By Ronnie Cohen

SAN FRANCISCO (Reuters) - The Coast Guard was searching the rough waters off Northern California on Monday for two adults and two young children missing after they radioed they were abandoning a sinking sailboat.

Someone aboard the vessel first made a distress call late on Sunday afternoon that the 29-foot (8.8-meter) craft was taking on water and sinking in the frigid waters south of San Francisco, roughly 65 miles west of Half Moon Bay, the Coast Guard said.

The Coast Guard has so far been unable to identify those said to be aboard the boat, and no one has been reported missing, but Coast Guard spokesman Chief Petty Officer Mike Lutz said the agency was nevertheless taking the call seriously.

A little more than an hour after the first distress call, the vessel's operator reported that the four people aboard the boat were abandoning the craft, and the Coast Guard lost radio communications with the caller.

"The weather was pretty rough yesterday as it most always is in the Pacific. It's always rough and always cold. And they started taking on water," spokeswoman Petty Officer Pamela Boehland told CNN.

"Eventually, the water became too much for them and their electronics failed, their GPS failed, and they decided it was best to abandon ship," she added, describing the call.

Lutz said the boat reportedly had no life raft or electronic-positioning beacon. Some of the boaters were wearing life jackets, he said, but he was unclear how many.

The man from the missing vessel, possibly named the Charmblow, had indicated the group planned to use a makeshift life raft fashioned out of a cooler and a life preserver as a flotation device until they could be rescued , Lutz said.

MUCH OF CONTACT INAUDIBLE

But rescuers had not caught sight of the stranded boaters or their vessel by late Monday afternoon. Lutz said four helicopters and three boats would continue to search the ocean from Half Moon Bay to Monterey through the night and re-evaluate the effort Tuesday morning.

The San Francisco Chronicle identified those believed to have been on board the boat as a man, a woman, their 4-year-old son and his cousin, who was under age 8. Continued...