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Are Stabilizers Used on Commercial Vessels?

The commercial marine industry has been using stabilizer systems for ages in the form of paravanes, gyros, fins, ballast transfer and other systems. While roll stabilization on pleasure craft has been around for decades, the concept has taken-off in the past five years. These days, virtually all higher-end monohull yachts are built with some form of stabilization – from active interceptors to gyros to fins.

Old School Gyro

Gyros have been around for decades on warships and passenger vessels, but the recent boom in pleasure yacht gyro stabilizers is essentially the result of SeaKeeper’s introduction of vacuum enclosed flywheels. Other companies like Quick, Mitsubishi and Veem offer related products. Gyros are extremely effective for vessels in displacement mode, though they lose their effectiveness as vessel speed increases, in particular once a vessel gets up on a plane, exceeding its theoretical hull speed. Fins, on the other hand, become exponentially more powerful as speed increases.

Naiad Dynamics, Kongsburg, Quantum and others supply sophisticated retracing and non-retracting fin stabilizer systems for commercial and large pleasure craft. Retracting fin stabilization is powerful and effective, but it’s expensive and essentially needs to be installed during the build process due to the extensive hull modifications. The other primary difference is that retracting fin stabilizers typically extend outside the beam, whereas non-retracting typically remain within the maximum beam of the vessel. Non-retracting fin stabilizers are built by many manufacturers such as ABT, Naiad, Quantum, BCS, Wesmar, Side-Power, and others, and most now offer “any-speed” stabilization which basically means both underway and at anchor.

Retractable FinCruise Ship Stabilizer

Side-Power Vector Fin Stabilizers

Side-Power, the Norwegian company well known for bow and stern thrusters, offers a stabilizer solution for commercial vessels in the 45-130’ range. The product is called Vector Fin Stabilizers. These are hydraulic, non-retracting fin stabilizers that provide exceptional performance at “any speed” through their unique curved fin shape. The primary difference between a conventional flat fin and the curved Vector fin is the shape. The curved vector fin provides about 30% greater performance by directing the stabilizing force more vertically than a conventional flat fin. Retracting fins, mentioned above, direct their stabilizing force vertically, which is ideal, but in order to do that, the fins must be oriented horizontally. In most cases, this means they project outside the beam of the vessel. They are mounted in the hull at the chine so as to be as low as possible (in order to remain under water), while still on the side of the ship. When the ship is docking or in similar situations, the fins are retracted.

For non-retracting fins, mounting outside the vertical envelope of the ship is impractical, so they are mounted on the bottom of the hull instead, where they remain inside the beam. The problem with this is that they lose effectiveness, especially as the hull angle reaches 0 degrees of deadrise. A straight fin projecting perpendicular to a hull with zero degrees of deadrise becomes little more than a rudder. It would provide virtually no useful stabilizing force – no vertical force. Conversely, the greater the angle of the hull where the actuators are mounted, the more effective they become.

The Side-Power Vector fin is designed such that the face of the fin is curved between roughly 38 and 54 degrees (depending on size). This means the stabilizing force is directed as much as 54 degrees vertically, and that angle increases with every angle of deadrise. The ideal force angle is 90 degrees, but as discussed above, that’s only possible with fins mounted perpendicular to the side of the boat – or if Side-Power Vector fins are mounted on a curved or angled part of the hull, such as that shown below.  In this case, the forces are almost vertical, and thus almost ideal.

Commercial Curved Fin

So, the curved face of a fin mounted on the hull running surface becomes far more effective than a straight fin. And by keeping the fin within the vertical envelope of the hull, there is no danger of damage while docking or maneuvering.

The fin stabilizers are powered by hydraulic actuators – typically two hydraulic rams rotating a yoke which is splined to the top of the fin shaft passing through the hull. The actuators are welded or glassed into the hull, depending on hull material of course. Side-Power actuators typically operate at about 1400 psi at with a flow rate of between 9 and 17 gpm depending on size. This fits in well with the hydraulics on most fishing vessels, so can easily be integrated into an existing hydraulic system.

Actuators

For more information on Side-Power stabilizer systems, please contact Imtra at info@imtra.com, or call us at 508-995-7000

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