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      Abbreviated rules   07/28/2017

      Underdawg did an excellent job of explaining the rules.  Here's the simplified version: Don't insinuate Pedo.  Warning and or timeout for a first offense.  PermaFlick for any subsequent offenses Don't out members.  See above for penalties.  Caveat:  if you have ever used your own real name or personal information here on the forums since, like, ever - it doesn't count and you are fair game. If you see spam posts, report it to the mods.  We do not hang out in every thread 24/7 If you see any of the above, report it to the mods by hitting the Report button in the offending post.   We do not take action for foul language, off-subject content, or abusive behavior unless it escalates to persistent stalking.  There may be times that we might warn someone or flick someone for something particularly egregious.  There is no standard, we will know it when we see it.  If you continually report things that do not fall into rules #1 or 2 above, you may very well get a timeout yourself for annoying the Mods with repeated whining.  Use your best judgement. Warnings, timeouts, suspensions and flicks are arbitrary and capricious.  Deal with it.  Welcome to anarchy.   If you are a newbie, there are unwritten rules to adhere to.  They will be explained to you soon enough.  


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About Basiliscus

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  1. trickle down

    Kite foils have their origin in hydrofoil waterskis and boards. The Dynaflite Hydrofoil used struts in a triangle to join the two skis to the fuselage of a biplane hydrofoil and tail in the 1960's. That led the the Murphy/Holst kneeboard of 1972, and the first sit-down hydrofoil ski in 1984. Which led to the Air Chair of 1990. It originated the configuration consisting of a wing, fuselage and tail mounted to a single strut on a board. The Air Chair led to hydrofoil surfboards, pioneered in Hawaii by Laird Hamilton in Hawaii. I don't know if Hamilton was the first to use a hydrofoil surfboard, but he was the one that showed it could be used in big swell. From there, it was a logical step to combine the Flexifoil traction kite used for landsailing kite buggies to the hydrofoil board so the craft could be towed by the wind instead of a powerboat. So the kitefoil is the result of several lines of development, all of which predated the 34th AC and were going on pretty much in parallel with the Moth class. I should mention that people were flying hydrofoil sailboards as far back as the 1970s. But these did not use the fully submerged single-strut configuration that was pioneered with the Air Chair and used by modern kite foils.
  2. trickle down

    AFAIK, the Moth class was the first in which a foiling boat was competitive with a floating boat in a wide range of conditions. In 2000, Brett Burville won two heats at the Moth Worlds in Australia. That particular configuration was later ruled illegal in the Moth class, but it was the start of competitive foiling. (It was to be revived to meet the restrictions of the class rule for the A-class catamarans.) Hydrofoil boats had been raced earlier, but were not very successful. So, hydrofoils themselves predated the AC, going back to the 1950's. Prior to the AC, hydrofoils were stabilized either through the heave-associated area reduction of surface piercing foils, or feedback control systems like the Sam Bradfield invented wand that was first used in Moths by John Ilett. There were two big trickle-down aspects to the 34th AC in 2013. The first was simply the notoriety given hydrofoils by using them in the AC. This gave a professional cachet to sailing hydrofoils that had previously been the province of amateur experimenters. The second big trickle-down from the 34th AC was the principle of stabilizing the boat in heave through the mechanism of leeway coupling with L foils. This principle was discovered by Emirates and OTUSA subsequently discovered it for themselves. Leeway coupling made it possible to have the vertical lifting portions of the foil be fully submerged, avoiding the ventilation issues that plagued surface piercing V foils, while still having the stability of a surface piercing foil with no moving parts. Hydrofoils were attempted in the C-class catamarans, but were not competitive because the T foils used at that time resulted in giving the hulls less beam, and the loss of righting moment more than offset any drag reduction from the foils. It wasn't until after the 34th AC that hydrofoils became competitive in the C-class, by using the L foils and leeway-coupled stability from the AC. The L foils allowed the hulls to be at the maximum allowed beam, restoring the righting moment that had been lost to the T foils. So there's been an exchange of technology both ways, from smaller classes to the AC, and from the AC to other classes.

