reach its end stops at which time it is then no longer producing a torque. The sphere will remain on its end stops until the boat comes out of its turn. “
The key phrase here is “on its stops.” The Seakeeper reacts the same as the toy gyroscopes we all enjoyed playing with as kids. When a gyroscope, whether balanced on a string held by a 10-year-old, or mounted in a gimbaled sphere on a boat, is acted on by a side force, it reacts by moving, or “precessing,” at right angles to the direction of that force. (If you want to know exactly why, Google it. It’s all about angular torque.) Precession creates an immediate counter force, at right angles to the precession and in the opposite direction of the original force, which restores equilibrium. When the precession stops, the counter force stops, too.
The Seakeeper’s gyro is a heavy, rapidly spinning rotor inside a mount that can only tilt forward or aft, in what engineers call the “pitch plane.” It’s fixed in the athwartships plane. When the boat rolls, the Seakeeper senses the roll as a side force, and the rotor instantly precesses at right angles to it—either forward or aft, depending on the direction of roll. This creates the counter force that damps the roll. The strength of the counter force depends on the speed of precession. In normal rolling at sea, the boat heels one way, then the other, and the gyro responds accordingly, precessing this way and that, and maybe never hitting the stops.
But crank the helm over and the boat leans and stays put; the gyro precesses and quickly reaches the end of its range, with the heeling force still acting on it. When it stops, its counterforce stops, too, and so does stabilization. Without precession, no opposing force is generated. After an instant of minimal resistance, the boat steers, and heels, normally, with the rotor all the way forward or aft. When the boat levels out, the rotor returns to normal operation. If this were not the case, the Seakeeper could double as trim tabs—automatically offsetting any heel from wind, poor trim, fat Aunt Sally sitting on the gunwale, and so forth.
Precession happens on its own—it’s physics—but in an actively controlled gyrostabilizer like the Seakeeper, the hydraulic cylinders control the rate of precession and the precession oscillation range, constraining it to optimal limits. Left to its own devices, in certain conditions, such as boisterous seas, the drastic rolling of the vessel could, theoretically, cause the gyro to precess too rapidly and develop counteracting torque too great for the mounting structure to handle. Again, that’s the argument against passive gyrostabilizers. Gyros work better when they’re under control.
The Seakeeper 3 is designed for boats from 30 feet.