Anonymous wrote:

I focus on the trailing edge...

Here we go again! David and Slieve agree on the importance of having a well rounded leading edge on the sail, this or the other way.

I am not so sure about that. The leading edge of my sails should then be aerodynamic nightmares:

·         On the port tack, the mast turns my sail into a flat junksail, made worse by the Hong Kong parrels.

·         On the SB tack, the sail is undistorted, but the big mast is standing proud in the wind.

Still, my boats with cambered panels points well, and the VMG to windward is less than 5% worse than in a well-sailed Bermudian sister boat.

To get the best out of my sails, I keep an eye on the leech telltales. With attached airflow on both sides, the telltales are standing fine, despite that distorted luff. Best of all; it is not difficult at all to keep the boat somewhere in the groove. The sail’s alpha-tolerance must therefore be OK.

It could be that the lack of the last 2-5% speed to windward is caused by my not-advanced (or primitive) leading edge. Still, I stress that the big gain in performance to windward (10 – 50%) is achieved when replacing a flat sail with the cambered one. Anyone who have sailed their boat with a flat sail and then with a ‘plain’ cambered one, will verify this.

Improving the airflow over the leading edge, and hiding the mast, may possibly provide the final 2-5% improvement. I wouldn’t expect more than that.

Arne

You are right Arne, keeping the leech telltales flowing means you angle of attack is ok. So that's the most important part of getting good performance. But by making the luff of the more tolerant for small windshifts (or negligence at the sheet) you would have even better performance as the sail would be more forgiving.

I do agree that the result of all this may be small, but in pointy sails all these small improvements together make the difference when racing. Cruising a very different game.

Rudolf

I focus on the trailing edge...

Here we go again! David and Slieve agree on the importance of having a well rounded leading edge on the sail, this or the other way.

I am not so sure about that. The leading edge of my sails should then be aerodynamic nightmares:

·         On the port tack, the mast turns my sail into a flat junksail, made worse by the Hong Kong parrels.

·         On the SB tack, the sail is undistorted, but the big mast is standing proud in the wind.

Still, my boats with cambered panels points well, and the VMG to windward is less than 5% worse than in a well-sailed Bermudian sister boat.

To get the best out of my sails, I keep an eye on the leech telltales. With attached airflow on both sides, the telltales are standing fine, despite that distorted luff. Best of all; it is not difficult at all to keep the boat somewhere in the groove. The sail’s alpha-tolerance must therefore be OK.

It could be that the lack of the last 2-5% speed to windward is caused by my not-advanced (or primitive) leading edge. Still, I stress that the big gain in performance to windward (10 – 50%) is achieved when replacing a flat sail with the cambered one. Anyone who have sailed their boat with a flat sail and then with a ‘plain’ cambered one, will verify this.

Improving the airflow over the leading edge, and hiding the mast, may possibly provide the final 2-5% improvement. I wouldn’t expect more than that.

Arne

Anonymous wrote:

Slieve wrote:The double surface wing sail, with its rounded leading edge has the potential to be more α-tolerant, as long as the rest of the airfoil can produce a good overall cambered shape. If it does not then there may not necessarily be an overall gain.

Overall it would appear that it is the leading edge shape that effects the upwash and allows the higher α-tolerance, so that seems to be the best area for experimentation.

Cheers, Slieve.

That's exactly right, and causes me to wonder how a round LE could be added to the jiblets of a SJR. That would indeed be a performance-enhancer. Headfoils have this effect on bermudan headsails, if large enough. Cylindrical foam inside the luff, if soft enough to furl?

A round LE to the main panels, made by sections of sleeving around the mast, seems easier to do, but might not be so effective as attention to the luff of the jiblets.

Could the jiblets be soft wing sails? Rotating around a line in the luff as they are now?

They would probably need two or three small battens with a rounded nose to give the desired shape.

Rudolf

Oops Len! Could it be that you are sitting too deeply in your armchair and thinking too deeply?

We take it that 'Groove' refers to the top of the L/D curve, and we are really talking about how round topped or pointy the maximum point on the graph is. Every rig will have a particular angle of attack (α) which will give the best performance at a particular air speed, and the flatness/ roundness or width of the top will be dependant of the characteristics of the rig. This is sometimes referred to as α-tolerance.

I think it is fairly safe to say that with moderate airfoil shapes the shape of the leading edge tends to have the biggest effect on the α-tolerance, and the more rounded the entrance the better the tolerance. A flat sail with a knife edge leading edge will develop a knife edge separation bubble at a very small α, and any single surface will also be quite sensitive, but will be more tolerant as the camber at and close to the leading edge increases, due to the development of up-wash. This is the reason that we have experimented with jib shapes. The double surface wing sail, with its rounded leading edge has the potential to be more α-tolerant, as long as the rest of the airfoil can produce a good overall cambered shape. If it does not then there may not necessarily be an overall gain.

