Talk:High-performance sailing

Commentary on rewrite

Hi HopsonRoad, some comments, with due respect:

Perhaps we should not use the expression "Apparent Wind Sailing" since all sailing is use of apparent wind. Did Bethwaite really use this term?

Apparent wind is the difference of wind and boat velocities, ie (True wind velocity - Boat velocity) .. not the sum as you suggest.

I don't think your comments about 18 footers reads well (tripling? of what?), and it lacks acknowledgement of many other sailing craft which performed more efficiently than 18 footers, including windsurfers, kites, tornadoes, etc etc. There were also many foiling craft in the 1980's including one in NZ by David Knaggs.

Your section on "Apparent-wind-angle limit" contains errors and does not read well .. and the claim that 6 times wind-speed may be a theoretical maximum efficiency of a yacht is wrong. AC75 yachts are close to achieving that now, and there are very obvious inefficiencies in their setup, as evidenced by their spray and wake. On inspection of the Beta Theorem, the theoretical efficiency limit of a yacht is more likely to be:

{1/ [1/(foil lift-drag-ratio) + 1/(sail lift-drag-ratio)]}

By example .. a hypothetical "very light" yacht with "negligible" parasitic drag, and with a foil with LTDR 40 and a sail with LTDR 40, will sail at 20x wind-speed when sailing 92.9 deg off the wind.

(1/(1/40+1/40) = 20)

Beta = atan (1/20) = 2.9 deg

By this hypothetical example the efficiency of a yacht is clearly not constrained to 6x windspeed.

Charco21 (talk) 22:53, 2 August 2020 (UTC)Charco21

Hi Charco21, thank you for writing. Here are my replies, regarding your concerns:

• Thanks for calling the vector sense issue to my attention. See if I've fixed it properly. (HopsonRoad (talk) 11:36, 3 August 2020 (UTC))
• "Apparent wind sailing" is directly out of Bethwaite. He cites it as if it were an accepted term of art. Read about it on page1 of Higher Performance Sailing.
• Everything in the "Apparent-wind-angle limit" section is paraphrasing Bethwaite. See if you can read Bethwaite's words here. Your statement on AC75 yachts doesn't contradict this. Bethwaite doesn't suggest that 6 x is a theoretical limit, just a practical one until better streamlining is achieved. What other errors do you see?
• Your calculation is theoretical, not practical. Bethwaite wouldn't dispute the theoretical, just the practical.
• We need to remember that the article can only reflect what reliable sources have written, not our own work. (HopsonRoad (talk) 11:36, 3 August 2020 (UTC))

Cheers, HopsonRoad (talk) 23:24, 2 August 2020 (UTC)

Apparent wind

This should be clarified. An apparent wind can be separated into two components relative to the sail craft's frame of reference and orientation: an apparent headwind (or tailwind at slower speeds) and apparent crosswind. There is never any benefit to an apparent headwind. All of the thrust is due to diverting the apparent crosswind. Note that for a fixed heading with respect to the true wind, the apparent crosswind is sin(angle between true wind and sail craft's direction), which is constant for a constant true wind and heading, independent of the sail craft's speed. The overall efficiency determines the limit of speed for a given apparent crosswind and heading. Rcgldr (talk) 23:56, 4 August 2020 (UTC)

Thank you for writing, Rcgldr. I don't see any references separating V_A into components as you suggest. Take a look at Forces on sails#Components of force: lift vs. drag and driving vs. lateral force. The key is the forces of lift and drag resulting from the available angle of attack. Cheers, HopsonRoad (talk) 01:21, 5 August 2020 (UTC)

HopsonRoad I'd have to search for a reference. The one I recall was from a aerodynamics professor, more involved with wing design than sail craft. The paper was noting differences between a wing and a sail. A wing diverts a relative headwind downwards to produce lift which is perpendicular to the free stream (lift and drag combined are nearly perpendicular for an efficient wing, such as a Nimbus 4T glider with a 60:1 glide ratio). The goal of a sail is different. An efficient sail operating at high speed is generating a forwards (relative to the sail craft's orientation) thrust despite an apparent wind that is nearly a head wind. Compared to a wing, much of what could be considered as "lift" from a sail is being opposed by forces from the ground, ice, or water. By separating Va into components, it becomes clear that the apparent headwind can only contribute drag, and diversion of the apparent crosswind is the source of the thrust. It was also noted that the apparent crosswind only depends on the true wind speed and the sail craft's heading with respect to the wind, and is independent of the sail craft's speed. Some articles give the impression that a faster relative wind contributes to faster speed, but the faster apparent wind has no effect on the speed of the apparent crosswind, only an increase in the speed of the apparent headwind, which only contributes drag (not thrust). Rcgldr (talk) 04:44, 5 August 2020 (UTC)

