We're about to board the old Mariner now, all 60 of us, to find us some finbacks.

Whales.

Seventy-five feet long, some of them--charcoal-colored on top, white as a seasick city boy beneath. (The scientists call them Balaenoptera physalus, sometimes out loud.) Fin whales, as we salts like to call them, like to feed on the fish and plankton swept up in abundance along the steep canyons that mark the edge the continental shelf -- about 70 miles due east of this neon condomania called Ocean City, Maryland.

To get out there and back, we will be at sea from sunrise to sunset. And when we find us some whales, know what we're going to do? We're going to shoot them -- every one. That's right. The smallest thing anybody's toting is 50 millimeters.

Except for the Instamatics, of course. This is not a blubber hunt, see: This is a "whale watch." One of these day-long treks leaves Ocean City's Talbot Street Pier each month year-round -- two a month during the spring and summer. Forty-five dollars, some Dramamine, a little luck and a lot of rain gear can bring even the city's most hardened parallel-parkers safely gape-to- gape with an Actual Whale.

Today the 65-foot Mariner, normally a sportfishing boat, is filled to the bridge with adventurer/naturalist types, both veteran and virgin students of submarine mammalry -- plus a half-dozen binocular-breasted seabird watchers. Forty-five of the passengers are wide-eyed, diversely waterproofed high- school students from Grier, an all-girl boarding school deep in the Alleghenies of Pennsylvania, whose instructors of Animal Behavior and Cetacean (whale and dolphin) Biology believe in hands-on learning, when, where, as and if possible.

All hands, at the moment, are on deck under a cloudless Saturday sky, straining to hear Ron Naveen, the NOAA lawyer who organizes these trips. Naveen is on the foredeck, squinting into a megaphone.

"We couldn't have picked a better day," says Naveen, 36, who calls these trips, simply, "Whales and Seabirds of the North Atlantic." He took them up three years ago from his friend and fellow marine-mammal fan Ron Rowlett, who started them in 1974.

"The winds are out of the southwest at 5 to 10, and the seas are calm, about three feet," Naveen says into the megaphone, his sandy brown hair and beard set off by a pinkish cloth sun visor and round-rimmed glasses. "The fishermen tell me they've spotted fin whales 30 miles out all week. I think this will be a good trip."

Naveen is boyish and exuberant. He recently returned from the Galapagos, where he studied and photographed seabirds, iguanas and pinnipeds. The Maryland plates on his Honda Civic read "ORCA."

There is very little warning.

Three hours out of Ocean City finds the passengers scattered about two decks, most of the Grier girls squinting and shouting at each other over the drone of the engine, gazing into the spray at the bow, pointing off at birds and faraway trawlers, dozing in the sun, or fighting off queasy stomachs or backgammon advances in the main cabin.

Someone screams.

"Whaaale! Five o'clock!"

Sixty heads turn to starboard in time to see the black hulk of 40-foot finback as it breaches, sending up a 20-foot spray that, even a half-mile away, prompts involuntary gasps of delight all around. The whale sounds, showing off an impressive scar just above its dorsal fin before its fluke -- the tail fin -- disappears in a flat wash of current. Camera shutters click all around, and the captain throttles down to zip, easing toward the roiling whale track.

It seems dead quiet now, as everyone spreads out awkwardly, breathlessly around the perimeter of the boat to await the whale's return. It could take anywhere from five to 10 minutes. "Did you see it?" whispers one Grier student to another, their arms supporting each other against the starboard rail. "You see that?"

The boat rocks and creaks and sputters along. Then, two sudden sounds.

The first -- a rorshhhhhhh of water as the whale resurfaces, less than 100 yards from the stern, spouting as it rolls sideways into an unseen school of fish -- is followed almost immediately by the second: the high- pitched aaiiiiiiiiiaaah of four dozen schoolgirls abruptly brought closer to the subject than any textbook goes.

Even the grownups wear silly grins.

We will sight 13 whales today -- including a 70-footer who surfaces and rolls less than 40 yards off, mouth agape, and a group of five who put on a 20-minute show with a school of saddleback dolphins hitching free rides in their larger relatives' wakes. Plus a 30-foot basking shark which yawns by, just below the surface and less than five yards from the starboard rail, harvesting plankton. Plus countless gulls, gannetts and loons.

