I recently took a flight on a Boeing 737, and noticed that they have added a vertical section at the wing tips. The purpose is to increase the efficency of the wing by reducing the tip vortices. The idea occurred that we could do this on a Footy. It would probably be wildly impractical on a larger boat. The implementation would be a flat horizontal plate added to the top of a square-topped sail. Ideally it would pivot so that it would be mostly over the leeward side of the sail, but that may not be necesary. This would work very nicely with a McCormack rig. The mast could be vertical, and a square sail could be used, with its aft top supported by the plate, similar to a gaff rig. The plate could be very light, made from balsa or thin plastic, or even thin aluminum sheet. A stiffener, like the Z-bar, could be used for strength to support the gaff function, but it would have to be very light (a thin T-section might work)
The benefit (if any) would be an ability to point higher, and/or get more forward thrust with less heeling.
Has anyone tried something like this? I would be interested in any comments.
the keel bulb has the same effect, its called the end plate effect. The hull acts as an end plate for the upper part on the keel. for the sail, if you found a way to drop the boom to the deck, it would have a similar effect. I think an end plate at the top of a rig would cause too much drag and result in more leeway. if you used an aerodynamic bulb it might work, something like anti-turtling bulbs for multis.
Do a search of C Class catamarans, or International C-Class Catamaran Challenge and you will see them using solid (versus soft) wings. These are about as technically current and leading edge as there are in sailing today. If you look at history, the short, fat squat wings have given way to tall slender high-aspect ratio wings now current/common.
Magnus Clark (Toronto) often posted here before he and Teammate Fred Eaton took the championship cup from US Team Cogito this past September. Prior to that Steve Clark and Duncan MacLaine held the cup. A magazine article from before this past fall and the Canadian guy’s win. http://www.sailmag.com/cclasscats/
I only mention this information because those are the boats that are using wings for power. It is only my opinion, but if they were convinced capturing wing-tip vorticies would lead to more speed, they and the other teams would have done it some time ago.
ADDED: The 18 Square COYOTE catamaran of the early-mid 1980’s used a “deck sweeper” main sail (they were uni-rigs), and quite frankly, they didn’t see to have much more speed than my pin-head boat with mainsail foot about 2 + feet off the deck (trampoline)
The decision not to use vortex controlling tips on the wings of multihulls may be one of not being able to ensure that the airflow is exactly chordwise. If the airflow is not aligned cordwise the tips will add more drag than they can save.
On an airplane that sort of problem doesn’t exist except when landing in a crosswind or during gusts. Almost all competition sailplanes designed these days have wingtips like that.
Pete, that is not exactly correct. Fluid flow over a foil keel and an airplane wing doesn’t flow chordwise over the foil’s surface. Other than the wing endplates on some jets virtually all long winged aircraft have chordwise ridges along the wing to redirect the airflow across the wing. Look out the window of your next jet flight.
Of course jets travel at much higher speeds than Footies or even C Class Catamarans, so these effects are probably negligible for our purposes.
The reason for airflow to try to travel diagonally over a foil is a combination of surface drag and deflection caused by the large amount of disturbed fluid around the hull or fuselage.
The only time I would consider an end plate for a Footy sail would be on the storm rig, but not for the end plate effect. Having a soft sail, say kite shaped, mounted to form a tee at the top of the sail would give you a lifting surface when the boat heeled (and a higher aspect ratio), much like the lifting effect of a winged keel on a 12 Meter. Its one way to beat the storm rig rule. If it were made to be detachable then it would provide you with two variations of strong weather rig, sort of like reefing.
The nearer you get to the wingtip the more diagonal the flow gets. This (as I recall from an airforce text book I read many years ago) is because the higher pressure air under the wing is trying to get to the low pressure area on top of the wing. This (according to the book) causes both a diagonal flow mostly at the bottom of the wing, that hits the top flow and causes the vortex as they combine. The winglet reduces the effect considerably. Prior to that aircraft used Hoerner tips. I’ve seen a lot of Hoerner wing tips and I wonder what Hoerner would have thought of them since there were major differences between various implementations. I also wonder what he would have thought of winglets. (or thinks of them, if he is still around and was not one of those who developed them)
I think the kite idea will cause more drag than it is worth, but that is just a gut feeling.
I was toying with the idea of a rigid airfoil sail for a storm setup. Also something that will look about like a proa sail.
I am still recovering from the WRAM show, so no work on my footy, but I did get some very light mylar to play with.
I am just a dabbler when it comes to aerodynamics or hydrodynamics, but a dabbler with almost sixty years of trying to understand this stuff, from Junior High to the present. The problem with me is that I find about a dozen or two other subjects equally interesting and all of them to time consuming.
