The young halter-topped woman from the Mazda Miata sets down her drink and peers through her Vuarnets from under the cafe umbrella at the Bridge Restaurant. The show is about to start. Again.

The drawbridge is descending across Knapps Narrows, the 50-foot-wide waterway that separates Tilghman Island from the rest of the world. A watery traffic jam of eastbound cabin cruisers, runabouts, sailing yachts, crab boats, skipjacks and charter fishing craft is backing up all the way to the Bay.

A three-knot tidal current is sweeping that line of vessels bridgeward, where vertical clearance with the span down is maybe 10 feet. Horns are honking, motors are revving in reverse, and a bare-chested stud with a lot of gold chains is struggling to dock his thundering testosterone-craft beneath the eyes of the waterside throng.

"Ah, Knapps Narrows," sighs Anthony Prisendorf, 60, of Great Barrington, Mass., waving his beer mug at the aquatic circus from beneath another umbrella nearby. "Remember when you skippered us through that bridge sideways? What a triumph of maneuvering that was!"

Ah, yes. The scent of impending nautical disaster at Knapps remains eternal. It's what gives the place its panache.

Elsewhere on the summer Chesapeake, sailboats race and cruise, powerboats rumble and wash, crabbers tend their pots and trotlines and fishermen angle: separate cultures in a common estuarial world. The one place where they all have to deal with one another is Knapps Narrows, the unsung weekend adventure of the Upper Chesapeake.

The tide-ripped, constantly shoaling Knapps channel, maybe a mile long, is the fastest boat route from Annapolis to the coves and crab houses of Oxford and the beguiling anchorages off the Choptank River. It's such a popular weekend shortcut that retired bridge tender Calvin Cummings, 70, a Tilghman native, once logged 810 vessels through in a single 12-hour period. Tilghman Islanders call Knapps' single-span drawbridge the busiest in the nation.

The shores of the Narrows are far sleepier, with a few bed-and-breakfasts, boatels and assorted soft crab farms. They're a prime area for canoeists and kayakers who watch the ospreys, herons and egrets. And an optimum viewing ground for weekenders like Prisendorf in search of nautical arm-waving, picturesque watercraft, and the occasional bridge-jump, dock collision and dismasting.

"It's certainly colorful out there and, amazingly enough, people rarely seem to get hurt," says J.C. Cappelmann, 48, who manages the Knapps Narrows Marina after 24 years as a charter skipper in the Mediterranean, the Caribbean and the South Pacific. "But sometimes I just have to turn away rather than watch. Most of the people on those boats would die if they went offshore."

Most watercraft, of course, make it through Knapps without incident, whatever their type. "But it can be pretty wild, at times," sighs charter fishing captain Bill Fish, 49, of the 46-foot Nancy Ellen. "The pleasure boaters are on vacation. Those of us who work on the water have to deal with them while we're coming home from work."

According to several of the bridge tenders, the boating cultures that crowd the narrows break down roughly as follows: Long, sleek speedboats are theoretically in a hurry, but mostly want to be on display for those at the restaurant tables, so they'll circle or idle until the bridge opens. Cabin cruisers often know the rules of the road better than the speedboaters and always contact the bridge tender because, as one operator put it, "they just love talking over the radio or the loud hailer, or blowing their horns." Sailboat captains appear to know more about operating their vessels than power boaters, but often act as if they expect the bridge to open just because they show up.

For those who understand the conditions, check the tide level in advance and talk by radio with the drawbridge during their passage, "there's nothing really difficult about handling the conditions," says Mike Richards, 60, who books sunset cruises out of Knapps on his ketch Lady Patty.

"The problem is the Chesapeake. It's the most forgiving place in the world to sail. There's not a single natural rock to hit. We're almost devoid of conditions like fog or high wind or tidal currents that keep a mariner on his toes. So people tend to forget what can happen when you concentrate all the forces that do exist here. And when the tide's running they converge at Knapps."

Converging with them are the tides of change. Once a drowsy backwater that old-timers remember wading across as children, Knapps is now a destination for tourists and retirees as well as weekend mariners.

If the narrow workingmen's houses just off the water still show plywood patches and a reassuring collection of crab pots and boat parts in the back yards, the antiseptic future looms just blocks away: transplanted urbanites in crisp new homes flying decorator flags adorned with blue herons.

"We're where St. Michaels was 10 years ago," says Tilghman Realtor Rondy Alstrom. "There's no ATM machine here and you have to drive to St. Michaels for a bottle of milk. But the sunsets are world-class, the people are friendly, hard-working and self-reliant and the island itself is a little bit of heaven." Despite its modest population of about 1,500, she notes, Tilghman Island now has its own Web site (www.tilghmanisland.com).

Just down the road from Alstrom's Tilghman Island Realty, Tilghman native Geraldine Dudrow, an indestructible 91, took a break from cutting her lawn in the heat. Contemplating the various cultures now colliding at Knapps, she decided she could live with the changes.

"I used to know everyone on the island," she said. "We didn't have a lot of 'foreigners' from outside. Now they retire and move here to developments like that one, Tilghman-on-Chesapeake. They all seem like nice people to me, but I can't say I really understand them. Tilghman-on-Chesapeake's not on the Chesapeake at all. It's on the Choptank River. You s'pose they don't realize that?"

Alstrom says she sells town houses on the bay side of Knapps for $180,000 to $300,000, usually to retirees from the Baltimore or Washington area. "Sales were very slow for the past five years or so, but this year it's crazy," she says. "My inventory of unsold houses right now is very small."

