Photo By Senior Chief Petty Officer Terence Juergens | Construction Mechanic Chief Nate Emmett, and Equipment Operator Second Class Jonathan...... read more read more
Chesapeake Underwater Signature Range
Seabee Diver innovation and dedication shine through during Underwater Construction Team ONE’s most recent mission
Story by Lieutenant Luke Millen, Underwater Construction Team ONE
July 2020
NORFOLK, Va. (NNS) Innovation runs deep in the history and heritage of the Seabees who make up the U.S. Naval Construction Force.
Born in the days following the attack on Pearl Harbor in 1941, Seabees were known to use whatever was available to continue on with their mission of building remote island bases in the Pacific Theater of WWII. What may have been an old fuel drum to the normal eye, to a Seabee, it was part of a roof, a wash bin, or a table. A bulldozer may be a great earth mover, but with a Seabee behind the wheel it can also destroy enemy machine gun nests.
In today’s Navy, a Hardigg Case is used to store and secure a variety of equipment but the Seabee divers of Underwater Construction Team (UCT) 1 have found another use for it: as an underwater concrete bucket. Thus, the Seabee’s “Can Do” spirit lives on today at the project site of the Chesapeake Underwater Signature Range in Norfolk, Virginia.
UCT-1, located on Joint Expeditionary Base Little Creek-Fort Story in Virginia Beach, Virginia, is one of only two units in the Navy that brings an underwater construction capability to the fight. For over 40 years, UCT-1 has provided underwater construction, maintenance, inspection, and repair capabilities to commanders all over the globe. Whether it is a pier that needs to be inspected, a channel that needs to be cleared, or recovery of objects underwater, Seabee divers have answered the call.
Engineers at Naval Surface Warfare Center, Carderock Division in Bethesda, Maryland, came to UCT-1 with a particularly complex project request; install an underwater signature range in the Chesapeake Bay. This range, once complete, will be used by Explosive Ordnance Disposal-related units to measure underwater influence effects of unmanned underwater and surface vehicles.
PREPARATION
While UCT-1 has installed similar sensor ranges before, this project posed its own particular challenges unlike anything seen before. In order for the array to accurately measure the signature properties of the vehicles, the sensors had to be accurately placed and aligned to a stringent set of requirements. From the sensor array, the data cable connected to each sensor would then have to be run 1,000 feet to the termination point. None of these measures would be a tall task were it not for the environment in which this array is being installed, or the size of the materials.
The location in which the array was being installed offered unique challenges to any diving mission, not to mention being a major construction operation. The close proximity to the deep water channel meant that countless freighters, car carriers, and warships make their way past the project site on a daily basis, resulting in massive wakes on their tails.
More importantly, at this particular choke point between two peninsulas that cordon off miles of inland waters, tidal currents run fast and change quickly. Ebb tides are known to last hours longer than flood tides, as the water recedes from the Bay at speeds of up to 2 knots. Flood tides do not typically run quite as fast, but slack tide, when the water is not flowing in or ebbing out, is ideal for precision underwater construction work.
The basic components of the array consist of the sensor base, the sensor, and the cable. All materials used were non-metallic and non-magnetic in order to prevent interference with the signature range operations. A 4-foot-tall, 6-foot-diameter plastic tub, when filled with 6,000 pounds of non-magnetic concrete, serves as a stable platform upon which the each of the sensors live. The sensor assembly includes a large dome that houses the sensor itself placed upon a series of flanges that can fine tune adjust the level and alignment of the sensor. Without the concrete, the system weighs over 1,000 pounds and measures over 10 feet tall.
EXECUTION: PHASE I
The project was broken into four phases to delineate major milestones in the installation of the array. During Phase I, which began in March 2020, the team was tasked with preparing the worksite for the placement of the sensor tubs. Clumps, in this case, heavy concrete blocks attached to buoys on bottom would demarcate the line on which the array would lie. A travel line on bottom would also be placed between the array and the termination point, so a diver could swim from one to the other. This brought about the first major hurdle for the team, how to moor the team’s 36-foot dive boat so that it could easily maneuver with precision over the project site?
Led by the ingenuity and seamanship of Chief Builder Craig Claudio and Construction Dive Detachment Bravo, the team set out to build four concrete anchors capable of holding the vessel in moor. With a four-point moor, the vessel would be able to hold position over the range regardless of winds or currents, and would have the maneuverability to shift position in any direction. Each anchor was hand-crafted in a shape representative of a Pearl Harbor-style anchor, and weighed between 650 and 750 pounds. Placement of these anchors in a square box shape around the worksite marked the end of Phase 1.
