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sailquik said..

barney831 said..
The little experiment that I suggested is not for me, I've already done it on ice, snow, land and water - it is for you. I know what the results are but it can be enlightening to experience it yourself.

But you are right, it is more difficult to do quantitatively on the water than the ice and it gets more difficult the faster you go. So do it in a light offshore 20 knot wind where there is smooth water with plenty of depth.

What You KNOW the results!

That is not the impression you gave in the early posts.

So why dont you just tell us what your results are

I would also be interested in a descrption of the design of your speed boards, sails and fins that you say you have done these experiments with, and the conditions you did them in.

You can attach image files so just convert your PDF to an JPEG.

I'd like to see the arrangement of the telltales relative to the leading edge of the sail, as I think the arrangement that Segler described (telltale on a strut 18" in front of leading edge) would be adversely affected by the upwash in the airflow caused by the sail.

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sailquik said..

barney831 said..
The little experiment that I suggested is not for me, I've already done it on ice, snow, land and water -

What You KNOW the results!

For the numbers you gave us Sailquick, 40 knots in 30 knots of wind at 125 deg, Beta = asin ((30/40)* Sin 125 deg ) = 37.9 deg.
Inverse sins, asin, sin -1, they go by a few names to keep it confusing, are on your mac calculator app. Just make sure you tick up the scientific option and use degrees not radians. 2 degrees out in wind estimate gives about a 2 degree error in Beta.

Always worth repeating experiments. I see Barney has done it for ice, snow , land and water but not weedy, very shallow water.
Hence the request now for a comparison? " So do it in a light offshore 20 knot wind where there is smooth water with plenty of depth."

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Ian K said..
2 degrees out in wind estimate gives about a 2 degree error in Beta.

Which is why I dont think my experiments show anything very useful, or probably Barneys for that matter either. There are far too many variables and unknowns without sophisticated/accurate real time data measurements of wind speed and wind angles, not to mention a host of others.

As a side note, this has got me thinking again about what could be learned using teltales on sails.

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sailquik said..
Which is why I dont think my experiments show anything very useful, or probably Barneys for that matter either. There are far too many variables and unknowns without sophisticated/accurate real time data measurements of wind speed and wind angles, not to mention a host of others.
As a side note, this has got me thinking again about what could be learned using teltales on sails.

With Daffy on this. For those that have windsurfed a long time "feel" tells them more than visual observations. Because windsurfers have a direct connection to the sail and a direct connection to the board they can feel the most efficient trim by countless automatic micro adjustments. Whilst for yachts and iceboats with winches and pulleys etc a visual clue is essential. No one tells geese the most efficient way to fly is in a V formation because the tip vortices of the bird in front and to the side provide an upwash. They know from feel and experience this is the most efficient way to fly as a group.

Minimizing the upwash effect in front of the sail is exactly why the strut is at least 18" long. You could make it 5 meters long if you want, but it would be difficult to attach securely to the mast or luff.

Anyway, when I first did this, I had the telltale attached to the leading edge of the sail. All it did was hug the surface of the sail regardless of point of sail. Moving it out there a ways gets it out in cleaner air. Yes, of course, you want to get it out of the leading edge boundary layer. For me 18" seemed to be enough.

And, yes, a good slalom board will be faster than a formula board in all points of sail except upwind. When cranking steeply upwind with a good fin, nothing can touch a formula board, either in raw boat speed or vmg. But ya gotta be massively powered, thus the huge sail, to make a good upwind vmg. I have been in many races, underpowered, when the non-planing Kona racers beat me to the weather mark. Hate that.

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sailquik said..

barney831 said..
The little experiment that I suggested is not for me, I've already done it on ice, snow, land and water - it is for you. I know what the results are but it can be enlightening to experience it yourself.

But you are right, it is more difficult to do quantitatively on the water than the ice and it gets more difficult the faster you go. So do it in a light offshore 20 knot wind where there is smooth water with plenty of depth.

What You KNOW the results!

That is not the impression you gave in the early posts.

So why dont you just tell us what your results are

I would also be interested in a descrption of the design of your speed boards, sails and fins that you say you have done these experiments with, and the conditions you did them in.

You can attach image files so just convert your PDF to an JPEG.

I didn't say initially that I have results and I won't say now what the results are - because I don't want to introduce the possibility of bias into other peoples' experiments.

This point may be moot, however, because it doesn't look like anybody is interested in doing the little experiment and reporting the results.

Nevertheless, the effort was worth it for me to see the apparent wind at 90 degrees to the true wind while standing on a board at >30 knots.

One way to absolutely ensure that the telltale is in clean air is to put it onto a rod a few feet above the top of the mast. It is a little harder to see, but it is definitely out of boundary layer flow way up there.

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yoyo said..

sailquik said..
Which is why I dont think my experiments show anything very useful, or probably Barneys for that matter either. There are far too many variables and unknowns without sophisticated/accurate real time data measurements of wind speed and wind angles, not to mention a host of others.
As a side note, this has got me thinking again about what could be learned using teltales on sails.