You meet more than whales.

There's Tom McIntyre, a NOAA colleague of Naveen who's been on some 35 whale watches since '74, and whom everyone calls Mac. Megaphone in hand, Mac circles the foredeck most of the trip, narrating the sightings in passionate bursts of fact-filled chatter. "Yeah, old megamouth, that's me," he chuckled later, tilting a can of Busch below his thin white mustache. "They're always on my case about that."

Then there's Madelon Kelly, 31, a marine biology and animal-behavior teacher who's brought students from Grier on these trips for four years. Kelly is standing at the bow rail with Cynthia Moody, 25, also a Grier science teacher and also wrapped in about a half-dozen layers of clothing, the outermost of which is waterproof. Kelly and Moody are almost impossible to distinguish from their 45 like-attired students, all of whom drove the eight hours from Tyrone, Pennsylvania on Thursday and camped two nights on the cold sands of Assateague.

"This summer, I'm taking three students up to the Bay of Fundy, off the coast of Maine, on a two-week Earthwatch project," says Kelly, standing with one knee bent, her feet braced a yard and a half apart against the capricious lurch of the deck. Her face, framed by a blonde, saltwater-dampened pageboy, has been buffed pink by the sun and wind. She looks serenely natural in the midst of this great volley of elements, and it's hard to imagine her at a chalkboard.

Then there's Captain Darryl Nottingham, an extra-large man in white stretch-knit short sleeves who smiles a lot but rarely leaves the bridge, where he is either manning the wheel or watching the mates from the bunk behind it. He amiably disputes nautical distance estimates with Naveen, McIntyre and Charlie Potter from the Smithsonian Marine Mammals Division.

There's mate Salty Dog (his real name is Brian Sawdy), a 28-year-old former tool- and-die maker who gave up the trade five years ago to run sportfishing rigs. "Now I starve to death in the winter, I make a ton of money in the summer and I'm happy as I can be," says Salty, whose rail-thin frame and wide-legged gait give him the air of spider as he heads toward the cooler, grinning behind his sunglasses and beard.

There's Peggy Edds, 31, an animal behavior specialist who teaches at the University of Maryland and has spent the last four years here and at the head of the St. Lawrence River documenting -- through long- lens photos of these whales' distinctive dorsal fins and identifying scars -- the fin whale's migratory habits.

And there are, finally, The Grier Girls. "They get past the 'Oh gosh isn't he cute' stage really quick, because they're interested," says Naveen. "It's refreshing."

"They are really the best possible group to have aboard," McIntyre said later. "They're enthusiastic, they're excited. And they're knowledgeable."

By 4:30, they are also pretty tired. Most of the passengers are strewn among the camera bags, blankets and cookie containers in the cabin. This has been the warmest, driest spot on board since we turned, an hour before, into a southwest wind that blows 50- degree spray across the decks. It looks kind of like a refugee camp for preppie Haitians.

A handful brave the cold spray and wind on the bow with Kelly for the entire trip back. One of them -- Jenny Young, 17, who has been on Mariner three times in two years and will go to the Bay of Fundy with Kelly this summer -- declares this trip among the best. "I can't believe . . . I saw his face, she gasps of an anonymous whale.

"I'd give it a ninety-nine," says Pam Stone, another Grier veteran.

"This is a first for me," says Heddy Sahakian, a 17-year-old Grier senior leaning wearily against the cabin door. "I saw the sun rise this morning, and I'm seeing it set tonight. You are seeing history."

Sahakian, who's thinking about being a writer, is silent a moment. Her eyes narrrow. "You're going to put that in, aren't you?"

WHALES AND SEABIRDS -- Trips through late summer -- when chances are best of whale sightings -- leave Ocean City May 29; June 12 and 26; July 3 and 17; August 7 and 21; September 11 and 18. For brochure or reservations (required early) call Ron Naveen at 301/299-2425. Trips continue fall and winter, primarily for seabird sightings. "Absolutely uncomfortable weather" postpones trip till following Sunday; bring seasickness medicine and layered clothing plus rain gear. Young children and pets are "inappropriate."