Fin ?

combination, fin lifts windward rail, wind gets under board.
Smaller fin, or more weight forward would help control this.

Imax1 said.. It would be so great if we had that super flat windy water to play in.

Where I come from that's only flatish, a long way from super flat.

Research tail walking.

Are you having this specific problem, or just interested in the physics of the situation? All good either way, just asking because you'll get different answers if youre having problems...

LeeD said..
>>>> Raked back sail produces lift.
>>>

Lift from sail, is pushing nose down! That's why less downhaul helps reduce tailwalking, and more downhaul helps unstick the board. Sheeting out in a gust will also initiate tail walking

In the video I notice a blurry white shape,
could it be Casper the friendly ghost ?

Subsonic said..
Are you having this specific problem, or just interested in the physics of the situation? All good either way, just asking because you'll get different answers if youre having problems...

No body can explain physics in windsurifing.
Fin cant lift nose,just opposite ,flexibile fin can lift tail and put nose down, but fin can lift windward rail up.
Sail dont produce downforce at all,just opposite sail ALLWAYS produce "upforce" becuse it is lean to windward,sailor body mass is what produce "downforce" or so called mast foot pressure,but if your harness lines stay 100% horizontal there is no downforce at all..etc etc

www.guycribb.com/userfiles/documents/downforce.pdf









Guess who has more mast foot pressure of these two?

LeeD said..
Not applicable.
Both sailors are in control.
Tailwalking occured as control is lost.

Are you mad......both sailors are totally out of control and just about hanging onto their rigs. Its a speed course and they are using way too much sail area but are also going ridiculously fast.

fpw9082 said..

Subsonic said..
Are you having this specific problem, or just interested in the physics of the situation? All good either way, just asking because you'll get different answers if youre having problems...

No body can explain physics in windsurifing.
Fin cant lift nose,just opposite ,flexibile fin can lift tail and put nose down, but fin can lift windward rail up.
Sail dont produce downforce at all,just opposite sail ALLWAYS produce "upforce" becuse it is lean to windward,sailor body mass is what produce "downforce" or so called mast foot pressure,but if your harness lines stay 100% horizontal there is no downforce at all..etc etc

www.guycribb.com/userfiles/documents/downforce.pdf









Guess who has more mast foot pressure of these two?

Mast foot pressure is relative. You can tell by the trim of the board that the first sailor likely has more mast foot pressure. If you transfer some weight from your feet - especially back foot into the rig then you can level the board out & we call this mast foot pressure.

fpw9082 said..

Subsonic said..
Are you having this specific problem, or just interested in the physics of the situation? All good either way, just asking because you'll get different answers if youre having problems...

No body can explain physics in windsurifing.
Fin cant lift nose,just opposite ,flexibile fin can lift tail and put nose down, but fin can lift windward rail up.
Sail dont produce downforce at all,just opposite sail ALLWAYS produce "upforce" becuse it is lean to windward,sailor body mass is what produce "downforce" or so called mast foot pressure,but if your harness lines stay 100% horizontal there is no downforce at all..etc etc

www.guycribb.com/userfiles/documents/downforce.pdf









Guess who has more mast foot pressure of these two?

Every bit of physics in windsurfing is explainable, but theres just that much of it going on that it can sometimes be hard to determine what exactly is causing something specific. Especially when targeting a single picture, which is not even a split second of what is going on.

what if i told you the sail can and does produce down force?

Madge said..
Are you mad......both sailors are totally out of control and just about hanging onto their rigs. Its a speed course and they are using way too much sail area but are also going ridiculously fast.

I have to point out that both sailors ARE in control. 'Out of control' means they would be crashing or about to crash.
They woud be cretainly feel very well powered up. Perhaps feeling that they could not hold much more power without crashing, but that is not being 'out of control'. They would probably be feeling that they better get everything exactly right, as one small error could put them 'out of control' and into a big crash.

There seems to be a common misconception that to go as fast as possible on a speed run, one has to use the biggest sail possible. This is not actually the case. One has to use the most effecient sail size possible, and there is a difference. You are looking for the best lift to drag ratio. There is no gain on using a sail 2 sq meters larger and then having to rig it extremely flat and twisted to reduce its lift so as to remain in control. That very large sail will have far more drag when a smaller one will likely have the same amount of lift and far less drag.

Now of course the situation in a course or slalom race is a bit different. The overriding factor there is often the need to maintain as much power as possible during the inevitable lulls, and to be able to have maximum acceleration from starts and gybes. That is often worth carrying more sail and more drag at top speed. Just dropping off the plane for a few seconds in a race can take you from first to last in a very short time and is worth trying to avoid at all costs (carrying more sail and drag at top speed and having to be really fit, strong and skilled to control it for the, often, relitively short duration of the race is the 'cost')

decrepit said..
But look at the geometry, and draw some vectors.
The COE of sail forward lift is high, the drag from board and fin is low. This produces a turning moment, pushing the nose down. So more downhaul, shifts sail COE downwards, reducing the turning moment.

But you forgot one thing,wsurf have universal joint and sailboat has fixed connection.
Universal joint can not transfer moment on board ,it can transfer only forces.
So if COE is higher/less downhaul than "mast foot pressure" will also increase,because sailor must transfer more his body weight on boom to compensate increase in sail lever arm(COE moves up).

So you are right,but your explanation is not technically correct.
Do you agree with my observation?

(If windsurf have fixed connection-like sailboat,every even small change in sail pressure or change in COE position,will move board in roll or pitch direction.So board will be imposible to ride..)

fpw9082 said..

www.guycribb.com/userfiles/documents/downforce.pdf

Are the forces with 2006 kit the same with modern kit and is the sailing 'style' still the same?
If not, pointless talking about 2006 unless you still use old kit.
Maciek Rutzowski has said they tend not to use seat harnesses so much in slalom sailing because the boards are wider.

Doesn't boom hight significantly change the MFP therefore affect the way the board rides as well? Lower boom > higher MFP.