With Daffy on this. For those that have windsurfed a long time "feel" tells them more than visual observations. Because windsurfers have a direct connection to the sail and a direct connection to the board they can feel the most efficient trim by countless automatic micro adjustments. Whilst for yachts and iceboats with winches and pulleys etc a visual clue is essential. No one tells geese the most efficient way to fly is in a V formation because the tip vortices of the bird in front and to the side provide an upwash. They know from feel and experience this is the most efficient way to fly as a group.

I find that when I wear a helmet that covers my ears I loose a bit of that "feeling", for some reason i find it a bit harder to finesse the sail and board to the wind, that's why I wear my cycling helmet which doesn't cover my ears.

I'm the opposite Choco, always have earphones in, can't hear the wind so it never seems as windy. Also lets me listen to some old Aussie tunes and hear my speed readout.

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choco said..

yoyo said..

sailquik said..
Which is why I dont think my experiments show anything very useful, or probably Barneys for that matter either. There are far too many variables and unknowns without sophisticated/accurate real time data measurements of wind speed and wind angles, not to mention a host of others.
As a side note, this has got me thinking again about what could be learned using teltales on sails.

With Daffy on this. For those that have windsurfed a long time "feel" tells them more than visual observations. Because windsurfers have a direct connection to the sail and a direct connection to the board they can feel the most efficient trim by countless automatic micro adjustments. Whilst for yachts and iceboats with winches and pulleys etc a visual clue is essential. No one tells geese the most efficient way to fly is in a V formation because the tip vortices of the bird in front and to the side provide an upwash. They know from feel and experience this is the most efficient way to fly as a group.

I find that when I wear a helmet that covers my ears I loose a bit of that "feeling", for some reason i find it a bit harder to finesse the sail and board to the wind, that's why I wear my cycling helmet which doesn't cover my ears.

I find the same thing but luckily my Gun helmet lets enough wind through to get a feel on wind direction. I think we all unconsciously use our face and hearing to judge apparent wind direction. When your nose is as big as mine it makes a great telltale for feeling wind direction :)

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Jetlag said..

choco said..

yoyo said..

sailquik said..
Which is why I dont think my experiments show anything very useful, or probably Barneys for that matter either. There are far too many variables and unknowns without sophisticated/accurate real time data measurements of wind speed and wind angles, not to mention a host of others.
As a side note, this has got me thinking again about what could be learned using teltales on sails.

With Daffy on this. For those that have windsurfed a long time "feel" tells them more than visual observations. Because windsurfers have a direct connection to the sail and a direct connection to the board they can feel the most efficient trim by countless automatic micro adjustments. Whilst for yachts and iceboats with winches and pulleys etc a visual clue is essential. No one tells geese the most efficient way to fly is in a V formation because the tip vortices of the bird in front and to the side provide an upwash. They know from feel and experience this is the most efficient way to fly as a group.

I find that when I wear a helmet that covers my ears I loose a bit of that "feeling", for some reason i find it a bit harder to finesse the sail and board to the wind, that's why I wear my cycling helmet which doesn't cover my ears.

I find the same thing but luckily my Gun helmet lets enough wind through to get a feel on wind direction. I think we all unconsciously use our face and hearing to judge apparent wind direction. When your nose is as big as mine it makes a great telltale for feeling wind direction :)

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choco said..

Jetlag said..

choco said..

yoyo said..

sailquik said..
Which is why I dont think my experiments show anything very useful, or probably Barneys for that matter either. There are far too many variables and unknowns without sophisticated/accurate real time data measurements of wind speed and wind angles, not to mention a host of others.
As a side note, this has got me thinking again about what could be learned using teltales on sails.

With Daffy on this. For those that have windsurfed a long time "feel" tells them more than visual observations. Because windsurfers have a direct connection to the sail and a direct connection to the board they can feel the most efficient trim by countless automatic micro adjustments. Whilst for yachts and iceboats with winches and pulleys etc a visual clue is essential. No one tells geese the most efficient way to fly is in a V formation because the tip vortices of the bird in front and to the side provide an upwash. They know from feel and experience this is the most efficient way to fly as a group.

I find that when I wear a helmet that covers my ears I loose a bit of that "feeling", for some reason i find it a bit harder to finesse the sail and board to the wind, that's why I wear my cycling helmet which doesn't cover my ears.

I find the same thing but luckily my Gun helmet lets enough wind through to get a feel on wind direction. I think we all unconsciously use our face and hearing to judge apparent wind direction. When your nose is as big as mine it makes a great telltale for feeling wind direction :)

I have used both types of helmets, uncovered ears and covered ears. The biggest difference I noticed, is that now my ears are warmer.

