What your saying is clear and easy to follow. Once you understand how the boat goes forward, you understand how drag is working against what the sails are trying to accomplish.
Oh also you don't want the leading edge to be in the center of the foil but rather more forward to the foil. If you look at airplane wings that is the case the leading edge is really close to the front of the wing. When you look at a sail it's getting good angle of attack the leading edge is toward the luff of the sail.
The best example of lift that I have seen, and use it to this day, is a sheet of 8 x 11 paper held at the corners of the 8" side with the 11" tag dangling. Hold the paper up to your mouth to create an arc and blow across the top side of the paper. Observe the results. You are not applying "wind" pressure to the underside of the impromptu foil... only to the top side. the speed of your breath creates the low pressure on the top and the stagnant air on the underside becomes the high pressure, creating the pull or lift of a foil/sail. Granted sails work in a wide range of points and are subjected to 360 degrees of wind so push or pull is a relative thing. But I thought you may like to try the paper thing just for fun.
Another good one Herb. I know that you said you will talk about keels later, But, you showed how the sails make power to move the boat sideways. You probably should have told them that the keel helps the boat to move forward and not be pushed-pulled sideways.
I just want to say that you make a great team ,crew couple ! You seem to stay positive no matter what and succeed because you believe in yourselves ! I wish you safe and enjoyable sailing and less refits ! Take care and thanks for sharing your adventures with us !
This explanation is based on equal transit theory and it's largely incorrect. There is no physical principal that mandates air molecules split by the luff have to translate across the sail, to the leech, at the same rate. If the air between windward and leeward doesn't travel at the same rate then Bernoulli's principal doesn't apply. Sails work by efficiently changing the momentum of air according to Newton's 1st & 3rd laws.
You're making this too easy... ;-) Sail physics has been moving it's way up my to-study list for a while. That was a great into to it! I have a much better visual idea of whats going on now. Thanks again!
I'm curious if anybody else had pointed out the flaw in your illustration. You're illustration shows the curvature of the wing being horizontal which is not correct. The curvature of the wing is vertical. Running just aft of the head running all the way down to just behind the tack. So the part of the sail that is the trailing edge is from the leading edge aft do the edge of the leech and ultimately the clue as well. But the leading edge is vertical. Like you said it's a wing stood on its side vertical rather than horizontal. The reason why you see the leech flipping around it's because the air is stalling on the trailing edge. Your explanation is correct put your visual seems to indicate otherwise. Though your belly explanation was great for downwind.
The air on the windward side will have a slightly shorter path to run than the air on the leeward side of the sail. Since the air on the leeward side of the sail is running a bit faster, it creates a slightly lower pressure area on that side of the sail and sucks the sail into that void. When a sail is “full of air” it’s actually being sucked into a void on the other side of it, and through the rigging, pulls the boat along with it to drive the entire yacht forward.
@@RiggingDoctor Great thanks for explaining this. Just one more thing to have 100% clear understanding, as the air on the leeward side has a slightly longer path, why it has to run faster?
Archit Kumar when the air is split by the sail, the air on the inside of the sail (windward) has a shorter path than the air on the outside of the sail (leeward). This is because the inside curve is slightly shorter than the outside of the curve. So the air on the inside moved slower while the air on the outside moves quicker. The easy way to visualize this is that the air “wants” to stay together so the air that was split at the beginning of the sail “wants” to rejoin at the end of the sail. Since they run different length paths, the inside runs slower and the outside runs faster. The reality is the air on the outside is accelerated by the curve of the sail and some other complicated aspects, but it works very closely to the simpler way of thinking about it.
What you may have learned in school about how a wing or a sail generates lift is probably wrong. They taught us that the air moving over the top surface of the wing (leeward side of the sail) has a longer distance to travel and needs to go faster to have the same transit time as the air on the lower side of the wing (windward side of the sail). But this is wrong. There’s a video that shows this well, th-cam.com/video/UqBmdZ-BNig/w-d-xo.html It’s the curvature of the sail that causes the lift. There’s force on the windward side of the sail because the curvature of the sail deflects the air. A wing works the same way. Now there are two parts to this force, one that pushes the boat sideways and one that pushes the boat forward. The keel in the water resists the sideways part of the force, so the boat moves forward. The keel can be much smaller than the sail and still counteract this force because water is much more dense than air.
