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Everything You Ever Wanted to Know About Marine Stabilizers

On an Even Keel

If you’ve ever been tossed around on a boat, you know what an asset a good stabilizing system can be. And luckily, these days, there are more ways than ever to keep your yacht from rockin’.

StabilizersIf you’ve ever been seasick, you likely won’t soon forget the feeling. And if you’ve never been seasick, consider yourself among the lucky. Seasickness is perhaps the worst effect of a rolling, unstable boat, but it’s not the only one. Broken dishes, inability to move around onboard, and even serious falls can result from a boat that’s being tossed about. Which is precisely why marine stabilization systems are big business, with several manufacturers constantly competing to figure out the best way to keep your boat stable and able. I recently spoke to some of the leaders in the industry to see what their systems can do for you.

Still Waters
Jeff Smith is the captain of a fully custom 80-foot Weaver sportfish. He was in charge of building the boat for her owner, and knew that he had to put a premium on cruising comfort. He decided to do so by installing Seakeepers, and he hasn’t looked back. “The Seakeepers are fantastic,” he says. “I would never build another boat without them. I use them when we’re underway, trolling, and at anchor. At anchor in a harbor, with a 1- to 2-foot chop you can’t feel a thing. It’s amazing, really.” Hard to find a better endorsement for a product than that.

Perhaps one of the most common types of stabilization systems we see onboard boats that we test is the gyro stabilizer from Seakeeper. And I can tell you why that is from experience: They work. But how?

“Simply put, we’re spinning a flywheel at a high rate of speed inside a vacuuming encapsulation, and like any spinning mass it wants to maintain its orientation,” explains Andrew Semprevivo, director of global sales at Seakeeper. “So as the boat rolls, the gyro tilts fore and aft, which is called precession—that’s a physics term [Editor’s Note: Get used to it]—and it does this as it’s spinning, which creates torque that pulls up on starboard and down on port, or vice versa, and that in turn reduces roll.”

Seakeeper stablizer
Seakeeper uses a flywheel and the torque it generates to keep boats from rocking too much.

An internal electronic sensor detects the waves coming in and adjusts the speed of the gyro’s precession, and effectively its torque, meaning your boat negotiates the ocean’s surface like a surfer adjusting his body to meet boils on the face of a wave.

Seakeeper, which has a majority market share for gyro stabilizers (Mitsubishi is another major player), claims it can reduce roll 70 to 90 percent at rest. It has two models—neither of which are particularly light—the 8000 (which weighs 1,200 pounds) and the 26000 (which weighs 2,900 pounds). Depending on the size of your boat, you may need more than one. One 215-footer with a Seakeeper installation required five 26000s. That might sound like a lot of added weight, but for the people onboard in a rough sea, I’d guess it was worth every ounce.

Imtra stabilizing fins.
Imtra utilizes horizontal planes to add extra leverage to its highly able stabilizing fins.

The other main technique for stabilizing boats is, of course, to use fins. And perhaps nobody does fins better than Naiad. Naiad is a company that makes a whole range of motion-control devices, for military, commercial, and pleasure boats alike. However for monohull yachts, it recommends its well known and well respected fin stabilization system. Which is pretty much exactly what it sounds like. Fins on either side of the boat stick out into the hull envelope, which is the area of water that would be contained if lines from a boat’s keel and gunwale met to form a right angle below the water.

Charles Egan, Naiad’s technical documentation engineer, says that from there “an electronic motion sensor [detects] even the slightest bit of movement in the water and commands the fins to rotate accordingly. So, for example, if the boat’s rolling to starboard, the fins will turn counterclockwise to counteract that motion.” The fins can be used underway, where they can reduce roll up to 90 percent, or at rest, where the reduction is closer to 70 percent.

Quantum’s XT system utilizes expandable fins in the hull envelope to keep the boat steady at rest or underway.

At the moment, Naiad is adapting a system used on high-speed ferries to the leisure market. Those fins are curved and hang off the transom of a boat, effectively controlling roll and pitch despite being quite small. Of course, they work best at speeds of 20 knots or more, so their potential owners will be self-selective, but the possibilities are quite exciting. As is something just a wee bit on the smaller side.

