The Cromwell’s ocean swimming cove on private property between Black Point and Diamond Head will become an official public resource, a state board decided Friday.

In a 5-1 vote, members of the Board of Land and Natural Resources moved to take ownership of the site, which was developed in 1938 as a private boat basin by wealthy heiress Doris Duke. The deal will relieve part — but not all — of a liability issue for the nonprofit foundation that’s giving the basin to the state for free.

The Doris Duke Foundation for Islamic Art offered the basin to the state in a June letter after the board in April and May rejected a foundation plan to partly fill the basin with boulders removed from its 140-foot-long breakwater to prevent more people from making risky dives and getting hurt.

Department of Land and Natural Resources staff recommended against accepting ownership, partly over the state inheriting liability for such accidents that in the past included two people becoming para­plegics and one becoming a quadriplegic.

The board, however, put more value on public recreation than fear of liability.

“The state has liability every day,” said board member Thomas Oi. “For the state to preserve this (site) is a good thing.”

Stanley Roehrig, another board member, referred to liability as an uncertainty. “On the other hand, this is a situation where this could be a valuable ocean resource facility for the public,” he said.

A state law protects Hawaii taxpayers from liability for injuries people suffer in the natural environment or on improved property within parks or trail systems as long as hazards are disclosed by proper signs. But DLNR staff said that as a man-made structure in the ocean, Cromwell’s wouldn’t qualify.

Some of the liability issue will be lessened because the foundation will keep ownership of the inland retaining wall that since 1938 has included an easement for public shoreline access along the top of it. After the three bad accidents, the foundation built a fence on the makai edge of the wall that has reduced jumping, though some people still jump from the wall or even the top of the fence.

Board member Keone Downing said his decision was eased because the foundation will retain the wall and the easement.

“They will still have liability because they still own the wall,” he said.

Board Chairwoman Suzanne Case said the board, which governs submerged lands, was in a difficult spot because it had told the foundation it couldn’t dismantle a man-made structure that had become both a public recreation resource and a safety hazard. “This is an unusual situation,” she said. “I think this is a good middle resolution.”

The fifth vote to accept ownership came from Samuel “Ohu” Gon III. Member Chris Yuen voted against state ownership because he said he didn’t want to create a new land management responsibility to which DLNR was opposed.

In addition to the liability issue, DLNR argued that Cromwell’s didn’t rise to the level of a public resource because relatively few people use it.

“It’s not something that can serve a large part of the community,” said Ian Hirokawa, a DLNR special projects coordinator. “There’s access, but it’s not easy access.”

DLNR instead had supported the foundation’s $2.5 million basin alteration plan.

Yvonne Izu, an attorney representing the foundation, floated the idea that the foundation could restrict public access to the cove as an alternative to altering it or giving it to the state.

Izu also mentioned that she believes the basin is technically already owned by the state because a deed from the Territory of Hawaii that conveyed the basin to Duke in 1938 in exchange for land that became part of Kailua Beach Park was invalid. DLNR deems that deed valid.

Duke, whose married surname was Cromwell, had the cove built as a private yacht basin by dredging a rocky shoreline that had previously been altered to create a saltwater swimming pool. Instead of berthing boats, the 9-foot-deep basin became coveted for swimming, snorkeling, shoreline fishing and surf-break access by the public.

Duke died in 1993, and the foundation manages a museum at her ornate estate, known as Shangri La. The foundation said in a statement after the board’s Friday decision that it was pleased and looks forward to finalizing the transaction that will involve defining exact boundaries for the property conveyance.