Good point! The next few topics will make much better sense having the actual model present, I will be sure to touch on “lift” with a marker on paper before we go further into other topics.
@@RiggingDoctor Suggest doing the old standard display of blowing over the top of a strip of paper and showing how it rises to demonstrate the Bernoulli effect. (HS Science Teacher)
@@RiggingDoctor Both of you could possibly qualify for a 100 ton captains license if you document your journey enough. Usually they take your word for "360" days of sea time if you say so when you own a boat. It helps to have something to back it up. This will qualify most people for jobs, lower insurance, school jobs. The Charleston Sea School has a 5 day course to qualify for the certificate. Soo....just saying it might not hurt for either of you to do it. Hey you could then take charters out in Maryland later....
Love your tutorial videos. I think your video would be even better if it explained why a boat moves forward if the pressure force on the sail is perpendicular to the bow of the boat.
Check this out. This transatlantic racer from the mini 650 class is packed with all of the most recent innovations. Even the resin used to build the boat is recyclable.
@Jim Nickles That is the worst challenge for a boat designer: How to match looks and performance. But then again, beauty is in the eye of the beholder, and in any case, it's not beauty that moves a boat through water.
@@RiggingDoctor My designs aren't that bulgy in the bow, but that's more or less the principle we're after nowadays: Fuller sections in the bow, to keep the bow from nose diving at high speeds. Check this one : th-cam.com/video/wJivEpepdlo/w-d-xo.html. Note how to safely broad reach at full blast in 30 knots, you take two reefs in the main, and hoist all the sails you have forward of the mast. Safer to pull a boat through water than to push it through.
Actually there is a video that you put out when you were sailing that shows your sails beautifully formed into a wing. Also in the video you are making note of it and I think you were also saying that you were getting your best speeds. Sadly I have no idea which video that is. On a side note, too bad your sheet sails didn't form as I believe you hoped. I have no idea why I didn't happen other than I have no idea how sails are made. The cool part is you got me thinking on how does the leading edge get created. I mean on an airplane there are structural sparse that create the curvature of the wing. Sails don't have that. So I have spent a lot of time trying to visualize in my mind how that is being created given my knowledge of airplane wings and airflow. I was always shown that the air went straight along the bottom of the wing and the air flowing across the top of the wing is weaker and therefore creates a force differential which then creates Lift in the direction of that Force differential which in sailboats we want that lift to be pointed towards the bow. We are told that if the air flow is not direct then it is stalled and starts to swirl so maybe the airflow that is filling the sail is stalled air on the underside but then you would think the tell tales would also stall so obviously I don't have a good visual on that yet
That’s why a good sailmaker is imperative! They make the sail so that it has a bit of a belly in the front that way it will take the right shape when the sail is in the wind. When it’s set right the wind flows evenly across both sides. Trimming with the tell tails is the trick to getting the flow perfect!
hey you will confuse people if you say you will generate more power with more curves !!! Thats only when going down wind!!! Going up wind, you need a more rigid curve
Not entirely. The curve develops the power so more curve is more power. The trouble is the angle of attack increases so you can’t sail as close to the wind. For serious upwind performance, a flatter sail lets you point higher due to the shallower angle of attack, but it will still generate less power (though still plenty of power) than the same sail with a deeper belly and a deeper angle of attack sailing further off the wind.
We enjoyed your explanation. For a masterclass in how to teach your child to tell the time (NOT), type - Dave Allen - "Teaching your Kid Time" into TH-cam. He is an Irish comedian. You may find it useful when teaching your own child eventually!
@@RiggingDoctor Just to say thanks for your videos. My husband finds most sailing couples irritating for one reason or another, but he thinks your videos are extremely good, as do I.
