The sleek, powerful form of the attack submarine USS Connecticut (SSN 22) seemingly floated upon its concrete keel blocks in the vast dry dock, silent as if it were deep under the waves, while a crew of engineers underneath it prepared a tiny robot to perform a hull inspection Apr. 1.

What once was the stuff of future-tech journals is fast becoming a reality as the Puget Sound Naval Shipyard & Intermediate Maintenance Facility and Naval Undersea Warfare Center Division, Keyport partner to enable an innovative robot climber to perform U.S. Navy submarine hull inspections.

While hull-crawling robots have been rolling along decks and hull-climbing robots have been scaling the vast steel walls of commercial ships’ hulls in the civilian sector for several years now, it was the vision of Chris Stone, an engineering technician at PSNS & IMF, that realized the technology was potentially the right answer to a very difficult question: how to speed up hull inspections for U.S. submarines.

It is a question and quest that would take him seven years to realize.

Whether an active duty fast attack submarine is being dry-docked for maintenance and repairs, or a ballistic missile boat is being dry-docked to begin the mid-life refueling and overhaul process, an inspection of the hull is performed.

The current method for the initial hull inspection when a boat enters dry dock is an expansive, time-consuming effort by shipyard workers using small, hand-held sensors.

“I spent hours doing inspections on the side of a hull,” Stone said, holding his arm up and mimicking the scanning motions he went through. By 2012, Stone was certain there had to be a more cost-effective way to conduct these hull inspections.  Researching the problem, Stone came to believe a climbing robot would be the right solution. He learned PSNS & IMF’s innovation lab had even obtained such a robot and was willing to let him use it for his early testing.

“The innovation lab is built to do rapid innovation and prototypes,” Stone said.  The lab is a miniature development center, but can only carry an idea or experiment only so far. The testing in PSNS & IMF’s innovation lab conducted very quickly determined the machine would need its own built-in vacuum motor in order to keep itself on the hull without a long hose connecting it to a vacuum motor.

After six years of testing and ideas, Stone was finally able to have PSNS & IMF purchase a climbing robot from the manufacturer in 2018.  The next step was overcoming the fall protection installation problems.  Not fall protection for the operators; they would be safely on the dry dock floor.  No, the fall protection was to protect the robot should its vacuum motor fail.  The last thing Stone wanted was an expensive robot falling off a submarine and shattering on the dry dock floor.

Fortunately, the manufacturer had developed an automated fall protection system for the larger climbers with a winch which Stone had bolted to a heavy steel plate attached to a pallet.

“The pallet provides a location to store all equipment as well and can be moved around by a forklift” Stone said.

A line runs through two anchor points on the submarine hull to the robot, and then down to the winch.  The winch does not lift the robot; it only keeps a low level of on tension on the line to keep the robot from getting fouled by its own safety gear.  Otherwise, it would be used to lower the robot safely to the dry dock floor should the vacuum motor fail.

Six years and one robot later, Stone finally had a workable platform.  Now he had to tackle the sensor problem.  The sensors must be held level at a specific distance from the submarine’s hull in order to be effective.

The initial idea was to use a spring-mounted roller that touched the hull, but this immediately created several problems.  The first was paint damage.  In order to be effective, the roller could not be covered in soft, paint-protecting neoprene like the climber’s treads.  It was a steel roller that could mar and scratch paint.  The other problem was the springs themselves.  The springs had to be strong enough to maintain the correct sensor height when the climber was inverted underneath the hull.  However, Stone said this inadvertently resulted in the springs lifting the climber off the hull.

“We were trying to find out who could help us build the height-control system,” Stone said.  This resulted in him taking a little trip 10 miles up the road to NUWC Division, Keyport in the summer of 2018.

Occupying a small peninsula in the picturesque town of Keyport, Wash., NUWC Division, Keyport’s mission is to be an innovation and technology leader for all manner of undersea and naval technology.  NUWC Division, Keyport possesses a great deal of flexibility because its tools and equipment are dedicated to design and rapid prototyping.   Stone spent a week with Tyler Paine, the NUWC Division, Keyport engineer who would lead the effort designing an auto-height sensor system.

“It was a great idea to try, but the issue was that the springs that push against the hull to maintain a constant offset also pushed the crawler off the hull,” Paine said, echoing Stone in his assessment.  This use of springs is called a “passive” system, and Paine recognized the need for an “active” system utilizing displacement sensors and electric motors to control the height of the device.

Money and schedules are always a consideration in any project, but this is where NUWC Division, Keyport’s status as an innovation center was an advantage.

“We were funded to develop a second-generation prototype,” Paine said.  He and Stone worked in a flurry of activity over that week, an effort that resulted in some demonstration parts even being completed.  More importantly, they had a plan.  Paine and the NUWC Division, Keyport team then spent a few weeks building the new attachment and testing its components before delivering the unit to Stone at PSNS & IMF for integration to the robot’s body.

Stone began running tests on sections of hull plating set up at PSNS & IMF.  Early tests in the lab were a resounding success.  Meanwhile, back at NUWC Division, Keyport, Paine and his team were refining the auto-height attachment’s design to increase reliability and efficiency.

“This has definitely been a team effort,” said Paine.

PSNS & IMF took delivery of the newly revamped crawler with the auto-height attachment in February of 2019.  However, it remained to be seen how the climber would perform on a real submarine.

By April 1, the sleek, powerful form of the attack submarine USS Connecticut floated upon its concrete keel blocks in the vast dry dock at PSNS & IMF as the tiny robot was readied beneath it.  The assembled climber looks like a miniature, neoprene-treaded tank.  The device weighs less than 70 lbs. and can be lifted to the hull by two technicians.  The device is steered with a remote control held by its operator, and its vacuum motor’s loud whirring created the illusion the device was cleaning the dry dock floor.

A breeze chilled by sea water rolled over the dry dock door as the team readied the robot for the critical test.

“If we can get one section done, that’ll be a success,” Stone said from under his hard hat.  Stone and Paine were slightly tense as they watched two technicians lift the robot to the underside of Connecticut’s hull.  Stone took a breath and switched on the vacuum motor.

Seven years’ worth of struggle successfully sucked itself to the side of the submarine, and began slowing and steadily sliding along on its singularly solitary sortie.

There was no cheering or backslapping at the climber’s success.  Instead the robot was methodically run over the side of Connecticut’s hull for more than two hours, doing a test inspection to prove the auto-height sensor system was as effective as the robot’s vacuum motor.

Smiling with the success of his creation, Stone said the next planned step is for the Portsmouth Naval Shipyard to begin supplying hull climbers to the shipyards in the near future.  If this plan holds true, Stone said PSNS & IMF and NUWC Division, Keyport would continue their partnership and supply the sensor armature with Paine’s auto-height mechanism to the shipyards.

Stone and Paine, their creation smoothly moving upside down along Connecticut’s hull, acknowledged the robot and sensor would still need improvement but were satisfied the test has proven them right.  Stone said the challenges he faced over the past seven years have been worthwhile.

“We had a lot of setbacks to get here today,” Stone said.  “But we pulled together as a team to get to this point.”

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