Nice video

I sat through that and I found it to be hard work, partly because of over thinking.
Windsurfing is complex, but I wonder if we don't actually need to know the science of how the kit works, when really we just need to learn to drive it. Did anyone offer you any science advice when you learned to ride a bike?

On the plus side, the basics are correct in this video and the graphics are helpful. But if you simply google 'how a yacht sails upwind' then you'll get a simpler explanation.
The way we turn the board is also more complex than explained in this video - because we move the sail area backwards and forwards over the centre of lateral resistance, and we also carve turn the board on its rails.

I also cringed slightly when the board's ability to sail upwind as solely attributed to the fin stopping sideways drift. Because of course you don't actually need a long fin to go upwind, you just need to plane and for the board of offer sideways resistance - and that sideways resistance comes from the rails and planing spray as much as it comes from lift from the fin.

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Basher said..
- and that sideways resistance comes from the rails and planing spray as much as it comes from lift from the fin.

That's a new one on me.

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Shifu said..<< That's a new one on me.

Depends how much of the board is in the water, and how fast it's going. At low speed more board under water so the rail gives more resistance, and the fin produces less lift, this is why in marginal conditions you can point higher in buoyancy mode than by planning. At high speed most of the board is above water and the fin is powered up.

As to planning spray, I'm not sure. I guess if the spray is heading downwind, there could be an equal and opposite force on the board upwind, I normally try to get windward rail up, so which way is spray going?

We can go upwind using the rail, just as kitesurfers do - although our rig loads work slightly differently.

My point was that it's a mistake to think all the sideways lateral resistance comes from fin lift.
Freestyle boards go upwind on their rails very efficiently, even where a small fin is fitted. The sideways resistance comes from the planing footprint of the board, but of course a fin can add to that.

It's a common error to think upwind work is solely about the fin. For sure, a long fin can help you point higher, but too big a fin can sometimes slow you down. It's planing upwind efficiently and with good stance that's important, more than simply fitting a long fin to your board.

The planing spray issue is a more controversial claim - is the spray ejected at the rail helpful in getting us upwind or is it simply a side effect of hydroplaning? I'm not discounting it as a plus.

If you're on a big old board then the windward performance may be helped by the leeward rail being in the water - and older boards used to have big chunky rails for that reason. But modern freestyle boards sit above the water more and go upwind on the windward rail. It might be interesting to find a photo which shows which way the spray flies.

Heading upwind efficiently is also a function of how well you snake through waves and chop, choosing a path which gives you optimum speed in terms of ground made good - and again this is not really about the fin.

Huh? ... that video is completely wrong... has he has never heard of "lift" or "low pressure" ?

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mathew said..
Huh? ... that video is completely wrong... has he has never heard of "lift" or "low pressure" ?

It makes my life easy...sails just need to be dead flat as profile does not produce lift. Can get rid of the 3D software.

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mathew said..
Huh? ... that video is completely wrong... has he has never heard of "lift" or "low pressure" ?

It's the photon particle theory of propulsion. He's a rocket scientist.

I took it as an entry level video, just the basics. In that form, i think its fine.

Hopefully his next one is something along the lines of "planing and the dynamics of windsurfing at speed"

What I liked about the video is that he talked about apparent wind. Most discussions omit apparent wind.

The video seems to explain a few things about windsurfing, but it seems rather half-baked. The explanation why the board does not go downwind is correct if you are fully planing, riding the fin with absolutely minimal water contact. That applies only to advanced windsurfers in some conditions; at other times, rail resistance is quite important, too. For beginners on beginner boards, the water line of the board plays a much larger role than the fin.

But when he explains steering, he explains sail steering in non-planing mode, although the stance of the windsurfer is a planing stance. While the explanation may be correct, it is rather confusing in the context of the video.

The "no go" zone is an important concept for beginners without sailing background. But showing 45 degree angles on a freeride, fin-only board is nonsense. Such angles may be possible on a powered formula board or race board, but most intermediate windsurfers will find it quite hard to point higher than 20-25 degrees on a freeride board.

Using a perfectly flat sail at the beginning of the video, and then stating that "the profile does not lift the sail upwind", may give a beginner the wrong impression that the profile of the sail is unimportant. Giving that learning to rig properly is one of the harder things to learn for beginners, that's the wrong message. But it's a not an unexpected consequence of the particle theory of propulsion.

Too bad Jim Drake's explanations (check australiankiteboarding.com.au/j-kiteboarding/jim-drake-physics-of-windsurfing.html for links) were published before Youtube became the standard "education" channel.

And why did the sail appear to be clew first in the bit about going faster that wind speed?. Is this something we didn't know about?

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Subsonic said..
I took it as an entry level video, just the basics. In that form, i think its fine.

Hopefully his next one is something along the lines of "planing and the dynamics of windsurfing at speed"

I understand that philosophy - I'm with Basher, you dont need to know the physics of bikes to learn how to ride; when you want to know the physics, you want something that gives you something approximately correct.

Then at the 6 min mark, there is some discussion of lift - great. But completely misses the point of why you would ever want to discuss "lift" - you would almost-never discuss "lift" as being some type of direction of travel. [ You can get "lifted" off the water in a gust and a "lift" is used on a racecourse, but those are advanced and racing skills, not beginner skills. ]

The explanation is very wrong - IMHO windsurfing shouldn't be explained as particles-bouncing-off-a-surface.