EXECUTION: PHASE II
The COVID-19 global pandemic shut operations down for the rest of the spring, and it was picked back up by Construction Dive Detachment Charlie (CDD/C) in June 2020. Det Charlie brought a new set of eyes to the most highly anticipated and discussed evolution of the project to date: deploying the sensor tubs and placing them on bottom. Sea state, winds, currents, tub strength, tub weight, diver safety… each of these aspects brought a myriad of concerns to the discussion table when the team was war gaming ways to deploy the tubs. How could one safely get a 700-pound tub into the water under control? How could one safely lower the tub from surface to the bottom at 25 feet of seawater against strong currents? How could one accurately lay the tub on bottom in precisely the location it is meant to be? These were the pressing questions that needed to be answered.
To address the matter of tub deployment into the water, CDD/C, under the guidance of Chief Construction Mechanic Nate Emmett, set to work building a platform for the tub to roll from off of a 9-meter Rigid Hull Inflatable Boat (RHIB). All accessories were cleared from the deck, and a platform was constructed so that the tub had a level surface to roll on clear of the gunwales. Cargo straps would be used to hold the tub in place during transit to the project site, and wheel chocks would be on either side for added security. Once it came time to deploy, the straps would be released, and the chock pulled on one side so that the tub safely rolled off into the water.
Figure 3 – Construction Mechanic Chief Nate Emmett, and Equipment Operator Second Class Jonathan Moore assist the Commanding Officer of Underwater Construction Team ONE, LCDR Seth McGuire out of the water after placing 5,000lbs of grout into underwater sensor tubs.
In order to combat the currents and maintain precision the team devised a way to guide it into place. A “template line” was constructed and placed on bottom. This template had marked out with tape the precise location of the edges and center of each of the eight tubs as the specifications called for them to be. At the center point, a direct embedment anchor, or “duckbill anchor”, was secured in the seafloor with a tagline coming out of the sand. When preparing the tub for deployment, the tagline was sent up through the center of the tub and back to a deckhand on the dive boat. Once the tub was in the water and ready to be dropped down via lift bag, the tagline was pulled taught, providing a nearly straight vertical highway line that the tub would travel down. Having a line through the tub with a secure point on bottom and topside also mitigated the possibility of the tub going astray on descent.
Ultimately, the plan came together without a hitch. The ballet between the dive vessel and the tub carrying vessel was orchestrated with excellent communication each time, and all eight tubs were sent down to bottom in a near straight line. Multi-beam survey data proved that all tubs were installed successfully. This level of accuracy, achieved with a set of direct embedment anchors and copious amounts of line, is a nod to the ingenuity and craftsmanship of the sailors at UCT-1.
To cap off Phase II, all tubs required roughly 6,000 pounds of concrete in order to be safely secured on bottom. A concrete pump was not feasible for this scope of work, so the planners were left pondering a way to get 75 concrete bags, weighing 80 pounds, down to the divers to be placed in the tub. Various sacks and bags proved to be difficult to manage both on topside and on bottom. The solution that got the job done was a Hardigg Case with countless 1-inch holes drilled through it, and a rigging bridle attached. With the Hardigg case rigged to the hydraulic A-frame on the 36-foot workboat, five to 10 bags of concrete could be lowered down to the divers at a time.
EXECUTION: PHASE III
Phase III is arguably the most complex and risky evolution of the entire project. During this phase, the sensor must be connected to the data cable on a spool, placed on its pedestal on the tub on bottom, then the cable must be unspooled 1000 feet to its termination point and laid safely on bottom. The aforementioned environmental risks still play a major role, but the risk to mission is significantly increased. Because the entire system between the sensor and cable reel are connected, with no way to disconnect, once those materials begin to enter the water, there is no turning back.
Yet, the Seabees find a way. Utilizing the 36-foot workboat in a four-point moor, a 19 foot inflatable boat to carry the cable reel, and the 9 meter RHIB to hold a SCUBA team, the sensor and cable installation started successfully. At this time, one sensor and cable have been successfully laid on bottom. While divers from the workboat installed the sensor, the inflatable boat unspooled the cable travelling between preset anchor points, and the SCUBA team from the RHIB swam the cable out to termination.
Figure 4 – Equipment Operator First Class Joseph Rodriguez places 80lb bags of non-magnetic grout into an improvised weight-handling basket for divers to place in sensor tubs on the sea floor.
CONCLUSION
Overall, the CUSR Project will take CDD/C through the end of July. Once all the sensors and cables are installed, the bundle of cables will be jetted (or buried) into the seafloor for added protection. Hurdles will arise, and successes will surely follow. All told, this work will save the USN nearly $1.25 million when compared to what it would have cost to contract the project in the private sector. The diving, small boat operations, construction, and seamanship experience that the entirety of UCT-1 gained on the project is invaluable. These Seabee divers will come out of the project more capable, more confident, and more ready to support the Fleets around the world.
| Date Taken: | 07.15.2020 |
| Date Posted: | 08.18.2020 10:23 |
| Story ID: | 376228 |
| Location: | NORFOLK, VIRGINIA, US |
| Web Views: | 239 |
| Downloads: | 0 |
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