wingmast/shroud interaction- hardware

[Paul Scott]

I've been searching for a couple of hours now, and I can't seem to ask the right search question to; what kind of design solutions have been come up with that allow a wing mast to rotate enough to be effective downwind, and not bang into (or or have it's motion be limited by) the shrouds and mess up the shape of the main? For example, the A class sites don't have anything I can see. This seems kind of basic.

Anybody have any suggestions? Pics? Sites? Search words?

Thanks,

Paul

[Steve Clark]

Most A cats hang all four shrouds from a single tang or modified T terminal on the leading edge of the mast.
This is pretty simple and good enough for little rigs.
On the wings, we have used a radial ball bearing race which is centered on the axis of rotation. This is the Frisbee like disk you see sticking out of the wing profile on pictures of the patient ladies.
On Cogito we made a hinged gantry that hung from the internal tube. Which was the structural bit.
In either the wing rotates without winding up the shrouds.
SHC

[Paul Scott]

Thanks, Steve. Much appreciated.

Paul

[tspeer]

Contact with the shroud is not necessarily a show-stopper. We built a landyacht with a rigid wing, and attached the shrouds to tangs on the sides of the wing. The forestay was attached at the leading edge. Despite the separation of the shrouds and forestay, there wasn't any difficulty in rotating the wing. At large angles, the leeward shroud would lay along the side of the wing, but it was slack (or nearly so) and posed no problems.

[Paul Scott]

Tom, thanks. How close to 90 degrees to the longitudinal centreline does that system allow the wing to get? I know you're talking about a landsailer, which doesn't see wind direction like 90 degrees very often, but inquiring minds would like to know. Does the leeward shroud slack allow the wing more rotation?

Paul

[tspeer]

Originally Posted by Paul Scott

...How close to 90 degrees to the longitudinal centreline does that system allow the wing to get?

It was pretty far out - past 60 degrees and perhaps close to 70 - 80 degrees, IIRC. The wing was tapered and the reduced chord near the hounds helped to allow more wing rotation for a given amount of slack.

I know you're talking about a landsailer, which doesn't see wind direction like 90 degrees very often, but inquiring minds would like to know.

Actually, a landyacht needs to be able to sheet out very far to accelerate from a standing start. Unlike a boat, the static friction means there's a threshold of force from the sail below which the yacht will not move at all, and in marginal conditions, it will only move on a beam reach. For example, in 5 kt of wind, the aerodynamic lift on a Class V (49 sq ft, 4.6 sq m), is on the order of 6 lb (3 kg). The rolling resistance is at least half that. So the lift has to be oriented pretty far forward to overcome the resistance.

To start, the pilot pushes the yacht to build more apparent wind, and then jumps in, but it still helps to be able to sheet out and fall off toward a beam reach to get going.

Once the yacht is "hooked up", then it sails close-hauled at all points of sail.

Does the leeward shroud slack allow the wing more rotation?

Yes. The limit to the wing's rotation is the leeward shroud wrapping around the trailing edge. The more slack in the leeward shroud, the farther the wing can turn. To some extent, this is true when all the shrouds come together at a point ahead of the leading edge, as well.

It's common for landyachts to be set up with very loose shrouds as the wind picks up. That lets the rig lean to leeward, reducing the heeling moment and adding down-force for better traction. When a gust hits, the axle flexes and the shrouds become even more loose.

[Paul Scott]

Consider my horizons expanded. Thanks, Tom.

(It's a good thing my boat was in the yard today. If not, all Fraternal Units would have been hog tied on the rail. What a beautiful day.)

Paul

[TTS]

You can try to contact Ben Hall at Hall Spars
Email should be ben@hallspars.com unless it has changed. Ben first put the wing on his new Peter Cogan designed A-Cat in September, leading up to the Ronstan A-Cat Worlds. He is blazingly fast down and off the wind, but is still searching for speed up-wind. If you cannot conact him through Hallspars then post a note through the usaca.info site.

http://hallspars.com/Categories.aspx...7-790e4e1e31d1
A-Cat Wing Experiment A Success
by Ben Hall

After sailing with a new wing mast at the A-Cat Worlds in Florida, all I can say is that it was awesome. It was a fun week and I learned a lot about sailing with a wing.

Dave Hubbard, the wing's designer, visited the regatta site and advised me on sail trim and offered moral support before the racing began. Dave has a long history of wing mast designs, including C-Class winners Patient Lady and Cogito as well as the 1988 America's Cup winner (Dennis Conners' 60-foot cat). His help was invaluable and saved me from learning everything the hard way.

How did I finish using the wing mast? I finished in the same place I normally finish at the Worlds. [Ben finished 30th out of 100.] Of course I was hoping for better results, but I'm happy that I was getting more out of the wing every day. My past performance is the only reference I have to measure the success of the wing, and based on this week of sailing I know it hasn't reached its full potential.