    Boat 1 had the daggerboard ahead of the forward beam and was a little faster upwind, but wasn't as stable, which made it harder to do the flying gybe. Boat 2 had the beam moved forward and the daggerboard moved behind the beam - we called it the leap frog change. This made the boat more stable in the vertical plane when flying, but created some lee helm that hurt upwind performance. The changes to wing trim during the regatta alleviated the lee helm and improved the upwind performance.
  4. I like Herreshoff's configuration. This figure shows the principal aerodynamic features of a wingmast/sail section: What you'd like is for the sail be just outside of the separation bubble on the windward side, because then you don't get the separation, recirculation, and losses associated with the separation bubble. That's exactly what the Herreshoff patent was designed to do. Mark Pivac used a sail very much like Herreshoff's on his Spitfire hydrofoil catamaran. The ETNZ double surface sail also avoids the separation bubble, but it also adds thickness to the section further back where you don't want it. It would be possible to tension the leeward sheet on the ETNZ more than the windward sheet and let the windward sail be supported by the leeward sail. Of course, that also means both surfaces have to be strong enough to carry the leech tension, so the weight would be a lot more than for a single sail. Putting a control arm at the head is helpful, but what about mid leech sag? It is still going to take a lot of leech tension to control that twist.
  5. A soft wingsail is something of an oxymoron. I suppose in the future it may be possible to have materials that act as you propose, but they're not available now.
  6. This is nothing like a wingsail - it's just a double-surface soft sail. What makes a wingsail superior to a soft sail is not the fact that it is thick. From an aerodynamic point of view, it would be better to make a wingsail thin, but the structure won't support it. What makes a wingsail so maneuverable is the torsion loads are reacted internally through the ribs and D-tube structure. The sheet only has to carry the loads needed to rotate the entire wing, and even those can be reduced by appropriate choice of the pivot axis, providing some aerodynamic balance. In contrast, a soft sail controls twist through leech tension. This requires very high sheet or vang loads, which affects the structure of the entire boat. It significantly increases the energy from the crew needed to trim the sail. And it is impossible to reduce the heeling moments by using negative lift at the head, as was done by the AC72 and AC50 wingsails. The mainsail shown is a single element section that won't have anywhere near the high-lift capability of the slotted flap sections used in the AC and C-class wingsails. The surface texture of the soft sails is also much rougher than the smooth film, increasing the profile drag and decreasing the maximum lift. Granted, profile drag is not a large component of the total drag, but it isn't negligible, either. About the only aerodynamic benefit I can see for this rig over a rotating wingmast/single surface sail combination is a reduction in the windward separation bubble that forms at the mast/sail junction. It can be reefed, which is an advantage over the hard wingsail, although I'd be very surprised to see them using reefed sails in an America's Cup race. It would be more likely to have different sized sails for different conditions. Cost is another interesting factor. The wingsails were expensive to build, but once built they weren't that expensive to operate - Clysar film is cheap. They were long term investments, like the hulls, and could (with a stable Design Rule) be used for multiple campaigns. Sails in an America's Cup campaign are disposable items, good for only a few races at most. The sail budget for an AC campaign is at least as much as the cost of building a wingsail. The double-surface sail shown in the video may be an advance over conventional soft sails, but it's no wingsail.
  7. Exactly. They should race with a class that doesn't require more power than can be generated by the crew and wind. That is, after all, the whole point of a sailing competition.
  8. I don't have a problem with regenerative electrics. You could use supercapacitors in place of the accumulators. The class rules could specify the supercapacitors had to be discharged when the boat left the dock, leaving them to be charged by the crew and boat. For that matter, I don't have an issue with batteries of limited size so they could get the boat through a maneuver but not a leg of the course. Energy storage is fine, so long as the energy comes from the crew and the wind. If you want to put up a wind turbine to power the systems, go for it. What I wouldn't want to see are the engines that were used in the 33rd AC Match or battery powered systems like the AC45F that had enough energy to keep the systems running for the whole race.
