The submarine Montpelier at sea a day after its Oct. 12, 2012, collision with the cruiser San Jacinto. The absence of the ship's upper rudder is clearly visible. Repairs to the submarine have been more extensive than first envisioned. (MC2 Mike DiMestico / US Navy)
WASHINGTON — More than a year after a collision that tore off the upper rudder and damaged the hull, the submarine Montpelier remains under repair at Newport News Shipbuilding, Va. The work, envisioned early on as needing only a few months, turned out to be much more extensive, and the ship isn’t expected to be returned to full service until April.
The work has involved completely rebuilding the rudder assembly and replacing a large chunk of the pressure hull over the engine room.
“I can’t recall another collision that directly impacted the aft control surfaces,” Rear Adm. Michael Jabaley, the deputy commander for undersea warfare at the Naval Sea Systems Command, said during an interview Nov. 18. “This repair has been a lot of things that we haven’t done before.”
The Los Angeles-class nuclear-powered attack submarine was on maneuvers with the cruiser San Jacinto off the northeast Florida coast when, on Oct. 13, 2012, she was struck by the cruiser’s bow while rising to periscope depth. The sub tried to dive back down, but the stern was smacked by the cruiser’s large underwater sonar dome.
“There were actually two significant impacts between the San Jacinto and the Montpelier,” explained Jabaley.
“The first was on the aft starboard side of the engine room, causing a fairly significant dent in the pressure hull” — the portion of the submarine containing the crew, reactor and operating machinery.
“Then there was a bounce away, then a second impact in the vicinity of the rudder. That separated the upper rudder and knocked the lower rudder out of alignment, such that the lower rudder was scraping against the non-pressure hull when it was operated.”
The impact also caused a crack in the non-pressure hull, an area consisting largely of ballast tanks and free-flooding spaces.
No damage was suffered by the ship’s nuclear reactor, the Navy said.
Divers inspected the collision damage while the sub was at Kings Bay, Ga., and initially it appeared only a few months would be needed to repair the Montpelier, which had been scheduled to deploy soon after the exercises.
But when the submarine entered drydock some weeks later at Newport News, the true scope of the damage became more visible.
“Once in drydock it became apparent there was a significant dent in the pressure hull,” Jabaley said. “And there were two areas of additional damage in the non-pressure hull.” Together, “it resulted in significant growth in the scope of the repair work we had to do.”
The dent was relatively shallow — not even three inches deep at most — but it was serious.
“The strength of a submarine in terms of resistance to sea pressure, or events in a shock environment, such as a mine or torpedo detonation, comes from circularity,” Jabaley said. “We have tight specifications to make sure the pressure hull is as close to perfectly circular as possible. In this case, the dent was almost three inches deep, greatly exceeding our requirements. So it demanded full-scale replacement of a large segment of the hull in order to certify the ship for further operations.
“That’s not an easy task to cut that piece out, put another piece in and restore it to conditions of circularity.”
The dent was about 12 feet by six feet, but the shipyard cut out a section about 17 and a half feet by 11 and a half feet. “You have to go well beyond the dent to make sure you’ve captured everything,” said Jabaley.
Compounding the repairs was the location of the dent — just outside the densely-packed engine room, filled with complex machinery.
“This was in a place in the engine room where there was a ton of interference,” Jabaley said. “All this stuff adjacent to the hull had to be protected — removed in many cases — to allow this huge section of the pressure hull to be removed. Then a replacement section had to be fabricated and reinstalled.”
The veteran submarine engineer said he couldn’t recall a similar submarine repair job.
Fixing the rudder assembly presented a different set of challenges.
“The rudder is arranged with a big yoke in the middle for the propeller shaft to go through,” he said. “We had to remove the [propeller] shaft in order to repair the rudder. It wasn’t as simple as the top piece came off, let’s replace the top piece. We had to completely remove the components.”
Rather than fabricate a new rudder, the needed parts were taken off a decommissioned sister ship, the Salt Lake City.
The non-pressure hull near the rudder also needed repair.
“Completely restoring the rudder — a complete rudder assembly, including fabricating new parts, harvesting parts from another submarine, putting it all together and making it work within the tolerances required both for hydrodynamic performance, control of the ship, acoustic performance, all of the very strict requirements we levy upon ourselves, is a difficult task,” Jabaley said.
While the initial repair contract was for $32 million, the final tally is expected to come in around $60 million, he said.
The Montpelier, commissioned in 1993, is projected to have a service life of 33 years, taking her to 2026. When repaired, the ship is expected to carry out seven full deployments over its remaining 12-year life span.
Repairs to the San Jacinto were simpler, and completed in only a few months. The cruiser deployed in July and was recently operating in the Red Sea.