A water transit expert threw some cold water on Hercules' dreams of a ferry connection to San Francisco this week, telling the City Council that dredging costs are much higher and ridership projections lower than at other potential East Bay ferry terminal sites such as Richmond and Berkeley.

And the San Francisco Bay Water Emergency Transportation Authority, the umbrella organization of bay ferries and their operators, is far less sanguine than it was just a few years ago about air-cushioned hovercraft vessels as a possible answer to Hercules' shallow coastal waters, said John Sindzinski, planning manager for the agency better known by its acronym WETA.

The bay's existing ferry runs between San Francisco and Alameda, Harbor Bay, Oakland, Larkspur, Sausalito, Tiburon and Vallejo use more conventional watercraft such as catamarans.

"A hovercraft facility is totally and absolutely incompatible with a catamaran facility," Sindzinski said, noting that there would have to be separate landing facilities at San Francisco's Embarcadero terminal, as well as separate maintenance provisions for the two types of craft.

That view was challenged later by Charles Ivan King, a hovercraft promoter representing the firm EPS Navy Systems who attended the council meeting. King said in an email Wednesday that some existing terminals could accommodate hovercraft, or separate hovercraft ports could be built at relatively low cost.

Hercules is the only site on the transportation authority's potential expansion list that would require significant dredging to accommodate conventional watercraft. WETA has estimated it would cost at least $17 million just to dredge a channel from Hercules' mud-mired shores to deeper bay waters, plus about $3 million every two or three years for maintenance dredging.

The cost does not factor in possible environmental add-on requirements, depending on the level of contamination of the mud with pollutants from industry and other sources.

Another rap against hovercrafts is that the boats are too small, with a capacity of about 150 seats, making them uneconomical, Sindzinski said. By comparison, the M/V Solano, on Baylink's San Francisco-Vallejo run, has a capacity of 300.

But officials at Griffon Hoverwork. of Southampton, U.K., a world leader in hovercraft design, have said that developing larger-capacity hovercrafts would present no formidable technological challenge. Russia's giant Zubr military hovercraft, the world's largest, reputedly can carry up to 500 troops or eight amphibious tanks.

Hovercraft also have the reputation of being loud, which would make them a hard sell, especially in San Francisco, Sindzinski said. But Griffon officials say that perception applies to 1960s-vintage hovercraft, and that modern hovercraft are much quieter.

Sindzinski's latest ridership projections to and from San Francisco, which several council members questioned, are 416 to 565 one-way trips a day for Hercules versus about 1,000 each for Berkeley and Richmond. The previous projection, which is still on WETA's website, was for 1,022 one-way trips daily between San Francisco and Hercules.

Moreover, a Hercules-San Francisco commuter connection already exists, in the form of the popular WestCAT "Lynx" bus, which logs about 400 daily round-trips on weekdays, according to WestCAT general manager Charles Anderson.

In addition to dredging for a conventional vessel, Hercules would require a terminal building at a cost of more than $25 million, Sindzinski estimated.

Building additional docking space at the San Francisco terminal for East Bay routes would cost about $25 million to $30 million per berth, Sindzinski said.

Councilman William Wilkins, noting that Hercules has "fought hard and long" for a ferry as part of the planned Hercules Intermodal Transit Center, urged Sindzinski to "help keep our dream alive." Sindzinski promised his agency will continue to work with Hercules.

A Hercules-San Francisco hovercraft would not be the first trans-bay hovercraft service.

In 1965, San Francisco and Oakland Helicopter Airlines, which no longer exists, briefly ran a hovercraft commuter service on a trial basis. A video clip can be viewed at http://bit.ly/KCWq5w.

Contact Tom Lochner at 510-262-2760.