A leading surfer group is mobilizing against a plan to replace the failing Royal Hawaiian Groin with a new structure that is about 10 times larger.

Keone Downing, son of big-wave surfing pioneer George Downing, said Save Our Surf objects to replacing the circa 1927 groin with a new 180-foot T-head structure, which would change its ocean floor footprint from about 550 square feet to more than 5,000 square feet. Downing said implementing this plan — the preferred alternative in the final environmental assessment published by the state Department of Land and Natural Resources — would create an unsightly structure, change the quality of Waikiki’s waves and lead to a potentially dangerous influx of predatory eels.

“The ocean user includes a big group of surfers,” said Downing, who also sits on the Board of Land and Natural Resources. “If need be, all will come out to support the cause. I think if my dad asks for numbers, numbers will appear.”

DLNR will hold a public hearing at 6 p.m. Tuesday at the Waikiki Community Center, 310 Paoakalani Ave., to receive testimony on whether the preferred design or another should be part of the project’s conservation district use application. This latest meeting is an outgrowth of a public hearing in February 2016 at which DLNR offered proposals to fix the failing groin.

Other options still in play are adapting the existing groin and using it as the core of a new 160-foot-long rock L-head groin, or adding a new 160-foot-long vertical concrete wall groin.

Dolan Eversole, Waikiki Beach management coordinator for the University of Hawaii Sea Grant College Programs, said DLNR will winnow feedback into a recommendation for the Land Board, which will have the ultimate vote on the project.

DLNR said the expected time frame for construction is dependent on regulatory approvals but could start sometime in early 2018. The department hasn’t taken a final position on the groin’s design, but the preferred alternative has gotten support from the Hawaii Lodging &Tourism Association and Waikiki Beach Special Improvement District Association (WBSIDA), which would fund 50 percent of the project up to $750,000 if the design moves forward.

“The WBSIDA agrees with the purpose and need for the project and the identified project urgency,” association President Rick Egged said in a letter to DLNR. “The project is urgently needed … and the 180-foot T-head option is not only effective for stabilizing the Royal Hawaiian to Moana Beach (hotel), but may possibly provide a slight beach enhancement to the west side of the structure.”

Mufi Hannemann, tourism association president, said the lodging organization also supports a 180-foot T-groin.

“Folks like Keone and others who use the water a lot have valid concerns, but if DLNR thinks we should have a longer groin, that’s what we need to do,” Hannemann said.

Sea Engineering Inc., the lead design firm on the Royal Hawaiian groin project and the state’s 2012 Waikiki beach nourishment project, has said the proposed sloping rock rubble mound would provide good wave energy dissipation and minimal wave reflection back to the shore breaks, which would experience negligible impacts.

But Downing disagrees based on the impact that T-head groins have had at Iroquois Point, a test model for Waikiki.

“Even though they feel Iroquois Point is a success, you’ll see the steepness of the slope and sand which cannot be held in Waikiki, which has a much shallower topography,” he said. “It is said that the rubble mound groin may increase marine life, but giving a place for eels to live may not be a good thing.”

He also questions why the design of the existing groin, which has held for about 90 years, could not be repaired or replicated.

“I don’t believe that there has been a study about why the groin that is there has held for so long,” he said. “They should take out the broken parts and repair the existing wall or replicate it.”

If that is not obtainable, Downing said, Save Our Surf favors a modified wall groin, which has a much smaller footprint and doesn’t use large boulders.

Kelly Sanders, area general manager for Marriott International hotels and resorts, who oversees the five Kyo-yo-owned hotels in Hawaii, said his hotel company doesn’t have a favorite option, but is eager to move past the status quo.

“We aren’t environmentalists. We are hoteliers trying to protect tourists. Whatever they do is better than what they have today,” Sanders said. “Waikiki Beach is the most famous beach in the world. We need to protect our assets just as you would any business.”

Sanders said storms and seasonal weather patterns have caused significant shifts in Waikiki Beach sand, which have affected public access and created safety hazards.

“Until we settle on a permanent solution, we will have to continue doing beach restorations. It’s a costly endeavor,” he said.

Sea Engineering has said the deteriorating groin, between the Waikiki Sheraton and Royal Hawaiian hotels, is all that is keeping a prime section of Hawaii’s most visited beach from being swept away. A study from Hospitality Advisors LLC has estimated that deterioration of Waikiki Beach could trigger losses of more than $2 billion in annual visitor spending, $150 million in tax revenue and 6,350 hotel industry jobs.

“The beauty of the beach is why we take a 10-hour flight to get here,” Elaine Lucas, a visitor from Sydney, said Friday as she enjoyed the shoreline by the failing groin.

Lucas’ husband, Michael, who was on his fourth trip to Hawaii, said Waikiki Beach is the main reason that the couple keep choosing Oahu.

“I’m glad they are working on maintaining the sandy shore,” he said. “It’s very important.”