As was discussed in the Theory of Operation section, the roll reduction capability of the gyro is directly proportional to the magnitude of its angular momentum.
The flywheel is spun by a brushless DC motor. The motor must overcome two forces to spin the flywheel; bearing friction and air friction. By spinning the flywheel in a near vacuum, we effectively eliminate the power needed to overcome air friction which allows us to spin the flywheel at a much higher speed. The higher the speed the smaller the flywheel since angular momentum is proportional to speed.
Note that the power required to overcome air friction increases as the cube of the speed. Power required is also proportional to the density of air.
The density of air is proportional to the air pressure so dropping the air pressure drops the density of air.
Until the Seakeeper Gyro, air friction from the spinning flywheel was the limiting factor on how fast the gyro flywheel could be spun, driving up flywheel weight and power requirements. Thus the Seakeeper Gyro spins three times faster than comparable products, cutting flywheel weight by two-thirds and halving power requirements. Moreover, because the critical components (flywheel bearings and motor) are sealed for life in a near vacuum containment, they are forever isolated from the marine environment. In addition, cooling requirements are less, both because there is less heat and it is easier to dissipate.