A better analogy might be a propeller blade instead of an airplane wing. The angle of attack of the propeller airfoil isn't the airfoil angle with respect to its rotation disk, it's the vector sum of the velocity component around the disk plus the forward component of the disk moving through the air. The true angle of attack of the propeller blade airfoil is analogous to the apparent wind on a moving sailboat, and it's made up of two components. ~Anachronist (talk) 05:22, 5 August 2020 (UTC)

A propeller is a better analogy, but the reference I recall was comparing wings and sails. My issue is with articles that imply that faster apparent wind is the cause behind faster speed as an effect, which could be misinterpreted to mean a faster apparent headwind is increasing the thrust from a sail. Rcgldr (talk) 14:25, 5 August 2020 (UTC)

Both the aerodynamic force on a sail and the wind velocity are vectors so it is possible to resolve them into components depending on which co-ordinate system you choose to use. Early work in aerodynamics used a co-ordinate system parallel and perpendicular to the wing. Later, the current standard of parallel (drag) and perpendicular (lift) to the wind direction became widespread. I have seen treatments for sailboats that resolve the aerodynamic force into components parallel and perpendicular to the centerline of the boat, resolving the force into drive and heel (or leeway). Similarly, I can see where it might be illuminating to resolve the wind velocity into components parallel and perpendicular to the centerline of the boat, but I've never come across any literature that does this. Using the conventional coordinate system, by definition wind velocity is always 100% in the direction of drag. So, for the purposes of editing this article, the next step would be to find a reference that resolves wind velocity into components parallel and perpendicular to the boat. Mr. Swordfish (talk) 15:24, 5 August 2020 (UTC)

We shouldn't be looking for an innovative way of explaining V_A. We should be following the practice of reliable sources on the subject. So, unless reliable sources support the approach suggested by Rcgldr in the context of explaining forces on sails, and by consensus we determine that is a better approach than currently exists in the article, we should stick with the current approach. HopsonRoad (talk) 18:29, 5 August 2020 (UTC)

Rather than separate apparent wind into components, separating forces into components (F_r and F_lat) is already explained in Forces_on_sails#Components_of_force:_lift_vs._drag_and_driving_vs._lateral_force, and there is no need to duplicate that here. Rcgldr (talk) 21:59, 5 August 2020 (UTC)

From commons "VT = True wind speed VB = Boat speed VA = Apparent wind speed . . ."

With regards to the labeling of and differentiating between the antiparallel vectors boat speed and boat wind, there appears on reading and referencing the associated image(without referencing the commons description, it should be noted) to be an identical subscripted labelling for both vectors as V_B. While the written section and associated mathematical description do well to detail the apparent wind calculation with regards to boat wind, for those referencing the image to visualize the associated derivation, it can be a bit confusing. As a passerby, it wasn't my hope to unilaterally alter either the section description or the associated media, though it seems to me that the easiest rectification would be to specify that boat wind is antiparallel to boat speed by referencing boat wind as -V_B. Though as the associated media was uploaded by HopsonRoad, a modified image might best serve the purpose of the description, but this is to your discretion. The Intervocalic Sigma (talk) 21:36, 29 May 2021 (UTC)

Apparent Wind 2

Needs fixing:

β is magically introduced without any explanation - someone needs to say with this is the FIRST TIME it is mentioned (probably apparent wind angle - so if yes, spell that out).

This is an article about sailing. That implies SAILS. So this phrase needs to be reworded: "If the craft travels at VB = 10 knots with a tailwind of VT = -5 knots" - last time I checked, regular sail boats cannot sail downwind at double the speed of the wind. Introducing examples that are impossible does NOT help anyone understand things! — Preceding unsigned comment added by 110.143.72.26 (talk)

 Done Thank you for calling that out. HopsonRoad (talk) 23:04, 31 May 2021 (UTC)

VMG exceeding true wind

Would it make sense to change this:

"High-performance watercraft that can exceed the velocity of the true wind include..."

to something like this:

"High-performance watercraft that can achieve VMG in excess of the true wind include..."

