The tide was out so I had to use the rope ladder to get down into the Zodiac. As soon as you drop below the level of the pier, the city and the sun disappear and you're dangling in a jungle of algae-covered pilings, like Tarzan sliding down a vine into a swamp.

It's not doing a Zodiac justice to call it an inflatable raft. A Zodiac has design. It has hydrodynamics. It's made to go places. The inflatable part is horseshoe-shaped. The bend of the horseshoe is in front, and it's pointed; the prongs point backwards, tapering to cones. The floor of the craft is made of heavy interlocking planks and there's a transom in back, to keep the water out and to hold the motor. If you look at the bottom of a Zodiac, it's not just flat. It's got a hint of a keel on it for maneuverability.

Not a proper hull, though. Hull design is an advanced science. In the days of sail it was as important to national security as aerodynamics are now. A hull was a necessary evil: all that ship down under the water gave you lots of drag but without it the rest of the ship wouldn't float.

Then we invented outboard motors and all that science was made irrelevant by raw power. You could turn a bathtub into a high-performance speedboat by bolting a big enough motor on it. When the throttle's up high, the impact of the water against the bottom of the hull lifts it right up out of the water. It skims like a skipping rock and who gives a fuck about hydrodynamics. When you throttle it down, the vessel sinks into the water again and wallows like a hog.

This is the principle behind the Zodiac, as far as I can tell. You take a vessel that probably weighs less than its own motor, you radio the control tower at Logan Airport and you take off.

We had a forty-horse on this puppy-a donation-and I'd never dared to throttle it up past about twenty-five percent of maximum. Remember that a VW Bug has an engine with less than thirty horsepower. When you hit running speed in this Zode, if the water's not too rough, the entire boat rises from the water. The only wet part is the screw.