ISAF vs KITE Sailing

You turned it over yourself, Paul. As apparent draws forward, the boat must sail lower, not higher, thus USA2's "wind picks up" comment. I suspect you're real doubt is whether ACC boats can sail as high as 25 degrees (true) in light wind. I can assure you that they can. As soon as they can get attached flow across the keel (3-4 kts if the lift demands aren't too high), they are astonishing light wind fliers, and are extensively optimized for upwind (and also downwind) VMG work under those conditions.

I think USA2 cited actual readouts from the extensively available Virtual Spectator files of every race in the 2002-3 LVC and the 2003 AC. I would point you to these same sources, and include personal experience of my own, aboard one of the fastest ACC's (USA 76) and "looking over the shoulder" of the crew at the actual onboard instruments as they trained.

Dave

 

Wow, that's some strange reply. I think you better read my message again, draw some diagrams, and do the math.

The original claim was that you know ACC boats tack through 50 degrees. They don't. If you know this is shown on a particular VS file please provide a link.

As for "personal experience", it is rarely data with confidence. Your claim is right up there with the guy "who was there" when an Open 60 planed upwind into a 4 foot chop. No one else has ever seen an Open 60 plane upwind, not even the current boats with more sail carrying power than the boat he was on. Anecdotal evidence often morphs as time passes.

But I'm sure I won't convince either of you that you are mistaken, so I won't bother.

 

boats "drop off" the wind when it "picks up" because the AWA moves FORWARD. i dont think anything i said implied anything other than that.

 

No, it doesn't.

As BS approaches TWS the AWA moves forward.

Hypothetically (never happen in reality) your ACC boat is cruising along at hull speed of 13 knots BS, 32 degrees TWA, in 13 knots TWS. The AWA would be 16 degrees.

The wind "picks up" to 15 knots. You don't go any faster (ACC boats don't plane upwind) AND you decide to continue to sail at 32 degrees TWA. Your AWA is now 17.2 degrees. The BS vector is now proportionally less than the TWS vector. You could have poked up to 30 degrees TWA to retain the same 16 degrees AWA you had at the lower wind speed.

The wind "picked up" but the AWA did not move forward. It moved aft.

I've sailed a lot of high perfomance keelboats over the years. I've never encountered one that sailed higher in lighter air and went bown down as the breeze came on (until overpowered). Again, you might have to go bow down as the sea state changes, but that is not relevant to the discussion.

You stated that ACC boats could sail at 25 degrees TWA, but only in light air. Again, please cite some data we can review.

 

The virtual spectator readouts during the LV Cup and the AC itself and watching on TV. Also saw UBS trophy Newport.
I think maybe here we are misinterpreting each others comments to a certain degree, and also maybe we understand certain concepts differently, because on every boat that i have sailed on or seen sailing, or even read about sailing, if the wind speed and/or boatspeed increases, the AWA moves forward.
Lets say that USA-76 is doing 13 knots upwind in 18 knots of wind. The wind increases to 25 knots. If ORACLE was sailing at 30 degrees TWA in 18 knots of wind and the wind speed increases to 25 knots and they are still sailing 30 degrees TWA, the apparent wind speed increases while moving forward. Therefore, ORACLE falls off a little to keep the AWA at their boats optimum. I have never heard of a boat that the AWA angle moves aft if the boat keeps its course and speed as the wind increases. The AWA moving forward is the reason why all the supermaxis dont have symmetrical spinnakers. They are so fast that even if they sail relatively deep, the AWA angle is on the beam or forward of it. An example of this is Nicorette finishing the Sydney-Hobart race in 6 knots of wind. They were doing thirteen knots with an A-sail and main. So if someone can explain how its possible for the apparent wind angle to move aft with out slowing the boat, decreasing the wind speed, or turning the boat away from the wind, it would be appreciated.

 

You're looking at only one end of the equation, Paul--when wind gets high enough that the boat cannot accelerate. Others look at the regime where the boat CAN accelerate, and does.

You said, "I've sailed a lot of high perfomance keelboats over the years. I've never encountered one that sailed higher in lighter air and went bown down as the breeze came on (until overpowered)." and you also said, "As for "personal experience", it is rarely data with confidence. Your claim is right up there with the guy "who was there"..."

Which is it my friend; you can't actually have it both ways. Are you suggesting that your own experience/memory is inaccurate? Or that only OTHERS' experience is open to question? How many hours do you have in IACC boats? I'm no expert; I've maybe 100 hours in them. You must have much more, to make the statements you are making about a class which two of us, independently, are declaring is significantly different from "a lot of high performance keelboats." Or perhaps you're an IACC designer? Statistician? Tactician? Navigator?

I guess there's no arguing with an "expert." Have a nice day.

Dave

 

In either case that Paul B mentions, the AWA will still move forward...

 

Then you were seeing something different than some others who logged the same thing.

The "and/or" is where your mistake is. Increases or decreases in TWS and BS are independent variables in the equation. It is the relation between these two variables that determines the increase/decrease of the AWA (given a constant TWA). If BS doubles while TWS only rises by 10%, then the AWA is going to go Forward. If BS Doubles while TWS quadruples then the AWA is going to move back. The amount of movement is dependent on the TWA.

13 knots in 18 knots at 30 degrees TWA is 17.5 degrees AWA.

13 knots in 25 knots at 30 degrees TWA is 19.8 degrees AWA. That is not moving forward.

However, if the BS went up in a greater proportion to the TWS then the AWA would move forward. In your example, if the TWS goes from 18 to 25 that is a factor of 1.39. So if BS went up 1.4x (or more) 13 knots (18.2 knots) the AWA would move forward. So 18.2 at 30 degrees in 25 knots= 17.4 degrees AWA.

