Dave S

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About Dave S

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  1. Dave S

    INEOS Team GB

    Exactly. I think Dunning-Kruger applies here; what's being proposed is an incredibly complex solution to a problem that doesn't exist.
  2. Dave S

    Prada Cup

    Yeah - the rate control idea's quite plausible. No idea how the mechanics would work, but if it's already a thing in powerboats the systems should be mature. Like you, I'm not convinced either way.
  3. Dave S

    Prada Cup

    I think one of the best things you can do to keep costs down and make lower-budget teams viable is not change the boat. Billionaires will always find ways to spend money on a campaign, so all you can do is reduce the return on that investment; a stable rule helps in that regard because, after a few cycles, everyone knows which corner of the rule is optimal, so the designs converge, the gains to be made from a massive R&D budget are limited, and the risk of turning up on the start line with a dog of a boat is reduced. That's exactly what happened with the IACC class, and the 12 meters before it. The current boats are visually exciting (which the leadmines rarely were), faster than anything else out there (which the leadmines definitely weren't), appear to provide close tactical racing, and do make some concessions to cost control - soft sails and a platform that's easier to transport than a multihull. If the boats don't change significantly, I think we'll see more competitors in future cycles.
  4. Dave S

    Prada Cup

    I don't mean the horizontal foil at the bottom of the rudder, I'm wondering whether it's a trimmer for the rudder itself (ie to induce/remove weather and lee helm) In an aircraft, you control pitch by moving the stick backward and forward. This either moves the elevator, which is a flap on the back of the tailplane, or the whole tailplane. In order to balance the aircraft and allow you to take your hand off the stick, there's another control called the trimmer. This can either work aerodynamically, by moving an additional flap on the back of the elevator, or mechanically by adjusting a system of springs; both have a similar effect. Most often the trimmer is a separate lever somewhere in the cockpit, although some aircraft use a wheel or a servo-operated system. Im wondering whether this is something similar (but flipped through 90 degrees to operate in the vertical plane). The additional flap is out, both because the rules forbid it and because we haven't seen it, but a sprung system would be legal.
  5. Dave S

    Prada Cup

    That's what I was wondering. I suspect someone would have noticed if there was an actual trim tab on the rudder, but it could be some sort of spring-based trimmer, which is a common arrangement in aircraft.
  6. Dave S

    Prada Cup

    Yep - Jimmy bore away to push it as far as he could, then made a show of heading up big-time, which is all part of the game. As for safety - there comes a point, even in 28-foot leadmines, where the crossing boat is committed. From that point the onus is on the boat being crossed to avoid an actual collision; everyone know what they're doing, Jimmy was never going to hit them. The bit I liked was LR shouting "Starboard" at the same volume you would in a Laser. I can't remember whether the rules require you to shout in that situation, and I'm sure we'd all have done it, but the chances of them being heard aboard Ineos were about as great as the chances of Ineos not knowing they were there... I'll admit I was pretty dubious about these boats, but I think the event has been pretty awesome so far. Normally the AC is all about the design competition, and I love it for that; remember when the denizens of this forum figured out the dimensions and configuration of the Swiss cat from a couple of aerial photos of the boatyard, and got it right? This is the first AC for a long time where we've had all that intrigue, plus spectacular high-speed sailing, plus incredibly close match racing. I've match raced, and I've sailed skiffs, but I always regarded them as different branches of the sport; this is the first time I've seen the two brought together and actually work...
  7. Dave S

    Prada Cup

    I suspect that with these sails, the cunningham works mainly by putting compression into the mast; that was certainly the case when I sailed much lower-tech skiffs. It's a very different mechanism to stretching the cloth in a dacron sail. If that is the case, a second cunningham wouldn't be that useful (unless one of them breaks, of course!)
  8. Dave S

    INEOS Team GB

    That's the wrong measure, you want to be comparing VMG (though I don't have an informed opinion on which boats had/have the better VMG)
  9. Dave S

    Prada Cup

    That's par for the course in match racing. If in doubt, wave the flag and let the umpires sort it out. If you were making lots of spurious calls the umpires might have a word with you after the race, but it's not going to impact the way they call genuine infringements.
  10. Dave S

    Prada Cup

    Yeah. What if the race between Ineos and LR ended up with one of them capsizing and nearly sinking. Without the ghost race, you'd have the bizarre scenario of a boat with a big hole in the side that can't race being awarded a victory over another boat with a big hole in the side that can't race.
  11. Dave S

