Naval Surface Warfare Center, Port Hueneme Division's (NSWC PHD) Self Defense Test Ship (SDTS), which has a critical and unique role ensuring Navy ships are combat ready, recently returned from San Diego with a freshly-scrubbed hull and key information needed to prepare for a potential near-future dry dock.
Retired USS Paul F. Foster, at 44 years old and reborn as the SDTS, is scheduled for dry dock possibly in 2022—10 years from her last one, said Dave Moore, SDTS customer advocate/project manager for PHD.
Keeping the SDTS in top shape is vitally important to the command and the fleet because they use the remotely-operated Foster to safely sea test installed combat systems, such as the Evolved SeaSparrow Missile Block 2 and DDG 1000, on their defensive capabilities. This keeps the Foster busy nearly every month, Moore said.
Before dry dock happens, a dry dock package—which lays out anticipated repair and maintenance and costs—needs to be approved along with the funding request for the work, and a space at a dry dock yard reserved.
“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 said. “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 added.
NSWC PHD contracted Seaward Marine Services of Norfolk, Va. to do the hull cleaning, underwater maintenance and its proprietary Lamp Ray Remotely-Operated Vehicle (ROV), which crawls along immersed ships’ hulls and marine structures and 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 Lamp Ray performs a hull assessment, said John Tumber, Lamp Ray inspection manager, measuring metal thickness, paint thickness and cathodic protection 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 said. “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-foot SDTS in San Diego in March, first doing an extensive hull cleaning using the Submersible Cleaning and Maintenance Platform that crawled along the hull, 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 and prevent maximum efficiency.
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 while it also records data on the metal and paint thicknesses and cathodic protection 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 said. “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.
“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 OK,” he said.
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 said. “There were a few small spots with some minor corrosion, but nothing big and crazy.”
Hulls corrode from the inside out, he added, beginning where water collects in inaccessible spots. That means the crew has been doing a very good job of internal maintenance and preservation.
The roughly five-day process of hull cleaning, the hull survey and the data analysis cost about $180,000, Moore said. 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,” he added. “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.”