THE TALL SHIPS have been coming and going for months, but Riverfest will be graced by quite a fleet of not-so-small ships. Some will parade upriver behind Calypso from the Woodrow Wilson Bridge on Saturday morning; thereafter they'll be receiving visitors at the Maine Avenue docks. (Calypso herself will not be open to visitors because Capt. Jacques Cousteau will be aboard, needing some peace and quiet to rest up for his 75th birthday bash at Mount Vernon Sunday evening.)

Riverfest's visitable vessels include:

Alexandria, a 125-foot, three-masted topsail Baltic trading schooner built in Sweden in 1929. Originally designed to carry only cargo, she has been refitted for passengers, one of which you will dearly want to become the moment you lay eyes, much less set foot, on her (she's the vessel that has long graced the waterfront of her downriver namesake city). Berthed at the Gangplank Marina.

Cayenne, a sleek 61-foot sloop that was built to be fast and tough, which are the minimum requirements for blue-water racing, and turned out to be all that and beautiful also. She's a Southern Ocean Racing Circuit champion and now is based in Annapolis, from which she beats up on the regional competition. Also at the Gangplank Marina.

Mabel Stevens, a comely 45-foot racing ketch owned by Our Town's own Ned Chalker, and named after a beloved great- aunt. The vessel, built in 1935, often serves as Washington's official representative at sailing and ceremonial events. At the Gangplank Marina.

Sharon, an 85-foot schooner, may turn up at the Police Pier or may not, depending on wind, weather and whatever.

Chesapeake, our sturdy old lightship friend from Baltimore that long lingered along the Hains Point sea wall, is back. She will be at the Police Pier, faithfully performing her modern mission, which is to cast the light of knowledge over the slime-dark sea of environmental ignorance, warning us to steer clear of practices that pollute our planet.

Not so tall, but equally fascinating, are a pair of replica 9th- century Viking ships (well, boats). Fyrdraca, a 32-footer complete with dragon figurehead -- and figuretail -- is a 12-oared, full-sized model of the sort of vessel whose yellow and black- striped squaresail coming over the horizon augured death and destruction for enemy and innocent alike. Take a look at the cramped space (only a 9-foot beam) for her crew of 18 and the 14-foot, 15-pound oars they manned -- sometimes for days and weeks on end when the wind was foul -- and you begin to see what made the Vikings so mean. To give you an idea, it once took Fyrdraca four full days to make the passage between Washington and Chesapeake Bay.

In company with Fyrdraca at Gangplank Marina will be the faering boat Gyrfalcon, 20 feet long and also a faithful copy of a 9th-century Viking vessel. Building and using the boats is "a great way to gain historical insights into the way those early voyagers lived," a crew member said. "That's the official justification. They're also great to take out on the river with a bunch of friends and plenty of beer and ice for ballast."