By Warren Miller, Marine Construction Magazine
The challenge for rebuilding the wharf at the Port of Beaumont, Texas was substantial. The port had contracted with McCarthy Building Companies to rehabilitate several wharves whose steel pilings corroded over many decades and ultimately failed, causing a collapse of the wharf. Before new piles could be driven and new wharves constructed, the company and the port needed to know exactly where to extract the collapsed structure and debris in low-visibility water.
That wasn’t an easy task.
“We won the job for the Port of Beaumont and started in January 2022,” said Sarah Johnson, a senior field engineer for McCarthy. “One of the biggest parts of the job was the demolition of the existing structure. But it’s pretty difficult to demoout an existing structure that’s underwater and we can’t see.”
Added to the difficulty was scheduling.
“If McCarthy wanted a hydrographic scan, we’d have to go to a third-party service and it would take a couple days to get data from them,” Johnson added.
Before the construction started, the decision was made to look at buying a small, uncrewed surface vessel outfitted with sensors, a computer for mapping and communication capable of transmitting a picture of the underwater landscape. The company brought in Craig Turner, the geomatics manager out of the company’s Phoenix office who typically maps topography of dry land with sensor-equipped drones.
“I have a remote-sensing background and I’ve worked with LiDAR,” Turner said. “Even though the Port of Beaumont was our first venture into unmanned, subaqueous work, the data processing is very similar to what I’ve worked with. Operating it in the water was new.”
[LiDAR, an acronym of “laser imaging, detection and ranging,” is a method for determining ranges by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver.]
The team looked at the vessels of several manufacturers and opted to go with an EchoBoat-160 built by Seafloor Systems. The 3-by-5-foot boat is made of an HDPE hull and aluminum frame and weighs about 100 pounds before outfitting it with sonar, LiDAR and other sensors.
“They have different models,” Turner said. “We rented a larger boat at first, but we needed a crane to put it in the water. Now we’re using an EchoBoat-160 because it can be handled by two people dropping it in the water from a dock.”
The next challenge was building the team to operate the boat.
“I’m in Phoenix, so finding a place to do the training and a place for the boat to live was the first challenge,” Turner said. “The second was making sure we had a team who were committed to the technology. Sarah fit that bill. We completely trust her, and she picked up the training very quickly.”
The maps generated by the computer and sensors on the EchoBoat changed both the speed by which data was acquired and the accuracy of the data.
“For the first six months,” Johnson said, “There was a lot of guesswork as to what was down there. Divers couldn’t see more than a foot in front of them. But with the survey boat, we can launch it, do a couple of passes and get data that says, ‘oh, there’s an object right here where one of our piles is supposed to go.’ We’ll send that information to the engineer and depending on what they say, we’ll either decide to shift where we’ll drive the new pile a foot or so, or attempt to pull out whatever obstructions we’re seeing.”
The EchoBoat has also been used on the company’s work to rehabilitate the wharves at the Port of Freeport.
“It’s a little different use at Freeport,” Johnson says, “because we don’t have to look for debris. We’re mainly using it to verify that the dredge slope is accurate. We’re dredging at a 3-to-1 ratio and there’s a toe trench when it comes back up. Once it’s verified that that the dredge pass is accurate, we place rip-rap in the toe trench, then run the EchoBoat again to verify that the rip-rap is where it’s supposed to be.”
Reprinted from Marine Construction Magazine Issue I, 2023
