability - Next Steps (2002) International Maritime Organization, Standards for Ship Manoeuverability, Resolution MSC.137(76) (2002). Moffatt & Nichol, NCSPA Port Business Case Project (2011). Permanent International Association of Navigation Congresses (PIANC), Approach Channels, a Guide for Design, Final Report of the Joint Working Group PIANC-IAPH, Supplement to Bulletin No. 95 (1997). TEC Inc./PF Richardson Associates, North Carolina International Terminal, Review of Planning Concepts and Privatization Options (2010). United States Army Corps of Engineers, Deep-Draft Coastal Navigation Entrance Channel Practice, Coastal and Hydraulic Engineering Technical Note IX-1 (1999). United States Army Corps of Engineers, Hydraulic Design of Deep Draft Navigation Projects, Chapter 8 Channel Width APPENDIX B (USACE EM , 2006) United States Army Corps of Engineers, Wilmington District, Record of Decision, Cape Fear Northeast Cape Fear Rivers Comprehensive Study, Appendix D, Engineering and Design (1996). United States Army Corps of Engineers, Wilmington District, Section 905(b) Analysis, Wilmington Harbor Navigation Improvements, North Carolina International Terminal (2011) United States Army Corps of Engineers, Wilmington District, Wilmington Harbor Initial Appraisal (2010). 16