I do know that my boat was the fastest boat downwind in heavy air. In one race I passed 35 boats after rounding the weather mark back in 80th. I passed some boats to leeward, some to weather. It felt like an Indy Race, passing right and left on the track.

Then there were times when the wing proved slower. We sailed the first day in big chop. On port tack, sailing directly into the waves, the wing's higher center of gravity meant the boat was pitching more than usual. I didn't figure out the sail trim that day, so I know what I have to work on for the future. Also, I found that the wing could stall in bad air off the starting line but would quickly gain speed once I found free air.

I need more sailing time to learn trim in all conditions; only then can I truly evaluate the design. The construction of the wing was spot on - it held up perfectly throughout the week and even survived a hard capsize during a practice session. I have a feeling that 2008 will be the year of the wing.

Ed. Note: In case you missed it, here are excerpts from Ben's article published prior to the Worlds.

The wing is quite powerful in light conditions and very fast. I learned quickly that I can sail high and fast upwind, but initial downwind speed was off the pace. Then I loaned the boat to Glenn Ashby before the pre Worlds. Glenn trimmed the sail with less camber downwind, and found a whole new gear downwind.

I also had my first capsize when practicing for the pre-Worlds. Sailing in 20 knots, I flipped during a jibe. The boat wouldn't right in the typical into-the-wind position so Howie Hamlin suggested I point the masthead upwind and let the wing "lift" the boat. This worked a little too well! It was like a water start on a windsurfer, and luckily I held on the to crossbeams as the boat took off. Only a few small elements were damaged in the capsize. The wing was ready to go after minor carbon work.

My A Cat Wing has two elements. The wing is slotted and both elements have twist control. The controls are simpler than the standard A Class rig. The Wing has four controls: a 2:1 mainsheet, camber control (this adjusts flap angle from 0 to 35 degrees), twist for the main element, twist for the flap element. (The standard rig has: traveler, mainsheet, outhaul, downhaul, rotation, over-rotation, and diamond tension controls.) One big advantage is the ease of sheeting-in the Wing off the line and around the leeward mark. I am trimmed with one pull while the conventional sail takes several. Dave Hubbard was responsible for the elegantly simple design. My job was to build it and then try to figure out how to sail it up to Dave's design potential!

The length of the wing is 29 feet. The top two elements are a little over nine feet, and easily removable to facilitate transportation. The wing stores in a 21-foot trailer box that's six feet wide and two feet high. The boat sits upside down on top of the box. I can tow the entire set-up with my mini-van.

The weight of the wing is 52 lbs. The weight of all the stuff (mast, sail, battens, mainsheet system, boom and traveler) that I removed from my boat weighs 46 lbs. The all-up the boat should still be at the class minimum without corrector weights.

The rig can go from trailer to ready-to-sail in 30 minutes. De-rigging the other day from rig up to in the box was 12 minutes. It does require a second person (the "wing sherpa") to help lift the lower element out of the box and onto saw horses and also to put it into the box after de-rigging. To rig, the boat is flipped on its side, the wing is plugged into the step, the rigging is attached, the top two elements are installed, the boat is righted, the controls are rigged and you are ready to sail.

All the controls can be adjusted while on the trapeze. Upwind, with both twist controls centered (no twist), the camber is set at about 15 degrees, so all you do is adjust the 2:1 mainsheet to optimize the angle of attack. In big breeze upwind it is very easy to de-power by simply easing sheet a bit.

Downwind the flap angle (camber) is increased to 35 degrees and twist is induced in both elements by easing off the twist controls. Jibing and tacking are much easier because there is no boom to crawl under, and there's no traveler or end-boom sheeting to go around with the tiller extension.

[Paul Scott]

TTS- I'll give it a shot. I've tried to get through to him before on the company web site with no luck. Left me with the impression maybe he gets pestered too much. Hadn't considered using the A class site. Funny that the wing is faster downwind in the A cats, and the una rig is faster downwind in the IC's. Seems backwards.

Thanks,

Paul

[lesburn1]

This is the shroud attachment that Ben Hall describes in TTS' post



It rotates on the support tube that run up the main wing section, but rotates outside the wing.

[teamvmg]

Loosen the rig a bit.

Rotating rigs don't need much tension, the mainsheet will keep the forestay tight upwind.

[Munter]

The Australian NS14 class uses rotating wing masts and has done for the last 30-odd years. Common practice is to run the forestay and shrouds from a single tang at the leading edge of the mast. There is often contact between the side of the mast and the leeward shroud. To ensure that the rig can rotate appropriately for square running the boats use moveable shrouds that can slide forward. The same mechanism also gets used to adjust rig tension. With the leeward shroud car right forward the mast can typically rotate to slightly past perpendicular to the hull. Just don't let off both shrouds at once!