I have built a new sail with a “Top Hat”. It uses a cloth top hat, fastened to a thin wire frame, supported by a horizontal aluminum gaff, which in turn is supported by a 3/32" L-wire inserted in the top of the mast. The sail rig is a standard McRig, but has the limited height of a storm rig, and a very long foot (18"). The sail shape is trapezoidal. The Top Hat covers only the aft half of the sail. It is 3" wide and 6" long. The entire arrangement adds 0.3 oz to the top of the mast, which is obviously not good, and would be disastrous on a more conventional boat, like a Victoria, with a tall mast and short keel. But this mast is about the same height as the keel depth, so essentially it adds 0.3 oz to the keel bulb required, for a total gain of 0.6 oz. The sail area is 160 square inches, excluding the top hat. So there is a lot of area, but very low to the water, which should limit heeling and nose-diving.
It was quite warm today, and the ice has melted, so I was able to test it. It actually worked with regard to being able to sail and come about. The wind was very light, so we don’t know if the structure is strong enough to avoid twisting of the top hat or drooping of the gaff. The gaff will probably need to get some additional support at the aft end with a thin strut upward from the boom. It appeared to be faster than the Extreme storm sail that I had described in an earlier thread, so maybe it is worthwhile. However, it was obviously slower than some of the other Footys that sailed today, but they all had much bigger rigs more suited to the very light wind.
So the jury is still out on whether this is was a worthwhile endeavor, but it was fun, which is the whole point.
To all of you who contributed comments and ideas to this thread, please accept my thanks. Some of your ideas were obviously incorporated into this design.
Unfortunately, there are no pictures of it on the water, because we had an interesting variety of Footies sailing yesterday:
Hank Buchanan with a diagonal boat
Scott Spacie with his American Footy
Scott also brought a Cobra from Bill Hagerup
My 3-Liter Torpedo
Small endplates have been tried on offshore boats with conventional bermuan mainsails. The major benefits (to someone) seem to have ben slight increse in the size of the spar-maker’s bill and a slight reduction in the anti-spanwise flow of seagull st. The latter is almost certainly more than offset by the retained topweight/arodynamic drag of said s***l shit.
Angus- I am delighted that you have recovered sufficiently to provide your usual insightful comments. You are probably correct about the usefulness of this idea. However, the intention is to allow a very long upper horizontal section to the sail, unlike a Bermuda rig, so it is a little different. Whether it is different enough to be useful, remains to be seen.
The top hat, added to a Hoyt rig, will have very little cost in additional structure or weight.
Yes, I appreciate your point entiely and will (as usual) be fascinated too hear your results.
Never assume that because something has been established by the great and the good it is necessarily so. Yacht design was set back over 20 years by a piece of reserch carried out by Sparkman & Stephens and the Davidson Laboratory that suggested conclusively (as it seemed) that bulbs on keels could never be worth while - the drag increase would always more than outweigh the gain in stability!
My Hoyt rig is being re-riged this weekend and will be dressed for the occassion with … Top Hat but no tails or spats and cane
Pictures when done
Rgds
AndyT
You have referenced a very interesting rig. It looks like a conventional swing rig with the addition of endplates at top and bottom. I have never seen anything like it on a full sized boat.
I am not knocking in any way, but people should be aware that the boat shown in Fig 2.122 of the Designer’s Notebook of the site quoted by Earl shows Pen Duick III. She was designed by he French navy as a closely guarded secret and sailed by Eric Tabarley. She was very successful, winning the 1963 Fastnet overall by a consierable margin.
However it should be noted that she was a massive rule-cheater under the 1957 RORC rule. Her uadrilateal fisherman staysails were set only off the wind or (occasionally) in ghosting conditions. To windward she normally set her fully-battened foresail. This was itself a rule-cheat: she was rated a schooner (rumour had it that the two masts were identica but the aft one was stepped on a 1 franc coin to make the hight difference). This meant that there were no excess batten benalties on the foresail, which there would hve been had she been rated as a ketch). This must have saved at least a couple of feet of rating.
She was undoubtedly a very fast boat - light, narrow, aluminium construction, bulb keel, spade rudder …, but it would be foolish to delieve that he rig was a huge advantage per se. Futher, in very experienced and capable hands and (presumably) a very sophisticated design process, the quailateral sails were only carried with the winf free.
Aside from the plate, there’s a mast a the leading edge of the Main… This is basically a squared up swing rig.
Note that the Hoyt offers a huge benefit when sailing downwind on one tack (sail shifts aft.)