Wing mast practice

Any photographs Redreuben? It does sound good.
The problem is two mains are required, means weight, two sets of battens. There is a problem of the two luffs binding while hoisting, also reefing.
I've got drawings of a similar thing ... but never built it.
There was an Italian C Class cat Signor G with this setup, a sophisticated rig with a flap. Was beaten by full wing C but was still fast in later Lake Garda races.
Definitely the idea is worth pursuing.

 

Gary it was around 1990, it was on a television show called towards 2000 or Beyond 2000.
He was trying to promote it as super efficient for use on anything including supertankers ! Indeed he took out a patent. Now there is a line of inquiry as he is no longer in the local phonebook, nor are episodes of the TV show available it would seem.
The luff problems would be solvable, weight aloft would be a advantage/disadvantage judgement.
I don't think the skiff was the ideal platform but it is what he had.
A multi with the wide shroud base would have really made it go.

 

Again, thanks a lot for the responses and advise; a lot of information to experiment with, I like that.
Apart of course for the best possible aerodynamics I'm also looking for ways to quickly depower and adjust the sail because I'll also be sailing in shallow narrow tidal waters, sometimes crowded.

 

You'll be sheeting differently and using different twist as the wind changes. So even when using the same approach for trimming the mast, it will have a different rotation angle in the different winds.

Think of it like trimming a jib. You trim the to the telltales in much the same way in light winds and heavy. But you use different car positions and different sized jibs for different winds. I'm just presenting a way to determine the mast trim according to what you can observe while sailing.

It's probably not going to be possible to achieve the ideal mast trim all along its length. There's a good chance the bottom will have to have too much rotation in order to get the mast working well up top. You have to experiment to see what works best for your boat.

 

slot between sail and mast

If one looks at the last Americas cup winner, the wing they used had a gap, or slot , between the forward and trailing sections. If one looks at the wing of a passenger jet while at take off or landing, one will see the leading couple of feet (a bit less than a meter) of the wing extended and curled to form more of a cup. There is a gap made when this is extended. the reason for both of these is that it allows some air to bleed from the high pressure side to the low pressure side and help stave off seperation from the surface (prevents bubbles). the same can be true on a sail. Im building a cat and actually building a mast of playwood some .66 meter in cord and with a max thickness of 20cm. it will basically look like a triangle with a half circle atop the small dimension to make a "snow cone" shape...though there will be a bit of curvature along the long sides. I designed in about 50mm of gap between the mast and the sail so as to allow a bit of air to pass through and prohibit seperation.....and, through a small evaporator at the trailing edge of the mast, cool some fluid circulating down to the cockpit to keep my Vodka drink chilled ;-)

 

Gooday 'Nagila' This 'mast' of yours will be very interesting for sure. I've built a few wing-masts for several classes of racing cats - but never managed to keep my 'vodka' cold let alone even cool (probably drank it to fast - Vodka is my favorite drink - with anything will do - just so long as there's lots of Vodka)

Any chance of some more info: like, how big is the cat - weight - width - mast height - mast weight - all wing or some soft sail - sal area - purpose of the whole project ??? etc etc.

I'd sure be interested & if I win a big lotto & come & drop by - promis to bring lot-sa Vodka & drop in & see Doug Lord at the same time. Please keep us all informed - soulds like a great project. Thanks for keeping us in the loop. ciao, james

 

There are a lot of misconceptions about the role of the slot in a wingsail. It would be more accurate to say that the wingsail has two airfoils that interact with each other in close proximity. Simply bleeding air from the windward side to the leeward side is more likely to be detrimental rather than helpful.

The way the flap is hinged to the main element on a wingsail causes it to move to windward to open up the slot between the flap and the main element. The trailing edge of the main element pointed nearly tangent to the lee surface of the flap. Putting a gap between a mainsail and wingmast is like moving the flap aft on the wingsail instead of moving it to windward. Opening the gap this way hurts the performance of the wingsail. It's important that the flap just barely clear the main element trailing edge when tacking and actually have a small overlap when deflected.

With a wingmast and sail, there may be separation on one side or both, depending on the mast rotation. It is quite a different situation than exists at the trailing edge of the main element on a wingsail, and I wouldn't deliberately make the gap any larger than necessary.

The air bleeding through a gap between the sail and mast is not going to be directed parallel to the sail the way it is with the gap on a wingsail, because the sail can't move to windward the way the flap leading edge does on a wingsail. So the air going through the gap will act more like a jet a right angles to the sail, and this may make any separation bubble on the lee side worse rather than better. The air going through the gap at right angles will simply push the flow on the lee side further away from the surface, acting like a spoiler.

