Mayor Bill de Blasio will make use of the city's waterways to expand transportation here, he announced in a State of the City speech that aimed at New York building up housing in coastal neighborhoods.

His administration plans to spend $10-20 million a year to run up to six new ferry routes anchored on Wall Street, by 2018 that touch on each borough; the city runs the free Staten Island Ferry to lower Manhattan.

And the ferries in these neighborhoods, like Soundview in the Bronx and the Rockaways, would cost the same as a MetroCard swipe, the mayor vowed.

"We are the ultimate coastal city but somehow we haven't had a true ferry system in decades," de Blasio said. "We need to right this wrong, to open up great possibilities for our people, to take places that were isolated and felt isolated and give them opportunity and connection."

The ferry routes would bring to fruition a vision of a citywide system that former Mayor Michael Bloomberg had put forward.

"We think the demand is going to be very strong," said Kyle Kimball, president of the NYC Economic Development Corp., adding that the city will put out a global call for ferry operators.

Ferry service within New York is more expensive for passengers than subway and bus transit and for the city, which subsidizes service to keep down fares. On top of tens of millions it will cost to run the ferry system -- estimated to make 4.5 million trips a year the city will also spend $55 million to build the docks and other infrastructure for the initial routes.

Roland Lewis, president of the Metropolitan Waterfront Alliance, said successful routes, like those the East River Ferry runs, need frequent boats and affordable fares.

"As long as it's comparable to a bus and subway fare, I think it's a fair deal," Lewis said.

Assemblyman Phil Goldfeder, who criticized de Blasio for nixing the Rockaway ferry, praised the mayor's citywide approach to expanding transit options.

"By creating a more comprehensive ferry plan, you'd be able to subsidize Rockaway ridership with some of the more heavily traveled areas," said Goldfeder, who still wants a stopgap service for residents until the mayor's plan is complete.

Skeptics of ferries question the value in spending money on a relatively smaller number of people who live close enough to the waterfront or those who would have to pay for a subway or bus on top of a boat ride to complete their trip. Officials said 460,000 people live within a half mile of the planned landings

"If he wants to really move ahead on ferries, he'll need to find someone with a lot of cash on hand and a taste for risk," Gene Russianoff, staff attorney for the Straphangers Campaign, said in a statement calling on more fast bus routes.

Jeff Zupan, senior fellow for transportation at the Regional Plan Association said new developments, like the Astoria Cove housing project, could bring enough riders to a ferry route and prompt a developer to give long-term assistance to run them. He cautioned the de Blasio administration to add new routes incrementally to avoid bad ones that would be unable to attract riders accustomed to the subway.

"Each of them, one has to think about what the transit options are and whether they're really superior in time and frequency," he said. "And each is going to cost money, a considerable amount of money."

(with Matthew Chayes)