Select to expand quoteClausF said..
Ask any of the surfers on this video from Denmark about how their day was on the water, - they will all reply "It was bloody fantastic!!"... 
As cold as it looks in that video, those guys should be crashing their brains out, they can't feel their hands or feet 
Select to expand quoteClausF said..
Ask any of the surfers on this video from Denmark about how their day was on the water, - they will all reply "It was bloody fantastic!!"...
As cold as it looks in that video, those guys should be crashing their brains out, they can't feel their hands or feet
Select to expand quoteClausF said..
Ask any of the surfers on this video from Denmark about how their day was on the water, - they will all reply "It was bloody fantastic!!"...
As cold as it looks in that video, those guys should be crashing their brains out, they can't feel their hands or feet
Select to expand quoteClausF said..
Ask any of the surfers on this video from Denmark about how their day was on the water, - they will all reply "It was bloody fantastic!!"...
As cold as it looks in that video, those guys should be crashing their brains out, they can't feel their hands or feet
Select to expand quoteTe Hau said..ClausF said..
Ask any of the surfers on this video from Denmark about how their day was on the water, - they will all reply "It was bloody fantastic!!"...
As cold as it looks in that video, those guys should be crashing their brains out, they can't feel their hands or feet
Yes, actually in some parts of the video the temps were below 0?C.. Vikings..
Not quite to sort of crashes. Most of those are everyday standard get offs.
I was thinking more like these:
Does anyone know of an online apparent wind calculator that can give me an answer for these numbers? All the ones I have tried to use give me rubbish numbers or nothing at all. Or someone who can do the math? 
What I am looking for of course, is the apparent wind angle for the boat/board in this scenario:
True wind speed 38 knots.
True wind direction 270 degrees
Sailed course heading 135 degrees (=135 degrees off the true wind angle)
Boat/Board speed 45 knots.
Select to expand quotesailquik said..
Does anyone know of an online apparent wind calculator that can give me an answer for these numbers? All the ones I have tried to use give me rubbish numbers or nothing at all. Or someone who can do the math?
What I am looking for of course, is the apparent wind angle for the boat/board in this scenario:
True wind speed 38 knots.
True wind direction 270 degrees
Sailed course heading 135 degrees (=135 degrees off the true wind angle)
Boat/Board speed 45 knots.
Not going to do your homework for you Daffy but this diagram will help you work it out.
Thanks Roo, but that still does not make sense to me without an explanation.
For instance. the true wind angle should not change??
Anyone like to elaborate?
Andrew, Using formulas in Wikipedia I came up with:
Apparent wind speed = 32.41 knots
Apparent wind angle to the board = 55.9 degrees. The URL I used is
en.wikipedia.org/wiki/Apparent_wind
Thanks John. That makes sense to me.
So assuming a sheeting angle of about 30 degrees from the centerline of the board in the above example, (just a guess - could be more or less), that would give the sail approximately a 25 deg AOA. If the sheeting angle is less, say 20 deg. AOA is more, in this case 35 deg.
I wonder if we can somehow get a ball park figure for the optimum sheeting angle to the apparent wind on different courses from the true wind for a windsurfer using these calculations and assumptions?
For instance, I observed I could do around 26-27 knots speed on pretty close to a square reach, in, I estimate, around 16-17 knots of wind. (Flat water, IS86, Tribal speeded 27cm Koncept 6.2m sail) I am sheeted so the foot of the sail is right in against of my leeward rear footstrap. That suggests around 10 degrees sheeting angle to me, and I can feel the apparent wind is very forward.
But in 26-28 knots of wind I can only pull about 30-32 knots on a beam reach. Sheeting angle is very similar but maybe a little further out. (Flat water, IS50, 20cm speed fin, 5.0m Koncept.) Note: Quoting these speeds is tricky, because just a small change of course angle broader will quickly add knots to the speed, especially in the latter case.
On a speed board at top speed in 38+ knots of wind the sheeting angle is definitely out further.
What angle does this look like?
And another random example:
Quick question, what are you taking as sheeting angle? Center line of boom seems obvious to me, buy obvious to me isn't always correct.
In which case maybe 20deg, would be much easier to judge with an overhead drone shot
Yes. That is what I would call it. Centreline of boom V's drection of travel (not alwats quite the same as centerline of board as you can clearly see below).
As requested Although this is in lightish wind, maybe 15-16 knots:
So applying the above logic to a recent session I had at Lake George.
Wind speed = 30kts
Board Speed = 40 kts
Direction of board angle to wind = 135 deg
Apparent wind = 28 kts
Apparent angle of wind to board = 48 deg
I don't think I was holding my boom at 48 degrees to the direction of the board. It was probably more like 30, so I was chocking the sail, i.e. not sailing efficiently. I suppose this is why others were sailing faster
Select to expand quotesailquik said..