This was a pretty fine tutorial but gosh oh my ya just can’t top that good old how to make popcorn video you made a while back. I’m sorry. I’m starting to tear up here.
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What your saying is clear and easy to follow. Once you understand how the boat goes forward, you understand how drag is working against what the sails are trying to accomplish.
my teacher told me to watch this and I liked and gave a good sub
Oh also you don't want the leading edge to be in the center of the foil but rather more forward to the foil. If you look at airplane wings that is the case the leading edge is really close to the front of the wing. When you look at a sail it's getting good angle of attack the leading edge is toward the luff of the sail.
The best example of lift that I have seen, and use it to this day, is a sheet of 8 x 11 paper held at the corners of the 8" side with the 11" tag dangling. Hold the paper up to your mouth to create an arc and blow across the top side of the paper. Observe the results. You are not applying "wind" pressure to the underside of the impromptu foil... only to the top side. the speed of your breath creates the low pressure on the top and the stagnant air on the underside becomes the high pressure, creating the pull or lift of a foil/sail. Granted sails work in a wide range of points and are subjected to 360 degrees of wind so push or pull is a relative thing. But I thought you may like to try the paper thing just for fun.
Great! This is exactly what I wanted to understand. Thank you so much!
Glad to help with that :)
Good job....looking forward to the next one!
Bazinga! Another great video! Love you guys!
Thanks!!
Very informative herbie! Thanks dude!
👍
Another good one Herb. I know that you said you will talk about keels later, But, you showed how the sails make power to move the boat sideways. You probably should have told them that the keel helps the boat to move forward and not be pushed-pulled sideways.
I mentioned it very briefly when I talked about square sails on tall ships, but it will become a very in depth talk soon.
@@RiggingDoctor It was just a clarification, Sorry Herb!
I just want to say that you make a great team ,crew couple ! You seem to stay positive no matter what and succeed because you believe in yourselves ! I wish you safe and enjoyable sailing and less refits ! Take care and thanks for sharing your adventures with us !
Thank you very much 😊
Thanks for the info, can't wait to see more.
This explanation is based on equal transit theory and it's largely incorrect. There is no physical principal that mandates air molecules split by the luff have to translate across the sail, to the leech, at the same rate. If the air between windward and leeward doesn't travel at the same rate then Bernoulli's principal doesn't apply. Sails work by efficiently changing the momentum of air according to Newton's 1st & 3rd laws.
You're making this too easy... ;-) Sail physics has been moving it's way up my to-study list for a while. That was a great into to it! I have a much better visual idea of whats going on now. Thanks again!
I'm curious if anybody else had pointed out the flaw in your illustration. You're illustration shows the curvature of the wing being horizontal which is not correct. The curvature of the wing is vertical. Running just aft of the head running all the way down to just behind the tack. So the part of the sail that is the trailing edge is from the leading edge aft do the edge of the leech and ultimately the clue as well. But the leading edge is vertical. Like you said it's a wing stood on its side vertical rather than horizontal. The reason why you see the leech flipping around it's because the air is stalling on the trailing edge. Your explanation is correct put your visual seems to indicate otherwise. Though your belly explanation was great for downwind.
Herd...Good Stuff...BRILLIANT...cheers
Standing rig...too funny
Great video, thanks. Just I am confused by there is low pressure on the other side? Can you please explain a bit more about this? Thank you!!!
The air on the windward side will have a slightly shorter path to run than the air on the leeward side of the sail. Since the air on the leeward side of the sail is running a bit faster, it creates a slightly lower pressure area on that side of the sail and sucks the sail into that void. When a sail is “full of air” it’s actually being sucked into a void on the other side of it, and through the rigging, pulls the boat along with it to drive the entire yacht forward.
@@RiggingDoctor Great thanks for explaining this. Just one more thing to have 100% clear understanding, as the air on the leeward side has a slightly longer path, why it has to run faster?
