Waves hit the side of a boat, and the boat rocks. It’s been as simple as that since the first Neanderthal hacked out a log canoe, and for experienced mariners it’s difficult to envision anything else happening when waves and boats interact. So when Seakeeper told us they could reduce the rocking and rolling of a boat—virtually any boat over 30’—by 70 to 90 percent, our BS detectors blew a fuse. We decided that before we wrote about how these things worked, we’d need to test them first-hand for ourselves. Here’s what happened.

Yes, it’s true, on that Contender 35 the Seakeeper knocked out 90 percent of the rocking and rolling. We then proceeded to step aboard a very different type of boat that also had a Seakeeper installed, a Viking 62, and experienced similar results. How the heck can this be? Can a sphere sitting enclosed in the leaning post of a center console really overcome the physical motion of a boat? Eons of maritime experience tells us rocking and rolling must happen when boats and waves meet—what kind of black magic could change this fact? Hint: magic has nothing to do with it.

Contained in a leaning post or belowdecks, the Seakeeper can radically reduce rocking and rolling in boats of many different types and sizes.

The way a Seakeeper accomplishes its mission all boils down to torque, applied to counteract the motion of the boat. Imagine for a moment that the Jolly Green Giant is standing next to your boat as it bobs around in a port-side beam sea. He’s feeling helpful, so every time a wave rolls under the boat, he puts his hand on the port topsides and applies just enough pressure to hold that side of the boat level as it rises over the wave. And imagine that a moment later, he puts his other hand under the starboard side of the hull and lifts, just enough to prevent that side of the boat from tilting as it falls into the trough. Your boat would still rise and fall with the waves, but for the most part, it would cease to roll.

The Seakeeper is your Jolly Green Giant. Inside of that sphere, there’s a flywheel designed for the sole purpose of spinning as quickly as possible. The sphere is a near-vacuum inside, so this flywheel doesn’t have to fight against air friction and it can spin significantly faster than most other gyro-stabilizers (the exact RPM varies by model, but all spin at least 5,000 RPM and some go as high as 10,700 RPM). As it spins, the flywheel creates angular momentum, which produces torque that counteracts any force—waves, in this case—that’s trying to move it off of its axis. Since the frame surrounding the sphere is solidly mounted to the boat’s structure, that torque pushes and pulls to keep the boat as level as possible.

If you could see through the sphere in a Seakeeper, you’d see a flywheel spinning at extreme RPM.

Here’s an easy way to picture the forces at work: think of a spinning top. As long as it’s spinning quickly, momentum keeps it upright and level. Since the Seakeeper is powered and it always spins at a controlled rate, that momentum is always present.

The Seakeepers have another technical leg up on other gyro-stabilizers with their computer-controlled active control system. This constantly adjusts the attitude, or tilt, of the gyro, allowing it to provide full torque in a wide range of sea conditions.

If you’re still having a tough time wrapping your head around how this can possibly work to keep a boat from rocking and rolling, don’t feel bad. It is, in one way, a sort of maritime rocket science—this type of gyroscopic stabilizer, called a Control Moment Gyroscope, is also used for spacecraft attitude control systems. In fact, there are four of them in the International Space Station. But don’t worry too much about the physics. Just step aboard a Seakeeper-equipped boat, and feel the near-elimination of rocking and rolling for yourself.