Last week's article on boardsailing gave incorrect information on boardsailing lessons. Generally, group lessons cost about $60 for two three-hour sessions.

Nothing bothers boatman quite like gimmickry, and for five years he's been dismissing boardsailing as exactly that. But when people started boardsailing right in Washington, boatman broke down and gave it a try.

Guess what? No gimmick.

Boardsailing is the correct name for what everyone calls windsurfing, which is not the correct name because it stems from a brand name. Boatman's idea that it was a gimmick stemmed from the fact that a sailboard looks unseaworthy and goofy.

But give it a try and you discover the sailboard is the essence of sailing, so basic and unfettered that mastering it is mastering the sport.

"People who sail can't necessarily windsurf," agreed Jim DeSilva, a member of the Bic racing team who works at Potomac Boardsailing in Alexandria, "but people who can windsurf can sail anything."

You can't operate a sailboard, said DeSilva, "unless you understand the forces involved." He said it was obvious to him after he taught some boardsailing lessons that many sailors "don't really understand how their boats work."

Count boatman as such a one, who learned through a little shot at boardsailing something about the basic forces that propel and direct any sailing boat. He expects to learn more before he's done with the fast little boards.

A sailboard has no rudder, no steering apparatus at all. It's steered strictly and simply, at least for beginners, by placement of the mast, which is mounted on a gooseneck and goes in any direction.

All his life boatman has been mystified by the mechanics of "tuning" a sailboat mast. One trip on a sailboard, where mast-tuning is the basis of boat direction, and it all became obvious.

"To bring the board into the wind," said his instructor, "tilt the mast toward the stern. And to sail away from the wind, tilt the mast forward."

Each student in the class of six tried it on the sailboard simulator on the beach and sure enough, it worked. Later it worked in the water as well. You could steer without steering gear. "Why?" wondered boatman, who drifted home afterward and managed to figure it out with pencil and paper.

He pictured the underwater section of the little boat, with a daggerboard sticking straight down amidships and acting as a pivot. Then he pictured the mast moving forward and backward in relation to the pivot.

When the mast is tilted forward, he realized, it moves the center of force forward. The nose of the boat responds to the increased pressure by pivoting away from the wind, or downwind.

Tilt the mast and sail back and the opposite happens -- the boat's bow pivots into the wind because the center of force is behind the pivot, pushing the stern around.

It's laughably simple. And boatman laughed out loud that in all his years he'd never gleaned it before. But he'd been confused by compensatory equipment such as wheels and tillers and rudders, which offset the effects of an improperly tuned mast.

The education is only beginning. DeSilva says once the simple stuff is conquered boardsailing becomes more fascinating, especially when the wind pipes up and you start steering with foot pressure. "You can have fun with 10 knots" of wind, he said. "At 20 it gets really interesting. Heavy air is where the real nuances come in."

With his feet parallel to the sail angle, boatman pictured the little boat skimming along on plane, leaping from whitecap to whitecap, the sparkle of water on his flexed brown arms and the tiny pressure by his upwind foot that would round the board up into the wind inches from the dock, as a crowd clapped approval.

"No, no, no," groaned DeSilva, "push down with your upwind foot to go off the wind, not into it."

"Rats," thought boatman, picking up imaginary shards of boat after his imaginary crash at planing speed, "push upwind to sail downwind. How do you suppose that works?" ALL ABOARD -- Group boardsailing lessons are available every weekend at Thompson Boat Center near the Watergate and at Washington Sailing Marina on the Virginia side of the Potomac near Alexandria. Some private lessons are available at Belle Haven Marina below Alexandria. Generally, lessons cost about $60 for a three-hour introduction and certification. Boards are available for rent at about $8 an hour to certified boardsailors at all three locations. There's some question about how long boardsailing will be allowed on stretches of the Potomac between Chain Bridge and Wilson Bridge, where water-contact sports are disallowed for health reasons. The D.C. government and Harbor Police are trying to establish whether boardsailing is in fact a water-contact sport. Rentals and lessons have been available for two summers, and those involved say that so far there have been no reports of health problems related to water quality.