The dimensions of Hal and Margaret Roth's world are 35 feet x 9 feet 6 inches x the globe. Where they are is their destination, and where they are at the moment is Annapolis, in the cabin of their sloop Whisper, on which they have lived these past 13 years and 70,000 miles.

Hall Roth reclines on the settee behind the cabin table - there is not quite headroom to stand. Outside, the boatyard bustles with spring activity, and a few weekday sailors circle slowly under power, waiting for the Spa Creek drawbridge to unlock the door to Chesapeake Bay.

The Roths have been in Annapolis all winter, frozen in. "When are we leaving?" he asks with a wan smile. "One thing we never give is departure dates. Right now we're doing a little rigging work, and waiting for some fittings to be delivered from England. After that . . ."

Margaret Roth decides to make coffee. Within minutes she has expertly primed and lit the one-burner kerosene stove, and pumped a kettle of water. All heating, lighting and cooking on Whisper is by kerosene; all water is pumped by hand.

The device that holds her drip-ground coffee looks suspiciously like a sock. She holds it over each cup, in turn.

"We used to use the regular Melita filters," she explained, "but we found that in Argentina, everyone uses these. Not so expensive, either."

The Roths have also found no need for a refrigerator, and are not even fond of ice. In harbor, Margaret shops every day: "It's always a good excuse for a morning walk." On the galley counter-top is a small garden of alfalfa shoots, mung beans and lentils, growing in separate plastic containers. "We make a salad with them at sea. That is, if the whole garden doesn't tip over."

It is quiet in the cabin this morning. Steam rises from the coffee cups. Virtually everything the Roths own lies within three steps of the cabin table, steps well-practiced after 13 years.

Hal Roth has just been informed by a visitor, probably for the 1,000th time, that he seems to be living an idyll. He has not quite formulated his 1,000th reply when the telephone rings.

The telephone is sitting on the bunk right next to Roth's leg, and he picks up the receiver as if it were a rancid chicken neck. It is the outside world.

One gets the impression that the Roths will not be in Annapolis much longer.

The Roths are following a 20th-century yachting tradition built before them by husband-and-wife world cruising teams such as Eric and Susan Hiscock and Miles and Beryl Smeeton - other sailors of "mom and pop" boats, as Roth call them.

But the Hiscocks have grown old, and the stories of their perpetual travels in various boats named Wanderer are now told in books, on shelves. The redoubtable Smeetons, twice capsized while trying to round Cape Horn, have sold their boat and moved to Calgary.

So the torch is passed to the Roths. And in fact they have just returned from the Horn, 20,000 new miles under their keel, filled with fresh lessons of man and woman against the sea.

One thing is clear in the world cruising tradition: Cape Horn is where the dues are paid, and the rights to the idyll won. The Roths entered the Southern Ocean in winter, and when Margaret hung out the red thermal underwear to dry it froze solid on the lifelines.

Day after day Whisper drove southward, and the icy gales rose and fell as the pilot books said they would, and the Chilean ports and anchorages took on sterner and sterner visages. They explored the unknown fiords of the Straits of Magellan, with their spectacular waterfalls and brutal williwaws - gusts of high-altitude wind reflected by mountain crags and often clocked at more than 100 knots.

For this part of the journey the Roths had two other people aboard. Although the odds were against the ship being wrecked, extra hands were likely to prove of value. This time, the odds played wrong on both counts.

At 7:30 p.m., in a small bay in the Wallaston Islands 24 miles from the Cape, Whisper was struck by a westerly gale and driven on the rocks. Within minutes the cabin was filled with 39-degree water and a battle for survival had begun. The story of their eventual rescue nine days later by a Chilean patrol boat, and of the remarkable salvage and repair operation that permitted the voyage to resume, is told in Roth's latest book, "Two Against Cape Horn," which W.W. Norton has subtitled "A tale of high adventure at sea in one of the least known parts of the world."

But the story also is one of human behavior under stress. The Roth's companions are called, for legal purposes, just Adam and Eve. Eve did fine during the marooning, gathering mussels and wild celery and helping with the chores in the temporary camp they set up, Robinson Crusoe style.

Adam, although taller and stronger than Hal Roth, was a different story.

". . . When I looked closely at him, my heart sank," Roth recalls. "He was shaking in his boots. His eyes had become slits and he was almost crying. Instead of looking at me when he spoke, Adam looked at the ground."

