The 60-foot-wide catamaran Cheyenne has mostly sat idle on Newport Bay. (KENT TREPTOW, Daily Pilot / June 23, 2012)

An ambitious ocean exploration project sponsored by Sir Richard Branson appears to be floundering in the waters of Newport Beach.

The Five Dives Expedition previewed at the Newport Harbor Yacht Club last spring, with international news reporters flocking to see Branson atop a high-tech submarine.

But more than a year after the splashy announcement, the sub has still not performed a manned practice dive, and local organizer Chris Welsh has pleaded with city officials to give him $320 free monthly rent on a mooring for the 125-foot mothership catamaran, the Cheyenne.

Officials cut him a deal last week by reserving the space for the boat, but will be making Welsh only pay for the months the boat is moored.

"It had to be fair and equitable for everybody involved," said Harbor Commissioner Dave Girling, who studied Welsh's pitch and recommended the new rental arrangement.

Welsh reportedly told the Harbor Commission that he postponed the submarine expedition because a crack in its windshield wouldn't be able to withstand the expected 13 million pounds of pressure, and his engineers were fashioning a new dome.

Welsh did not immediately return calls seeking comment, except to say he has done a practice recently.

The Five Dives Expedition plans to go to the deepest points of the world's oceans, with Welsh piloting the first one to the Mariana Trench and Branson the second one to the Puerto Rico Trench. Researchers would accompany the men as they study sea life and ocean conditions.

Other dive "opportunities" are "monumental" for human pilots, reads the website of Virgin Oceanic, Branson's company. It's a sister to Virgin Galactic, which plans to sell seats on space flights.

As Welsh and crew deal with engineering problems, they have used the catamaran as a support boat for a paddleboarder traversing the Channel Islands for charity and to sink a dead fin whale off the San Diego coast.

The 60-foot-wide catamaran has mostly sat idle in Newport, its large Virgin logo and bright white hull drawing the attention of tourists.

Welsh says it provides more: It is an educational opportunity for the Newport Harbor Nautical Museum, he said in a letter to the Harbor Commission.

Officials were letting Welsh moor for free, beginning in early 2011, but some boaters complained he was getting an unfair deal.

Harbor Resources Manager Chris Miller said Welsh will be billed retroactively for the first half of 2012.

mike.reicher@latimes.com

Twitter: @mreicher