NEW YORK — Two hoax calls reporting an explosion on a motor yacht off New Jersey came from land, triggering a rescue effort that cost tens of thousands of dollars and raised questions about how to prevent such a waste of resources, the Coast Guard said Tuesday.

Deputy Commander Gregory Hitchen said at a news conference that the search operation on Monday evening cost at least $88,000 and lasted more than four hours. He said the emergency calls came from a radio that was being used by someone on land, not on the water.

An investigation has begun to determine who was responsible, and the agency is offering a $3,000 reward for prosecution of the person responsible.

Hitchen said the caller gave authorities a "specific blow-by-blow" on how the boat was filling up with water.

"Many hoax calls, you can tell immediately they're from children," he said. "This one was somewhat calm but was giving a convincing story as to what the nature of his emergency was."

The mission involving not only the Coast Guard, but local police and fire departments, was launched after authorities received an emergency radio transmission around 4:20 p.m. In at least two calls within about 5 minutes using the same radio transmission, the caller gave the name of the boat — the Blind Date — and reported it was 17 nautical miles east of Sandy Hook with 21 people aboard, several of them injured.

The caller also claimed the vessel sank but everyone had made it to life rafts. But Coast Guard crews and New York City police helicopters found no sign of any people or any distress in the water, and after several hours of searching it became increasingly clear there was no explosion.

"When they arrived on scene, helicopters looking down, they would have seen life rafts," Hitchen said. "And they would've seen smoke."

The caller also said the group didn't have a handheld radio or flares in the dinghy to communicate with rescuers.

At about 10 p.m., the Coast Guard made the decision to call off the search.

The two calls came in on a radio positioned somewhere in New Jersey or southern New York, possibly Staten Island, the Coast Guard said. They came in on a Coast Guard channel that is not typically used for emergencies.

Hitchen said the hoax put the public at risk by taking Coast Guard personnel away from a separate emergency call that came in during the four-hour-long search. The Coast Guard received a report of a person in the water off Bayonne, N.J., in the separate call but did not find anyone in distress.

Making a false distress call is a federal felony, with a maximum penalty of six years in prison, a $250,000 fine and reimbursement to the Coast Guard for the cost of performing the search. The Coast Guard and other state and local agencies responded to more than 60 suspected hoax calls last year in the northern New Jersey, New York City and Hudson River region.

Monday's distress call and search came nearly a year after a similar situation unfolded near Sandy Hook.

A call on an emergency radio channel was received in the early morning hours of June 14, 2011, with the caller claiming a 33-foot sailboat named Courtney Lynn was taking on water. Less than an hour later, another call came in claiming the boat was 90 percent submerged, and the four boaters were transferring to a small gray dinghy.