The Corry Jib Windmill

[wdyasq]

Here are some renderings of the Corry Jib Windmill, as I remember it.  As I recall, Will Corry built some prototypes and patented it in the late 60's or most likely the early 70's.  It was developed after a trip to the South Pacific Will took on a 28' Gaff-rigged Cutter.

The sails furl on rollers as the speed increases and, not shown, springs unroll the sails in lower wind. The black balls are weights that slide out due to centripetal forces.  I can't remember how the sheets are trimmed. Will pulled energy off an old truck differential on one model and with tires and friction on the outer rim on another IIRC.

In a conversation Will stated although he patented the device, it was a US patent and would not be worth patenting where the power was needed and would not be built where the power was cheap - as in the US at that time.  He pined the money would be better spent building another boat as opposed to enriching patent attorneys.

Ron

[Ungrounded Lightning Rod]

Ah, the "self-tacking jib" approach.

Downside is that each sail will "jibe" once per revolution - make a sudden swing from one side to the other with the wind behind it, building up considerable momentum before snapping the "sheet" (the line limiting its travel and transferring much of the thrust to the supporting structure) tight.  This energy is dumped into the line and support fittings themselves and dissipated there.

On a boat, and accidental (uncontrolled) jibe in a high wind can break the fittings, boom, or mast,  tear the sail, rip the mast out of the pulpit, possibly even damage the hull enough to sink right there as the mast is torn free.  A controlled jibe requires taking up the sheet against the force of the wind, which uses energy.

On this thing the lines and frame should be strong enough that things shouldn't come apart right away (except in a very high wind).  But I expect the constant snapping-tight will quickly wear out the sheets, and also the sailcloth, especially near the grommets.  Probably broken sheets first, torn sails after a couple sheet replacements.

Also:  It will be LOUD.  WHAP!  WHAP!  WHAP!  ...

A boom brake might help:  That's something like a cylinder on the boom with a couple turns of rope around it, with the other ends tied to the frame a bit beyond the ends of the boom's travel.  The faster the boom moves, the more the line tightens, and the higher the friction, regulating the speed of the boom's motion.

But a lot of your energy will go into friction on the boom brake - again wearing out the components, and NOT helping turn the genny.  IMHO if you're going to do something like this you need to figure out how to get that energy into generation rather than component wear.

[Ungrounded Lightning Rod]

Hmmm...

Looks like no boom on this.  That improves things a lot.  But I still want to see how the sails get from one side to the other on the jibe part of the cycle (lower-right in your diagram).  If it's just loose cloth it will flap and rub, again wearing out, stretching, eventually ripping.

[wdyasq]

Won't wear out on mine... I'll never build one.  I had comented on the mill and someone had said they could not find any information.  I put it here from memory and for information.  I tend to agree with most of your points.  It might be interesting to build such a beast and wear it out.

Ron

[finnsawyer]

It appears that the sails would naturally prefer to be delivering power inboard (Start with the one at five o'clock and follow it till it reaches the top).  At the top it will tend to snap out briefly, but won't stay there.  As the mill turns it will feather and the be blown back to the inside.  Therefore, it seems that one can simplify the design and make it automatic.  No weights or furling.  Also, the sails could be replace with curved sheets of a rigid material.

[Ungrounded Lightning Rod]

The problem occurs when a sail goes from six o'clock to five o'clock.  At six o'clock it's fully powered on one side, and at five o'clock it is fully powered on the other side.  To make the transition it suddenly snaps from one side to the other, picking up momentum which is dumped by yanking against and stretchnig the line that limits its travel - and also yanking against the place where the line is attached.  This stretches the rope and sailcloth (or whatever), and on any given cycle is likely to dump the energy by breaking a few fibers in the line or sail or distorting the sailcloth and line, rubbing thread against thread or fiber against fiber, sliding fibers aginst each other to permanently lengthen the thread or line, and heating the material.

Substituting metal for cloth increases the mass (and thus the momentum, and thus the energy that must be dumped by jerking the line and bending the metal).  It also removes the ability to make a slow transitin by letting the cloth collapse and rub against itself in a fold.