Knowing what he knows now, the captain whose sailboat was hit by an electrical arc in January says he wouldn’t have taken the 70-plus-foot vessel up the New River and under those power lines.
A 3D scan of the power lines, performed for The Triton by S-E-A- Ltd. of Ft. Lauderdale, measured them in a dip across the river that ranges from 103.5 feet on the north bank to 92.6 feet on the south bank.
As for the navigable portion of the river, the lines dip from 101.6 feet to 95.2 feet above the “apparent average high water line on adjacent banks,” said Christopher Karentz, senior maritime consultant with S-E-A- Ltd. who offered to measure the lines after reading last month’s story.
On that January afternoon, the sailboat with a 98-foot air draft was hit by an electrical arc, causing it to stop dead in the river with a fire in the engine room and destroyed electronics throughout. The captain and two crew were not injured.
That scanned height is consistent with the only information available about those high-voltage transmission lines — sort of. The NOAA chart for the river indicates “authorized clearance 80 feet” at those lines, and an FPL spokeswoman would only said the minimum safe distance is 20 feet.
Taken together, that could mean the lines are 100 feet above the high-water level of the river, which is true for the northernmost portion of the river, but not for the southern part.
“Wow,” the captain said upon hearing the numbers and doing the math. But after a pause, he said, “None of that makes sense to me. This boat has been up river before, and [another yacht] is up here now with a taller rig. … If I had known the actual height of those wires, I would not have gone.”
He said he is confident that his air draft number is accurate, but he noted that he was traveling on a falling tide, not quite to halfway, which might have provided another foot or so of clearance. The New River’s tidal range is about 2.5 feet, and initial surveys show the mast did not come in contact with the power lines.
Another measurement the 3D scan revealed was that of the insulators, which keep the power away from the pole. In this case, the insulators are 12.5 feet. That distances provides a good indication of safe clearance, according to an electrical engineer who used to work with FPL.
Still, electricity on power lines can arc as much as 20 feet or more, depending on the voltage.
FPL would not say how tall the pole on the north bank of the river is, how high the lines are or what the voltage is. A spokeswoman would only say that several high-voltage lines over the river range from 138,000 volts up to 230,000 volts.
Despite several indications that FPL staff were acquiring pole and line height information, the final conversation ended when The Triton asked if FPL would ever provide that data and the spokeswoman said no.
The Triton has filed a Freedom of Information Act request with the Army Corps of Engineers, which permits the pole and wires. It was not clear if that permit paperwork or the Corps’ statement of findings about the project will answer those questions.
Regardless, the 3D scan provides data that, while not official, is highly accurate.
The 3D image of the lines comes from a scanner shoots sine waves to measure distances. It takes millions of points in about 30 minutes to provide a point cloud of data that is then turned into an image.
S-E-A uses the scans to provide forensic analysis and origin/cause services, most often for insurance companies or lawyers involved in accidents, incidents and disputes.
“A lot of what we do ends up in a courtroom,” said Eric Sauer, a mechanical engineer with S-E-A who measured the scene in mid-May. “This is what creates those types of animations you see on NCIS or CSI on TV.”
The scan is accurate to within 2 mm, regardless of distance. Though typical scans take about 10 minutes, Sauer took two 30-minute scans, one on each bank of the river, because of the higher resolution required and the distance of the lines. The laser can scan to 120m and records data points at 908 nanometers wavelength.
“It measures phase shift, not what they call time-of-flight measurements, so it’s more accurate and faster,” Sauer said. “You could put it in a perfectly dark room and it actually does better.”
Each scan produce huge data files that a software program weaves together to create a point cloud. Sauer then removes irrelevant data (there were several Water Taxi boats docked on the south bank when these scans were taken) and adds relevant data (such as the water height, in this case) to produce images. It takes 2-3 days working with the software to create usable images.
“It’s a fantastic machine,” Sauer said. “The product that comes out of it is so far advanced that the time that goes into making it is minuscule.”
Karentz is working with marine industry clients to bring the technology to yachting. When no line drawings are available, taking a 3D scan of a boat hull is far more accurate than taking measurements with a plumb bob and level, he said.
“The applications for the machine is endless,” he said.
In a case like this sailboat accident, the scan can help remind mariners to abide by their charts, Karentz said. If the chart says authorized clearance is 80 feet, mariners should respect that.
The captain of the sailboat said he expected criticism from readers who thought he shouldn’t have taken a sailboat with 98 feet of air draft up the river.
“The real reason we’re doing this story is so we can encourage people not to go up there if they’re close,” the captain said. “Our mission for telling this story is not to see someone hurt or killed by a similar incident.”
Click to read related post, “Arc of electricity leaves yacht dead in water“.