The reason for this is their relative BS compared to the TWS. If you are moving at or above the TWS when sailing downwind the wind comes forward. Actually, if the TWS DECREASES and you maintain the same BS and angle the AWA will move forward. IF your BS decreases and you maintain speed and heading the wind will move aft. It is really simple vectors, shouldn't be that hard to follow.

This is the the whole idea behind "Sailing Esses" downwind. You heat to increase BS relative to TWS, this brings the wind forward, which allows you to bear off and milk the AWA and AWS until your BS begins to drop (repeat). Big boats like Nicorette do well with the speed builds and really build AWS.

As I said above, simple vector analysis. The BS should be seen as a vector of "WS" right on the nose. If this vector increases in relation to the TWS from some TWA, then the AWA moves toward the BS vector. If you decrease the BS vector relative to the TWS vector the AWA moves toward the TWS vector.

 

i think maybe we are misunderstanding each other terms here of "forward" and "aft" .

 

If like you are saying, that the AWA moves AFT when the wind increases while traveling upwind, that would suggest that if the wind moved aft far enough the IACC could set a Code Zero in over 20 knots of wind, while on the wind. There are reasons why Code Zeros are built for light air. Im not trying to get into an argument here, but may have already, but conventional logic and facts suggest that the AWA moves forward

 

Well Dave, let's look at one of your earlier claims:

I'm not sure I agree with your premise, but let's say you are right about this one thing.

So to have a faster VMG upwind than the TWS you have to be going really fast. I'll be conservative and say 10% greater than TWS. It will be more in practice, but I'll give you a break.

So let's say 10 knots BS in 9 knots wind. Let's give USA2 his 25 Degrees. AWA would be 11.8 degrees. I'm sure an Aeronautical Engineer like yourself would agree this isn't going to work, but let's move forward.

If the boat decelerates to 9 knots the AWA goes back to 12.5 degrees. You hit a wave, boat slows, AWA comes back, jib goes out, boat accelerates, AWA comes forward, jib comes in...all in the same TWS and heading. Obviously in the real world you would push the bow down as well to accelerate, requiring additional jib out.

As long as BS acceleration proportionally outstrips TWS the AWA will move forward. When it is reversed the AWA moves back. It is the relationship of these two variables that produce the result.

Ah, but my "personal experience" also includes some calculations to back them up. I'm not simply stating things like "AWA moves FWD as TWS increases" without proof. When will you provide calculations or data to support your end?

Dave, I'm nobody. I could tell you I've been a significant part of crews, as primary trimmer or tactician, that have won multiple National Championships and virtually every major keelboat series in California at one time or another. I could tell you I worked in the design office of a well known ACC designer, before the ACC rule existed. I could tell you I recently had dinner with a very famous Design Director for a winning ACC syndicate. But none of that matters, does it?

When will you provide any calculations or data to support your claims? I mean, while I am nobody you are someone trying to convince the world you know what the hell you are talking about. Arguing against simple mathematics isn't making you look too good.

 

Well, the AWA can never move farther aft than the TWA, can it? Vectors, two components, BS and TWS. The resultant AWA must fall between heading (vector of BS) and TWA (vector of TWS). So if you keep the TWA at 32, or 25, or whatever, the AWA can't get out to 40 or 50, or useful Code Zero angles. The AWA will be somewhere between Zero and the TWA.

Code Zeros are not allowed on "Upwind" legs during the AC or LVC. The ones used in the Volvo Race were really genoas, very large masthead ones. So it would make sense to use them in light air, if you could get the sheeting angles in enough. Most boats do use their biggest genoas in light air.


I don't want to argue with you either, but your conclusions are not the result of Logic or Facts. They are your opinion, and are incorrect.

 

Paul B,
could you explain the formulas you are using to come up with these AWA please?
thanks-
-usa2

 

I'm no math teacher, as you can see from my writings. However, I think you might use the diagrams from this site to make your own spreadsheet:

http://www.sailingusa.info/true_wind_calculator.htm

Just one last example that might make things easier:

Boat is at rest with the wind coming from abeam, 90 degrees. TWA is 90, AWA is also 90, regardless of TWS.

Boat is in zero wind and is motoring forward. The TWA is 0 degrees, winddex is pointing straight forward, regardless of speed.

Boat is at rest, anchored, wind on the beam again, at 5 knots. AWA is also abeam, right? Sails are raised, anchor is lifted and boat starts moving forward. TWS is still 5 knots. Boat reaches 5 knots of BS (hullspeed). Where is the AWA? It has pulled forward to 45 degrees, right? Half of the AW from Zero and Half from 90 degrees.

Now increase the TWS to 10 knots. BS remains 5 knots. Now twice the component comes from abeam compared to from the nose. Increase in wind velocity relative to the BS. With twice the velocity from the wind the AWA will shift aft toward the beam, to approximately 2/3 of the angle from Zero to 90 degrees.

If the boat then dropped the anchor and slowed to no BS then the TWS would again be increasing in relation to the BS, and eventually the AWA would be at 90 degrees.

So, on the same reach angle in the same wind, Nicorette going twice the windspeed will have the AWA full forward, Code Zero strapped, while the ferro cement slug dead on her stern will be seeing a near beam reach as she plods along at a quarter of the windspeed. It is all based on the proportions of the forces on each vector.

 

"On the same reach angle in the same wind, Nicorette going twice the windspeed will have the AWA full forward, Code Zero strapped"

And if it's the previous (1999) Nicorette with the original rudder in, the driver will be alternating between going "aaahhhh this is such fun, what a well balanced helm" and then "oooooooooooooohhhh ****" as the rudder loads and unloads as she speeds up and down swells. Never felt anything like that foil for shifting CLR back and forth but I only drove her once.