Cheers Larry.  I've had a few more thoughts re the issue of passive righting of a proa.  Rather than directly addressing your points I'll begin with a preamble.

Beginning by looking at existing in hull canting (i.e. the canting keel and canting foils on AC72's).  The brute force required for these active systems (working against the principal gravitational force) dictates hydraulics or some very clever engineering (or both).  The aim of the canting keel is to enable the monohull to sail more upright allowing hull shapes to be optimised and reducing the heeled rig down force.  I don't believe that you could convince me that this boat is still a monohull - forgive me for thinking that its an over-engineered imitation of a weight to windward proa, with the redeeming characteristic that stability increases as the boat heels (but does decrease again as the boat approaches knockdown).

Multihull hull shapes are optimised to sail bolt upright so the hulls are typically canted relative to the cross beam for craft that intend to fly the windward hull.  The foils and rig should therefore remain in the same plane as the leeward hull.

This preamble provides a couple of reasons why canting and righting are best effected in the crossbeams (if we are looking to gravity rather than buoyancy to provide the righting moment).  In conjunction with Rob's sheet release at 30 degrees heel, beam lock release at, for arguments sake 70 degrees (perhaps less if this is likely to throw the crew off the platform) could provide additional knockdown protection in a largely passive way.

I was slightly off track to suggest that the beam would return to its lock position passively once righted.  If the introduced cant is no more than say 20 degrees this may possibly occur (with body weight on the tramp), but must overcome the weight of the rig to leeward of the centre of buoyancy of the leeward hull.

The trapezoidal beams complicate the mater slightly as the hinges must be parallel and thus not perpendicular to the beam.

The idea of flexible beams scares me. I recall Rob's experience of breaking the Elementary beams when the windward hull slammed (can't recall whether this was due to a lull or backwind).  In order to have acceptable levels of fatigue, elongation of an epoxy matrix should be kept to something like 2%, if carbon is used in this matrix the limit is about 1%.  The beams would need to be very skinny.  I have some experience with engineering structures and finite element modelling, but gut feel is enough to caution me here.

For the sake pure speculation however I'll have a stab at it.  The crossbeams must be wide in section, shallow in draft and parallel.  Wide enough to prevent wracking of the plan form.  Shallow to permit flex around the axis of the lee hull.  Parallel to reduce torsional loads in an elongated cross section.  This craft would not fly the windward hull until a moderate angle of heel occurred.  Perhaps placing a lifting foil underneath the windward hull would enable drag reduction.  The real problem would manifest at a high angle of heel: the gravitational force that had flexed the beams would reduce as the angle of heel increased (in knockdown gravity would be almost pure compression along the beam).  The effect of the reduction in flex would be akin to a crossbow - a human catapult.  Say no more.

Regards,

David

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