If you could eliminate one thing from boating, what would it be—other than cost? If you said rough water, you'd not be alone. Uncomfortable gyrations have been the bane of seafarers ever since someone hollowed out a tree trunk. But, of course, no one this side of the New Testament can calm troubled waters. Ancient mariners poured oil on them to no avail. Modern active and passive stabilizers do a better job, but the former are complex in design and installation and protrude from the hull, where they can be damaged. The latter work only at relatively low speeds and aren't exactly aesthetically pleasing. And anyway, no one claims to eliminate rolling, only reduce it.
A cutaway of the Seakeeper Gyro shows its relatively small flywheel, which spins at about 10,000 rpm in a vacuum. Two snubbers have been deleted for clarity.
No one except Shep McKenney. For more than six months, he bugged me to take a ride on a 43-foot Viking equipped with his Seakeeper Gyro and Seakeeper Stability Control. "Nothing I can say will convince you," he said. "You've got to experience it, and once you do, you'll be convinced."
Had McKenney not been McKenney, I'd probably have ignored him. But since it was he and Bob Hinckley who bought The Hinckley Company in the late 1980's and invented the Hinckley Picnic Boat, I really had to fly down to Norfolk, Virginia, for a look.
The Seakeeper Gyro in the cockpit of a 43-foot Viking. Under normal circumstances the Gyro compartment and the area beneath the two hatches next to it would be the Viking’s fishbox.
On test day there was enough of a swell—two to three feet—running that if we laid the Viking beam-to, we could get her rocking pretty good. Said Viking is a pretty much an off-the-rack battlewagon (with a reputation as a pretty stable boat) except for the centerline plexiglas cockpit hatch through which, from my perch on the bridge, I could spy a stationary white, beachball-size orb. As the Viking set to rocking, McKenney said, "Now watch this," and flipped a switch on the bridge console. The orb tilted fore and aft a couple of times, and the rolling stopped. Stopped! And it didn't start again until he flipped off the switch. McKenney repeated the procedure, always with the same result. I observed the result graphically, in real-time on a monitor panel, but he was right—it was nothing compared to physically experiencing the Gyro, holding on as the Viking rocked, watching the orb tilt, and feeling the rocking stop.
Just as amazing is the Gyro's mechanical simplicity. It's a "control- moment gyroscope"—the same gizmo that stabilizes most spacecraft—inside of which is a spinning flywheel that, thanks to physics, makes it resist movement, in this case rolling. The resistance generated by any gyroscope depends on three flywheel characteristics: weight, speed, and diameter. The Gyro generates three and a half tons of force, not by spinning a large or heavy flywheel, as most gyros do, but by spinning a small one fast—like 10,000 rpm.
The left half of this graph shows the Viking’s roll with Gyro off. The right half shows the dramatic decrease in roll after it has been turned on.
According to McKenney, the reason no other control-moment gyro flywheel spins this fast is the enormous amount of energy it takes to overcome friction generated by air. The Gyro's flywheel spins in a near vacuum, virtually eliminating air resistance. But the trick isn't the vacuum; it's designing a cooling scheme for the bearings that works in a void where air can't transfer heat from them. McKenney says his company has licked this problem and performed the long-term tests to prove it.
The beachball-size Gyro installed beneath the Viking’s cockpit. Both snubbers are visible in the upper right-hand side of the photo. The fins provide structural support and also dissipate heat.
Indeed, durability through mechanical simplicity a main attraction. Other than the flywheel, the only moving parts are two cylinders that limit tilt rate based on input from solid-state sensors and lock the Gyro in place when it's off. And the only maintenance, McKenney says, is annual refreshment of the vacuum via a simple pump.
The Gyro is also energy efficient. It reportedly takes about 3 kW to spool up the flywheel. The unit becomes fully operational in about 25 minutes; full speed takes about 45 minutes and requires only about 1.5 kW to maintain. And you can't hear it unless you put your ear to the sole.
The Gyro can be mounted anywhere on the centerline that has sufficient structure to handle its forces—engine beds like our Viking's are ideal. Retrofits are doable, but McKenney's really looking for builders who will design their boats for the Gyro. Our unit, the Seakeeper 7000, can handle vessels to 55 feet and retails for $55,000 plus installation; prices should come down as volume goes up. Units can be combined to handle larger vessels, and the Gyro can be scaled down to handle boats of less than 30 feet.
Whether aboard a fast planing hull or a trawler, a yacht, or a commercial boat, the Seakeeper Gyro has the potential to change life aboard forever. I've seen it work, and I can tell you—this is the future.
What About Pitching?
Blocking water flow with a transverse blade produces a pressure field directly ahead of it. With the boat at speed, the blade extends about an inch to create lift equal to that of a trim tab.
A gyroscope can control motion in one plane at 90 degrees to the direction of its tilt. The Seakeeper Gyro tilts fore and aft to control movement athwartship (a.k.a. roll) because it's focused on movement at slower speeds, where pitching is not a big factor. To contol fore-aft movement (a.k.a. pitching), Seakeeper offers Stability Control, which relies on what the company terms "small lift-producing surfaces" on the transom. They look like trim tabs, but they're shorter and wider. More important, they react much more quickly because of their actuator design and the fact that they're controlled by a motion sensor. The system, which works only on planing hulls, was developed for fast ferries and navy ships and is based on the principal, graphically illustrated at right, that a small deflection creates a large pressure wave ahead of it that's sufficient to generate enough lift to produce a drop in the bow. The unit can be manually zeroed at any point and can actually raise the hull if zeroed with a slight deflection.
The left graph shows very quick blade deflections in response to pitching. At right, the outer parts of the graph show pitching with the unit off; the center shows the decrease in pitch with it on.
On our Viking the unit reacted quickly enough to reduce bow rise in three-footers to just a couple of degrees.—R.T.
This article originally appeared in the November 2007 issue of Power & Motoryacht magazine.