Humphree Interceptor
Humphree Interceptors are a lightweight and compact option for faster, sportier boats.

Humphree is a Swedish company that delivered its first Interceptor stabilization system to an Italian ferry in 2000. Like Naiad, it services the military, commercial, and pleasure market, and is notable for the size range of the boats it works with: up to 400 feet and up, as well as the compact nature of its stabilizers. A little less than three years ago Humphree USA set up shop in Virginia Beach, and since has worked with companies like Volvo Penta, Lazzara, Merritt, Viking, Marquis, and others. 

Kent Lundgren, president of Humphree USA explains, “The way the interceptor works is we mount one on the back of the transom—the size depends on the size and shape of the transom. We do a fair amount of custom-fit jobs that will fit any shape you want. It’s a flat surface and the blades move up and down on some glide surfaces inside the Interceptor. When you push it down hydraulically it creates pressure ahead of the plate which provides lift. We do the same thing as a conventional trim system, we just do it more efficiently, because we create less drag than some other systems.”

Quantum’s MagLift system
Quantum’s MagLift system uses spinning cylindrical tubes and the Magnus Effect to keep a vessel on the level.

Humphree also does it with less weight. The plates are only .25 to 3 inches tall, so whereas other systems can weigh 1,000 pounds or more, an Interceptor only weighs about 100 pounds. Obviously—because of its size and placement—the system works best for fast-moving boats, but if you’re a weight- and speed-conscious owner, a Humphree Interceptor might be exactly what the doctor ordered.

For some guys, simple is just never enough. And when it comes to mechanical wizardry, its hard to beat Quantum in the marine stabilizers racket. The company has two main products it sells on the leisure market. The first is its XT system, which is a retractable fin that works both at speed and while the boat is stationary. At speed the fin resides in the hull envelope, helping to reduce the relatively minimal roll most boats feel while propelling forward. Yet when the boat stops, or is moving slowly—and is therefore more susceptible to roll—the fins extend out, allowing themselves more leverage in the battle against the waves.

The other system Quantum builds is MagLift. Though it can be put on smaller boats, it’s more common on true megayachts, betweem 180 and 500 feet. (Perhaps because the cost extends into the millions.) As Quantum’s sales manager Mark Armstrong explains, “Quantum’s MagLift Zero Speed and Underway stabilizer is essentially a spinning cylinder. It works like a curveball and is based on a theory put forward by Gustav Magnus and sir isaac newton. The cylinder protrudes at 90 degrees to the hull and spins from 300 to 1500 rpm (depending on system size), and as water flows over the cylinder, you get what’s known as the Magnus Effect. Essentially the pressure difference created produces a very powerful lifting force. It’s very much like an airplane wing in a sense.” You get all that?  

Perhaps the company best situated to take a run at Quantum for sheer scientific exactitude is Side-Power, which is imported by Imtra. Side-Power prides itself on its advanced technology, and rightfully so. The company won the overall innovation award at the 2014 Marine Equipment Trade Show in Amsterdam, namely because they’ve taken standard fin technology and flipped it, so to speak. Phil Whittaker, large yachts specialist and product manager with Imtra, explains: “What we did that was different on the fin side, is our fins are curved in a more horizontal position. And what that does in effect is make the lift more vertical. And if you reduce the horizontal force the fins create you reduce their side effects—the sway and the yaw that you can see with some systems. We reduce wasted effort, essentially, and saw sway and yaw numbers drop somewhere between 30 and 50 percent.”

The Side-Power fins have reasonably sized actuators that stow easily in the boat’s hullsides, work at all speeds, and—get this—because they essentially create another plane that adds lift, Whittaker says they can even increase fuel efficiency as well. That’s a versatile piece of equipment to be sure, and one you’d do well to investigate on your own.

Should you choose any of these producers of stabilizing equipment—or for that matter ABT-Trac, a California based company known for durable and technologically advanced products—you should be in good hands. With a little bit of a legwork you can find the perfect system for your boat that will keep her steady, ready, and raring to go.

This article originally appeared in the August 2014 issue of Power & Motoryacht magazine.

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