The U.S. Coast Guard Monday night said it is not giving up on the search for four people -- including two young children -- who are presumed missing after a weekend mayday call from a sailboat saying it was taking on water.

The Coast Guard said its search had boats and planes scouring an area about 65 miles off the coast of Monterey.

Four helicopters and two planes ended their aerial search at nightfall, but the Coast Guard kept three Cutters in the waters off Monterey trying to find any sign of a missing sailboat and the four people who were aboard.

The Coast Guard released a recording of the mayday call made from the sailboat. On it, the boat operator can be heard saying: "Coast Guard, Coast Guard. We are abandoning ship. This is Charm Blow. We are abandoning ship."

That was the last call from the 29-foot sailboat Charm Blow at around 5:20 p.m. Sunday.

"We still think that there is somebody in actual distress, so that's why we're throwing all these assets at it," said U.S. Coast Guard Petty Officer Pam Boehland.

The Coast Guard spokesperson said even though there are no other reports of a missing boat and they haven't been able to trace a boat with the name Charm Blow, there is no evidence the radio call is a hoax.

"There's a lot of elements that lends credibility to the fact that there are people out there," said Boehland.

A Navy E-2 Hawkeye From Point Mugu joined three Coast Guard and one Air National Guard aircraft in the search Monday.

"You don't have to be out of sight of land to drown. The ocean can be a dangerous place. Everyplace is a dangerous place," added Boehland.

Kame Richards sells custom sails and other boating equipment from a shop in Alameda.

He told KTVU there are no regulations requiring boaters to file what's known as a "float plan," or to even carry an inexpensive locator beacon known as an EPIRB. However, he said it's a good idea.

"When it becomes activated by water, it starts transmitting on a frequency that airlines pick up, so they can find out exactly where you are," said Richards.

In the case of the Charm Blow, the Coast Guard says there was no life raft or survival suits.

One of the last messages from the boat said they were trying to fashion a raft out of ice chests and life rings.

"If they were able to build that makeshift life raft, it's a possibility that would increase their chances," said Boehland.

Coast Guard vessels plan to be out all night continuing their search. At first light Tuesday morning, more aircraft will be up hoping to spot those four people and find them alive.