(FORTUNE Magazine) – In a few days, maybe, Jim Clark will be able to relax. Friends will fly in for a big party in Amsterdam, a bottle of champagne will be smashed, a brass band in wooden shoes will ride around on bicycles playing "Louie Louie," and Clark's remarkable new sailboat, the 155-foot Hyperion, will be christened at last. But at the moment, a scant 72 hours before the launch festivities, he is one tense tycoon. It isn't just that he still has to debug some of the software he's written for the boat, or that Crown Prince Willem-Alexander of the Netherlands has indicated he may attend--or even that Clark's latest business venture, Healtheon, has just taken a pop on the front page of the Wall Street Journal. What's gnawing at Clark is that Hyperion, his magnificent obsession of the past three years, is beginning to draw the public's attention, and if the public misunderstands what he's up to here, it may giggle, or worse.

Already, sober publications have written that Clark will be able to sail his boat remotely, from his desk, via Netscape. (Oh, great, a 298-ton remote-control toy!) Much has been made of Hyperion's multimillion-dollar price tag (ha!) and huge cutter rig, which gives it what may be the world's tallest mast (need one even go into that?). The cultural timing is terrible too: As the economy threatens to sour, essayists already are comparing Silicon Valley entrepreneurs like Clark with the last decade's Wall Street vulgarians.

"People are treating this sensationally," Clark says. He's right, and it's too bad, because this project, like the career that made it possible, actually is sensational.

Clark, a 54-year-old Texan, founded two Silicon Valley startups that really did touch a lot of people's lives: Silicon Graphics, which brought 3-D computer design to everything from automobiles to movies; and then, 12 years later, Netscape. Healtheon, which is supposed to rationalize medical data using the Internet, has just canceled an initial public offering, but it may well go public once the market regains its composure. Besides putting together a personal fortune of some $500 million, Clark has built wealth on a scale that few can match. "That's all I've ever done, is build businesses," Clark says, a chart of Auckland Harbour glowing behind him on a flat-panel display dimmed for night vision--part of the navigation program that he has written for Hyperion. "This," he says, "is a hobby."

That's one word for it; other people might call it a full-time job. Clark has been putting in 40 hours a week writing code for the computer network that will give his vessel an elaborate, bespoke intranet. The system won't sail the boat; Clark will have a professional crew for that. But it will be a tool for sailing unlike any the world has seen. It will gather information from all Hyperion's systems--engines, generators, tanks, navigation electronics, steering gear, video jukebox, heating and air conditioning, and more--and beam it to 22 touch screens installed all around the vessel. It will measure the loads on stays, sheets, and halyards, alerting the crew if they become dangerously stressed. It will warn if an unintended jibe is imminent, a potentially lethal event in a boat this size. It will store some 30,000 pages of boat data, including digital photos of construction details, so if the propeller falls off in Fiji, mechanics can see how it was installed.

To build the system, Clark has hired three software engineers and formed a little company called Seascape. He has written a new set of Unix tools to build the applications, and as the system has grown elegant and strong, he has mused aloud about commercializing the technology--if not for sailboats, then perhaps for process control or for the wiring of smart houses. Talking about that possibility makes him uncomfortable, though, because here his enthusiasm collides with his business sense: "Thinking up applications is fun, but that's exactly what most engineers do wrong," Clark says. "They build something because it's technologically neat, and then try to find an application for it. The right way to start a business is to see the market need, say 'What technology could I do to give that market a kick in the pants?' and then build that technology."

The roots of the Hyperion project are much simpler. Like a lot of guys, Clark wanted a bigger boat. Like just a few guys, he could afford whatever boat he wanted. He started sailing relatively late in life--boats weren't part of his childhood in Plainview, Texas, and he had never really been on the water before dropping out of high school to join the Navy. He bought a 55-foot sloop to celebrate the IPO of Silicon Graphics, then moved up to a 92-footer and developed a taste for sailing and diving in places like Palau, the Solomon Islands, and Papua New Guinea. He started fiddling around with programs for electronic navigation, dissatisfied with the software available commercially.

