SAN FRANCISCO — Google plans to include a dozen or so massive sails on its four-story barge under construction in the heart of the San Francisco Bay, creating a floating artistic structure the Internet giant promises will “stand out,” a newspaper reported Friday.

After weeks of speculation that barge would be “a party boat,” a data storage center and a store to sell its Internet-connected glasses, Google on Wednesday revealed that it plans to use the vessel as an “interactive space where people can learn about new technology.”

The San Francisco Chronicle reported that it obtained planning documents for the vessel from the Port of San Francisco through a public records request. The documents shed more light on a project shrouded in mystery. Google has been tight-lipped about the barge and has managed to conceal much of its purpose by constructing it on docked barges instead of on land, where city building permits and public plans are mandatory.

The Chronicle reported that the sails shaped like fish fins are meant to instill in visitors a sense of seaworthiness while aboard the boxy 50-foot-tall, 250-foot-long structure made of recycled shipping containers. The documents submitted to the port boast the completed project will be an “unprecedented artistic structure” and promises the “structure will stand out.”

A company called By and Large LLC submitted the planning documents. The Chronicle reports the company has close ties to Google and some are speculating the name is a play on the word “barge.” Records and other official accounts identify the project as Google’s.

The documents refer to the barge as a “studio” and “temporary technology exhibit space” that will “drive visitation to the waterfront.”

The Internet giant’s actions at Treasure Island appear legal. But the mystery surrounding the bulky floating building — and a similar one off Portland, Maine — is generating rumors and worries.

Google has dodged public scrutiny by essentially constructing a boat, not a building. Thus it doesn’t need permits from San Francisco, a city with copious inspection and paperwork requirements for builders.

Still, privacy experts, environmentalists and legal authorities say the company’s refusal to divulge many details and the air of secrecy it has created around the project may backfire because Northern California residents are highly protective of one of the most scenic and environmentally sensitive bays in the U.S. Environmental groups and others have hinted at filing lawsuits if they feel the final product will harm the bay.

The planning documents say there are plans to sail the boat around the bay, mooring at different docks monthly. Google also has ambitions to sail the vessel out of the bay and up and down the West Coast.

The planning documents were submitted in September. San Francisco Port spokeswoman Renee Dunn Martin said the documents are “part of a preliminary proposal. They haven’t come back to us with anything concrete.”