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Sailing Theory Tutorials - Forces on Sails and Foils
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- Опубликовано: 16 авг 2024
- In this video, the lift and drag forces on the sail of a boat are combined to form a resultant "Effort" Force vector.
The forces on foils below the water are discussed and the idea of leeway is introduced to explain how the foils experience flow at and angle of attack and generate lift just like the sails.
The effort and resistance forces are combined on a simplified 2D model of a sailboat to show how the boat develops thrust, which propels the boat forward.
Hi Everyone,
I made some changes to my channel this winter that resulted in YT deleting all of my comments/replies on these videos. It's really a shame, because I feel like I have answered quite a few theory questions in the comments section over the years. If you have a question, even if it looks like it's been asked before, please don't hesitate to post a comment, I'll do my best to get back to you.
Cheers,
JH
Finally! A great explanation about what is meant by “lift” when taking about foils, not just the sails. Thank you
My physics teacher is making me watch this, I hate her stupid class but this video does a fantastic job of explaining this topic and making it easy to understand, much better than my teacher. Good job.
Thank you for your video! I learned quite a lot and refined some of my knowledge.
I don't quite agree with "Boats Experience just Enough Leeway", though.
My students often try to accelerate the boat sailing close hauled with no speed after setting sails or a bad tack.
What this leads to if that the boat is actually going sideways a lot.
As I understand it, the first second that the wind fills sails in such a situation and the water starts flowing, the direction of it's flow should be opposite to the direction of "E", combined forces of the sail. And even if the sail is trimmed perfectly, the angle of attack on foils is to big, so they stall. A lot of drag is generated, which results in either the boat heeling a lot, or drifting sideways if hiked.
Also, the rudder is useless in this situation, so the boat usually can't be controlled. It can head up or bear away, but it's not relevant in my question. What happens underwater, when sails seem to be trimmed perfectly and the boat points very well, but drifts sideways?
Of corse, as you gain any speed angle of attack changes drastically and foils lift starts to help in acceleration, and then the boat flies as you said - easy in going forward and really bad in going sideways.
But I don't like seeing my students crashing into each other on a start line because of this misunderstanding :)
I would be really greateful if you could clarify.
Thank you!
Hi Ivan. I think you're spot on. I'd add a couple of points to clarify this aging video and its explanations:
1. My use of the expression "Just enough leeway" doesn't imply that the amount of leeway your boat experiences is desirable or even beneficial, just that it is this missing piece of the vector equation. Maybe I could have used different language for that part.
2. My description really only applies once the boat is moving and once the sails are trimmed within a reasonable range for the direction of the wind. Starting from a stop is sort-of outside the scope of this video.
You might want to give this article a read: gentrysailing.com/pdf-theory/Origins-of-Lift.pdf
Excellent presentation, take a bow
Awesome work, thanks! Keep em comin'
Can we measure the force created by the sail by measuring the tension on the sheet with say a force meter or a simple digital scale.? Could this single measurement assist triming of the sail. Much like a the resulting speed increase or decrease with triming the sail for max speed?
You can certainly get a sense of how much load there is on the sheets, and relate it to the force on the sails, but you have to remember that as you sheet in and out the magnitude and the direction of the forces on the sails changes. The farther you sheet in, the greater the sideways, heeling, component of the force will be, so you can't say that more load in the sheet will equate directly to more thrust force driving you forward.
At 2:00 when the Lift vector was added, how do you know where to place it along the sail?
@@howarthsailing Thanks for your reply Julian! Which is the "other" video you referred to? Doing some study on the AC75s, their twin skin mainsail is almost as effective as a solid wind sail, and I'm expecting the CoE to be well forward on the sail.
Could not follow this.