A Californian originally, she moved in 1979 by way of Baltimore to a house on the Choptank side of the Narrows near an outboard runabout named Knapp Time. There, she says, she's regularly entertained watching weekend yachtsmen struggling with the vicissitudes of her deceptive little waterway.

"I've seen 40-foot skipjacks go through that bridge sideways," she says: "Sixty-foot sailboats hard aground. The one I really remember, and it's terrible to laugh about it but I do, was the couple on the rented yacht who misjudged the current while trying to dock. The man shouted at his wife to get a line around the piling, but while she still had both arms around it the current took the boat out from under her. She started yelling. He kept telling her not to scream. Didn't want people to see how he'd screwed up, you understand. But she was left hanging and eventually slid into the water--right down all those splinters and barnacles."

Knapps Narrows, of course, is about more than boat traffic, drawbridges and nautical brinkmanship. Some would call it the feedlot of soft-shell crabs. Local watermen plying the Choptank's creeks and the Tilghman shoals glean their catch for peelers--crabs showing signs of molting in the next three to five days--and sell 4,000 to 5,000 a week for 50 cents apiece to William "Pete" Aerne, 75. Aerne, crab wrangler for Harrison's Packing Co., puts the peelers out to pasture in a dozen or so waterside "floats"--awning-shaded tanks on land through which fresh bay water circulates constantly--until their supreme moment of softness. Then they're invited to dinner, often at Harrison's Chesapeake House Restaurant nearby.

Aerne says he handled maybe twice as many crabs during the 1980s, "but now there's others in the business and it's all we can do to supply the restaurant."

The fluctuating fortunes of Chesapeake crabdom are profoundly mysterious. Some watermen like Capt. Wade Murphy Jr., 64, of the skipjack Rebecca T. Ruark, decry pollution and overharvesting and see only a crustacean apocalypse ahead. But others, like Jack Cummings, 71, arguing good-naturedly with him on a bench in front of Fairbank Tackle, speak guardedly of glimpsing better days. Last year Tilghman crabbers were lucky to bring in a bushel a day--worst year they can remember. This June they're already bringing in seven to nine bushels a day. But they wonder if the bounty can last.

Capt. Fish, of the Nancy Ellen, doesn't care because the rockfish are biting. His biggest problem, this particular day at Knapps Narrows Marina, is that some of his favorite fishing clients--a bunch of great old guys in their eighties--refuse to wear their hearing aids on the water because the wind makes them whistle. "They have a great time but can't hear a thing I say. Tangled lines all morning," Fish says.

High above the tidal, social and economic currents of Knapps Narrows, Rick Murphy, 41, of Easton, looks down from his air-conditioned bridge tender's shack, which has a breathtaking view all the way to Poplar Island. He's a new recruit to the bridge-tending ranks that once were firmly in the hands of Tilghman Islanders. Now the state highway department runs the bridge, which has produced more than a little cynicism locally.

In fact, the brand new mint-green $7.7 million drawbridge is the source of much head-shaking among Tilghman Islanders, who see it as an unneeded taxpayer rip-off that takes longer to open and close than its predecessor, needlessly backing up auto traffic on both sides of the narrows.

The story on the island is that a few years ago some tourist tripped while walking across the old drawbridge, fell down and sued the state because the bridge didn't have a sidewalk.

"Of course it didn't have a sidewalk," growls Wade Murphy. "Knapps Narrows don't have anywhere you need a sidewalk to go!"

The next thing the islanders knew, the state had authorized the new bridge, which took nearly two years to install, with much inconvenience to local boaters. "But here's the thing," says Murphy: "They poured concrete on the bridge to make that sidewalk which don't lead anywhere, then forgot to allow for the sidewalk's weight! That's why that bridge takes longer to raise!"

Tilghman Islanders insist there was nothing wrong with the 60-year-old former bridge, which is being recycled to St. Michaels as a new entrance for the Chesapeake Bay Maritime Museum. They say the new bridge has broken down repeatedly since it opened. "Damn thing is run by a computer!" steams Murphy. "They had to send to Florida to get a guy to reprogram it. They don't even have any parts!"

A spokesman for the Maryland State Highway Administration in Annapolis professed to have no information at hand on the drawbridge controversy, and bridge tender Rick Murphy (no relation to Wade) appears distressed when the subject is raised.

The new bridge is the only one he's known, and he's proud of it. It's true it takes a bit longer to raise and lower--maybe two minutes--but that, he says, is largely a function of the multiple traffic gates that go up and down in sequence with the bridge.

"We opened it 400 times over Memorial Weekend," he said. "Seems like it's open more than it's closed on busy weekends, but I try not to leave it up more than 10 minutes at a time. Longer than that makes the people in the cars mad."

He looked out over his domain, scanned the Narrows for approaching boats, and looked disappointed when he found none. Then, fingering his impressive electronic console that boasts six dials, 35 lights, 19 switches, three buttons, a foot pedal and a horn, he asked:

"Want me to raise it for you?"

But no boats are coming.

"That's okay," he said, hopefully. "We could call it a test?"

CAPTION: Where the water meets the road: The new Knapps Narrows drawbridge holds up traffic while a boat takes this popular bay shortcut.

CAPTION: At the marina: Kayakers on their way to the drawbridge; below, Kathy Mathews and her daughters, Samantha, 5, left, and Michelle, 10, watching the boats.