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Check out my second video for additional clarity on the science behind lift and forces on the sail. czcams.com/video/jHCXTiepjKY/video.htmlsi=ZtNHVwr3rOmgybMN

Thanks for your comments. Please check out my second video which explains, through visual simulation and experimentation, the forces on the sail. czcams.com/video/jHCXTiepjKY/video.htmlsi=jcvjX1JSKw4ms-QX

Glad you liked it!

Maybe. Something to think about. Thanks for the suggestion

Must have...

Other instructors have found this video helpful. Admittedly some of it may be over the heads of a newbie, but nonetheless helpful. Regards.

@todomikolov9520 Glad you liked the videos. When it comes to harness length, I think it is easy to speak about power vs control, but I don’t believe harness line length has much to do with power, but would have some influence on control. Harness line length may have an influence on whether the sail is more “hidden” or exposed to the wind, but I would say that the greater influence on harness line length is the size of the individual, the height of the boom, and the type and position of the harness. The selection of length will depend largely on arm length allowing for a comfortable grip on the boom and enough control to allow rapid response in gusty conditions. Harness type, seat vs waist, will also influence the length as you will want to be able to get in and out of the harness quickly when needed. Of course, the boom height relative to the height of the harness hook is also an important factor. The power comes more from sheeting out or in the sail and not from the harness line length. The harness length may be able to be adjusted at most by 5 inches, and since it is a loop, this is only a maximum difference of 2.5 inches which is not very great. I hope that helps a bit.

@@3denlightenment Thank you so much! Surely it helps :)

Thanks. Good to know.

You're welcome

True. Thanks.

You're welcome!

You're welcome 🙂

I would appreciate specific areas you feel need corrected. It has been reviewed and substantiated by hundreds of thousands of people and supported by science.

@@3denlightenment Oh no, I don't review all its passages. Let's say that for windsurf - to go upwind: depitcing/visualizing wind particles impacts on sail and its component is almost useless in realizing how it works. Same so in scomposing those forces (in upwind direction)! In the video it is used the word "dynamic forces", the meaning? That it depends on velocity? That may be informative about module, not on DIRECTION of forces! So It doesn't help much in understanding HOW the windsurf can go upwind, too. The fact the windsurf can go upwind (45 degree o something like that... from wind's direction) lays in aerodynamics, so it is ABOUT THE PRESSURE between the sides of the sail, that is given by the FORM of the sail. It is right some parallelism with wings, that are present in the video. But I find that the video loses its direction after that. Then, how feet are "solid" or press ON the surf surface. No... that is almost about equilibrium of windsurfer against sail. The steer is about MOMENT of forces. Does the video use the word "moment"? Moment derives by feet pushing the surfboard (so involving some "direction", so no merely press down) or handling the sail, or both. I'm not an expert but these are my 2 cents :)

Thanks for the explanation. If I understand correctly you believe that the wind flowing over the surface of the sail profile will cause a low pressure on the sail i.e. Bernoulli's pressure and this low pressure will cause lift pulling the sail...however this is incorrect. If you watch my second video I conduct an experiment showing that basically it is newtons forces on the sail from direct pressures from the moving particles (dynamic forces) which provides the pressure on the sail allowing the board to move forward and upwind if needed. You speak about 'moment' which comes from momentum which is defined as mass x velocity. The foot pressures on the board would not be considered moments since they virtually have no velocity. You lean back against the sail with your body and legs at a certain angle and they, through gravitational and wind pressure, provide force on the board which translates to force on the fin allowing you to steer. Watch all three of my videos which should clarify somethings. All the best.

