Beating her way across the broad, sylvan Susquehanna River in central Pennsylvania, the Roaring Bull is as idiosyncratic and outlandish a boat as you'll ever see. Like her nearly identical running mate, the Falcon, she is a wooden sternwheeler -- a boxy, ingenious contraption that tugs a raftlike barge along at its side to carry up to four automobiles on the 10- to 20-minute crossing between Millersburg on the Susquehanna's east bank to Crow's Landing, two miles south of Liverpool, on the west.

One of America's great rivers, the Susquehanna is long, scenic -- and shallow. This last characteristic is the salient one for the historic Millersburg Ferry, located about 25 miles north of Harrisburg. The need to operate in as little as two feet of water has defined the type of vessel that has plied this route since its inception in 1817.

"These are work boats and everything is for real," says Jack Dillman, the ferry's captain when I cross, pinpointing the special charm and interest of the Roaring Bull and Falcon. Not restorations, they feature a design so uniquely suited for its place and function that it has survived.

"Captain Jack," a self-styled "river rat," worked on the ferry briefly in the 1940s before a stint in the Navy; he returned in 1970 and was in charge until December 1988, when the ferry was leased to other operators for the 1989 season and he tried to retire.

Things didn't go well, however, so the town of Millersburg bought the ferry -- and persuaded Dillman to come out of retirement to train new pilots and to take the wheel himself part-time.

Jack Dillman loves to talk about the ferry, and -- since the passenger deck is adjacent to the open wheelhouse -- he'll chat his way across the river, filling in anyone who's interested on the service's history and operational details.

The ride is slow, all the better to enjoy the aromatic freshness of the river and the lovely, ever-changing vistas of rocks, rapids and tree-clad hillsides. The ferry zigzags, following a channel that kisses islands like Halfway, Cunningham's and Little Sand, then sneaks around Suicide Curve.

The Susquehanna is all soft grays on a soft, hazy summer afternoon at Millersburg. "Ferry is running," reads the hand-burned wooden sign at road's end. "Drive down the hill and I'll come and get you." I see the Roaring Bull inching toward me across the smooth, slate-colored river. As it draws close, I can begin to decipher its perplexing architecture.

Two cars and two vans ride on a low, sideless "flat," lashed to the reddish-brown wooden rectangle of a boat that provides the power. In front is a covered deck that looks just like the porch of a summer home. Back of it is the wheelhouse, behind that the cabin, and to the stern a large roofed, open space housing the power plant: a 1949 Ford flathead V-8.

As the Roaring Bull nears the shore and begins to swing in for a stern-first landing, I can see the twin white wheels paddling away. Once the flat is made fast to the slip, vehicles roll gingerly off, the loose boards of the decking clamoring thump-thump-thump. (Since the boats must come out of the water each winter to protect them from ice, the decking is not secured. The planks -- which are removed first, making the flat much lighter -- do double duty as a skidway for this operation.)

For all its apparent antiquity, the Roaring Bull is in actual age remarkably young, having been carpentered together in 1977. Near-sister Falcon, painted gray rather than boxcar red, dates from 1974. But both are essentially identical to an earlier Falcon, built in the 1920s, which initiated the gasoline-powered, sternwheel design now in use. The wooden hulls and superstructures simply wear out after 25 years or so and have to be replaced, though some parts are carried over from vessel to vessel.

(The steam-powered sidewheel Enterprise, the first paddlewheeler on the Millersburg Ferry, entered service in 1873. Before that, boats were poled across.)

"Let's-try-it-this-way" technology is how Dillman describes the evolution of the Millersburg ferryboats' design. "A little bit of it originated with me, a whole lot of it was carried over from my predecessors. Of the 14 paddlewheelers used by the Millersburg Ferry, 11 were designed and built by us. Once designing was done on the back of an envelope, but now we have to submit detailed plans to the Coast Guard."

We'd left from the North Street Landing in Millersburg, which put us in the low water channel, hugging the loose stone dam across the river -- to the innocent eye it looks like any natural riffle -- that makes the ferry possible by raising the water level slightly. (In high water, the ferry makes a more direct crossing from a landing just upriver.)

"When the water's low this is like a single-track railroad with passing sidings," Dillman says. "If we're running both boats we really have to plan where to meet." He knows every inch of his stretch of river, in its every mood. "When Flat Rock is out of the water, we have to use the low-water channel."

We pass Marty's Buoy (named for Jack Dillman's son-in-law, who hit it once when he was steering), Eastern and Western Patch buoys, Cunningham's Island. Dillman tugs at the enormous horizontal metal wheel that nearly fills the wheelhouse and makes a delicate adjustment to the throttle, which is just a spool with wire wrapped around it.

Behind the wheelhouse, steps lead down into the cabin, a space that gives the Roaring Bull a bit of the feel of a houseboat. Painted the same red as the exterior, the comfortable room has a couch, an old secretary desk with creaky swivel chair and a rocker. The centerpiece is a wood-burning stove.

"You'd be amazed how comfy this room is on a snowy November day," Dillman says. Right now it is suffused with the peaceful vibration and rollicking putter of the gasoline engine. The steering cables rattle in the walls like scrambling mice.

On these walls are framed photos of historic Susquehanna boats -- the earlier ferries and the "coal-digger steamers," similarly constructed boats that are close kin. From coal mines to the northeast, coarse black residue washed down feeder streams into the big river, where it collected in pockets. For decades, dredging this coal from the river bottom was a flourishing industry.

The Millersburg Ferry was once a four-boat operation, Dillman tells me. "Pop Hunter, my mentor, used to boast that we sometimes had 20 automobiles on the river at once."

The slip on the west shore adjoins Ferryboat Campsites, a full-service operation with 250 sites. And how do those on the west side of the river summon the ferry? Hinged on a tree by the slip is an old white door, with operating instructions hand-lettered in black: "To signal for ferry turn out." Thus "opened," the door is visible from the Millersburg side.

After the cars roll off, Betty Hoy -- Dillman's wife and first mate -- brings out a bag of bread scraps and feeds the flock of Canada geese that cluster around her. Some are goslings, still fuzzy.

Time to go, and Jack and Betty hoist the apron off the slip and lean on the poles to swing the cumbersome ark until it's headed for Millersburg -- a distant cluster of brick and white clapboard buildings peeking through trees, with church steeples poking up above them.

Paddles churning, the Roaring Bull sets off at 4 knots -- the maximum speed in low water, which means the crossing will take 20 minutes. Showing broadside, it makes a sharp zigzag for Suicide Curve -- "from the shore, it looks like she'll never make it," Dillman had told me -- then recedes at a stately pace, bound once more for Millersburg. The Millersburg Ferry operates from around April until December, when ice in the river mandates closure. Service begins about 7:30 a.m. and continues "until the streetlights come on in Millersburg," according to Jack Dillman. Fares are $3 for cars, $4 for vans, $2 for motorcycles and 50 cents for pedestrians. Cruises for up to 35 people are available at $40 an hour, $60 for two hours, and catering can be arranged; for information, call (717) 692-5418.

Occasionally, in the heat of summer, low water halts operation of the ferry. A call to the Ferryboat Campsites at (717) 444-3200 will confirm that it's running. Karl Zimmermann is a freelance writer in Norwood, N.J.