Busting Gyro Myths
Gyro Myth 1
Angular momentum alone defines the stabilizing performance of a gyro stabilizer
In fact, just as important is the way in which precession motion is controlled. The major considerations that define the performance of a gyro stabilizer are: flywheel angular momentum, the precession range allowed, the maximum precession rate allowed, and the ability of the gyro stabilizer to maintain full precession range when vessel rolling rates are low. All of these considerations are handled differently by the various vendors of gyro stabilizers. Understanding exactly how each unit works will allow the most informed selection of the best gyro system for your application. A good place to start is to find out exactly how much stabilizing torque is generated across a range of rolling periods. This will unearth many of the considerations discussed above. It is also very important to understand what the operational envelope of the gyro stabilizer is. Will the unit continue to operate in rough conditions when you need it most? In what conditions (if any) will the unit shut down or de-rate to protect itself?
Gyro Myth 2
Actively driving the precession faster than proportional to rolling motion produces more stabilization torque
This is theoretically possible, but not a practical reality. The resulting uncomfortable harmonics introduced into the rolling motions of the yacht would create a significantly less comfortable experience for those on-board. Given that there is a finite range of precession available before the stabilization torque starts to increase rolling motion, if you accelerate precession motion through some of that range then you need to decelerate this motion somewhere else in the cycle. These accelerations can be felt by guests as ‘wobbles’ in the rolling motion that are hard for a human to predict and therefore make walking and general balance more difficult. So while it theoretically possible to do this, it is not a practical solution. If it sounds too good to be true…then it probably is.
Gyro Myth 3
Without the precession braking, no roll stabilizing torque is produced
In fact in very small waves where the gyro is not overpowered, a vertical axis gyro could work without any control system whatsoever. A horizontal axis gyro would also work a little, but the very high resistance to precession of the slew ring bearings used on these systems would significantly limit the stabilizing torque generated. Stabilization torque is not caused by the precession axis braking torque, it is caused by the precession oscillation rate combining with the angular momentum of the flywheel to generate torque in the roll axis. The precession braking is only applied to manage the precession motion to within a nominated precession oscillation range and in most cases also to limit the rate of precession oscillation so that the gyro torque created is effectively capped allowing the supporting structure to be designed to withstand a defined maximum level of load.
Gyro Myth 4
Gyros Must be Located On Vessel Centreline
Because a gyrostabilizer produces a pure torque, it can theoretically be located anywhere on the vessel. The stabilizing torque will always neatly oppose the rolling torque whether on or off vessel centre-line, or whether forward or aft.
To avoid high vertical accelerations that might shorten the life of the bearings, VEEM recommends that the unit(s) are located aft of mid-ships. However when required it is possible to locate them up to 70% of LWL forward of the transom.
So long as the overall mass distribution of the vessel is maintained, there is absolutely no performance disadvantage to locating the gyro(s) off center- line.
If the gyro(s) are located more than 2m above the waterline, please discuss this with VEEM. The flexible rubber isolation mounts may need to be transversely supported to prevent over-load.
In most cases, the convenience of electrical power supply and suitably strong supporting structure will result in the gyro being located within the engine room. This has the added advantage of enclosing the gyro within a noise lagged space. Where the gyro(s) are located outside of the engine room, noise isolation considerations should be addressed.
Gyrostabilizers can be conveniently located as far from the owner’s spaces as practical. This helps to eliminate annoying night-time noise, and to ensure that service technicians do not need access to the owners spaces.
So in summary, the gyro can be located:
• Up to 70% LWL forward of the transom
• Off centre-line
• Up to 2m above waterline
Gyro Myth 5
A spinning flywheel will provide stabilization even it it is NOT free to precess
In fact, a pre-1900 gyro stabilizer invention claimed to work without precession. This was eventually debunked and the invention discredited. The stabilizing torque is created by the combination of the flywheel’s angular momentum and the precession oscillation rate. If the flywheel does not precess, no stabilization torque is generated. This is how a gyro stabilizer can be turned OFF without stopping the flywheel from spinning. The precession oscillation axis is simply locked.
Gyro Myth 6
A spinning flywheel inherently wants to remain in its current position.
In fact a spinning flywheel does not have any inherent stability, or tendency to remain at its current orientation. As we have discussed above, a flywheel does have very specific gyro-dynamics that cause it to bend and applied torque through 90 degrees as a rate of precession, or to bend a rotational motion through 90 degrees as a torque. However there are many specific flywheel applications where the flywheel does provide a stabilizing influence. These include the spinning top children’s toy, the front wheel of motorcycle or bicycle, and happily, a marine gyro stabilizer. However each of these applications applies gyro-dynamics in a unique way, and is not related to any inherent stability of a flywheel, but the way that it bends torque through 90 degrees.