Coast Guard investigators want to know why it took more than a week to report the disappearance of singer Olivia Newton-John's (search) photographer beau, who vanished from a fishing boat last month off California, officials said yesterday.

Investigators have reportedly spoken to the Aussie singer about Patrick Kim McDermott (search). Newton-John was in Australia at the time he disappeared.

McDermott's ex-wife, B-list actress Yvette Nipar (search), finally called cops on July 11 — 10 days after he vanished.

"The relationships, the friendships are all part of the investigation," said Chief Warrant Officer Scott Epperson. The delay in calling police has hampered the probe, he said.

"Who knows what the exact thinking of the family was when the bells went off that said, 'Hey, this guy isn't around, we better call someone and report him missing,'" Epperson said.

McDermott's fishing gear was found on the chartered boat when it docked and his car was at the marina. Authorities are looking into the possibility McDermott fell overboard and drowned or faked his death.