The design of soft wing sails for cruising

[CT249]

I still can't understand why you'd bother with a pocket luff unless you were looking for very high performance, and even then they are not always an advantage. Many high performance windsurfers discard the pocket luff in favour of simpler styles, and the new Wasp Moth, designed by the leading Moth designer, is discarding the pocket luff as well.

There's an enormous testbed out there called the real world, which has been showing for decades that leading-edge devices don't come close to providing as much increase in performance in practice as they do in some theories. They are fun in their way (which is why I own three wing masts and about 20 sails for wings or with pocket luffs and camber inducers) but they can also be a massive hassle. There are also some experts who say that pocket luffs only work in extremely high performance craft with very flat sails, such as windsurfers and Moths. That seems to be well borne out in reality.

As an indication of the issues, after 30 years of development, the latest windsurfer sails are often twice as heavy as the very first Windsurfer sails of similar size, and that's all because of the pocket luff, camber inducers and full battens. It's a major price to pay for the supposed advantage of a cleaner leading edge.

 

[GregAWS]

Production wing sail

I haven't posted in this thread for a while. However, I have been busy none the less. In the past year we have commissioned the K8 Sports boat, fitted with our Semi Rigid Wing (SRW). K8 #1 was first launched on August 29 and has more than met our expectations.

Within weeks of the K8 Sports hitting the water for the very first time, we sold K8 #2. This new boat will be gong to the USA and we are confident that there will be more to follow it.

The K8 Sports is the world's first production boat to feature our SRW technology. The SRW, or semi rigid wing, uses a patented technology that creates a semi rigid aerofoil structure but is still capable of being easily hoisted, reefed and stowed. The SRW is a breakthrough in practicality, usability and reliability of wing sails. It’s simple, lightweight design means that the SRW can be applied to a wide range of sailing yachts. The SRW is the simplest and most practical soft wing sail system on the market.

Nicolas Goldenberg of G Yacht Design has worked with Advanced Wing Systems to design a light, fast, user friendly and enjoyable, 8m sports boat. "The K8 is unlike any other sports boat on the market, simply because all other boats have been designed for conventional rigs. The initial design brief from Advanced Wing Systems was to create an exciting sports boat that is easy to sail with a small crew. The K8 has modern, powerful lines to take advantage of the extra power of the wing. The wide chines provide narrow heeled waterlines and high stability allows the boat to be sailed with 3-5 crew. The trend is away from sports boats which require a crew of 6 or more super athletic members, and the SRW makes this easier to achieve."

The K8 has been nominated for the pretigious Yachts and Yachting Sports Boat of The Year award (http://www.yachtsandyachting.co.uk/2016-sportsboat-of-the-year-k8/)

There is also a good write up in Seahorse magazine which gives a bit more information about the SRW. You can find a copy of that article here: https://www.facebook.com/AdvancedWingSystems/posts/923207771095623

See it in action here: https://www.facebook.com/AdvancedWingSystems/videos/910411365708597/?theater

 

[mfly]

I thought about the tacking for the Bamboo Snake foil. And it won't automatically flip its snake head around after cross the eye of the wind. The sailor must go the mast and flip the joints around, or have some other mechanism to invert that section of the foil. Might be difficult with a big sail.

 

[mfly]

"I still can't understand why you'd bother with a pocket luff unless you were looking for very high performance," -CT249

true, for what I'm doing, i place simplicity and ease of use over performance.

 

[brian eiland]

There's plenty of evidence, both theory and practical, that a low quadrilateral sail (square sail, lug sail, gaff sail, junk sail) is both more efficient and easier to live with, downwind, than a tall, narrow triangle. C A Marchaj did wind tunnel testing on this many years ago. Some weekend cruisers never sail upwind, so they ought to be happy with such a rig, if they could break the triangular habit.

On the other hand, there's plenty of evidence, both theory and practical, that a tall narrow quadrilateral sail (AC wing and others) is more efficient upwind. Fast multis never go downwind, the apparent wind is always forward of the beam, so they're happy with the tall narrow quadrilateral.

In between, there all the folks like me who want to sail across oceans, up and down narrow rivers, through the difficult channels between islands where the wind comes at you from all directions, seemingly at once. To make us happy, the rig has to perform well and comfortably under many different conditions - which sometimes equates to fast, but not all the time. There's nothing worse in a cruising boat than having a rig which won't slow down. You wouldn't accept a car that only had two speeds - top speed and stop - would you? In the same way, a cruising boat must be able to sail at the right speed. That's why I'm interested to hear what the theorists have to say, but in the end, I'll be going for the moderate rig, capable in all conditions. There's a well-known phrase that applies here: "Good Enough".

Just found this subject thread, and doing a quick read thru this morning,...found this quote and just had to make reference to it over on another subject thread 'Aftmast Rig"

Thank you David

 

[brian eiland]

Im curious at what your trying to achieve David? I can only assume 1 of 2 things... 1 - your either trying to make something better than you already have, (2 iterations of a ketch soft wing rig) or have had in the past (pure junk rig). OR 2 - you like experimenting with stuff like this as a kind of hobby... either way i can understand entirely.

Im also curious if you could quantify your improvements? when i say quantify, i mean in numbers, such as boat speed vs apparent wind angle?

Reading through what youve done in the past - there is a PDF available for download on Davids building of the wing junk rig here btw - http://www.google.com.au/url?sa=t&r...=kmDXnD1A2dahF5AJZGb0Vw&bvm=bv.60983673,d.aGc

I can see youve put in alot of effort into this over the years...

