The bolts that hold the main engine frames to foundations on the ship's hull appeared to be improperly installed aboard the amphibious transport dock ship Somerset (LPD 25). (U.S. Navy)
A new issue involving improperly installed bolts has emerged in the latest ships built by the Avondale shipyard near New Orleans, delaying the delivery of one ship and affecting another.
Similar problems were discovered in 2010 among most of the ships of the LPD 17 San Antonio-class, 26,000-ton amphibious ships of an advanced design under construction by Huntington Ingalls Industries (HII) for the U.S. Navy.
The LPD 17s have a long history of problems, beginning with multiple issues on the San Antonio, delivered to the Navy in 2005. The shipbuilder and the Navy have been struggling ever since to fix problems on each ship in the class and improvements have been seen on all subsequent ships.
The latest problems were discovered in mid-July on the Somerset, a ship launched in April and christened on July 28. When an inspector noticed the bolts that hold the main engine frames to foundations on the ship’s hull appeared to be improperly installed, further inspections were ordered on the Anchorage, a ship that was on the verge of being delivered to the Navy.
More bad bolts were discovered on the Anchorage, causing the Navy to delay accepting the ship from the shipbuilder and the movement of the crew on board.
“An Ingalls machinist discovered a dimensional issue with some fitted bolts and it was reported to the Navy the week of July 16,” Beci Brenton, a spokesperson for Huntington Ingalls, said Aug. 1 in an email statement about the problems on the Anchorage.
“The discrepancies are related to the fitted bolts’ ability to withstand shear forces during a shock event; there are no issues with fatigue loading or normal operation of the systems.
“Initial inspections indicate a high percentage of the bolts are compliant with the specification and do not need replacement,” Brenton continued in the statement. “All non-compliant bolts will be replaced. We have all the material on hand to complete the repairs and we are currently evaluating the progress on bolt replacement to assess if there will be an impact to sail away.”
Sail away is the point at which the ship leaves the shipyard and heads to its new homeport. In the case of the Anchorage, the ship is scheduled to leave in October for her base in San Diego.
The ship had been scheduled to be delivered to the Navy on July 23 — a moment when legal custody of the ship transfers from the shipbuilder to the U.S. government — and the crew would have moved aboard immediately after a signing ceremony.
Delivery of the Anchorage now has been delayed until September, Brenton said. There is no word yet on a new sail away date.
The discovery of new bolt problems on the two ships came as a shock to Ingalls and the Navy, which carried out successful sea trials on the Anchorage earlier this summer. Both the Navy and Ingalls thought they had avoided the sorts of fundamental problems that had plagued — to varying degrees — most of the earlier ships of the class.
The Navy’s Naval Sea Systems Command, or NAVSEA, confirmed the discrepancies with the fitted bolts were discovered after the acceptance trials were completed on June 22.
While certainly similar, it is not yet clear if the new fitted bolt issue is the same as the problems discovered in 2010.
Both the Navy and HII continue to investigate the issue, and neither has issued a statement concluding a specific cause for the latest problems.
Problem Limited to Avondale
The Anchorage is the seventh ship of the LPD 17 class, the Somerset is the ninth. The Avondale shipyard is scheduled to permanently shut down in early 2014 after the Somerset’s delivery, currently scheduled for the fall of 2013.
Ingalls Shipbuilding, a larger shipyard in Pascagoula, Miss., will build the rest of the LPD 17s. A $1.5 billion construction contract for an eleventh ship was just signed with the Navy on July 27.
The new problem is limited to ships built at Avondale, according to the Navy.
“The fitted bolt issue has been determined to be related to fitted bolts fabricated only at the Avondale facility in New Orleans,” NAVSEA said Aug. 1 in an email statement.
“Therefore, the issue potentially exists on ships that were built at the Avondale facility. HII and the Navy are developing inspection plans for the in-service ships to determine if similar discrepancies exist.”
In its statement, NAVSEA further described the issue.
“During the week of July 16, HII discovered and reported to the Navy possible issues with fitted bolts associated with propulsion system components (i.e., engines, main reduction gears and line shaft bearings), as well as steering and stern gate components.
“The HII/Navy team developed an engineering-based inspection and replacement plan and HII has begun the removal, inspection and replacement, as required, of selected fitted bolts which is expected to take about six weeks. The repair work schedule will not conflict with crew training or certification. The Navy plans to accept delivery of the ship once all bolts are inspected and replaced as needed.”
Navy and Ingalls engineers say the problem doesn’t immediately affect a ship’s operations but that, over time, stresses in the ship’s power train begin to throw the affected elements out of line, causing vibrations that can potentially wreck a ship if nothing is done.
Each of the ship’s four main propulsion diesel engines has 126 bolts, and the main reduction gear features 16 fitted bolts out of a total of 32.
Tolerances for the bolts reach thousandths of an inch.
Each bolt is custom-machined on a lathe to exactly fit the dimensions of each bolt hole, ensuring an exact fit.