@@3denlightenment First: it is wrong to simulate a sail with a wing with double profile. Ok? And it is correct my issue about PRESSURE: in fact you see it when you blow OVER a sheet of soft paper (NO DIRECT NEWTONIAN IMPACT or "hits") that you hold by your hands from ONLY one side: the paper LIFTS because of velocity of the air over the paper is greater than velocity of the air under the paper. So different pressure on the faces of paper. Idem on a sail you have two sides, and different pressures on the two sides. You could define a "difference pressure" that you see it definitively "forges" the soft sail surface shape. You FEEL it on windsurf when going in upwind direction: the curvature of the sail (which is not rigid like a rigid WING, but it is more like the soft PAPER), bloats and pushing the sailing mast "ahead", so direct toward the semispace where the wind comes FROM. Ahead! About moment: NO! A moment is a "Newton* Meter" entity. You mistankely wrote about momentum (another and different entity involving velocity). Moment (in italian "momento") is about lever, couple or torque. It may involve rotations: its numerical value is a module of force multiplied by the distance between application point (of force) and the point where you calculate the so "referred" moment. So, on windsurf, you could push your feet downward in many way. But as on ship where you could walk on its bridge without change shilp-gait-stability, also like that on a surfboard: so the application point/s of feet may be changed WITHOUT involving new directions. But as rigid bodies, windsurf has a center of mass, so you can calculate MOMENT about that point. And also defilne "DIRECTION" by barycenter and board nose. Suppose a windsurf moves along an upwind direction, and it is stable in that. if you move the sail-mast leaning it nearer the nose (of windsurf), then it happens that there is more wind hitting the sail in a REGION between barycenter (center of gravity) and bow of windsurf, causing a change; image schematically this REGION force and its APPLICATION POINT, so a moment, a rotation from the previous stability, and in that case the windsurf obvously bears away. It works the other way about luffing. But again, (not starting by handling the sail, but BY your FEET), you could impress on the windsurfboard a moment (so a force with its application point and direction, and considering the distance of center of gravity of windsurf) , that involves a "rotation" around that center of gravity on the plane that is imposed by water surface, and so you have steering or change of direction! In the end: when you bear away from wind provenience, your body weight moving upward and nearer the sailing mast, all of this is involved: in your new equilibrium to react to sail force: but it is not merely pushing perpendicular over the board like walking on a bridge on a ship that changes direction. YOU MAY (or may not) impress a moment (referring to windsurf barycenter). IT IS in the way (pushing direction/s) of HOW you push your feet downward: so you have an entire vectorial semispace of (many) directions to choose from. Some of these previous explained things are ALMOST automatic by just the resisting to the sail-force while windsurfer body moving toward board's nose: so even if the MERELY moving of the windsurfer weight/body upward/downward along the windsurfboard (while contrasting the sail's force) seems to do the "trick", it is NOT the ultimate RECIPE, and it is NOT the ultimate reason of "steer", but really it almost MATCHES steering as a "side effect" by changing previous equilibrium forces, the EXACTLY-case given by the resulting of impressing a MOMENT (remember, the center of gravity of windsurf). Moment is the ultimate reason of steering.

@@3denlightenment Why have you deleted my definitive LAST explanation? Now it is lost. So let me just write that this video of yours is WRONG in many ways, as REAL Aerodynamics scientits should recognize after seeing it. 🙂

Your welcome!

Thanks! and thanks for the comment on the audio...I'll take note for the next one.

I also agree on this point as it distracts from the content imo. New to the channel. Excellent stuff & subscribed.

True, the two are significantly correlated. I was just thinking that people generally experience low wind conditions when learning and don't necessarily consider speed as a factor but just look at the straps and give it a try. Thanks for the comment.

I can remember when starting windsurfing, i was looking at the fast guys that were sailing with a close sail. So I would close my sail with no speed and couldn't figure out why I was drifting. Apparent wind is unfair with beginners 😂

Thanks. Yes, that second foot, no matter which one, can be troublesome. You'll have to point the board downwind a little bit before you get that front foot in

Good point. Thanks for bringing that up.

Thanks, and yes the Gybe would be a great one. I've been thinking about that too. Gotta feel like I've mastered it first LOL...but it's on the list!

Thanks! I've never foiled before, but the physics wouldn't be that hard to figure out. I'll put it on the list.

@@3denlightenment that would be so good! Thank you

I've not found anything as comprehensive on this so I worked it out based on my physics background

You're welcome!

Thanks. Will do!

