Since it was towed into Portland Harbor on a barge earlier this month, a four-story windowless building has been a source of intrigue. Its purpose and its owner’s identity have been kept secret.

Twenty-seven hundred miles away, residents of San Francisco have been puzzled by a four-story windowless building rising from a floating barge at the end of Treasure Island, a former Navy base in the middle of San Francisco Bay.

Additional Photos Like a structure in Portland Harbor, the building on a barge in San Francisco Bay is likely a Google floating data center, experts say. Daniel Terdiman/CNET A mystery barge floating in Portland Harbor bears a strong resemblance to another in San Francisco Bay. Both have been sources of intense speculation. 2013 Press Herald File Related Headlines Mystery barge may be floating showroom for Google

That project is also a secret.

But clues have emerged that indicate the two projects are connected.

The two barges – the one in Portland and the one in San Francisco – are owned by the same company.

Moreover, a website that covers technology news has linked that company to the search engine giant Google.

Some experts who were shown photographs of the structures speculate that they could possibly be prototypes for floating data centers that would use ocean water for cooling servers and ocean waves for energy.

Google was granted a patent in 2009 for such a structure.

According to Google’s patent application, a fleet of data centers would float three to seven miles offshore in water 165 to 230 feet deep.

Both structures appear to be made from modular rooms – or possibly shipping containers – stacked on top of each other. Many have small slats instead of windows, and each has a section that slants down to ground level at a 45-degree angle.

The lack of windows and egress stairs on the exterior of the buildings rule out the possibility that they are floating hotels, said Joel Egan, the principal at Cargotecture, which designs buildings using shipping containers.

“If it’s Google, it is probably a data center,” he said.

It would be beneficial to have a lot of water available to cool the servers, said Jonathan Koomey, a Stanford University research fellow and expert on data centers.

The use of saltwater as a cooling source would be problematic but surmountable, he said.

Koomey had been aware of the mysterious structure in San Francisco. When told of the one in Portland, he seemed startled.

“I am very surprised to hear there is another one,” he said. “This is fascinating.”

He said it’s hard to imagine why Google would want a floating data center. One possibility, he said, is that it could be transported by sea and used in disaster recovery efforts.

The exterior of the structure in Portland was built in New London, Conn., by Turner Construction, one of the largest construction management companies in the United States.

It is now in Portland on the barge that brought it here. It is docked at the Rickers Wharf Marine Facility, where Cianbro Corp. is scheduled to do a significant amount of interior work on it, including the installation of undisclosed technological equipment.

Peter Vigue, chairman and CEO of Cianbro, said the company has signed a nondisclosure agreement with its customer, which has made secrecy a priority, he said.

The registration number on the Portland barge is “BAL 0011.” The registration number of the barge in San Francisco Bay is “BAL 0010.”

According to online registry of vessels, both barges are 250 feet long and were built in 2011 in Belle Chasse, La.

And both are owned by the same company, By and Large LLC, based in Wilmington, Del.

That company is also the current tenant of the building alongside the pier where the San Francisco Bay project is under construction, according to Daniel Terdiman, a senior writer with the online technical news organization C|NET who has been trying to uncover the mystery of the San Francisco project.

In his story posted online Friday, he said a California man, Tim Brandon, was named by the Treasure Island director of island operations as a point of contact for the project. Terdiman said Brandon’s LinkedIn profile identified his current position as “Senior Transaction Manager, CBRE @ Google.”

He said he called Brandon, using the phone number Brandon had provided to the Treasure Island official, and reached a Google extension that was no longer in service.

After Terdiman contacted him through LinkedIn and sent him an e-mail earlier this week, Brandon changed his LinkedIn profile, Terdiman said. Brandon now lists his current position as just “CBRE” and his top responsibility as “Lead and manage all acquisition and disposition activity for Silicon Valley portfolio.”

Google did not return an email inquiry from the Portland Press Herald asking for a comment. Terdiman said Brandon also declined to comment.

Terdiman late Friday updated his story to note that a similar mystery structure is located in Portland.

“Now the question is, if there’s one in San Francisco Bay and another in Maine, are there more out there?” he asked.

Tom Bell can be contacted at 791-6369 or at:

[email protected]

Twitter: TomBellPortland

Send questions/comments to the editors.