SAN FRANCISCO -- Google's (GOOG) mystery barge is still under wraps but new documents obtained Friday show the giant tech company has quietly promoted it to local officials as "a curious and visually stunning" structure, with sails "reminiscent of fish fins," that will serve as a floating exhibit hall at sites from San Francisco to San Diego.

Google hopes to move the vessel around to various ports in San Francisco Bay, staying no more than a month in each location -- at least in part, apparently, because of a state law that discourages putting new structures on the bay for an extended period of time, according to documents and emails submitted to the Port of San Francisco.

Google barge plans
An artist's rendering of Google's barge structure in San Francisco Bay. (Photo by By and Large LLC)

But the project may have fallen behind schedule. A proposal submitted to port officials indicates the company hoped to move the barge to a pier at Fort Mason this month, from its current mooring at Treasure Island.

Negotiations with the Bay Conservation and Development Commission, a state agency, "seem to be going at a glacial speed," a Google attorney complained in an email to San Francisco officials this fall. Commission officials have said they can't consider a permit for the project until they get more information from Google.

Google didn't respond to a request for comment Friday, after acknowledging earlier this week that the company is behind a project that's fueled intense speculation and drawn national attention. A lease application released by the Port of San Francisco confirms Google is the sole owner of a shell company that owns the barge, and another vessel with a similar structure that's been spotted in Maine.

A reporter who visited Treasure Island on Friday saw no signs of activity and no workers on the 250-foot barge moored there. The structure on the barge appeared unfinished and partly covered in scaffolding.

When finished, the four-story structure is planned to have more than 13,000 square feet of exhibition space, a large open atrium, catwalks offering "views down through the atrium" and a roof deck with "sightlines of the spectacular San Francisco skyline and waterfront," according to the proposal submitted to San Francisco officials.

Twelve tall spires on top of the barge will support sails "reminiscent of fish fins, which will remind visitors that they are on a seaworthy vessel," the proposal enthused. It described the project as a "temporary technology exhibit space," dubbed "San Francisco Studio."

But the documents are noticeably vague about what kind of technology would be exhibited. In its statement earlier in the week, Google denied initial speculation that it was building a floating computer center. That statement didn't address another theory that Google may use the vessel as a floating showroom for its wearable computing device, Glass, and other cutting-edge products from its secretive Google X division.

Instead, Google's proposal says the project will draw visitors to waterfront sites, help promote San Francisco as a tech center and provide "a platform for local organizations to engage with guests and gain visibility in a unique way."

Google is hoping to attract up to 1,000 visitors a day while the vessel is moored at various sites including Fort Mason Center, Angel Island, Richmond and Redwood City, the proposal says. To help regulate the flow of visitors, the company said it will use an invitation system.

The barge won't stay in any place for longer than a month, according to the proposal and a separate lease application, which asserts that those temporary moorings should avoid running afoul of state law that restricts permanent structures on the bay. BCDC Executive Director Larry Goldzband, whose agency enforces that law, said Friday that he couldn't evaluate that assertion without more information from Google.

Eventually, the Google proposal says the barge could move on to San Diego and other West Coast locations. But despite the eye-catching sails, it's most likely the barge will have to be towed to each location, since the floating platform isn't designed to be a sailing vessel.

Local and regional planning officials say they haven't approved any permits or leases for the project. Officials at the Port of San Francisco and the National Park Service, which oversees Fort Mason, have said their talks with Google are still in a preliminary stage.

At the Port of Redwood City, Executive Director Michael Giari said he hasn't been contacted by anyone involved in the project. Giari said he would need to know more before making any commitment, but he noted, "We're the closest port to Google's headquarters" in Mountain View.

Staff writer Pat May contributed to this report. Contact Brandon Bailey at 408-920-5022; follow him at Twitter.com/BrandonBailey.