Voyager 2.0 Self Trimming Wingsail Behaviour - Instability and Oscillation
When the Self Trimming Wingsail on a monhull is caught in irons (head to wind) it is prone to severe oscillation as depicted in the video below.
There’s a number of factors that may affect this, and some testing needs to be done isolate these factors.
Reduce the Rotational Inertia of the Wingsil Assembly.
The rotational inertia of a body is related to the mass x radius squared. Hence, the static balance could be maintained by doubling the counterbalance mass, reducing its distance on the counterbalance arm to half. This change would have the effect of halving the rotational inertia.A test to see if this change reduces the instability is reasonably practical to perform.
Monohull versus Multihull
Many Self Trimming Wingsail implementations are done using Multihull vessels. Multihulls have much different stability curve compared to a monohull. A Multihull exhibits maximum stability at zero angle of heel, which is completely the opposite of a monohull which has zero stability at zero angle of heel, and progressively increases as the angle of heel increases reaching a maximum at 90 degrees.It’s possible that the effect is not apparent in Multihull because they are so stable at low angles of heel.
Lower the Centre of Effort
Lowering the Centre of Effort of the sail may reduce the rolling effect. This could be done by tapering the sail shape with a reduced chord length at the top compared to the bottom of the sail.Avoid Going Head to Wind
One way to avoid the situation is to always perform a gybe when changing tack.This has been the most effective solution, by far.
Avoid Going Dead Downwind
It turns out that heading dead downwind can result in the same rolling effects as pointing too high.
Hence, its important to tack downwind, and avoid sailing too square.
The rolling effect while sailing downwind is not as pronounced as when sailing too high to windward. The boat can still sail downwind while rolling, but it is likely that the rolling effect could induce unnecessary wear and tear on the vessel and the rig.
Also, although I haven't verified it by preparing polar performance diagrams yet, but its likely to be faster to tack downwind.
Update...
Wingmill, Flutter Pump or Oscillating-Wing Power Generator
It turns out the instability that a monohull with a wingsail can exhibit, can be used for benefit.
The oscillation effect can be used for devices such as pumps, as demonstrated in this video:
The oscillation effect can be used for devices such as pumps, as demonstrated in this video:
Note: This is part of the ongoing development of a low cost autonomous oceangoing sailing drones, utilising a self-trimming wingsail. This is the Voyager series of sailing drones.
