Between heats at Nancy’s Snack Bar in Oak Bluffs on Saturday Jon Holden, last year’s winner of the Martha’s Vineyard annual oyster shucking contest, inspected his knife doubtfully.

“I hate this knife,” he said, peering through his aviator shades at the black-handled Oxo brand shucker, “I wish I never bought it.”

He is used to a stubbier blade with an angled tip for a better purchase on the opening hinge of the oyster. A good shucking knife is crucial, particularly because of variations — from brittleness to hinge size — in the shell.

There are four motions to shucking an oyster at competition level. First, lodge the knife in the shell hinge. Second break the opening with a twisting movement, then force through the blade to sever the tendon at the back and pop off the shell top. Finally slide the blade under the oyster to cut the muscle at the base.

Sport shucking is global — Galway, Ireland, hosts an annual international contest, where everything from a stray shell shard to improper presentation can result in docked points.

At Nancy’s, though, the key was just to get the oysters on a plate, ideally still in the half-shell.

“It’s just a fun contest, for charity,” said Mr. Holden, with a wave of his knife hand. Mr. Holden put in five years at Nancy’s restaurant as a cook, and is now a manager at the Oyster Bar on Circuit avenue.

Mr. Holden was dogged by his poor equipment. He tried out a better-fitting chain-mail glove and resorted to borrowing a competitor’s knife for the final rounds. Though he won the heats handily — even showboating a little for the crowd before flipping the shell top off his final oyster — the reigning champion was eventually upset by Chris Jones of the Coop DeVille restaurant.

Twenty shuckers from around the Island came for the contest, which is in its second year as an Island Affordable Housing Fund benefit. It brought dozens more spectators who spent the three hours slurping bivalves and shouting encouragement.

Jimmy Hoe and Teddy Karalekas are two Island shuckers so seasoned they are not allowed to compete in the annual contest. Mr. Hoe performed in an early showcase round and then watched the rest of the afternoon’s events from the sidelines, wearing a T-shirt with a large oyster drawing that read: Eat It Raw. He runs a shellfish bar outside the Newes From America pub in Edgartown during the summer months and has shucked so many oysters over the years that he has developed a mound — or midden — of shells in his backyard.

Last October he witnessed this first-hand just how serious shucking can get when he competed in the Cape Cod Oyster Shuck-Off.

“The Wellfleet oysters are shaped differently, and they splinter easily” Mr. Hoe said. He was penalized 10 seconds for infractions on the first day and failed to qualify for the final heats, despite logging one of the fastest times.

It is not unusual for exceptional shuckers to be excluded, said Mr. Hoe, pointing to the example of William Young Jr., also known as Chopper, who can no longer compete in the Cape Cod Shuck-Off. He receives sponsorship gear from Evinrude and can have an oyster ready to eat in five seconds.

As for Mr. Hoe, he is considering having another stab at the Cape Cod contest this fall.

“I’ll have to get hold of some Wellfleets first and tune up,” he said.

Patrick Manning, executive director of the Island Affordable Housing Fund, prefers fundraisers like this with a popular draw rather than what he calls the wine and cheese circuit. “It’s about education,” he said, under the shade of a Nancy’s umbrella. “A lot of people think they make too much [money to qualify] for affordable housing. Well, no you don’t — get on the list.”

On Martha’s Vineyard, he observes, people can earn a lot of money without being able to afford property at market rates. “The people who need help are police officers and bank managers,” he said.

Formerly a New York legislator, Mr. Manning was hired by the housing fund in early 2007 to manage the organization’s fund-raising arm. Last year, he pointed out, the fund was the biggest money raiser on the Island after the Hillary Clinton campaign. Today’s event is no exception: a volunteer who was counting money opposite Mr. Manning had earlier sold half a dozen oysters for $100. Mr. Manning himself managed to flog a plate for $20 to a table that didn’t even want them and handed them back for re-sale. In total, the volunteers raised $2,000 on the day.

“It’s a cause everyone can get behind,” said Mr. Manning before taking the microphone to thank everyone for their support.

Moments after his win Mr. Jones was celebrating with a beer by the PA system. He made the 2007 final and puts this year’s win down to a tweak in his preparation technique.

“I started drinking at 7.30 in the morning instead of 6.30 a.m.,” he said with a chuckle. He has already settled on a home for his Heineken Light neon sign, the top prize donated by the event sponsor.

“It’s going in P.J.’s love shack,” he said. The love shack is a garage on Cape Cod and P.J. is a friend who taught Mr. Jones to shuck as a 17-year-old.

“I owe him one,” he said.