The Self-Defense Test Ship (SDTS) at the U.S. Naval Surface Warfare Center’s Port Hueneme Division (NSWC PHD) (Port Hueneme, California, USA) recently returned from San Diego with a freshly-scrubbed hull and key information needed to prepare for a dry dock.
Retired USS Paul F. Foster, at 44 years old and reborn as the SDTS, is scheduled for dry dock possibly in 2022—about 10 years from the vessel’s last one, says Dave Moore, SDTS customer advocate/project manager for PHD.
Dry Dock Package
Keeping the SDTS in top shape is important to the command and the fleet because they use the remotely-operated vehicle to test installed combat systems, such as the Evolved SeaSparrow Missile Block 2 and DDG 1000, on their defensive capabilities. Before dry dock happens, a dry dock package—which lays out anticipated repair, maintenance, and costs—needs to be approved. Other criteria include a funding request for the work, and reserved space at a dry dock yard.
“As we’re writing our [dry dock] work package, the hull needs to be checked in case there’s corrosion that’s eaten through,” Moore says.1 “We need to know, so when we write the package, we can tell the shipyard maintenance crew to be careful here, or replace hull plating there. It also gives us an idea of how good the ship’s paint job has held up.” The extra information also reduces the chance for surprises that could escalate the cost of the dry dock and the ship’s downtime, he adds.
Underwater Maintenance
NSWC PHD contracted Seaward Marine Services (Norfolk, Virginia, USA) to do the hull cleaning and underwater maintenance. Its proprietary Lamp Ray remotely operated vehicle (ROV), which crawls along the hulls and marine structures of immersed ships, inspects them for damage. The company has held the Navy contract for underwater ultrasonic ship hull scanning since 2000, and general ship husbandry and diving services since 1972.
The vehicle performs a hull assessment, according to Lamp Ray inspection manager John Tumber. The ROV measures metal thickness, paint thickness, and cathodic protection (CP) voltage—a corrosion prevention technique the Navy uses that charges the hull at a certain voltage to slow down corrosion.
“The inspections give them a lot of information to help plan for potential dry dock—to see if and what needs to be replaced,” Tumber says. “Depending on what’s going on—they may be able to extend the dry dock cycle, or they may have to speed it up.”
Seaward spent about a week with the 564-ft (171.9-m) SDTS in San Diego in March, first doing an extensive hull cleaning using the submersible cleaning and maintenance platform that crawled along the hull. That hull cleaning was followed by divers, who did a more specific inspection and cleaning of the sea chest pumps, intakes, overboard discharges, and two propellers by removing barnacles and other sea growth that cause clogging.
Lamp Ray Goes to Work
Then, the Lamp Ray went to work. As the ROV moves along a ship hull’s exterior, an acoustic tracking system that works like sonar sends out sound waves that bounce off the ship and back to the device, tracking exactly where on the hull the machine is. It also records data on the metal and paint thicknesses and CP voltage in each spot. The Lamp Ray then sends the information back to a data-collection system via tethers.
“There is a network of little microphones [transducers] we hang on the ship,” Tumber says. “They are calibrated to the ship’s shell plate drawings. We digitize those original drawings, and the tracking systems will correlate the data gathered to the specific position on the ship’s hull.”
Seaward then compares the metal thickness from the ROV survey to the metal thicknesses recorded on the ship’s original drawings. This is the first-ever assessment done on the SDTS, according to Navy officials. “We track the vehicle, so we know where it’s supposed to be in a particular spot—if it reads a half-inch thick, and it supposed to be half-inch thick, it’s okay,” he says.
Completed Assessment
The completed assessment comes in a book with the three items’ measurements and an analysis. For the SDTS, the scan generated 468,000 readings of metal thickness, 130,000 readings of paint thickness, and 280,000 readings of hull voltage. Seaward also highlights any potential trouble spots to make them easier to find and provides percentages.
“The Foster looked pretty good for her age,” Tumber says. “There were a few small spots with some minor corrosion, but nothing big and crazy.” Hulls corrode from the inside out, he adds, beginning with where water collects in inaccessible spots. That means the crew has done a good job of internal maintenance and preservation.
The roughly five-day process of hull cleaning, the hull survey, and data analysis cost about $180,000, Moore says. He expects the STDS to be in dry dock for three to four months.
“Seaward was flexible and professional, and was very good at trying to meet our schedule needs,” Moore says. “We are trying to be proactive in understanding the material condition of the ship before it becomes a problem. The benefit is to keep the ship operational, so it can go out and do the testing to support the fleet.”
Source: U.S. Naval Sea Systems Command, navsea.navy.mil.
Reference
1 “Self Defense Test Ship Gets its First-Ever Hull Assessment to Clear the Way for Potential Dry Dock,” NAVSEA News, April 15, 2020, https://www.navsea.navy.mil/Media/News/SavedNewsModule/Article/2150466/self-defense-test-ship-gets-its-first-ever-hull-assessment-to-clear-the-way-for/ (July 30, 2020).