International Dredging Review

International Dredging Review

Engineers Lengthen Corps Dustpan Dredge Hurley to 353 Feet
By James H. Asbury IV PE
Marine Design Center
Donald V. Mayer
Memphis District Ensley Engineer Yard

The Corps of Engineers Memphis District Ensley Engineer Yard (EEY) and the Corps Marine Design Center (MDC) have completed the lengthening of the Corps of Engineers dustpan Dredge Hurley by 48 feet. The project increased the dredge’s length from 305 feet to 353 feet making it one of the largest vessels on the Mississippi River and increased the dredge’s dredging depth from 40 feet to a maximum of 75 feet.

The Marine Design Center in Philadelphia Pennsylvania is the Corps of Engineers national center of expertise for Naval Architecture and Marine Engineering and in partnership with the Philadelphia District’s Contracting Division services the Corps districts in procurement construction and repair of the USACE fleet. They have recently expanded their mission into all areas of marine engineering including shore-side support and harbor maintenance.

The Memphis District’s Ensley Engineer Yard is the Corps’ only true shipyard facility. Ensley has three floating dry-docks – the largest being 320 feet in length – a fully staffed welding and ship fitting shop and a complete machine shop. In the past eight years Ensley and the Marine Design Center have partnered to complete four major ship alterations including the installation of new bow thrusters and a ladder hoist system on the Dredge Hurley in 2003 a new main engine cooling system on the Towboat Mississippi in 2005 new kort nozzles and steering system on the Dredge Jadwin in 2007 and a stern swivel connection on the Dredge Potter in 2009.

The Dredge Hurley is operated by the Memphis District and was commissioned in 1993. Originally built to dredge to a maximum of 40 feet it replaced the 1933-built Dredge Burgess. Shortly after the Hurley entered the Corps fleet in 1993 engineers identified a need for it to be able to dredge up to 75 feet. The project was authorized in 1997 and concept engineering was completed in 1999.

In 2000 the Corps of Engineers received authorization and funding to complete portions of the overall lengthening project with the exception of the actual lengthening of the vessel. MDC and EEY partnered to install new azimuthing bow thrusters and a new ladder hoisting system consisting of a new A-frame and ladder hoist winch. The hoist winch was sized for the lengthened ladder in anticipation that the dredge would be lengthened in the future.

In 2007 after extreme high water on the Mississippi River leaders realized that a lengthened Dredge Hurley would significantly benefit the nation. Funding and authority to lengthen the Dredge Hurley soon followed. Again MDC and EEY partnered to complete the largest project Ensley has undertaken to date. MDC provided all engineering support to EEY handled all major supply contracts to support the yard provided project oversight and technical support and resource management support to EEY. MDC performed an analysis of the new power cable runs checked the cable sizes for voltage drop and selected the appropriate cable sizes.

On behalf of MDC the Philadelphia District contracted with Edgen Murray to supply the majority of the steel required for project procured new power cable from Eutex International contracted with Barnhart Crane and Rigging to supply crane and rigging services procured a new knuckle boom crane from DMW Marine shackles for hoisting the dredging ladder and new deck grating.

In July of 2009 Ensley Engineer Yard started the ladder extension project by fabricating a 49-foot ladder insert that would be installed in one of the existing spare dredging ladders. MDC supported EEY in providing templates for cutting complex angles in the pipe used for the ladder structure and provided nested drawings with part numbers for easy assembly of the plate steel sections of the ladder insert. When the insert section was complete Barnhart Crane and Rigging moved it from the fabrication shop to the waterfront where EEY used one of their cranes to place it on a barge with the existing ladder sections to be extended.

Ensley then cut the spare ladder into two sections and inserted the new section between the existing sections to make the ladder 108 feet long. Through the regionalization process EEY enlisted welding talent from several other districts including Detroit St. Louis and Vicksburg for this project.

The initial plan for extending the hull was to build the hull sections in place on Ensley’s 320-ft drydock but EEY and MDC determined that building the horn sections in the fabrication shop floor would be more productive than building in place.

After EEY ironed out the logistics of building a steel structure of that size work began on fabricating the horn insert sections. Each horn section was 48 feet long 20 feet wide and 12 feet high. Building indoors prevented any weather-related delays kept workers close to their restrooms and break areas and caused morale in the shop to reach an all-time high. EEY asked MDC to develop a plan to get the horn sections out of the shop and into the dry-dock. Ensley also simultaneously constructed the new A-frame outside the shop. To remove the horn sections from the fabrication shop EEY opened their rear shop door to 30-feet by 16-feet enabling them to handle and remove these sizeable steel sections.

The Philadelphia District issued a contract to procure rigging services and awarded the contract to Barnhart Crane and Rigging. Barnhart came into EEY’s facility with two Goldhofer trailers lifted the horn sections off the shop floor and set them on the trailers then drove the horn sections to the Barnhart facility on President’s Island in McKellar Lake. EEY then moved the Dredge Hurley on the 320-foot drydock about a mile down and across the lake to Barnhart’s facility using the USACE towboats M/V Strong and M/V Ward. Barnhart moved the bow sections to their new location and placed the new horn sections into the drydock with their derrick crane and the drydock was moved back across the lake to the EEY yard.

To simplify installation of the horn insert sections EEY and MDC moved the cutline forward 30 inches from the original design location. This change moved the support for the rear A-frame legs forward of the original design location and required design of a new structure. MDC’s engineers analyzed the structure came up with several alternatives and presented them to EEY’s fabricators. MDC and Ensley engineers designed a new structural bulkhead that would be inserted through a slot cut in the deck of the new insert that would provide the required structural support for the A-frame. MDC engineers also designed a new foundation for the ladder hoisting winch as the winch was moving forward with the A-frame from its original location.

After completion of 90 percent of the structural welding tenders moved the drydock back over to Barnhart’s facility where they placed the extended ladder and new A-frame on the vessel. The drydock then traveled back to EEY’s facility where workers completed all structural welding pulled new power cables through the new horn sections and reconnected to the loads and installed new deck grating.

This project was a success thanks to the close partnership developed between the Marine Design Center and Ensley Engineer Yard. This partnership developed over the past eight years has resulted in the Corps of Engineers’ ability to tackle major ship alterations to capital equipment. Marine Design Center’s engineering expertise in marine engineering and naval architecture and overall project management coupled with Ensley’s production and repair facilities allows them to tackle almost any floating plant project for the U.S. Army Corps of Engineers.