Servo-controlled fins have long been the most popular and proven method of minimizing the roll of the sea, but they’re not the only solution. Gyrostabilizers are becoming common in the luxury recreational marine market, and now manufacturers are beginning to move them into the commercial maritime industry â€” even though the technology has been around for nearly a century.
Fin-controlled anti-roll systems can be effective under certain conditions, but come at a cost: Mounted to the outside of the hull, they can snag seaweed or be damaged by grounding and create drag that affects fuel economy. They’re also speed-dependent and nearly useless at anchor or below cruising speed.
Gyrostabilizers work at almost any speed and have no parts external to the hull. They’re essentially made of two parts â€” a mass rotating on an axle and a gimbal, or external support ring.
|A Mitsubishi gyrostabilizer. The first gyrostabilizers were made for the military a century ago. In recent years they have become popular in luxury recreational vessels. (Photo courtesy Mitsubishi Heavy Industries)|
The axle, which is mounted to the gimbal, rotates at about 90º to it, and the gimbal is mounted to the hull’s stringers. Relying on the physics of angular momentum, the gyro directly opposes the force causing the roll by applying torque to the hull.
Maryland-based Seakeeper and Mitsubishi Heavy Industries are the two big players in the maritime gyro market. Both got their start outfitting luxury yachts, and until recently, Mitsubishi’s product was available exclusively through Italy’s Ferretti Group. That contract has ended, and their gyros, like Seakeeper’s, are now available on the open market.
The first large-scale maritime gyroscope was installed in a U.S. Army ship in 1917, and they were used later in some trans-ocean liners, but the technology fell out of favor. Mitsubishi brought an updated version, the Anti-Rolling Gyro (ARG), to the maritime market in 2004. Seakeeper introduced its system a few years later.
Both companies bring a different approach to the design. Not surprisingly, both sides say their system is the preferable option, but the reasoning behind the designs shows a difference in philosophy.
Seakeeper’s flywheel, which is the rotating mass, spins in a vacuum to eliminate air friction and cut down on power consumption. Mitsubishi’s spins at ambient air pressure instead, and uses a passive damper system.
“The gyro creates energy that’s absorbed and released in the form of heat, and that heat needs to go somewhere,” said Rick Olson, whose Davie, Fla.,-based American Spin Doctors is the U.S. distributor for Mitsubishi’s ARGs. “We dissipate ours through free air.”
Because Seakeeper’s gyro spins in a vacuum, it can’t dissipate the heat through the air, so it relies on a cooling system. Brook Stevens, inside sales coordinator for Seakeeper, said the vacuum protects the flywheel motor and bearings from salt air and other contaminants, prolonging the life cycle.
There’s no manual input required for either gyro, except to turn them on and off, and there are no exposed moving parts. Both take up to about 45 minutes to reach full speed once they’re turned on, and require a genset or shore power to run.
Seakeeper uses a hydraulic active control system instead of passive dampers.
Olson said Mitsubishi’s early gyros used a similar system, but company engineers moved away from them in favor of simplicity. “A gyro naturally tries to maintain a vertical position,” he said. “You don’t need to do anything to it.”
Stevens said the active control mechanism adjusts the gyro in varying seas for optimal performance, and as a result, the company claims a 60- to 80-percent decrease in roll, compared with Mitsubishi’s claimed 50 percent.
But Olson said that, considering cost effectiveness and comfort, anything more than 50 percent is overkill. “It depends on how much gyro you want to put on the boat, but the target is about 50 percent,” he said. “It’s unbelievable the stability you get at 50 percent. That’s the most comfortable, affordable and effective.”
With the Ferretti contract ended, Olson said Mitsubishi is looking at new markets from sport boats to work boats. Similarly, Seakeeper recently began to expand from the recreational market into commercial and military markets, and recently hired a manager to increase that side of the business.
“We’re just sort of breaking into that sector,” Stevens said. The company’s gyros are used by the U.S. Navy, and the company recently installed one in the first production hull of an unmanned surface vessel designed for the military.
As he sees it, the potential benefits of gyrostabilization in the commercial maritime industry is clear. “The military term is â€¢fit to fight,’ which means you want your soldiers to get where they’re going in good condition, ready to go,” he said. “For commercial use, the safety issue is a big one â€” with so many guys basically living on board, we can eliminate seasickness and fatigue.”
But are gyros feasible or cost effective for the market? To some extent, that remains to be seen.
Seakeeper’s gyros come in two sizes â€” the smaller weighs 1,000 pounds and provides roll reduction for vessels with a full-load displacement of up to about 27 tons. For vessels up to about 90 tons, a single larger unit â€” which weighs about 2,900 pounds â€” will suffice. Multiple units can be combined to meet a vessel’s needs. The smallest is listed at $84,000 and the larger at up to $190,000, Stevens said, though those are MSRP and probably higher than dealer prices.
Mitsubishi offers three different sizes. The smallest covers a displacement of up to about 15 tons and the largest up to about 60 tons, though multiple gyros can be combined for larger boats. Olson said Mitsubishi’s smallest sells for about $42,000 and the largest for up to about $114,000.
“We’ve quoted for 300-ton boats,” Olson said. “In Japan, they first put these gyros on government boats, especially pilot boats. This greatly improves the safety for the guys working on them.”