Then one day in 1993 he was invited aboard a 143-foot ketch called Juliet, built by the Royal Huisman Shipyard in Vollenhove, outside Amsterdam. He was captivated by its grace, its accommodations, its acres of perfect mahogany joinery. (He wasn't the first to be smitten by the work of the Dutch master builders: As a 25-year-old, Peter the Great spent four months working incognito in an Amsterdam yard to learn the shipwright's trade.) "Juliet was a beautiful boat, and I thought, 'I would really like to be able to afford one of these,'" Clark says. "That was before Netscape went public."

Bingo. With Netscape's IPO in the summer of 1995, Clark was suddenly a billionaire on paper, and he didn't have to think about the money anymore. Published reports have put Hyperion's cost at $30 million to $50 million; Clark says those reports are wrong but doesn't want to get specific. "Okay, it's a big boat, and it's a reasonably expensive boat," he says. "But I also have a reasonable amount of money."

At first Clark thought he was interested in what passes at the Huisman yard for a stock boat: a 104-foot sloop. "I only had one stateroom for guests on my other boat; sometimes I found it would be nice to have two sets of guests. But as soon as you make it a little larger for the staterooms, everything kind of grows, including the crew area, because you need more crew to take care of it. It's almost like an inflationary spiral if you let it get out of control, because each thing justifies something larger elsewhere."

Clark picked two prominent naval architects to design his dream boat: German Frers for the hull and rig, and Pieter Beeldsnijder for the superstructure and interior. The design grew to its final dimensions: length, 155 feet; beam, 31 feet; draft, 16 feet (although a daggerboard slides out of the fixed keel for beating to windward). Most boats that size have more than one mast, but Clark wanted a sloop--technically a cutter, in this case--because of the rig's efficiency. That would mean building a carbon-fiber mast 190 feet tall. To put that in perspective, it will clear the Golden Gate Bridge by just 30 feet.

This would be the biggest boat the Huisman yard had built, and possibly the biggest single-masted boat afloat. And for Clark, of course, that was just the beginning.

Looming up out of the flat Dutch countryside in a canal in the little town of Vollenhove, mast piercing the gray sky, aluminum hull glistening with eight coats of flawless white paint, Hyperion doesn't turn any heads. People here have seen it all before. The family-owned Huisman yard, which was founded in 1884 to build cattle barges and fishing boats, has been building some of the world's biggest and most sophisticated cruising yachts here since the early 1980s.

Clark, walking along the damp bulwark where Hyperion is tied up as workmen race to finish the interior, is agitated. A German television crew wants an interview. The British press has reported recently that Clark will be sailing Hyperion from half a world away, using the Internet to trim its sails. The American press has reported that this won't be necessary: The boat will be able to teach itself to sail. Either way, the subtext is pernicious. (The weenies in Silicon Valley are worse than hedonists--they don't even know how to have fun!)

"This thing is being exaggerated to a point that's unreasonable," Clark says. "There is nothing that is terribly unique about this boat."

To an extent that is true. The hull shape, round-bottomed with a bulb fin keel, is not revolutionary. The giant, full-battened mainsail furls down into the boom--cool, but not unprecedented. To be sure, the boat's 17-foot launch (designed and built by Beeldsnijder) has a shower and pop-up cleats activated by compressed air, but those are details.

Below decks, Hyperion is classically lavish: owner's cabin and two guest staterooms aft, saloon amidships, galley and crew quarters forward. All of it is trimmed in Honduras mahogany, and the ports and windows are UV coated in order to prevent the woodwork from fading.

None of this looks especially high tech. But it's a safe bet that no other vessel afloat, leaving aside the world's navies, has more than 40 miles of copper wires for a nervous system.

Clark has been so immersed in the details of Hyperion's construction that, as he says, "I can't see the forest for the trees. That's one of the bad things about being an engineer, that you often don't step far enough away from a problem to see what the real problem is." As it happens, he's talking about applications for his programming, but the observation applies to the larger issue too: Evidently it never dawned on Clark that the idea of a computerized sailboat might strike people as odd.

