Perspectives Online

Remote control: A better way to survey swine lagoons

Dan Bailey, James Lamb and Glenn Clifton have found a better way to survey lagoon sludge, via this remote-controlled boat, powered by a leaf blower.
Photo by Dave Caldwell

Perhaps necessity is the mother of invention, but surely convenience and efficiency are aunts and uncles.

Consider a task North Carolina hog farmers call a “sludge survey.” The state Division of Water Quality requires farmers who use lagoons to treat the waste created by their animals to do a sludge survey of each lagoon annually (the vast majority of North Carolina hog farmers use lagoons).

A typical sludge survey involves two people and a small boat, says Dan Bailey, a livestock agent with the North Carolina Cooperative Extension Service in Sampson County. It’s one of those “there has to be a better way” scenarios, and Bailey and others appear to have found that way.

In this sequence of photos, Lamb launches and operates the remote-controlled boat to do a sludge survey. The boat’s attached sonar depth finder records readings on a computer memory card. Later, the data can be downloaded to produce a computer picture of the contours of the lagoon bottom.
Photos by Dave Caldwell
Lagoons are earthen pits. Waste is flushed with water from the barns in which pigs are housed to the lagoons, where it decomposes. The solid portion of the waste stream that is more resistant to decomposition sinks to the bottom of the lagoon, forming a layer of sludge.

To ensure that lagoons are operating correctly and have not filled up with sludge, farmers must certify annually that each of their lagoons contains at least 4 feet of sludge-free liquid treatment area. Most do this by rowing out into the lagoon in a small boat and measuring the liquid depth, either with a pole or a rope with a disk attached to one end. The pole or rope is let into the liquid disk first. The disk stops when it meets the sludge layer. The liquid depth can then be measured on the pole or rope.

It is this rowboat-in-the-lagoon method of determining the amount of sludge in a lagoon that Bailey and faculty members in the College of Agriculture and Life Sciences began to ponder several years ago.

Rather than a rowboat, Bailey and colleagues proposed, how about a remote-controlled model boat? Bailey credits Mark Rice, a Cooperative Extension specialist in the College’s Department of Biological and Agricultural Engineering, with developing the first boat in 2003. Rice had the boat custom made and attached a sonar depth finder. The 3- to 4-feet-long boat could be operated from the bank of a lagoon while the depth finder recorded the liquid depth.

It worked well enough, but its propeller kept getting tangled in vegetation.

Bailey recalls, “I said, ‘Mark, we need an air boat.’”

Rice responded with two words: leaf blower. It was a “eureka” moment.

Bailey, who describes himself as a fair carpenter, set about building an air boat. His first effort was made of wood and had a leaf blower mounted on the stern and a depth finder mounted on the bow. It worked well enough but tended to leak a little.

He turned to 6-inch diameter white PVC pipe for his second effort. He arranged the pipe in a “U” shape with the bottom of the “U” upturned to form a prow. The leaf blower and depth finder are mounted between the legs of the “U.” The result is a PVC sludge-surveying pontoon boat.

When Bailey demonstrated his boats to Sampson County farmers, they apparently liked what they saw.

Glenn Clifton and James Lamb, employees of Prestage Farms whose duties include sludge surveys, liked the idea so much they built their own boat. The craft they came up with is made of aluminum, but like both of Bailey’s boats, it relies on a leaf blower for power and a depth finder to measure liquid depth.

Lamb said doing a sludge survey the old way required two people to load and unload a rowboat and drag it to a lagoon. Then it took 10 to 15 minutes to row out into the lagoon and do the 10 to 12 depth readings required.

Using a remote-controlled boat, Lamb does sludge surveys by himself. He said a typical survey takes about five minutes. Rather than 10 or 12 depth readings, the depth finder measures depth constantly, recording perhaps 2,000 readings. The depth finder records the readings on a computer memory card, so the data can easily be downloaded when the boat returns to shore. Software is available that produces a picture of the contours of the lagoon bottom. Because of the increased number of readings, Lamb thinks a survey done with a remote-controlled boat is considerably more accurate than one done manually.

At the same time, Curtis Barwick, who does sludge surveys for Coharie Farms, is using Bailey’s pontoon boat.

“It’s so fast,” Barwick says of the pontoon boat. “It saves a lot of time.”

Barwick says he could survey five-to-six lagoons per day the old-fashioned way, while he can survey 12-to-15 lagoons in a day with the pontoon boat. With 80 to 90 lagoons to survey each year, Barwick adds, “It’s just going to save so much time.”

But efficiency notwithstanding, Lamb says the biggest advantage is what he calls improved safety. While he says he’s never fallen into a lagoon, Lamb points out that rowing out into a lagoon in a small boat always presents that possibility. That alone would seem to be a huge selling point for remote-controlled boats.

—Dave Caldwell