Rob:
My rig of choice is the Aerojunk.... which I've mentioned before. It is a split rig, with fore and aft sails with a split at the mast. The sail panels are flat fabric, and derive their shape from the batten cage, but are merely tied into the cage, rather than battens running in sewn pockets. The batten cage itself shifts side to side from tack to tack such that the mast is not in a position to disrupt airflow over the sail. It has all the advantages of a junk rig.... light sheet loading, instant reefing without having to tie in reefs or use furling hardware, just collapsing like a Venetian blind, doesn't flog, can be reefed while under power, has no sail track or cars, doesn't require winches, vang, traveler, etc, and the flat sails can be made by anybody, so they are inexpensive and easily replaced. It also can be a more or less rectangular rig, which puts far more sail area up higher with a shorter mast than is possible with a triangular sail. It's much like your Ballestron or Aerorig, in that both fore and main sail tack as one, but it does not require a pivoting mast, nor does the sail need to be held in tension to achieve it's shape. In short it's everything I want in a rig. It may not be the ultimate rig in efficiency...... drive for sail area.....or lift drag ratio, but a rectangular sail puts double the sail area up that a triangular sail does, all else being equal.
I've been toying with a variant (on paper), which has a third sail element that actually utilizes the mast to create a streamline airfoil shape, but is not neither wrapped around the mast or attached to it. This creates a 3 element two slot rig. The central sail element consists of two panels joined at their trailing edges, but with some gaps for air leakage. The leading edges run quite close to the mast, close enough that they capture the air spilling around it before it can develop that classic tumbling turbulent wake, some going into the space between the two elements, and some flowing around them. It's well known that the sides of a round object turn inward too steeply for airflow to follow, resulting in turbulence developing. It's also known that on something like a car door, if the gap is flush, in other words the two edges in alignment, it will create turbulence. If the second surface is below contour, it is worse, and if the second surface sticks out slightly there is less developed turbulence than if the two surfaces are in perfect alignment. These sailcloth panels being slightly out should both capture some inflation air, and streamline the flow over the outside. They would be tensioned by being attached just as the other sail panels are, to the battens.
This idea is just at the "napkin drawing" & mental exercise stage, but the idea is to eliminate the issues with soft wing sails, while offering the benefit of some streamlining of the mast. You wouldn't for example have a wet sail clinging to the mast as you struggle to drag it down. It's worth noting that Pete Hill went from a half cage bastardization of the Aerojunk concept to soft wing sails, and finally to a more or less true to design Aerojunk sail on Oryx. There really is nobody else in the sailing world as far as I know who builds and experiments at this level while global voyaging. Pete's hall of fame status is well earned.
H.W.
On 06/09/2018 07:52 PM, Rob Denney harryproa@gmail.com [harryproa] wrote:
My rig of choice is the Aerojunk.... which I've mentioned before. It is a split rig, with fore and aft sails with a split at the mast. The sail panels are flat fabric, and derive their shape from the batten cage, but are merely tied into the cage, rather than battens running in sewn pockets. The batten cage itself shifts side to side from tack to tack such that the mast is not in a position to disrupt airflow over the sail. It has all the advantages of a junk rig.... light sheet loading, instant reefing without having to tie in reefs or use furling hardware, just collapsing like a Venetian blind, doesn't flog, can be reefed while under power, has no sail track or cars, doesn't require winches, vang, traveler, etc, and the flat sails can be made by anybody, so they are inexpensive and easily replaced. It also can be a more or less rectangular rig, which puts far more sail area up higher with a shorter mast than is possible with a triangular sail. It's much like your Ballestron or Aerorig, in that both fore and main sail tack as one, but it does not require a pivoting mast, nor does the sail need to be held in tension to achieve it's shape. In short it's everything I want in a rig. It may not be the ultimate rig in efficiency...... drive for sail area.....or lift drag ratio, but a rectangular sail puts double the sail area up that a triangular sail does, all else being equal.