When I read the article I was at first questioning if it was talking about exceeding speed of the true wind in its direction of travel or if it meant the direct downwind component of its velocity vector (VMG) could exceed true wind. After reading it over a few times it seems like it is the latter. But only because I've read other things. Seems like it would be clearer if it was explicitly stating that it is VMG we're talking about here. — Preceding unsigned comment added by 50.238.167.160 (talk) 23:46, 22 August 2022 (UTC)

Velocity made good refers solely to directly into or away from the wind. The sentence should probably read, "High-performance watercraft that can exceed the speed of the true wind include..." Cheers, HopsonRoad (talk) 01:56, 23 August 2022 (UTC)

Thanks for the reply. Maybe I am misunderstanding the intent of your definition of VMG, but that doesn't seem right to me. I thought VMG basically refers to the component of the the boat's velocity vector in the direct downwind/upwind direction. But the boat's total velocity vector can be something different obviously. Basically it's the average speed of the boat in the updwind/downwind direction. Here is the first sentence from the link you provided: "Velocity made good, or VMG, is a term used in sailing, especially in yacht racing, indicating the speed of a sailboat towards (or from) the direction of the wind." So that's why I was proposing that it be worded that way. It's basically saying, "High-performance watercraft that can achieve a direct upwind/downwind component of their true velocity vector in excess of the true wind include..." But that seems kind of wordy when we have a nice term like VMG already that covers all that. I feel like changing as you suggest would not get rid of my initial confusion. I want something in there that explicitly states that the velocity we're talking about is in the direct upwind/downwind direction. Technically, you could argue that the way it's currently worded is sufficient since it uses the word "velocity" which is a vector. I just thought it would make it clearer to explicitly put it in terms of VMG since it's not immediately obvious that one should read "velocity" using its formal definition in physics rather than colloquially. In any case, I think changing it to "speed" would make it worse, in fact, because now we truly have no idea about what direction we're talking about. 50.238.167.160 (talk) 15:19, 31 August 2022 (UTC)

Thank you for your engagement, here. The intent for this encyclopedic article is to keep the concept simple. The point is that an anemometer reading on the sailing craft would exceed that taken at a fixed point without reference to what direction the craft was pointing or the wind blowing. This is a comparison of scalars, only. Comparing vectors or their components would not be productive, here. Cheers, HopsonRoad (talk) 21:23, 31 August 2022 (UTC)

Thanks and thank you for the answers. I was really just going to drop this but your latest reply has really got me scratching my head and has me thinking maybe I was wrong all along about my initial interpretation of the sentence. Now it sounds like you are saying all it means is that sail craft have the ability to go faster than the true wind ACROSS the wind in the direction of their travel. E.g., if the true wind is 10 mph out of the south, the sail craft can go say, 12 mph, on a 285 degree tack. Is that right? If so, I take everything I said back and I apologize for wasting your time because that is the opposite of what I thought it meant. I thought we were talking about VMG. I didn't think that going faster than the wind across the wind was really exclusive to high-performance sailboats or even that remarkable (though of course the multiples of true wind that high-performance sail craft achieve certainly is impressive). But maybe I'm just misinformed on that and it is really a rare thing.

In any case, would it make sense to add a section on high performance sail craft achieving VMG > true wind speed? The reason I ask is because I initially came to this page looking for confirmation that that is even possible. I think most people, even non-sailors, understand that sail craft can go faster than the wind across the wind. What is surprising to a lot of people (myself included at first and even a sailing friend of mine) is that a sail craft can achieve VMG > true wind speed. It is my understanding that land and ice boats have been doing this for some time (which is what I thought was meant by "Ice boats and land-sailing craft are often able to do so." which, along with the mention of the Blackbird, led me to think we were talking about VMG) but sailboats managing this is a relatively recent thing.

I don't know, maybe it's just me but I think achieving VMG > true wind is something really remarkable and counter-intuitive to most people and it is certainly something that is exclusive to high-performance sail craft. Just seems like if we're going to mention that high-performance sail craft can go faster than the wind across the wind (something that I think even lay-people understand), it might worth mentioning the even more impressive fact that they can achieve VMG > true wind somewhere in the article too. 50.238.167.160 (talk) 16:09, 2 September 2022 (UTC)

Ugh, I see it was changed to "speed" from "velocity". Like I said in my first reply to this, I think "velocity" was better since at least it's a vector quantity and since we're comparing it to true wind we can assume it's in the same direction. Just might not be obvious to a non-physics type of person who is not used to dealing with vectors. In any case, I think "speed" is worse for the reasons given. I guess I should have kept my mouth shut lol. 50.238.167.160 (talk) 15:42, 31 August 2022 (UTC)

See the above reply! Scalar quantities and more pertinent and easier to understand! Cheers, HopsonRoad (talk) 21:24, 31 August 2022 (UTC)