The SJR, with its short chord jibs has the potential to be the most α-tolerant of the single surface junk sails and experience suggests that the α-tolerance is on a par with a typical Bermudan cruising rig. We must remember that a surprising percentage of Bermudan boats are sailed by 'weekend sailors' who tend to happily to sail around semi stalled all the time.

Your idea of increasing the angle of the main panel to the batten makes for rather complicated thinking, and really we are only interested in the angle between the jib and main panels, therefore it would appear to make sense to simply fix the main panels on the batten and vary the jib panel angles, or sheeting angle. On a Bermudan rigged boat when close-hauled the performance tends to drop when the main sheet is eased out, and it is often best to think that the main sail is only deflecting and accelerating the air over the jib, and thus giving the best total force with high L/D to the whole rig.

Personally, I cannot envisage a 'main' panel at a sheeting angle to the batten with a loose leech, and the thought of adding a mizzen to the same batten sounds like drag with a capital 'D'. I still feel that it is the jibs with the forward facing slope that produce the L of the L/D ratio that is so important. A lifetime in aviation tells me that leading edge devices produce high lift at high angle of attack and that where trailing edge flaps may produce a small increase in lift, they always produce a greater increase in drag and a decrease in the L/D ratio (area for area, as some flaps increase the area before angling downwards).

Overall it would appear that it is the leading edge shape that effects the upwash and allows the higher α-tolerance, so that seems to be the best area for experimentation.

Cheers, Slieve.

Anonymous wrote: No question to be answered, in my opinion. The SJR and my wing sails are attempts to make modern cruiser/racers go as well to windward as possible, and that they do, quite well, but with differing characteristics though, the wing sails having a wider 'groove'.

I have thought about this for a while... be warned though, it is all arm chair reasoning. The idea that the SJR has a slimmer "groove" is interesting.

First, I think this was expanded on in some other post that I can't find right now. Groove being how fine the adjustment of the sheets has to be for optimum performance (performance in this case is speed) to windward. The reasoning being that the jiblets are 12 degrees different than the main panels are and so the range of angle where both panels are working is diminished.

The angle of the foil in the jiblets is more important than the mains and so more thought and experimentation has been done with this angle. The jiblet angle ensures the air leaving the jiblet flows properly as it encounters the luff of the mains and so is quite important to the performance of the main panel. However, this effect is about the leading edge of the main panel not the whole length of the foil.

It would stand to reason then, that the main panel could also have it's cord at an angle to the batten without affecting the air flow at it's entry. This would (could?) give a better balance between the two airfoils.

Ok, having said that, what are the problems with this idea?

• The main panels are twice the cord length and so introducing a lot of cord angle will make a rather more floppy/saggy sail that takes possibly more air to fill.
• The leach of the main panel would no longer work as support for the aft batten ends, a line would have to be rigged to do that job. The benefit of this is that the leach no long needs as much strength, the downside is added complexity (not a lot) and added wind drag of another line aloft, though only as much as the sail presented, less when reefed.
• probably more things I have not thought of...
  

Father thought on this... The large floppy mains with a large angle would probably be the most annoying part of the whole thing. Plus it uses more sail cloth and I'm not rolling spare change.

One of the good points about the JR in the first place is that small panels lend themselves to a lot less strain on the sail(s) and sail cloth allowing thinner material. It seems that the SJR lowers the need for cloth strength even lower by reducing the the panel size even more. Maybe, if the mainlets angle is increased to close to what the jiblets are one could use mizzenlets too...

Yes this would again create a more complex sail, but maybe not as bad as it at first seems.

• The luff of the mizzenlets would provide support for the batten's aft end perhaps removing the need for a line at the aft end of the battens, or at least allowing a thinner line of less windage.
• it may be possible that all panels could be made to the same pattern with the cord angle being reduced (if needed) for the mainlet and mizzenlet by just cutting or sewing an angled line when assembling.
• Greater cord angles could be experimented with because all panels can be adjusted.
• Sewing would be easier because the panels are smaller.
• Though each panel would see less stress, a spare set of panels could be easily stowed that would fit all positions should one of them "blow out".
• The whole rig may be more efficient because it is effectively three high AR sails.
• The battens would still need the same strength as always.
  

I do not think this is something one could design put in a boat and expect everything to just work. My guess is that the CE (not the CA) would move aft both because the mainlets would be working harder and the mizzenlets would be working as well. The CE may actually move closer to the CA than with full cambered sail for example who's greatest lift is in the first third of the sail. It would be best to experiment on a boat with well known characteristics with it's present sail perhaps something that still has it's stayed mast, so that optimal mast placement could be figured out before hand. The sail could be only used on the lee side of the mast and allowed to hang a little father out from the mast so it could be tried forward or aft easily. I would start with only two or three battens worth of panels high which would mean moderate wind would be needed to move the boat and find overall balance.

Should I finally manage to have the finances to play with this on a small boat, I will try it out. I think a trial boat needs to have some length so that the balance is not as "touchy" as may be found in an 8 foot dingy where the sailor's weight has a significant effect on balance already. Probably something in the 16 to 24 foot (5 to 7 meter) length would be good.