 

Tom, I understand about the two elements. Part of the reason for the gap is that, given my tiny budget, I need to have this gap for batten ends/ roller cars...though it may be a bit less than 50mm.My thought was that the leading edge of the sail would actually be in the lee (by just a bit) of the trailing edge of the mast and therefore instill a venturi effect. Hard to communicate with no drawing.... I am hopeful that, with a good bit of mast rotation which would otherwise instill a bubble, the gap will allow sufficient air in to stave off such a condition. while the initial vector of the airflow would be not parrallel to the overall airflow, it would certainly not be perpendicular either and quickly bend to fill the evil bubble which tries continually to turn my sail to the dark side. The vector of fuel going through the main jet in a carbuerator is perp to airflow but quickly turns to parrallel with the flow through the venturi...and fuel is much more massive than air by volume (MV squared and such) . also, going back to the airplane wing analogy, the orientation of the extended forward edge during take off and landing would seem to support my thesis...but alas, I must have the gap so maybe I seek only, through clever misrepresentation of theory and far flung analogy, to put a smiley face on it
The cat is 34'11" (I live 165 N miles from West End Bahamas and under 35=150$ vs 300$ for 35 and over) with a flat bottom of 2 ft in width (one half a sheet of playwood. I designed boat to be quick to build and to utilize few cuts and have little waste). It will have a 15.1 hull beam to length ratio, 1000 ft square of dacron in a heavily roached , square top main (thinking about employing yard arm[?] parrallel to boom) and jib. I will have a second roller furling system for a downwind chute. The second system I have never seen before but am eager to build. It will be horizontal furler from bow to bow of the hulls and lay just forward of fore stay. Overall beam will be 21 ft and there will be only net and trampoline between hulls excepting 5 ft near ship's middle (running fore to aft) of combined crossbeams, cabinets, galley etc. and of course a beam aft and one forward. Im using 1/2 inch BC exterior as it uses Resorcinal just like AB marine...and yes, not as many plys, more voids and I know using exterior ply will probably result in the boat sinking and me floating to an uncharted lepper colony protected by pit bulls with AIDS but this is a risk i have to bare visa vi being a poor person I called American Playwood association and chatted at length with a mech engineer who does certification about Marine vs exterior and feel comfortable with my approach. She will have a double berth 54" wide in each hull with a head/ shower. I will try to scan some drawings. Im expecting an unladen weight of 5,500 lbs or less and a 2000lb payload capacity which is enough for water , store etc for two poor people to sail the craibbean. I know that is a lot of sail but that is why I designed 4 reefs into the main ...may use a boom furller which makes reefing ever so much easier but then I would need parrallel battens and the top boom/yard arm [?] but that arm could be longer than the square top main which would be good as 1000 ft of sail area for 7,000 lbs just doesnt seem enough, but I used to like to put big V8 engines in little bitty cars too
"BETTER IS THE ENEMY OF GOOD ENOUGH" Sergey Gorschkov, Admiral, Soviet

 

Wing Sail

redreuben, is this it?

http://gre69.wix.com/advancedwingsystems#!Early-prototype/zoom/c1han/image18xn

 

Yep

Thats the one !
Same surname are you older brother or family ?
What is Pat up to these days ?
Pm me if you wish, I'm down near Freo.

 

Wing Sail

redreuben,

I have sent you a message re Patrick and contact details.

Re Wing Sail. The skiff actually had a Carbon/Kevlar/Balsa mast that weighed in at 11kg from memory. It was a two piece mast with a rotating nose section (structural) and a counter rotating control rod which fitted into a semicircular concave in the back of the nose section. The sails were attached to the counter rotating section. When rotated, the nose section went to windward (essentially like a leading edge slat) and the control rod rotated to leeward - pushing the leeward battens into compression and pulling the windward battens into tension. The amount of rotation controlled the thickness and camber was controlled by outhaul as you said. This rig was a real powerhouse! Subsequently we dropped the nose section and changed the control rod shape to form the leading edge shape and also to become the structural member. Quite a simplification of the system but at a lift penalty. I have subsequently modeled both configurations and the two piece mast has a 10-15% increase in lift with similar drag numbers. However, we are still modeling Maximum lift coefficients of up to and over 2 and Maximum L/D of around 100 (2D models in Xfoil) for the single mast section setup.

Patrick tells me that you sailed with him on Kenny's boat which had the sails off the skiff but the simplified mast arrangement. The mast was made of aluminum. I know this was a pretty ugly set up with a high gooseneck and very short boom for the boat as the sail was literally picked up off the skiff and put onto Kenny's boat. However, it "went to weather like a train" as you said.

With the recent interest in wing sails created by the America's Cup, we have dusted off the old designs and refined then quite considerably. The key improvements relate to twist control and batten design as well as improved plane forms. We have also developed a wing for a Moth which we are currently testing. Sail fabrics have improved considerably since our skiff was built in 1987 and weight if far less of an issue. The Moth sail is very weight competitive with a standard moth sail.

I have attached an image of the leeward and windward sides of the wing on my 7.2m sports boat. Have a look at the telltail patterns - you won't see this on normal sails! We know from both the Sportsboat and the Moth that we are getting very good 3D flow characteristics across a wide range of wind speeds and angles.

Anyway, there is more information at www.advancedwingsystems.com or www.scoop.it/t/soft-wing-sails

Cheers

Greg