Glad you liked it...there are more coming

You're very welcome. Glad you liked it. There'll be more coming

Thanks. Glad you liked it ☺️

The model is a sail. You are right, it is not a wing. There is not a flat side on the underside of the model. It is hollow like a sail. It has a thin membrane over 3 struts simulating the thin shape of a SAIL. There are SO many videos where a sail is described as a wing. I am constantly showing the differences in the video. Your scientific discussion is appreciated.

Sorry. Watch this video here czcams.com/video/UqBmdZ-BNig/video.htmlsi=smeaY7Av6tCWbI2H

I agree, but so many explanations center around the curve of the sail and the wind flowing over it. The explanation of lift is often given as a function of air flowing over the leaward side ...which makes it like a wing. Newtons explanation is the air moving and striking the windward side. The windward side of a sail is curved as you state, but the wing has a straight flat bottom, but both provide surfaces for receiving the Newtonian force.

Thanks for your comment. You are right about the sail not being perfectly shaped like a wing, but you see a LOT of explanations comparing a sail to a wing and relating it back to Bernoulli's principle. I only bring up the wing explanation to briefly show that it doesn't explain what is happening. In my second video which you can see here: czcams.com/video/jHCXTiepjKY/video.html I tried to put more clarity into the relationship between sail angle, the relationship between the wing and the sail and the generation of lift. Feel free to check that out.

You almost have it. You are missing the fact that when the wind strikes the sail, the angle of energy transfer depends on the angle of the sail. The energy transfer is approximately perpendicular to the sail in a downwind direction. That transferred force has two components, a down wind component and another component perpendicular to the wind (never upwind). The key piece is that the lateral force (driving the board forward) is NEVER upwind (not possible for wind to transfer a force against itself). As you angle your board upwind, the downwind force continues to be opposed by the fin and the lateral forward component continues to push across the wind (forward) but the board slices upwind until it points upwind at 45 degrees. At 45 degrees the resistance provided by the fin is the SAME downwind and across the wind no matter the width of the fin. The key factor again is that the wind force has two force components, downwind and across the wind, never upwind.

Thanks for your reply. I understand what you are saying. Check out my second video. Hopefully it will clarify the situation.

Glad to be of help 😊 Good luck with your sailing!

There is no vortex lifting the plane or pushing the sail. Any turbulence forms behind the wing or sail and is the result of a partial vacuum as a result of the more rapidly moving air on the outsides. That vacuum will only pull on the wing or sail (if it is close enough to it). In the case of a sail, it can only pull it downwind (drag) and is very unstable. Turbulence is not desired for aircraft or sailing vessels. People seem to have different "beliefs" related to Bernoulli's principle and Newtonian forces, but in fact they are both acting. The model I put together demonstrated that it was the Newtonian forces which provided the most significant driver when comes to sailing ...and flight.

You're welcome. Glad to be of help ☺️

You are welcome 😊

Glad you liked it.

Thanks for that contribution to the discussion. Your description is absolutely correct and would make a nice addition to the 3D Enlightenment video collection. Thanks for that! Cheers.

Thanks for the input. I agree that the center of "effort" on the sail in relation to the center of lateral resistance provided by the fin are essential in describing the pressures driving the steering of the board and I should have discussed this. The steering section of the video was meant to focus on that experienced by beginners in low wind and provides some practical advice to accelerate a turn. I also agree that under higher speeds, the rail provides a significant contribution to a carving turn through the water. When it comes to pressure on the feet, this remains important and I'm not surprised that you can turn the board even on one foot. That is because the pressure shifts between your one foot and the mast base due to the change in the center of effort when the sail is shifted forward and aft. So, although not discussed in the video, the mast base also provides pressure on the board. Perhaps a video to clarify steering would be beneficial. Thanks for your input.

Wow! Thanks very much 😊

True, but there has to be the partial vacuum or sucking force first before there is the pushing force from the positive pressure side. So without the low pressure there is no pressure difference and no movement, that is why it is important to acknowledge it..

True, with a totally flat wing you can fly, but there must be an angle of attack to capture the dynamic pressure.

Thanks very much 😊

Thanks. Glad to be helpful. Enjoy your new found sport!!