Besides the easy handling, easy reefing, safety side of things, the only benefit i can see your after with a wing junk rig, is to improve the upwind performance in light airs compared to the pure junk rig? Is this a fair assessment?

Another way of achieving a similar end, is via the rotating wing masts with roller boom furling... easy reefing, everything controlled from the cockpit, very clean and no fuss... downside is very expensive... But the point is, a rotating wing mast with conventional sail, can be just as efficient as a wing. The double surface around the entire windward side (not including the leading edge of course) is not as important as you might think - assuming we are comparing to a rotating wing mast that is. A standard fixed mast used by most is very inefficient tho.

I do alot of kitesurfing, have done for over 10 years... these kites are simply flying wing sails, pure and simple. There are full foil kites with double skins top and bottom, and also single skin kites on the lee side with a round leading edge. There is not a discernible advantage to the double skin kites, they do not win all the races or competitions - in fact the single skin kites win more races - mostly due to their increased popularity no doubt. If there was a clear performance advantage, the double skin kites would be winning everything...

The way i see it, is the inflatable leading edge single skin kite designs are effectively like a "leading edge slat" on an airliner wing - which forms part of the high lift devices used to increase the Cl for take of and landing.

You can see in the above pic, there would be a turbulent and discontinuous flow area where the number 4 is circled. This doesnt present a problem for the most advanced aircraft in the world today and they extend these leading edge slats to improve the Cl on take off and landing. Not to be confused with the trailing edge flaps, which are only fully extended on landing as they also desire increased drag for landing. On take off, the trailing edge flaps are only slightly extended to limit the drag and acheive acceptable L/D ratio.

With correct trim or AoA, there is not some huge drag or lift penealty if there is a slightly turbulent area directly behind the leading edge on the windward side of a heavily cambered sail or wing thats trimmed properly. So the idea that there is great benefit in a double surface in this area is kinda misplaced. Provided there is sufficient area and shape to get the stagnation point in the correct location with clean flow, thats the important part. A rotating wing mast with correct trim achieves this - and is why its still used on the fastest ocean racing yachts in the world today. Im only mentioning racing yachts because its proves the point of efficiency, they need to be efficient for maximum power to weight ratio. We can use the same ideology for cruising, but simply reducing sail area to reduce the total horsepower. So again, reducing rig size can be acheived by increasing efficiency. Decreasing rig size, decreases all the loads on the boat, decreases weight, and decreases costs - all of them exponentially.

Interesting posting Groper. Had to repeat it for a reference later.

 

[brian eiland]

Tackable Square Rig?

If its just a matter of a concave shape to the windward side perhaps you could try the windsurfer approach and induce camber? The rendering was done to illustrate the concept and is not intended to represent a particular foil shape but it seems to me that using some variation of a camber system it might be possible to induce any shape you want, at least at the batten locations,

A complete non-starter, I think, Timothy.
From an instructional website:
"To get all the battens sitting in the correct position, sailors may have to give the entire sail a sudden flick to force the camber inducers to move. Or it can be common for sailors to have to kick the lower battens to get them to flick around to the other side."
On a 40 sq m sail? Yeah, right.
Please try to understand that I've spent the last 35 years thinking about this subject, and have thought of, designed, built and discarded all kinds of ideas and notions like this. What I'm seeking in this forum is input from other sailors and experimenters who are working, hands-on, in this field. The ideas part is the easy part - anyone can do it, and many do. The hard part is turning an idea into a practical ocean-going rig.

I had given some thoughts of this basic idea to possible making a 'reversible cambered square sail' like that utilized on Maltese Falcon, rather than a fully rotation mast to 'tack over' the square sail.
http://www.runningtideyachts.com/dynarig/

Had an older interesting patent reference, but I will have to find it.

 

[brian eiland]

Standoff batten rig for flexible airfoil conformation on both tacks

http://www.google.com/patents/US4924793

A rig battened with standoff battens presents a concave camber towards the wind on both tacks while remaining on one side of the mast as each batten comprises a member of a rigid leading portion connected to a flexible portion continuous to a semi rigid trailing portion. A holder attaches to the leading portion and the trailing portion to hold off the batten with presprung bow like arms. A ring part of the holder fixed on the opposite side from the arms attaches the batten assembly to the mast. Lines lead from the winch to the points at which the holder attaches to the batten such that on winching the arms are drawn back and the rig flattens out. Additionally the connection between the lead and the flexible center can be pined and the connection between the holder and the rigid leading part can be pined to an adjustable bracket part of the leading portion to enable it the leading portion to move out of curve with the batten to amplify the camber of the rig.

 

[brian eiland]

only got to page 8 and ran out of time to review,...interesting subject thread
Brian

 

[dustman]

Just curious if you can run into problems reefing if the battens are too light? I was considering making foam core composite battens for a small 65ft2 wing sail, but concerned they may be too light to come down smoothly if pressed against the mast.

 

[dustman]

This means that when deeply reefed the CE drifts further aft, when we would like it to come forward. The wing sail, as I've drawn it, does the opposite; the CE comes forward when deeply reefed.

Thank you David, this saved me from a serious oversight in my soft wing sail design.

 

[Squidly-Diddly]

how about a hybrid soft-wing with inflatable elements to make it closer to perfect Hard Wing as mentioned in OP's first post?

If the Inflatables don't work it should still be just back to Soft Wing. Try to make the Inflatable inserts able to double as air mattress/life-savers in a pinch.