When you think of motor yachts, you probably think of powerful, fuel-guzzling diesel engines, creating enormous amounts of pollution and ever-higher operating costs. Surely we can do better, but still enjoy the water.

An interesting answer is here, in the form of the DSe Hybrid, essentially a 40' yacht with every square inch of its decks covered with solar panels. During a sunny day, you can cruise indefinitely at up to 6 knots (this is about 8 mph) using solar power alone.

How does it do it? Well, to start with, the boxy vessel has a lot of room on it for solar cells, so it's in a perfect position to grab the sun's energy.

Second, the catamaran design has two thin hulls as the only part of the boat that's actually in the water. This makes it extremely easy to push and so it can use low power engines to operate.

Third, six knots just isn't that fast. In fact, it's about the same speed as sailboats typically run. Because of the mathematics of water resistance, pretty much any vehicle, including this boat, is more efficient the slower it is driven. At the same time, this is not an outrageously slow speed - as I pointed out, many sailboats run more slowly, even under power.

So what happens when there is no sun, or if you want to operate at night? The yacht has twin diesel engines which can generate power for the electric motors to run the boat to 13 knots, which again is a fairly respectable speed on the water.

This is a really clever idea. They have made the world's first viable perpetual motion machine, as long as you let it stop at night. As long as the sun shines, you can dawdle along.

After all, who's in a hurry when you're in the sun?

The DSe is expected to be available in Fall 2008, for about $500,000. Pre-production discounts are available.

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