Hi Everyone, I made some changes to my channel this winter that resulted in YT deleting all of my comments 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

Thank you for this video! Your explanations and drawings were very clear!

Your wind tunnel app is treating the sail as rigid, which is why it can sustain an angle of attack which is impossible for a sail. This isn’t the primary way that sails work; what they actually do is change the direction of the wind by guiding it in a curve aft, so the vessel is driven forward by the equal and opposite reaction. This is why it is ok for a mainsail to luff a little in the backwind of the jib as long as the airflow is clean of both windward and leeward sides of the leech; that’s where the power comes from.

@viarnay

3 жыл бұрын

If you have your sail properly set they should be rigid

Thanks

15:00 You can't do experiments on simulations, they simply regurgitate the ideas of the designer. Develop a hypothesis and then test it in reality. Testing on a model that incorporates the hypothesis is the ultimate circular argument.

Why does the stagnation line curves like this? What force is dragging the air towards the sail?

@howarthsailing

2 жыл бұрын

Streamlines are PUSHED by higher pressure towards lower pressure. In this case, the relatively higher pressure on the windward side of the sail pushes the stagnation streamline to leeward before it contacts the front of the sail or mast.

8:59 No, it doesn't. It either goes over or under. Check Babinsky's video. Sometimes the smoke arriving at the so-called stagnation point flicks over the top and sometimes it flicks under the bottom. It never stops.

@howarthsailing

Жыл бұрын

As I understand it, there's an infinitesimaly small amount that does stagnate but it really doesn't matter though, the dashed line helps us understand where the air divides to pass on each side of the sail. We are not analyzing a sail design here, we are just developing a visualization of how the air is moving over a sail and being careful to avoid the commonly used, incorrect explanations of longer and shorter distances.

@alans172

Жыл бұрын

​@@howarthsailing If it "really doesn't matter", then why introduce it at all? You are just confusing your readers by harping on about it. Why don't you just say that: "It is the point where the air divides...." and save yourself and your readers the hassle of struggling with the myth of the stagnation point. It was introduced by misguided mathematicians who needed to seed their PDEs in order to get some sort of correlation with nature.

@howarthsailing

Жыл бұрын

@Alan Smith Hardly harping, you're commenting on a video I made in 2018 where I explain as clearly as I can, the flow over a sail, visualized. There's plenty of literature to support the stagnation streamline, and stagnation point, I am not the author of those works. Feel free to link to the content you prefer. Please take your argument somewhere else.

If you trim a sail with the angle of attack of the luff such that it rises above the oncoming streamline your sail simply doesn't work. Just try it.

@alans172

3 жыл бұрын

@@howarthsailing Wrong, wrong, wrong. You are obviously not a sailor, otherwise you would see that the turbulence under the sail is because it's head to wind! If you rotate the sail to a sensible tacking angle of 40°, the flow is smooth below and above the sail, with separation and turbulence downwind.