"Prepare to gybe," said Karen Brooks.

"Ready," her crew responded.

"Center the main."

"Centered."

"Helm's to weather. Gybe-ho!"

Brooks drove from Stamford, Connecticut, to Annapolis the other weekend to learn how to sail. She's barely five feet tall. A week earlier she hadn't known a mainsail from a yard sale. But a Sunday, after nine hours of instruction, she was manning the helm and barking out orders to a crew of three as their 24-foot sloop churned happily along where the Severn River meets the Chesapeake Bay.

"If anybody had told me I'd be ordering people around on a sail boat like this i'd have laughed out loud," she said.

The wind shifted, recapturing her attention. "Prepare to come about," she said, and laughed out loud.

Twenty-two years ago an entrepreneur named Jerry Wood was down on his luck. His family's toy company had gone kaput and he was scratching around Annapolis, looking for any way to make a few dollars.

"Say, buddy," said a tourist from Washington, "you know anywhere I can rent a sailboat for the day?"

Wood and his father both had a 20-foot wooden catamarans. Circumstances being what they were, Wood said, "For $20 you can use mine."

It was found money to Wood, who a few weeks later put an ad in the paper offering rental sailboats. A couple of months after that he decided to offer sailing instruction, since the cost of repairing damage done to the catamarans by neophyte renters was cutting into his profits.

And the other weekend Karen Brooks and 169 other students became the latest in a string of some 50,000 to 75,000 would-be sailors to enroll in the institution that developed from that modest initial venture -- the Annapolis Sailing School.

Annapolis is the grand dame of East Coast sailing schools, and moving along today at a clip speedier than ever before. Last year some 7,000 students passed through one or another of its courses, almost doubling the total from the year before. That's just at the Annapolis location. There are eight other Annapolis Sailing Schools, all under Wood's purview and spread from San Diego to Wisconsin to the West Indies.

It's not a chartering operation; if you say the word "charter" around Wood, general manager Rick Franke or any other school official you get a dirty look.

Partly that's because they fought for a break on their insurance rates by proving to insurers that they were giving instruction, not boat rides. And partly it's because over the years they've honed techniques to a fine, simple edge that enables them in a weekend to give a willing and interested student the tools to actually sail a sailboat, which is no mean feat.

This does not mean that Annapolis Sailing School can teach a confirmed and hopeless landlubber to sail in a weekend, or even in a week. "Some people never will learn," agreed Jane Gaffer, who does publicity and promotion for the school. But for those with any knack for boats and the water, it builds a solid little bridge.

About two-thirds of the people who take the Annapolis classes choose the basic learn-to-sail curriculum. On the weekend we're talking about, 106 of 170 students enrolled selected it. In the interest of seeing whether in fact a person could pick up enough information in four three-hour sessions to make it worth the $125 tuition, Weekend went along.

The schedule calls for one hour in the classroom and two hours in the boat, mornings and evenings Saturday and Sunday, with a break each day for lunch.

Weekend arrived at school headquarters in Eastport, just across the drawbridge from Annapolis, at 8:10 Saturday morning, 20 minutes early, and was astonished to find the vast majority of students already in the registration line.

After registration, enrollees are broken up into groups of about 28 and assigned to senior instructors. They repair to proper classrooms next to the docks on Back Creek for the first hour.

Thus begins a carefully orchestrated series of classroom sessons that starts with the absolute basics and builds with successive installments until students are prepared to yell things like "hard a-lee" or "douse the main" and actually have some idea what they mean.

Weekend fell into a class taught by George Peterson, retired Army man, veteran sailor and instructor and, of all things, humorist. "We have an anchor drill," said Peterson, hoisting a 12-pound Danforth with chain. "If anybody falls asleep, I yell 'Anchor!' and heave it at them."

Peterson spiced up the first lesson in basic terminology and rigging a boat with some old sea lore, including the advice to watch which way the seagulls are facing if you can't figure out wind direction, and a discussion of the origins of some terms. He said starboard, for example, was the side of oldtime sailboats where the steering board was.Larboard was the loading-board side, but the difference between shouts of "lardboard!" and "starboard!" proved a bit skimpy in raging storms, so larboard become port, which was at the shore-side end of the loading board anyway.

At hour's end Peterson split his students up into groups of four for actual sailing and made the most judicious move of all. He separated husbands and wives.

"We resented it at first," said Gene and Amy Goott of Washington, "but they knew what they were doing. We'd never have learned anything."

The problem with unorganized sailing instruction is that it's usually overwhelming. "How do you expect to improve our distance made good to the mark if you keep back-winding the jib and luffing the main?" the typical sailor might ask his novice crew, which will reach for the rum.

"The problem to me was that yacht clubs always started their learn-to-sail programs with a discussion of the difference between a brigantine and a barkentine," said Wood. "I didn't think that was necessary."

So Annapolis keeps it basic. Students aren't even expected to take notes.

The hardest thing in the first lesson is finding your boat among the 50-odd A.S.S. vessels scattered around Back Creek.

Then you cast off for what Peterson calls "white-knuckle time."

He works it out this way: "The first morning you learn to handle the tiller. That afternoon you learn to handle the tiller and the main sheet and be able to light your pipe. And by Sunday evening you should be able to handle the tiller and main sheet, smoke your pipe and drink a beer."

Sailing instructors aboard the boats are less refined than Peterson. Mostly they are teenagers and college students who have spent much of their lives on sailboats. They have the basics but sometimes their terminology gets a little wacky, like the young man who described to Weedend's crew the complicated sequence of manuevers required to heave to in a storm. "There, he said on completion, "now you know how to heave-ho.

By Sunday, the senior instructors are throwing out about as much information as the world's smartest sailing neophyte could handle. Peterson was rattling on about international right-of-way rules, recommended anchor scope, tides and currents, navigational aides, procedures if aground and a host of other esoterica.

Even Weekend, who has in fact sailed for some years, was picking up intesting tidbits he'd never heard before. Peterson included some of his own personal observations and prejudices, such as "Never initiate waving to a power boat. If they wave at you, you can wave back. This rule is fast, except if you are aground in need of a tow, when it may be waived."

Brooks was the star pupil on Weedend's boat. She picked up things so quickly that her own mind couldn't keep up with them, and you could almost watch the brain wheels racing along to fill in the right words for whatever latest intuitive discovery she had made.

By Day 2 Goott was comfortable with the helm and feeling better about sail trim, but the third party on the boat was struggling. That's all right: Weekend overheard her husband chatting with another student about the relative quality of roads in Italy as compared to Switzerland. They evidently have some options if sailing doesn't work out.