I've been toying with a variant (on paper), which has a third sail element that actually utilizes the mast to create a streamline airfoil shape, but is not neither wrapped around the mast or attached to it. This creates a 3 element two slot rig. The central sail element consists of two panels joined at their trailing edges, but with some gaps for air leakage. The leading edges run quite close to the mast, close enough that they capture the air spilling around it before it can develop that classic tumbling turbulent wake, some going into the space between the two elements, and some flowing around them. It's well known that the sides of a round object turn inward too steeply for airflow to follow, resulting in turbulence developing. It's also known that on something like a car door, if the gap is flush, in other words the two edges in alignment, it will create turbulence. If the second surface is below contour, it is worse, and if the second surface sticks out slightly there is less developed turbulence than if the two surfaces are in perfect alignment. These sailcloth panels being slightly out should both capture some inflation air, and streamline the flow over the outside. They would be tensioned by being attached just as the other sail panels are, to the battens.
This idea is just at the "napkin drawing" & mental exercise stage, but the idea is to eliminate the issues with soft wing sails, while offering the benefit of some streamlining of the mast. You wouldn't for example have a wet sail clinging to the mast as you struggle to drag it down. It's worth noting that Pete Hill went from a half cage bastardization of the Aerojunk concept to soft wing sails, and finally to a more or less true to design Aerojunk sail on Oryx. There really is nobody else in the sailing world as far as I know who builds and experiments at this level while global voyaging. Pete's hall of fame status is well earned.
H.W.
On 06/09/2018 07:52 PM, Rob Denney harryproa@gmail.com [harryproa] wrote:
No pics (yet) and no previous posts. The idea is to progress the Bucket List rig which had no mast bearings, sail track or batten cars, but required more strings and tension than was desirable, and had the unstayed mast drawback of extra windage and disruption at the front of the sail. Neither is a deal breaker, but it would be nice to eliminate them.
So, the next step was a sail and fairing which are free to rotate, but the fairing automatically aligns with the apparent wind when the sail is sheeted on, giving an aerofoil shape. To test this, I needed a mast, which was a good excuse to try a simplified build system, which has produced three pieces of tube which are being joined together, and one piece which is in the bin.. The build system worked well, and will now be in the plans. One of the benefits of a fairing is the mast does not need to taper. A non tapered mast is lighter, stiffer, easier to lay up and has less wastage.
The 3 main challenges with soft/partial wing rigs are i) weight, ii) controlling twist, which on a fast boat should be minimised and iii) stopping the leading edge deforming.
At the same time, we had an idea for lighter, simpler rudder mounts which would apply to all the boats, so this had to be tested as well. The first attempt showed they would work, but that modified ogival sections were not ideal, despite being easy to build.
Current status is I am building Speer foil blades which will go in the new mounts once they are modified to fit. I have built a test piece of fairing, which worked, but the build method won't scale up very well. I'll try another piece this week. The mast is in 2 pieces, soon to be one. I have an old rectangular sheet of unshaped dacron which will do for the sail. The mast will be mounted mid tramp, the same as on the Volvo proa http://harryproa.com/wp-content/uploads/2017/10/volvoproa.pdf. Not because it is better than in the lee hull, but because it is interesting and opens up some possibilities not available with in hull masts.
I would have liked to do all this on Bucket List, but experience has shown that all experiments should be done on the smallest boat available, which is Elementarry.
More as it happens.
On Sun, Jun 10, 2018 at 12:43 AM, '.' eruttan@yahoo.com [harryproa] <harryproa@yahoogroups.com.au> wrote:
Rob Denny said;
| I am experimenting with 'safe', cheap wing sails.
| Mast method looks good and will be in future plans, although yesterday's effort was a shortcut too far and is in the rubbish.
This is to make it easier to find the info on these.
I have not found anyplace Rob has talked about this before. Can someone tell me what to search for? Whats he talking about?
He promises pics eventually, so yay! Has he ever posted any?
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Posted by: StoneTool <owly@ttc-cmc.net>
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