You wouldn't expect a guy named Seaman to live anywhere but on a boat and work for anybody but a Navy.

Which is exactly what Clay Seaman does. For the last couple of years he let the Navy furnish his digs aboard the aircraft carrier America. Then he was transfered to Washington, where he works as a lawyer in the judge advocate general's office.

No doubt it's hard, after two years of free living on the open ocean, to imagine tying yourself down to a four-walls apartment with a long-term lease and a fat monthly payment.

So when Seaman arrived he brought his house with him. This time it wasn't 2,000 feet long and it didn't have airplanes on the roof. It was, instead, 40 feet long and 30 years old, and it had holes in the roof where the rain came in.

Seaman picked up his 1947 Chris Craft in Virginia Beach and Powered his way up the Chesapeake, into the Potomac and on up to his new home. He checked around and found that getting a place to put his house in the nation's capital was a challenge.

Or at least it used to be, before Tom Rowan got going.

For years liveaboard boat facilities in Washington were almost always under-the-table arrangements because almost all the marines are leased from the National Park Service and NPS doesn't abide houseboating.

But in the last 18 months a startling transformation has occurred on the Southwest waterfront, which five years ago looked a lot like Berlin just after the bombing stopped. Tom Rowan started building docks, and every time he got one finished people came clamoring to his Gangplank Restaurant with money in their fists, asking for space for their boats.

Rowan has built about 220 slips in the last year and a half and they're just about all taken. Before he's done he'll have 350 boat spaces stretching more than a quarter of a mile in front of Hogate's and the other monolithic waterfront restaurants and motels of the new Southwest.

Cliff Persson is the marine construction expert Rowan talked out of going to Nigeria so he'd stay around and build the Gangplank docks. Persson says he can't understand it. "You read in the papers and you watch television and they say the dollar's falling, prices are up, unemployment is up. But evert time we finish a dock, it's full."

Part of the reason may be that Gangplank is providing room for people like Seaman who want more than a place to park. They want a place to live.

"Look," said Seaman, "I paid $8,000 for the boat, I pay $90 a month for the slip and I'm building some equity." And he has something to do with himself in his off hours.

Like putting in a water heater, a shower, a stereo, a new electric galley, a microwave oven, an air conditioner and fiberglass to cover all the leaks in the leaky roof. That's in the last six weeks.

There's plenty more like Seaman at Gangplank. Single women, single men, young couples, even families living aboard old, rebuilt cruisers or new luxury houseboats. Finding out how many isn't easy, because there's a bit of a fine line on liveaboards. Some folks live aboard when they feel like it but have access to other digs when the going gets rough, like in the dead of winter.

Rowan says he's trying for a 15 to 20 per cent complement of liveaboards. It helps security to have regulars around all the time, he said, but higher populations than that would overload facilities.

The business of overloading facilities is ticklish, anyway. Harbor Police and housing officials say there is no law on the D.C. books against living on a boat. But there is a law against dumping sewage from a docked vessel. The Gangplank liveaboards appear to be in violation of that law, according to John Brink, head of air and water quality control for the District.

Brink cited a D.C. regulation barring discharge of any waste, treated or untreated, from any vessel berthed at a marina, dock or basin.

Since Gangplank has no shore tie-ins for sewage from boats, boat owners would have to cast off their lines and maneuver out into the river every time they had to flush in order to be in compliance with the law, Brink said.

The sewage problems notwithstanding, life on the rolling wave is and apparently will continue to be a booming enterprise in Washington.

Once the new Metro tunnel under the ship channel is finished there will be boat docks stretching from the Wilson Line pier clear up to the gates to the Tidal Basin, according to current plans. Unless things change dramatically, it looks they'll all be full.