I must go down to the sea tonight,

To the lonely sea and the sky,

And all I ask is a tall ship,

And a Global Positioning Satellite,

To steer her by . . .

Yes, mariners, it's come to that: The offshore sailor's best friend -- a starry, starry night -- has been outshone by technology.

There was a time not long ago when a ship's navigator plied his trade in a musty warren of paper charts, sharp pencils and dog-eared books, using an old bronze sextant to gather information from the heavenly bodies, fixing a position based on his relation to them.

But with SatNav and Global Positioning Satellites coursing around the earth 24 hours a day, plus low-frequency Loran signals beaming across the sea from towers on shore, the only time a navigator has to look skyward now is to rest his eyes from the VDT.

This I learned on a recent voyage to Bermuda. The navigator aboard the 62-foot aluminum racer Merrythought was no sallow manipulator of parallel rules and dividers. He was, instead, a chain-smoking computer jockey called "Fast Eddie," and his warren was a buzzing hive of electronic gizmos.

You name it and Eddie Adams had it and used it -- plotters, fax machines, radar, single sideband, VHF, computer, printer, digital displays.

Everything that mattered had a backup and everything interfaced so that every five minutes an update of information came spitting out of the printer behind Adams's head. It gave the latest compass heading, wind direction, wind angle, water temperature, velocity made good to the destination, speed over the ground, speed through the water, position, set and drift, time of day, estimated time of arrival and on and on and on.

Adams could fall asleep at the controls, as he did more than once, but the gadgets never slept.

"Any traffic?" the crew topside might shout down as fog enshrouded the hard-charging craft.

"You've got one boat down to leeward on a parallel course two miles off, but we're pulling out on them," Adams could reply, punching up a few buttons on the radar set, "and there's two up ahead six miles going our way, but they must be big boats because we're losing ground to them."

And where, exactly, were we? If that question has plagued seafarers since Magellan's time, it plagues them no more.

His ability to accurately place Merrythought on an empty, featureless sea was so refined, Adams said, that if you were sitting in the middle of the boat you'd better add 30 feet to the reading when he gave it, to compensate for the information coming in via antennas on the stern rail.

Adams didn't need paper charts to keep track of where he was in relation to land, either, although he did keep a set going as a backup in case the wiring frizzled.

But that was just a formality, because the Trimble Navigation graphic display terminal was keeping a running update of our progress on its prestored, computerized electronic charts of the entire East Coast.

As the Trimble got signals from its three navigation informants -- SatNav and Global Positioning satellites soaring around in orbit and the Loran towers on shore -- it automatically and constantly fixed the vessel's whereabouts, pulling up the appropriate chart on an LCD screen in the Trimble and pinpointing the boat's progress on it.

This brave new world of yachting comes to us largely thanks to the Department of Defense, which way back in World War II (when it was the War Department) came to the conclusion that military vessels needed a system to determine exactly where they were at all times.

The government began installing Loran (long-range navigation) towers up and down the coasts and equipping its vessels with receivers. By triangulating low-frequency Loran signals from different towers, captains could make a precise fix on location. The receivers later became available to the public.

The subsequent advent of onboard computers to analyze the ever-changing Loran data made it possible to instantly calculate speed through the water and speed over the ground and to project estimated arrival times, precise direction to various targets and other information once shrouded in imprecision.

The development of Loran opened up new areas for commercial and sport fishermen too, because captains could easily relocate gear left far from land. Offshore lobstermen today leave pots 100 miles or more offshore, marked only by small buoys, and go back three days later to the exact spot, guided by Loran, which beeps when they get there.

But Loran's range is limited. Several hundred miles out to sea, the signals grow so weak and the angles from towers on shore so tight, the information is unreliable.

Enter SatNav and Global Positioning satellites, which do the same job using signals from orbiting stations on high. Tom Closs Jr., who specializes in navigation equipment for sailboats at Electronic Marine in Annapolis, said GPS is on the verge of completing a planned network of 21 satellites, which by 1992 will provide 24-hour-a-day coverage to properly equipped yachts anywhere in the world.

Combine that information with the availability of weatherfax to see where storms and fair weather lie, plus radar to determine who else is around, and you might as well be walking down K Street at lunchtime for all the mystery left in a sea voyage.

But don't get too cocky, says Closs, who uses all the latest gadgets on his offshore racer Fun. "We sometimes pay too much attention to all the information we're getting electronically and forget to sail the boat right," he said.

"It's fun to play around with, but is it always worthwhile? Maybe not," he said.

Anyway, even Closs, who makes his living on electronics, concedes it's an imperfect science, fraught with peril. Anyone who works in a computerized office knows how often the gear breaks down, even in immaculate, temperature-controlled, dust-free, level, dry surroundings.

Imagine that same gear laboring under an onslaught of green saltwater breaking over the bow as you beat and bang into 15-foot head seas, with crewmen and equipment crashing around.

"Stuff breaks," said Closs. "No doubt about it. We tell our customers: 'Don't ever figure on even the remotest chance that you won't need need paper charts when you go to sea.' "

Or musty old books, a good sextant and a clear, starry sky. Just in case.