Adam, in fact, became thoroughly useless, as Roth recounts it. He slept 10 or 12 hours at a time. He dropped things. Back-breaking labor was required to salvage the vessel, but Adam did none of it. Worst, from Roth's point of view, Adam was wasting one of the great photographic opportunities of his career. There were thousands of feet of 16-millimeter film aboard, and two still cameras. Roth mentioned it at one point, and recorded Adam's reply:

"You're absolutely right," said Adam in his deep bass voice. "We must start on a systematic shooting schedule and chronicle every aspect of this experience." In the end, the photographer never took a picture.

Hal Roth's conclusion regarding his crew seems characteristic in its straightforwardness:

"It is not my purpose to mock Adam and make sarcastic comments on his behavior, but simply to observe that when fear grips a man it changes him, and he becomes wretched and useless. Adam was the biggest person in the party and he should have been the strongest. Fear bled his strength away and he became the weakest."

So the idyll fades, replaced by tales of howling gales and shipwreck and strong men broken by the severity of the test.

Or does it? After all, the sun is still out in Annapolis, and the coffee Margaret Roth has made is still hot, and "Two Against Cape Horn" has been chosen an alternate selection of the Book of the Month Club.

"In a way it's simple, why we do this," Hal Roth says. "We like to visit all over the place, and we like to be among new people, whether it's in Polynesia or South America. People ask us, 'How do you fight boredom?' But you know, we think of this boat as a little floating house, and there's always something to do. We both live here, and I work here - there are two typewriters aboard all the time."

"How can we live without TV, they ask," Margaret adds. "Well, I read, I walk, I sew. Sometimes at sea, if it's an easy passage, we'll play chess. We listen to the radio. The BBC is very good, you know," she says, her British accent rising for an instant.

The Roth's life of discovery apparently began pretty much with their discovery of each other.

In 1944, Hal found himself in he service, eventually to log more than 1,500 hours in B-25s, mostly as a flight engineer in the United States and Canada. He had studied engineering, but after a series of "non-descript jobs" found himself called up for Korea, and more of the same.

In the meantime, he was spending every summer hiking in the Sierra Nevada and writing travel stories about it.

Margaret was born in Bombay, where her father was a civil engineer. During World War II she served as a WREN radio mechanic with the British Fleet Air Arm. After a stint as a secretary for NATO in Paris, she came to San Francisco and met a non-sailor named Roth. Before long they had bought Whisper, in British Columbia, and sailed her to California.

"Then Hal got tired of sailing around San Francisco Bay," Margaret recalled. "It was the same every time - sail from Sausalito down past the city waterfront, and back. If you tried to go under the Golden Gate Bridge into the big Pacific swells, our guests would immediately get seasick."

The Roths overcame this problem by leaving their friends behind and circumnavigating the Pacific basin on a 19-month double-handed voyage. After that they sailed around Vancouver Island and back; then came the journey around Cape Horn to Maine: then the trip from Maine to the Bahamas and back; and then from Maine to Annapolis.

These voyages were punctuated not by semicolons but by remarkable incidents of beauty and violence, many of which take on renewed reality to a listener in Whisperhs snug cabin.

"On the way back from the Bahamas to Maine we got into a cross-sea in the Gulf Stream off Cape Hatteras," Roth said. "It wasn't blowing that hard - maybe 40 knots - but the seas were confused. Three big ones came up from behind and rolled us 130 degrees."

that is, virtually upside down.

"We know the precise angle," Roth continued calmly, "because of the mark on the ceiling made by stuff that fell out of the drawers."

Robert Persig, whose book "Zen and the Art of Motorcycle Maintenance" made him the philosopher of toolboxes, also has examined long distance sailing, and has written of a phenomenon called "cruising fatigue." What most people don't realize, Persig says, is that after a while, all sunsets can begin to look alike.

Roth, however, doesn't warm up to the Persig warning. After 13 years, his idea of a good time still is "sailing into a new harbor, chart in one hand, tiller in the other, with the engine off."

"Look," Roth says, "I just got into boats in 1962 because it looked interesting. Took some courses, like anyone who wants to start from the beginning, anyone who wants to make a cruise."

The phone rings again. He rolls his eyes, mutters an oath, and plunges into conversation with a distant editor.

Three steps away, at the galley, Margaret is asked if there isn't something, after all, that she regrets about this life.

"Yes," she replies confidentially, turning her back so as not to disturb Hal. "You know, we did not want to actually land on Horn Island itself, but conditions weren't right. I'd like to go back - and do it." CAPTION: Pictures 1 and 2, Margaret Roth, from the book, "Two Against Cape Horn"; at left: Hal and Margaret Roth, by Hal Roth and Christian Williams; Picture 3, The Roths, from their book, "Two Against Cape Horn."