A leading surfers group, with a track record for stopping projects, turned out in full force Tuesday to make waves against a plan to replace Waikiki’s aging Royal Hawaiian Groin with a design that has a much larger footprint.

Members of Save Our Surf, mobilized by Keone Downing, the son of big-wave surfing pioneer George Downing, said they want the circa-1927 groin repaired or replicated. If that is not possible, Downing said, they favor a modified wall groin, which has a much smaller expanse and doesn’t use large boulders.

Surfers and water users made up the largest portion of the crowd of 50-plus gathered at Waikiki Community Center for a public hearing called by the state Department of Land and Natural Resources to discuss replacing the failing groin with a 180-foot T-head groin, the preferred alternative in the final environmental assessment. Sea Engineering Inc., lead design firm on the Royal Hawaiian Groin project and the state’s 2012 Waikiki beach nourishment project, 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.

Sam Lemmo, administrator for DLNR’s Office of Conservation and Coastal Lands, said the hearing would help decide whether the preferred alternative or another should be part of the project’s conservation district use application.

Other options include building a new 180-foot-long rock L-head groin; a new 280-foot-long rock L- or T-head groin; adaptive reuse of the existing groin as the core of a new 160-foot-long rock L-head groin; and a new 160-foot-long vertical concrete wall groin.

“I don’t think that we’ve even come close to making a decision,” Lemmo said. “(Sea Engineering) gave us what they think is the best-engineered solution for this situation, and they gave us four alternatives. They seem to be leaning toward the T-head groin.”

Project consultant Scott Sullivan, vice president of Sea Engineering, said adapting the existing groin would result in a 20 percent larger footprint since it’s so unstable. The smaller wall design would work but isn’t often used, Sullivan said.

“Making it a T-head groin now wouldn’t add much to the cost, and you sure wouldn’t want to go back in 10 years to add another arm,” he said, adding that the 280-foot option wasn’t worth the extra money.

The Hawaii Lodging &Tourism Association and Waikiki Beach Special Improvement District Association, which would fund 50 percent of the project up to $750,000, support the 180-foot T-head groin. But Downing, who sits on the Board of Land and Natural Resources, said it could create an unsightly structure, change the quality of Waikiki’s waves and lead to a potentially dangerous influx of predatory eels.

“Not once did you mention anything about the effect on surfing. This is the beauty of Waikiki. It’s not the sand and beach for tourists,” said Robert Peters, who was part of Save Our Surf in 1969 when the group marched on the Capitol to stop a multigroin project planned for Waikiki.

Jim Hayes was the only resident who testified in favor of the 180-foot T-head groin, although there were other supporters at the hearing, who elected to stand on previously submitted testimony.

“I see the proposed project being an improvement from an aesthetic point of view, and perhaps there’ll be sand on the Ewa side of the groin,” Hayes said. “It would be so much nicer if you could continue to walk on sand from the Ewa side of that wall.”

Lemmo said DLNR will use feedback from Tuesday’s hearing to devise a recommendation for the Land Board, which will take a final vote during an April meeting. The department will continue to accept written testimony for the next two weeks, he said. Testimony should be sent to DLNR, 1151 Punchbowl St., Room 131, P.O. Box 621, ­Honolulu, HI 96809.

The expected time frame for construction is dependent on regulatory approvals, but it could start sometime early next year, Lemmo said.