“;What do you do all day?”; a friend asked me about sailing for days on end.

The answer: fix the boat.

I was only half joking. The definition of cruising, another female sailor recently wrote, is repairing your boat in exotic places.

There are times, though, such as this week in Mexico's Sea of Cortez, when all boat systems are functioning, the autopilot is driving well and there's nothing I have to repair. (Read: Craig is here doing the repairs.) And so, as we head south in light winds, I get to choose between reading, listening to recordings or sitting in the cockpit staring at the water.

Mostly I choose to stare. At home I couldn't bear to sit and do nothing for hours on end, but at sea it has rewards.

One is freedom from thinking. Moving waves are so hypnotizing, my mind soon becomes a complete blank. To be free of all thought is so relaxing that when it comes time to do something, I must force myself to move. Best of all, this deep calm is free. It's meditation without mantras, tranquility without drugs.

Of course, waves can quickly become too much of a good thing. During periods of strong tradewinds or storms, the waves get too tall to support their own weight and then crash over in angry white roars. Like a forest fire, this might be awesome to watch, but it's also terrifying.

When the wind is light, though, as it was last week, it wrinkles the surface of the water in ripples.

Oddly, this breeze left patches of water flat and glassy. I thought the boat would slow down in those mirrorlike places, the size of several city blocks, but it did not. The wind was still there, just slightly off the surface. The boat didn't lose speed in the calm spots, but it did lose the sweet tinkling sound of sailing through ripples.

Other sounds replaced it, though: the belly flops of manta rays. All day long mantas 4 or 5 feet across leaped from the water, sometimes 6 to 8 feet high. Some turned somersaults in the air, others flapped their wings like mad and all hit the surface with loud, visible splashes.

No one knows why rays do this. One theory is that belly flopping might be a way of shaking off the remoras, or suckerfish, that stick to mantas. Most photos in my ID books show remoras stuck to mantas, and those hitchhikers look like a burden.

Another reason for leaping might be predator avoidance.

What kind of predators? we wondered. And then, in another major benefit of staring at the ocean, we saw one. In one of those glassy spots, a large dark dorsal fin cut the clear water so perfectly it looked like a scene from you-know-which movie. And it headed straight toward the boat.

The shark swam to the hull and then, uninterested, moseyed away. It happened in such slow motion I was able to get pictures of our 6- to 7-foot-long shark, handy for identifying the species.

Our visitor was a dusky shark, a species found in warm waters around the world. Dusky sharks grow to 14 feet long and swim on the surface to depths of 1,300 feet. Ours stayed at the surface for as long as we could see it.

Duskys are found in the Sea of Cortez (aka the Gulf of California), but sightings are unusual.

Sightings of any shark species here are unusual due to overfishing.

This then was a remarkable day because in sitting there staring, I spotted two more sharks after the dusky.

Someone had to do it. Craig was busy fixing the sea-water pump.

Susan Scott can be reached at www.susanscott.net.