I really dont think there is anything practical gained about the feelings of having your ears exposed. I can see the wind angles on the water ripples and foam lines, and can feel the pressure in my sail to get feedback of optimum angles. I think it is more likely placebo effect, (like knowing you have a 200gm lighter board - which must make you faster, right?) which of course is quite valid, as positive thoughts always help.

My new mantra: :Negative thoughts make you slower"

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barney831 said..

I didn't say initially that I have results and I won't say now what the results are - because I don't want to introduce the possibility of bias into other peoples' experiments.
This point may be moot, however, because it doesn't look like anybody is interested in doing the little experiment and reporting the results.
Nevertheless, the effort was worth it for me to see the apparent wind at 90 degrees to the true wind while standing on a board at >30 knots.

I am very interested in doing the experiment Barney. I am just laid up with a back back at the moment and even then it may take a while for me to get the right conditions to try it. Yes, I am quite sceptical that I will get a meaningful result, but if you say it is worth a try, it is worth a try.

But keeping you results a secret is not the way of science.......

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segler said..
One way to absolutely ensure that the telltale is in clean air is to put it onto a rod a few feet above the top of the mast. It is a little harder to see, but it is definitely out of boundary layer flow way up there.

Upwash can be significant, and I assume greater at high angles of attack, so even with an 18" strut in front of the mast I think the flow direction could be distorted.

In the photo below, it is worth keeping in mind that these are smoke streams in a wind tunnel which would be completely horizontal without the presence of the wing section. Close to the leading edge there is substantial deformation of the streamlines, but there is also deflection of the streamlines at the left edge of the photo, well upstream of the wind leading edge.

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sailquik said..

barney831 said..

I didn't say initially that I have results and I won't say now what the results are - because I don't want to introduce the possibility of bias into other peoples' experiments.
This point may be moot, however, because it doesn't look like anybody is interested in doing the little experiment and reporting the results.
Nevertheless, the effort was worth it for me to see the apparent wind at 90 degrees to the true wind while standing on a board at >30 knots.

I am very interested in doing the experiment Barney. I am just laid up with a back back at the moment and even then it may take a while for me to get the right conditions to try it. Yes, I am quite sceptical that I will get a meaningful result, but if you say it is worth a try, it is worth a try.

But keeping you results a secret is not the way of science.......

I sympathize, I too am recovering -
from a broken pelvis that happened early in December; too soon old, too late smart.

No secrets here but I'm trying to decide if I have enough time and energy left to publish a short monograph or even a paper or two on the mass of windsurfing data that I have collected since I retired from getting paid for a living in '96. The cost-benefit ratio is extremely poor.

The simple experiment that I suggested doesn't have to be quantitative and it doesn't have to be in 40 knot winds. If speed sailors do everything by feel, it is worth the feeling to stick a telltale on the centerline of your board a couple of inches back from the nose and observe when the apparent wind is 90 degrees from the true wind. A telltale on the front of the deck should be below the most of the flow induced by the sail. You can check this by rapidly sheeting out to zero AOA and observing if there is any motion of the telltale correlated with the sheeting out motion of the sail.

If you are going windsurfing anyway it is a zero cost experiment.

Bon Chance!

Looking at the photo Pacey supplied even a telltale on the nose of the board would be 10-15 degrees out.

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yoyo said..
Looking at the photo Pacey supplied even a telltale on the nose of the board would be 10-15 degrees out.

How is this plagiarized photo relevant in any way to the simple experiment that I proposed?
Qualitatively? or Quantitatively?
Never heard of proper references? Pacey (whoever that is?) did not do this work!

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barney831 said..

yoyo said..
Looking at the photo Pacey supplied even a telltale on the nose of the board would be 10-15 degrees out.

How is this plagiarized photo relevant in any way to the simple experiment that I proposed?
Qualitatively? or Quantitatively?
Never heard of proper references? Pacey (whoever that is?) did not do this work!

It's not plagiarism, its a photo illustrating basic physics off the internet. And the comment was in reference to Segler's strut based telltale, which I felt would need to be a bit longer in order to avoid error due to upwash effect.

Footstrap insert in the nose of the board and a pole sticking up from there, should be able to get it above the bent air. I'll do it one day when we get water in our run.

Senor Quick said....
" (like knowing you have a 200gm lighter board - which must make you faster, right?) "which of course is quite valid, as positive thoughts always help........

......how differently we think, my take is.......... "my board's heavier so it goes through the chop leading on to the run better and it has momentum so doesn't slow in the lulls, so it must be faster, right?

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Te Hau said..
Senor Quick said....
" (like knowing you have a 200gm lighter board - which must make you faster, right?) "which of course is quite valid, as positive thoughts always help........

......how differently we think, my take is.......... "my board's heavier so it goes through the chop leading on to the run better and it has momentum so doesn't slow in the lulls, so it must be faster, right?

Actually, mine was a sarcastic comment. I like your theory better.

And it doesnt really matter what you believe, as long as it helps you be positive.