    Prada Cup

    This is known as arbitrage; in principle you could write a tool to scan different online betting sites and automatically place pairs of bets (or sets where there's more than one competitor) that guarantee a profit, whatever the outcome. In practice, your tool would have to be very fast indeed, and you'd need a lot of capital to make it worthwhile, because other people have already got there. The effect of the arbitrage is to bring the odds at different bookmakers into convergence (because the arbitrage bets themselves shift the bookmakers' odds, just like any other bets), so any remaining margins are very small. Isolated arbitrage opportunities probably still exist, but beware of FX risks or liquidity issues (finding yourself unable to place both sides of a bet and being stuck with a significant position). Exactly the same principles apply in financial markets, which is where the term arbitrage comes from.
  12. Dave S

    Prada Cup

    Oh, come on, it's just a cultural difference. Embrace a bit of cultural diversity! Americans like to wave their flags around, have flagpoles in their gardens, take every opportunity to sing their national anthem with their hands on their hearts. Most of the rest of us find it a bit over the top, but it's not doing anyone any harm. Kiwis like to go on (and on, and on) about how good their national sports teams are. Again, most of the rest of us find it a bit OTT, but it's pretty harmless. Italians like waving their arms around and getting over excited, which most of the rest of us find a bit OTT The French are incredibly proud about all sorts of things that the rest of us don't quite understand The Icelandics are so proud of their language that they have a national institute to veto new words that might not be Icelandic enough and come up with more Icelandic alternatives and so on Most of us have some national pride, and many of us display that in a way that other nationalities find a bit weird or excessive. Cultural differences make other places and peoples interesting. Don't beat up other nationalities and cultures for not being like yours...
  13. Dave S

    Main sheeted to windward

    OK. The glider's an easier example to pick because it has no engines, but the physics and terminology are the same. Here's a pretty standard diagram showing the important terms: Key points: Lift is (by definition) perpendicular to what sailors call the apparent wind (relative wind in the diagram) Drag is (by definition) in the same direction as the apparent wind. This will be a combination of parasitic drag (various friction-like effects) and induced drag (primarily caused by things like tip vortices, which is why long thin foils and end plates are good) The chord line is not very important other than to the aircraft's designer; so is the angle of incidence (angle between chord line of wing and fuselage). In sailing terms, this means the direction the boat's pointing in and the angle of the boom relative to that are only of secondary importance Thinking about it, I was wrong when I suggested using the direction of the boat's travel as a reference; from an aerodynamic perspective it's more correct (and easier) to reference everything to the apparent wind direction. Unlike an aircraft we also have a set of foils in the water. It seems reasonable to consider the vertical and horizontal foils separately. Here the direction of travel is important, because that's what defines the "relative wind" for the underwater foils. As for Coriolis - this just isn't a factor at the scales we're talking about. Water spirals down the plughole in either direction regardless of which hemisphere you're in, and the direction will be down to currents in the water at the time you pulled the plug, asymmetries in the plughole etc. It's very easy to reversee the direction of spiralling while the bath is draining, and anyone with access to a bath or kitchen sink can try this for themselves. It does affect weather systems, but they're much bigger and continue rotating for days. In perfect conditions Coriolis force could generate enough wind shear over the height of a mast to be measurable, but in practice, just like the plughole, that will be overwhelmed by local conditions. Anyone who's sailed in a narrow river with high banks will have seen this on an extreme scale. Wind gradient can be a factor, and anyone who's landed a small aircraft or especially a glider on a windy day will be very familar with this; it's not uncommon for the wind speed to be 20 knots greater, as little as 300 feet above the ground. In general the wind direction at 300 feet is not noticeably different to ground level. What this means is that the top of a boat's mast will often be in more breeze than the bottom (but generally from the same direction). When the boat starts moving the apparent wind comes ahead, but to a lesser extent at the top of the mast because the true wind strength is greater (if you're not sure, just draw a couple of vector diagrams). This is one of the many reasons we sail with twist.
  14. Dave S

    Main sheeted to windward

    Also bear in mind that the boat's not travelling in the direction it's pointing in (because leeway), so a force perpendicular to the fore-and-aft axis of the boat still has a forward component in the direction of travel. Draw a line through the mast in the direction of travel, and the boom's probably still to leeward of that line. Now, you *could* toe the foils on these boats in so that the hull doesn't make any leeway at all at a certain speed, but as far as I can observe they seem to make leeway just conventional boats. I suspect that toeing the foils in would make the whole configuration very draggy when they're both in the water, and once the hull's out of the water who cares if it's going sideways? Completely off-the-wall thought: If the hull's travelling sideways it'll be pointed into wind from the perspective of the direction of travel; could that actually make it more aerodynamic?
  15. Dave S

    INEOS Team GB

    In principle yes - remember Blue Arrow? In practice, very unlikely on these boats; if I understand the configuration correctly, the angle of incidence of the main foil is fixed, so the only way to get the negative angle of attack required for a downward force is by pointing the whole boat down the mine (in which case both foils will generate downforce). Trim tabs can alter the amount of lift (at a given speed and angle of attack) but they generally can't reverse its direction.