With Friday night's closure of the Alaskan Way Viaduct days away, riders of the West Seattle water taxi to and from the downtown waterfront are both nervous and excited.

The nine-day road closure is almost sure to bring more passengers aboard the fast-moving catamaran, and some riders are concerned that the 77-foot vessel suddenly will become overcrowded and start running late.

But they also are excited, figuring new attention could help assure the water taxi's survival during the current hard budget times.

"I worry budget cuts will kill the water taxi," said passenger Chris Dunn, who rides it to Pier 50, then walks to his job at Harborview Medical Center. "I want this to get a foothold and get it as full as it can get, but don't kill it. It's a real fragile thing right now."

The water taxi, named the Rachel Marie, cruises at a speed of 24 knots, reaching its destination in 10 minutes.

It has been operating since the late 1990s; King County had contracted with Argosy Cruises before taking over the route last year.

The water taxi, which originally operated only during summer, now is in its second year of year-round service. It had 172,000 passenger boardings last year — a huge increase over 2010. But its most-popular sailings currently carry only about 60 passengers, less than half its capacity.

Transportation officials say they can't predict how much ridership may rise when the viaduct closes Friday night, but about 94,500 vehicles cross the West Seattle Bridge on an average weekday.

During the closure, northbound lanes will be blocked between the West Seattle Bridge and South Royal Brougham Way around the clock, as will southbound lanes between the Battery Street Tunnel and the West Seattle Bridge.

The closure is to allow crews to complete connections to new lanes that will replace the viaduct between South King and South Holgate streets.

Officials are encouraging commuters to adjust their work schedules, work from home, carpool or take buses, light rail — or the water taxi.

One thing worries rider Megan Henley: If the water taxi suddenly jams with riders, will there still be room onboard for her baby's stroller?

Henley rides the boat from West Seattle every day with her 8-month-old son, whose day care is across the street from her work downtown. She said driving won't be a desirable option because the water taxi already is so much faster — even if she misses a run and has to wait for the next, it's still faster than commuting by car, she said.

Sherman Lohn rides the water taxi three days a week to his job in downtown Seattle and Bellevue with King County's health department.

"I think it will be really crowded and will run late," he said, "but there's not a lot of alternatives. I thought about taking vacation time but, nah, I'll just figure it out."

Rider Brian Fenske agrees. "I'm afraid there will be a mob of people," he said. "I'll have to stand in line and miss a boat, but it's still far better than a bus."

During the road closure, the water taxi will expand its schedule, adding a 6:15 a.m. departure from West Seattle, a half-hour earlier than the normal first sailing. More midday runs also will be added, and extra parking will be available in West Seattle.

Diana Reid, a graduate student at the University of Washington, worries that her midterms will coincide with the viaduct closure, and she doesn't have the flexibility to take a later boat. "It will be interesting to see how crowded it gets," she said. "I hope people who have the flexibility will stay at home."

Phil Jones, a longtime water-taxi commuter, believes a crowded boat will bring a better sense of community — maybe even thawing the "Seattle chill" he sees, where riders stake out a booth and don't talk to each other during the short ride.

Added his friend Robin Murphy: "I'd rather see it full than just 20 people on board. We'll be all right."

Susan Gilmore: 206-464-2054

or sgilmore@seattletimes.com