Gyro Stabilizers
The Mitsubishi MSM control moment gyro (CMG) applies the same principles of gyro-dynamics as the Seakeeper gyro, but the application is much less sophisticated, and therefore, less useful and effective.
The most important difference is that the Mitsubishi gyro spins its flywheel at ambient air pressure, which because of air friction, limits flywheel speed and requires substantial electrical power to overcome that friction. The Seakeeper Gyro, by contrast, spins its flywheel in a near vacuum. The result is that air friction is eliminated, thus greatly reducing power consumption and allowing a faster turning, lighter flywheel that reduces weight.
In addition, the two devices are controlled differently, resulting in substantial differences in effectiveness. The Mitsubishi gyro is regulated by a passive damper, which requires that it be “tuned” to one optimum point of sea states. Conversely, the Seakeeper product is actively controlled by state of the art motion sensors and processors, with the result that the full output of the gyro is available in the lowest and highest sea states, resulting in much greater effectiveness over a range of conditions.
Finally, the Seakeeper vacuum containment provides a durability advantage because it isolates the most critical components (flywheel motor and bearings) from salt air and other contaminants entirely -- a unique advantage for a marine product.
Despite these advantages, the Seakeeper Model 7000 gyro stabilizer is about two-thirds the cost (per Nms) of the Mitsubishi MSM-4000.
It should also be noted that there is a difference in philosophy between Mitsubishi and Seakeeper, probably rooted in the difference in the relative effectiveness of the products. Mitsubishi’s recommended sizing (by Nms) of its gyros to boat size is about 1/2 to 1/3 of what we would advise. Our goal is to virtually eliminate boat roll as opposed to the Mitsubishi approach of achieving some roll reduction.
The table below summarizes the comparison between Seakeeper’s Model 7000 Gyro and Mitsubishi’s MSM-4000 Gyro.
| Model |
MSM-4000 |
Seakeeper-7000 |
|
| Type Control |
Passive |
Active |
Active provides better performance over a wider range of sea states |
| Angular Momentun |
5000 N-M-S@3,500rpm |
7000 N-M-S@10,000rpm |
40% higher provides 40% more roll reduction force |
Dimensions
(WxHxL)(Volume) |
100 x 70 x 70 cm
39.3 x 27.6 x 27.6 in
490,000 cc
29,902 cu. in. |
80 x 98 x 67 cm
31.4 x 38.7 x 26.5 in
525,280 cc
32,202 cu. in. |
Comparable size even with 40% higher angular momentum |
Power Consumption
Run/Spin-up |
3.0/4.3 kW single ph |
1.5 to 2 kW/3.0 kW single ph |
50% less run power even with 40% higher angular momentum |
| Weight |
700 kg
1,540 lbs |
455 kg
1000 lbs |
Almost 40% less weight even with 40% higher angular momentum |
Fin Stabilizers
Fin systems are speed dependent, always balancing fin size with projected cruising speed, so as to create minimum drag for desired performance. The result is that at zero speed they have no effect, and at less than cruising speed, performance drops off sharply. In contrast, the Seakeeper Gyro remains fully effective from zero speed right through planing speeds, including the roughest conditions when the boat has to slow down. Because the gyro requires no protrusions from the hull, it is not subject to snagging seaweed and flotsam or to damage from grounding.
