Pendulum Stability

Fins don't work at a dead halt, for sure, but so long as there's any forward momentum a properly sized set can do pretty well.
The cost of gyros is not only the wheel itself, but also the actuators, the control system, the mountings, etc.... all of which would be needed in ANY moving-mass damping system.
Consider also the speed of the roll- and thus how quickly the device must be able to move to counteract it. Fins only move a few degrees, tens of degrees maybe, and they're balanced so the actuator doesn't apply much force. A counter-swinging pendulum would have to swing through a pretty big arc to be effective, and it would have to swing through that whole arc in a couple of seconds tops.

 

Yes you're right but SWATH is a better concept for those sort of aplications since they accommodate some of the vertical component.

The problem with small boats is that they have a relatively high frequency dynamic response to a complex sea state.

shifted mass systems would need both low and high frequency response they need damping and tuning to the vessel , and would only work for certain ranges of frequency. Inevitably you will get a positive feedback for some sea states neccesitating the locking of the system. But oh.. the complexity.

Look up SWATH

 

Shifting Weight

The response of the small boat to shifting mass is probably complicated. For example, while sailing a very small dinghy, if it starts to heel I hike out further. But for that instant that my torso is moving outboard and my abdominal muscles are relaxed, the hull is actually UNLOADED. The boat will heel even more until I tense my muscles, put on the brakes, and lock the mass in the outboard position. Then, gravity will take over and the boat will right itself.

In Poida's inventions, the work to push the mass uphill will actually act to heel the boat somewhat further downhill (for a few seconds).

Or, am I all wrong about this?

 

Your body movement is a mechanical movement. A lever & fulcrum solution. BUT... if the solution was hydraulic there would'nt be the inertia ossue would there?