A charter fishing trip turned exciting Thursday morning when those aboard came within five feet of what they believed to be a surfacing great white shark.

Buddy Vanderhoop, captain of the charter boat Tomahawk III, was taking his charter customers out for a morning of fishing when they came upon the nearly 20-foot shark about a mile offshore, between Aquinnah and Noman’s Land.

“Oh, I know this was a great white shark,” said Mr. Vanderhoop, a well-respected fisherman on the Menemsha waterfront. He estimated that the fish weighed at least 4,000 pounds. The distance between the fin and the tail was at least ten feet, he said, leading him to believe that the shark was therefore nearly 20 feet in length.

Mr. Vanderhoop’s boat is a 27-foot center console boat with a green hull. The shark was not that much smaller than the boat, he said.

“It was the highlight our summer. It was certainly the highlight of our day,” said Ray Drop, 71, of Edgartown and Park Ridge, N.J., who, along with his son Eric, 25, was out fishing with Mr. Vanderhoop and snapped several photographs.

Mr. Drop said they left the dock around 7:10 a.m., and saw the fish at about 7:30 a.m. “We were on our way to the fishing ground. We saw it in the distance and Buddy turned toward the fish. We tried to get close. It didn’t seem bothered by us at all. It was cruising,” Mr. Drop said. “It was heading westward.”

“We watched it for ten minutes,” he said. “What surprised me was how brown its color was for a great white. It was relatively brown in the fin and on the top,” he said.

Mr. Drop said he was amazed by both the size of the fish and the size of the boat they were in. “We were bobbing up and down nearby,” said Mr. Drop. “What if we had fallen overboard? We’d have been this fish’s lunch.”

After they saw the shark, the trio proceeded to visit a number of different fishing spots, before they got into bluefish near the Elizabeth Islands, Mr. Drop said.

Mr. Vanderhoop said he observed ten to 12 gray seals, a popular meal for sharks, on Noman’s Land.