In front of an estimated spectator fleet of 600 powerboats, Don Onken’s American Ethanol, a 51-foot Mystic Powerboats catamaran driven by Slug Hefner and throttled by Mystic principal John Cosker, hit 206 mph today during the GLOC Performance Boat Challenge Shootout on Oklahoma’s Grand Lake O’ the Cherokees. It was the top speed of the event so far, which resumes tomorrow at 10 a.m. (CST) and runs until 4 p.m.

In hot and sticky conditions, Cosker and Hefner piloted American Ethanol to a top speed of 206 mph at the GLOC Performance Boat Challenge Shootout today. Photos courtesy/copyright Jeff Helmkamp.

“We had a good day and the boat was running great, the best it’s ever run,” said Cosker of his 51-foot creation, which boasts almost 8,000 hp. “The way this shootout runs is absolutely awesome. The start is about 200 yards from the dock. You can do two passes, one up the course and one down the course, in about 10 minutes.”

Cosker said that neither direction on the course was faster than the other. “Our first run going one way was 199 mph and our second run going the other way was 201 mph,” he said. “Our fastest run was to the north, but I think it was pretty equal. And the wind was a crosswind, not on our nose or tail.”

Today’s hot and humid conditions are expected to persist on Sunday.

Cosker and Hefner, who has a new 50-foot Mystic catamaran with Mercury Racing 1550/1350 engines under construction and broke the 200-mph barrier for the first time today (“He did it four times and he did great,” said Cosker of his cockpit partner), do not plan to participate in tomorrow’s top-speed contest.

“Don (Onken) wants to save the boat for the Lake of the Ozarks Shootout,” said Cosker, who’ll share the cockpit again with Hefner in the late-August event. “I don’t see anybody going out and finding another 20 mph tomorrow. We put the boat on the trailer, and unless something changes it will stay there tomorrow.”

For more action from Saturday’s top-speed contest in Oklahoma, check out the slideshow above.

Kenny Mungle and Michael Lee Lockwood laid down the second fastest speed of the day by reaching 185 mph in Gone Again, Mungle’s 32-foot Skater Powerboats catamaran powered by twin 1,550-plus-hp Sterling Performance engines.

“We put it back on the trailer and made a prop change, but by the time we got finished the runs were done for the day,” Mungle said. “We are going to start over in the morning. How much is left in the boat, we don’t know.”

Not far behind Mungle and Lockwood today with a 184-mph run were owner/throttleman Garth Tagge of Cumming, Ga., and driver Jim Melley in an open-cockpit 36-foot Skater catamaran.

According to Geoffrey Monical, one of the event organizers, 20 boats competed and combined for a total of almost 80 top-speed passes. This is the second year the GLOC Performance Boat Challenge Shootout has been held.

In an impressive performance Garth Tagge and Jim Melley ran 186 mph in Tagge’s 36-foot open-cockpit Skater.

Editor’s note: Look for additional coverage from day No. 2 of the GLOC Performance Boat Challenge Shootout tomorrow.

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