Original Date: 07/21/2003
Revision Date: 01/18/2007
Best Practice : Engine Room Raft Outfitting
Electric Boat Corporation, Quonset Point Facility’s advancements in modular construction enabled the assembly of an entire engine room on an independent raft outside the confines of the main hull. With the use of digital photogrammetry, the raft can be accurately end-loaded into the hull. By assembling the raft outside of the hull with specially designed staging, schedule and labor costs have been reduced.
Historically, the main propulsion unit and propulsion plant machinery were installed on-hull in very cramped quarters. The key locating dimension for all machinery was the propulsion shaft alignment. Each component had to be landed and fitted to achieve a proper alignment. This required considerable work, and removal of equipment and staging was frequently required for each component installed. This installation sequence did not allow for flexibility, and delays in an individual component installation would cause rippling delays in the overall schedule.
Electric Boat Corporation, Quonset Point Facility’s (EBQP’s) design/build philosophy and advancements in modular design and construction resulted in a different approach to the shipboard loading and installation of these components. EBQP developed a customized workstation for the off-hull integration of all major engine room components into a single raft. The raft is modularly constructed in a controlled environment with readily available services, walkways, and work platforms to provide trade workers unrestricted access for outfitting. The entire raft is then end-loaded into the hull section. The modular construction allows the entire raft to be resiliently mounted as a unit rather than individually mounting a host of support equipment. The 473-ton raft is loaded into the hull section with a tolerance of less than 3/4" while maintaining optimum shaft alignment. This is made possible with the use of digital photogrammetry which pinpoints the location of each component on the as-built unit that best suits the optimum shaft alignment.
By combining modular construction with the unique staging and the photogrammetry process, construction spans have been compressed by an estimated 42% between the first and third hulls and resulted in a reduction in labor hours by 38% between the second and third hulls. This allowed EBQP to test many of the key components in an easily accessible environment and complete the ship service turbine generator-main propulsion unit reduction gear alignment prior to landing the raft into the hull.
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