In which pictures?
Bugger forgot to bring my protractor from the shed!
I was referring to the overhead shot.
Select to expand quoteJohn340 said..
>>>>>
I don't think I was holding my boom at 48 degrees to the direction of the board. It was probably more like 30, so I was chocking the sail, i.e. not sailing efficiently. I suppose this is why others were sailing faster
don't forget the angle of the leading edge is very different to the boom angle. if the boom angle is the same as the wind, you're not getting a lot of lift.
I think max lift is when the leading edge is aproaching the apparent wind angle?
You fellows have all forgotten your year 12 trigonometry. ( I'd forgotten the details but I knew there was something called the Cosine rule so I googled it )
revisionmaths.com/gcse-maths-revision/trigonometry/sine-and-cosine-rule
The cosine rule
C*C = A*A + B*B - 2AB Cos(A)
A,B and C are the sides of any triangle and A is the angle opposite side A. (You'll see that when A is 90, Cos of 90 is zero it reverts to the old pythagorus rule)
So knowing the board speed, the wind speed and the angle between them the cosine rule is the one to use.
A*A = W*W + B*B - 2W*B * Cos(135 -90)
here A is apparent wind strength W is true wind B is board speed.
Put the numbers in and apparent wind is 28.33 knots
then you can find the angle by using the sine rule
A /sinA = B / sinB = C / sinC
28.33 / Sin( 135 - 90 ) = 30 / Sin A
Sin A = 30 X 0.707106 / 28.33
A = 48.4 degrees. - Agrees with John's method.
Select to expand quoteJohn340 said..
I don't think I was holding my boom at 48 degrees to the direction of the board. It was probably more like 30, so I was chocking the sail, i.e. not sailing efficiently. I suppose this is why others were sailing faster
You will need to add some angle of attack on your sail to generate the power. Typical wing AoA is around 15-20 degrees, so you holding at 18 is in the ballpark. Each sail would have its own optimum AoA though.
Select to expand quoteVRBones said..You will need to add some angle of attack on your sail to generate the power. Typical wing AoA is around 15-20 degrees, so you holding at 18 is in the ballpark. Each sail would have its own optimum AoA though.
Yes, I think the AOA will be different for different sails, but I think even different sails would be very close, maybe within a few degrees.
Select to expand quotedecrepit said..sailquik said..
>>>>
Therein is another question, apparent wind angle, relative to centerline of board, or direction of travel?
I think the telltale and protractor with a mast cam, would work, you can see the angle relative to board, and probably get an estimate of yaw from the wake.
Select to expand quotebarney831 said..
The attached video is of a quad going 25 knots in 5 knot winds with a 3.4 m^2 sail. There is zero leeway and the rear blades are running exactly in the track of the front blades.
Can't be zero leeway, the video shows the blades throwing ice particles to the lee side, Can't do that without an angle of attack. Maybe the rear blades are running the same track due to a chassis mis-alignment?
Select to expand quoteIan K said..barney831 said..
The attached video is of a quad going 25 knots in 5 knot winds with a 3.4 m^2 sail. There is zero leeway and the rear blades are running exactly in the track of the front blades.
Can't be zero leeway, the video shows the blades throwing ice particles to the lee side, Can't do that without an angle of attack. Maybe the rear blades are running the same track due to a chassis mis-alignment?
The blades are asymmetric (chisel profile), rockered and aligned. They are generating lateral resistance without any yaw angle of the board. The centerline is in the direction of travel and it tracks like it was on rails.
Select to expand quotebarney831 said..
The blades are asymmetric (chisel profile), rockered and aligned. They are generating lateral resistance without any yaw angle of the board. The centerline is in the direction of travel and it tracks like it was on rails.
Ah. So there's a fair bit of tuning to get the rear blades to slot in behind the front ones? You don't just bolt them on square and hope for the best?
Select to expand quoteIan K said..barney831 said..
The blades are asymmetric (chisel profile), rockered and aligned. They are generating lateral resistance without any yaw angle of the board. The centerline is in the direction of travel and it tracks like it was on rails.
Ah. So there's a fair bit of tuning to get the rear blades to slot in behind the front ones? You don't just bolt them on square and hope for the best?
The L/D of the blades is an order of magnitude higher than the sail (or a fin). I just unbolt the wheels and bolt on the blades. The trick is in precision grinding of the blades to the optimum profile in 3D. Not sure that I'm quite there yet.
Keep in mind, what I said above only holds for lighter winds. When the wind gets stronger there is some AOA on the blades and the front and back tracks separate slightly.
I get similar results for my I5.6 quad mini and my windski.