  9. The AC72s were allowed to have battery powered hydraulic valves, but the motive power of the hydraulics themselves had to be manual. That is apparently not the case for the AC75, which will use battery power to actually move the foils. I thought the use of powered systems in the 33rd AC Match was wrong, and wish they weren't going this route for the 36th AC Match. There were things outlawed in recent matches that I think should have been allowed. Like regenerative hydraulic systems that would have extracted power from slow retraction of the dagger foil, essentially using the weight of the boat sliding down the board to recharge accumulators before being reset by extending and tacking onto the the opposite board. I believe this qualifies as use of the natural forces of wind and water, as the energy comes from the boat flying back up on the opposite tack. I think it would make more sense to allow the control systems to be hydromechanical with accumulators but no battery power for the actuation of valves. Any kind of mechanical feedback control would be permitted. Essentially we're talking about aircraft flight control technology circa 1960. This would also encourage the development of controls technology that would be usable by cruisers and offshore racers where reliance on electronics for safety-critical functions is problematic. One of the problems is this kind of hydromechanical control technology is a bit of a lost art. Today's engineers understand CAN busses and there is a lot of off-the-shelf hardware available, but they don't have any experience with mechanical flight control systems.
  10. I wouldn't call it a clarification, more like a speculation since it didn't come from BMQR. After all, who talks about "Vmg courses" instead of "windward-leeward courses"? Maybe that's a translation from French? But it is a way of getting to more sensible numbers. Here's a guess at filling out the rest of the picture, assuming the figures represented boat speed instead of Vmg. I'm guessing Vmg downwind to be 15 - 44 kt, and 13 - 28 kt upwind. Apparent wind angles of 18 - 24 deg downwind are not very different from the catamarans. I still think they are too tight for Code 0s to be useful when foiling.
  11. I think these numbers are, um, shall we say, "optimistic"? I've made some guesses as to consistent boat speeds and angles to match these Vmg numbers. Upwind, the boat has to touch 50 kt, and it looks like downwind it will be doing 55 kt over a fairly wide wind range. (Note that I've multiplied the downwind apparent wind angle by 10 to get a better fit to the graph scale.) Apparent wind angle here is defined as between the apparent wind vector and the course through the water. In order to do these kinds of speeds without cavitating, the foils will have to be thin - on the order of 7% of the chord. This is interesting when you consider the volume needed to provide the stated amount of ballast. Steel and carbon composite are similar in stiffness, but steel can bend more without breaking. So I suspect the foils may be solid steel, but I've not tried to work out just how much area that would be for the weight. There was an interesting line in the presentation where they said the foils may be one-design except for the trailing edges and control systems. This would lock in most of the section shape and cavitation characteristics. I haven't looked at the hullborne numbers, yet. But one thing is clear - for those that want to see Code 0s being set and dowsed, there will either be Code 0s or foiling, but not both in the same race. There's no point in flying a Code 0 when the apparent wind angle is less than 15 deg.
  12. If you're going upwind, meaning you can't lay the mark and a tack will be needed, then the fastest speed to windward (Vmg) is the rate of progress toward the mark. The velocity component toward the mark is not very useful when on upwind and downwind (meaning a gybe is required) legs. Dead downwind of the mark, the velocity component toward the mark equals Vmg. When the boat approaches the layline, the velocity component in the direction of the mark is near zero, but the velocity toward the mark equals the boatspeed just after tacking on the layline. That's why Vmg is always referenced to the wind direction.
  13. In principle, you can lift off at any speed if you give the foils enough area. If the foils are small, you have to sail fast to get to takeoff speed and this means you need to have a decent wind. If the foils are very large, even though the takeoff speed is low, it still takes a decent wind in order to push all that claptrap through the water. In between the two extremes is a size of foil that will allow the boat to take off in the least amount of wind. Just where that optimum lies will depend very much on the details of the hull, rig, and foil design. Especially for a fully submerged foil system, the foil size that will take off in the least amount of wind will not necessarily be the most competitive design. If both boats can foil, then its foils may be oversized and the top end limited. It will probably win if it can foil when the other boat cannot. But that's not guaranteed. The drag due to lift is high at low speed and it's possible that a slowly flying boat could have more drag than a hullborne boat with small foils. A boat can lift off at 9 kt boat speed might not be competitive. Lift is easy. It's really all about the drag.
  14. You can capsize a foiler to windward by easing the sheet. I've also pitchpoled a landyacht backwards when the mast fluttered in a tack. Before the ease, the leeward foil has an angle of attack that produces enough lift to oppose the heeling moment. The rig is also producing a bow-down pitching moment that is opposed by the stern foil. When you ease the sail, suddenly both the heeling moment and he bow-down moment reduce or go away, but the foils are still producing the same lift and thus the same righting and bow-up pitching moments. Unlike a displacement boat, in which the righting moment drops off as the boat comes upright, the righting moment from a foil doesn't drop off the same way. And may even get worse as the boat pitches up. The result is a "High, ho, Silver! Away!" moment as the boat pitches up and heels to windward.
  15. Thanks. Yes, it was. I was a flight control engineer in a previous life.