May 2002 Excerpt
for Prototype Mast Aboard USS Radford
By Leslie Spaulding
AND WEST BETHESDADuring this past winter, Carderock Division personnel
upgraded portions of the prototype Advanced Enclosed Mast Sensor (AEM/S) System
aboard USS Radford (DD 968). The AEM/S mast design has paved the way
for the composite mast on LPD 17 Class, as well as efforts to install a composite
helicopter hangar and composite remote minehunting system (RMS) enclosure
on the DDG 51 Class.
This work involved upgrading the masts ladder access and fall protection systems to meet Navy standards and INSURV inspection criteria. Also the work accomplished addressed overheating issues with the main radar, and designing and installing a composite foundation that allowed for the relocation of the INMARSAT antenna and the new installation of the ROS Fire Control camera.
The USS Radford AEM/S mast is a composite structure which encloses the radar and antenna systems. Unlike conventional masts, the access path to the upper levels is totally enclosed within the structure, with a total vertical climb of 76 feet, serving five platforms or landings.
In August 2001, an INSURV report identified several discrepancies within the AEM/S mast pertaining to personnel access and fall protection. Since the mast was built as a technology demonstrator, the installing activity chose commercial grade ladders and fall-arrest systems, with the emphasis on performance of the structure and electronics contained within.
Hull Outfitting Section (9782) representatives Stephen Grasso and Anthony Venti were tasked to perform a visual and operational inspection of the five ladders (three fixed and two portable) and the existing commercial fall arrest system and provide solutions.
Two main discrepancies were identified along with several secondary problems. First, the existing fall arrest system was attached directly to the vertical ladders. This violates Navy climber safety requirements. Per specifications, fall protection systems shall be mounted back to the ships structure, independent of the ladder. This ensures that the impact load generated from a fall is transmitted directly back to a suitable structure, and not dependent on the integrity of the ladder assembly. The second discrepancy was that one portable ladder did not have any associated fall protection system. Personnel free climbed the ladder without any protection. Secondary problems included inadequate fall protection for personnel when climbing off of or on to the top of a ladder, as well as a poor design and inadequate material selection of the portable ladders mounting foundation which attached to the ships structure.
To solve the problems, Grasso and Venti, teaming with Ed Devine (651), designed and engineered a fall protection system around commercial fall protection components to meet the Navys safety and operational requirements. To provide protection for the portable ladders, the NSWC design team selected commercial-off-the-shelf, self-retracting lifelines (SRLs) mounted to anchor plates on the underside of each level, close to the access openings. SRLs are commonly used in the commercial and industrial sectors. While unconventional by Navy fall protection standards, these SRLs provide full protection for personnel during their total climb and descent. Two SRLs were mounted at each portable ladder location, one for primary use and one reserved for back-up (emergency rescue). For the fixed ladder, the existing fall protection system was retained but was augmented with additional support structure, engineered to transmit the impact load (from a fall) back to the ships structure. As for the inadequate portable ladder mounting foundation, Devine, redesigned and engineered the mounting foundation which ensured safety and increased strength and reliability when personnel attached the ladder to the ships structure. Design upgrades were installed by NSWC during a brief in-port period last December. Additionally, the ladders were successfully tested to prove their strength and adequacy.
The lessons learned from USS Radford will be incorporated into the LPD 17 AEM/S design.
INMAR SAT Antenna
While work was underway on the ladders, Composite Systems Section (6551) personnel Michael Bergen, Ed Devine, and Lindsay Miller reconfigured the mast to accommodate the reinstallation of a fire control video camera. This camera was part of the original prototype, but was removed to make room for an INMAR SAT antenna, which is a communications satellite that enables the ship to send and receive email. The original design would not accommodate both pieces of equipment.
USS Radford requested Code 6551 develop designs to accommodate both units. The engineers took into consideration several requirements: antenna performance must not be degraded; signatures and maintenance requirements must be minimized; the field of view for the remote optical site (ROS) camera must be provided; and the structure must be stable. There were concerns about placing conductive foundations so close to the antennas.
The engineers developed a design that would meet the criteria: a cantilevered fiberglass sandwich structure. This structure is basically an L-shaped platform, which is mounted above the ROS video camera. The INMAR SAT, which weighs 200 pounds, sits on the cantilever. The structure was manufactured using layers of glass reinforced vinylesther plastic wrapped around a foam core for stiffness. The fabrication of the parts was done under contract to Atlantic Marine Plastics and Capital Industrial Supply.
Since the fix, like the mast, was a prototype, there were no installation guidelines. Therefore, Bergen, Devine, and Miller performed the installation, so they could resolve any technical issues that arose.
The neat thing about this project is that it demonstrates Carderocks ability to directly support Fleet needs, said Miller. Generally, here in West Bethesda we dont design, fabricate, and install things on Navy ships by ourselves.
The installation was done by trial and error. When they first hauled the structure up, they found that the dimensions were slightly off. Fortunately, the contractor was willing to resize it immediately, so the installation could take place.
It was fairly scary up there, said Miller. We were really high up, connected by safety harnesses. The first four days, we had ideal weather. But the fifth day we were up there with gusts of wind of 20 to 30 mph. This was the day they were painting, leaving no doubt in anyones mind that they were Navy workers as they left the site decked in Navy gray. Additionally, while they dangled 100 feet above the deck, they watched a taping of David Lettermans Top 10 aboard a neighboring ship.
USS Radford emailed their appreciation for the work done on the AEM/S.
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