HONOLULU -- Without passenger boats, bridges or tunnels linking the islands of Hawaii, the state's four island counties in some ways are as isolated from each other as they are from the mainland.

That may change when the Hawaii Superferry, a four-story catamaran, begins running from Honolulu, on the island of Oahu, to Maui and Kauai in a little over a year. A second boat connecting Honolulu with the Big Island is expected to start service in 2009.

"This is like the coming of the jet age. It's a new transportation mode," said John Garibaldi, president of Hawaii Superferry. "How much of the beauty of Hawaii do you experience from 20,000 feet in the air?"

Over the past several decades, other boat services have tried to provide a viable alternative to commercial airliner service to move people around the islands, but every effort has failed.

The latest ferry service was originally scheduled to start this year, and it still has a long way to go before its new July 1, 2007, launch date. Even if the $235 million project starts then, it's unclear whether it will be able to turn a profit.

Environmentalists, lawmakers, farmers and lawyers stand in the way.

Some are worried that the Superferry project is being rushed without researching traffic effects on each of the islands, without planning to prevent humpback whales from being struck by the big boats, and without protecting against invasive species such as biting ants spreading across the islands.

The ferry will travel up to 40 mph, with a trip from Honolulu to Maui taking about three hours, compared to about 40 minutes by plane. The shortest trip, from Honolulu to Maui, would be 89 nautical miles. The Honolulu-Big Island line would be the ferry's longest voyage at 140 nautical miles.

Plans for the Superferry have been moving along at an uneven pace for several years.

In a rush to take advantage of federal funding, a downtown Honolulu ferry terminal was completed in 2003. Transportation Secretary Norman Mineta visited the unused terminal two years ago and called Hawaii's ferry plan one of the nation's most ambitious and forward-looking transportation projects.

Past ferry services have never lasted long, said Panos D. Prevedouros, a University of Hawaii professor of civil and environmental engineering.

"They had issues with the waves. ... The ride was choppy and the demand was low," he said. "The current project is different. This is a full-sized ferry that can transport hundreds and hundreds of passengers at a low price."

Some state legislators have questioned Superferry officials over how they will be able to compete with the soon-to-be four interisland airlines, which recently offered $39 one-way promotional fares.

Superferry officials argue that they will cater to a different kind of customer than the airlines, and that they don't believe the low airfares will last. Regular airfares range above $72 one-way.

One of the keys to the Superferry's success is its plan to allow vehicles onboard with the passengers.

Families wouldn't have to check in their luggage, farmers could load their produce in vans and school buses could bring children on field trips, said Terry O'Halloran, who recently filled a job as public affairs director to help improve communications with critics of the project.

"The interisland ferry is going to connect the islands in a way we haven't ever seen before," he said.

Several lawmakers have threatened to withhold $10 million in harbor improvements because they say the Superferry hasn't adequately addressed some residents' concerns.