For instance: salt water and computers? That turns out not to be a problem on vessels like this, which generally have state-of-the-art climate controls (some people do like to hang Pissarros in staterooms, after all). In this case, outside air enters through vents on the mast, above the salt spray, and then is cooled and dehumidified.

But what if you're sailing along in the Indian Ocean, and the computer crashes? Actually, this is not at all like your laptop; it's more like the networks that operate factories. Electromechanical devices run the machinery; they are run by programmable logic controllers, which don't crash; and these in turn are supervised by Clark's software, which runs on 24 Silicon Graphics servers and integrates all the data on custom displays.

Some thought was given in the early stages to having the computer network tack the boat. "In principle, the boat is prepared for it," says Jan Bokxem, project manager for systems and electronics at the Huisman yard. "We could do it. However, you'd have to write a lot of software then, and there is an issue of safety." Besides, he says, "you have to ask yourself another question: What is sailing all about? It would mean then that suddenly there is no crew, you step on the boat, push the button, and the boat starts to sail. And you sit in the cockpit. Is there fun then left over?"

In terms of actually sailing Hyperion, "there's nothing that's really different from other boats that are built. It's just bigger," says Allan Prior, the boat's captain, a veteran of Whitbread and America's Cup races. "There's more control and more feedback. If you had to sail this by hand you'd need a crew of 30, and four or five engineers, to do what you can do with one engineer and a crew of eight, which includes three girls." (He can say that; he's from New Zealand.)

To a surprising degree, this project is driven by what you might call information aesthetics. Did anyone think that the founder of Silicon Graphics was going to have a bunch of fish-finder-looking readouts and crude analog gauges cluttering his bridge? Particularly when he had spent so much time on details like the contrasting yew and wenge veneers inlaid in the mahogany trim? "One of my objectives was to make the quality of the image as good as the quality of the woodwork," Clark says. Which is to say, sublime.

Clark and his engineers wrote programs to make digital dials turn smoothly, to display elegant real-time diagrams of generators and fuel systems, to control air temperatures, to select DVD movies or look up the weather in Hawaii on the Web, all from the same flat-panel screen. Clark even got into the guts of his anemometer to increase the sampling rate for wind speed. "In my past experience, they deliver that data once every two seconds," Clark says. "I want it 20 times a second. Why? Because I do."

Beyond all that, there is the potential that someday, somehow, this work will save a life. Big sailboats at sea are subject to unbelievable stresses, but until now nobody has known just what they are. At rest, Hyperion's mast is loaded at over 120 tons. Who knows what the stresses on the rig will be in a gale?

Soon Clark will, and boatbuilders and others are anxious to get their hands on the data. In an age when it is said that the ideal racing sailboat is one built so lightly that it falls apart the minute it crosses the finish line, knowing more about margins of safety may be a godsend. "It will be very, very useful," says Scott Zebny, a sales manager for North Sails, which sewed the sails for Hyperion--all 24,154 square feet of them. "It'll close the loop. It's never been done on the scale that he's going to do it."

When Peter the Great was working in the Dutch East India Company shipyard in Amsterdam, indulging the passion that played so great a role in opening Russia to the West, he got wind that two of his subjects were making fun of him. The two--noblemen who had accompanied him to Holland--said he was making an undignified spectacle of himself. Peter ordered that they be executed immediately. The burgomaster of Amsterdam pointed out that he didn't wield the power of life and death on Dutch soil; in a compromise, the critics were exiled, one to Batavia, the other to Suriname.

Clark is just going to have to find some other way to deal with people who associate "cybersailing" with his name. It helps that his name is associated with a lot of other things, including serial successful startups (and lately, that clamorous antitrust case in Washington: See story in this issue). Clark is already working on his next idea for a real business, one he'll turn to after Healtheon. And whatever else happens, he's got the boat of his dreams.

Hey, he earned it.