By Scott Curtis and Lt. Kristin Cronic
SERMC Public Affairs
The Navy's underwater repair specialists from Southeast Regional Maintenance Center's (SERMC) Dive Locker, Engineering Department and Waterfront Operations personnel recently accomplished a first of its kind waterborne repair on USS Fort McHenry (LSD 43).
Fort McHenry is undergoing a Phased Maintenance Availability (PMA) and required extensive repairs to a Controllable Pitch Propeller (CPP) control arm.
The CPP System allows ships improved maneuverability and require no reversing gear since the direction of the propeller thrust can be changed without changing the direction of the shaft. This is achieved by changing the pitch of the propeller blades using a control rod housed inside the shaft, which moves fore and aft, allowing the propeller blades to pivot to any pitch. It is susceptible to damage or failure due to its numerous hydraulic components and sealing rings.
The decision to perform waterborne repairs was critical, as it eliminated the need to dry-dock the Fort McHenry, saving the Navy considerable money. In addition to the cost savings, the waterborne repairs return the ship back to operational status more quickly than if they were dry-docked for the duration of the repair.
However, being waterborne creates unique challenges requiring new procedures and processes to complete the operation. SERMC Project Manager Leroy Gooden synchronized the project. "The evolution from start to finish involved intense team collaboration; no step of the process was simple or easy, but the concentrated coordination of all parties involved made it a safe and time-saving procedure," Gooden said.
In early January, SERMC and Sailors from the Fort McHenry made preparations for the propeller blade removal to expose the shaft hub. After the CPP oil was drained, it took SERMC divers six days to remove the blades and install a cofferdam around the shaft hub. Once the cofferdam was installed the divers could work in a dry environment and prevent seawater from entering the CPP system.
Once the cofferdam was in place and Oil Distribution (OD) box removed, the hub cone was disassembled and the valve rod section replaced, using a tool fabricated by SERMC to aid in the removal of the control arm. The procedure consisted of removing valve stops and fittings, evacuating remaining oil, and installing the hub cone end cover in order to maintain watertight integrity.
Next, SERMC divers disassembled the hub, and replaced the valve rod sections and completed reassembly in accordance with the design memorandum.
During the work SERMC divers found an oil leak in one of the blade ports and replaced the seals, adding a day of work and complexity to the job, but the Divers still finished their work eight days ahead of schedule.
The rest of the evolution worked through the process in reverse, concluding with SERMC divers reinstalling the propeller blades and performing a pressure test to ensure the system was operational and has no oils leaks.
Ship repairs like this are an example of the SERMC's ability to support Fleet readiness whatever the circumstances. "Our job is to get the ships repaired and get them back to sea on time, fully mission capable. To return ships to the Fleet on time we rely on outstanding Sailors and Civilians performing at the top of their trade" said Capt. Dave Gombas, Commanding Officer at SERMC.
"This was a great learning experience for our young Divers being able to work on such a big job," said Senior Chief Navy Diver Richard Stafford, SERMC's Master Diver. "I am proud of the level of professionalism my divers displayed during all the evolutions and the safe completion of the job ahead of schedule."
The Fort McHenry is approximately 70% complete through her 312-day PMA, which is scheduled to wrap-up in June.
For more information about SERMC, visit http://www.navsea.navy.mil/Home/RMC/SERMC/
For more information about USS Fort McHenry, visit: http://www.fort-mchenry.navy.mil/