Archit Kumar when the air is split by the sail, the air on the inside of the sail (windward) has a shorter path than the air on the outside of the sail (leeward). This is because the inside curve is slightly shorter than the outside of the curve.
So the air on the inside moved slower while the air on the outside moves quicker.
The easy way to visualize this is that the air “wants” to stay together so the air that was split at the beginning of the sail “wants” to rejoin at the end of the sail. Since they run different length paths, the inside runs slower and the outside runs faster.
The reality is the air on the outside is accelerated by the curve of the sail and some other complicated aspects, but it works very closely to the simpler way of thinking about it.
@@RiggingDoctor Great, thank you for explaining it in such an easy way!! Amazing!! :) :)
What you may have learned in school about how a wing or a sail generates lift is probably wrong. They taught us that the air moving over the top surface of the wing (leeward side of the sail) has a longer distance to travel and needs to go faster to have the same transit time as the air on the lower side of the wing (windward side of the sail). But this is wrong.
There’s a video that shows this well, th-cam.com/video/UqBmdZ-BNig/w-d-xo.html
It’s the curvature of the sail that causes the lift. There’s force on the windward side of the sail because the curvature of the sail deflects the air. A wing works the same way.
Now there are two parts to this force, one that pushes the boat sideways and one that pushes the boat forward. The keel in the water resists the sideways part of the force, so the boat moves forward. The keel can be much smaller than the sail and still counteract this force because water is much more dense than air.
Good talk, however a black/dry-erase board would have been less confusing/awkward. I did learn much so thanks!
Good point! The next few topics will make much better sense having the actual model present, I will be sure to touch on “lift” with a marker on paper before we go further into other topics.
@@RiggingDoctor Suggest doing the old standard display of blowing over the top of a strip of paper and showing how it rises to demonstrate the Bernoulli effect. (HS Science Teacher)
That would have been a lot easier to visualize than what I did there.
Thanks for the tip, I’ll cover it again in (hopefully) a clearer method!
Herby you should work nights at the Annapolis School of Sailing when you get around to going home....You already have the visual aids built!!
That's what I've been telling him!!
@@RiggingDoctor Both of you could possibly qualify for a 100 ton captains license if you document your journey enough. Usually they take your word for "360" days of sea time if you say so when you own a boat. It helps to have something to back it up. This will qualify most people for jobs, lower insurance, school jobs. The Charleston Sea School has a 5 day course to qualify for the certificate. Soo....just saying it might not hurt for either of you to do it. Hey you could then take charters out in Maryland later....
Now I *really* wanna see you go into depth about junk sails, and about how they're trimmed..
Love your tutorial videos. I think your video would be even better if it explained why a boat moves forward if the pressure force on the sail is perpendicular to the bow of the boat.
I was trying to keep it simple but that will be covered when I throw keels into the equation.
Check this out.
This transatlantic racer from the mini 650 class is packed with all of the most recent innovations.
Even the resin used to build the boat is recyclable.
Forgot to paste the link. Here it is:
th-cam.com/video/hY6taXLY2NE/w-d-xo.html
Thank you!
Wow!
That design with the blunted bow reminds me a lot of your designs ;)
@Jim Nickles That is the worst challenge for a boat designer:
How to match looks and performance.
But then again, beauty is in the eye of the beholder, and in any case, it's not beauty that moves a boat through water.
@@RiggingDoctor My designs aren't that bulgy in the bow, but that's more or less the principle we're after nowadays: Fuller sections in the bow, to keep the bow from nose diving at high speeds.
Check this one :
th-cam.com/video/wJivEpepdlo/w-d-xo.html.
Note how to safely broad reach at full blast in 30 knots, you take two reefs in the main, and hoist all the sails you have forward of the mast.
Safer to pull a boat through water than to push it through.
Actually there is a video that you put out when you were sailing that shows your sails beautifully formed into a wing. Also in the video you are making note of it and I think you were also saying that you were getting your best speeds. Sadly I have no idea which video that is.
On a side note, too bad your sheet sails didn't form as I believe you hoped. I have no idea why I didn't happen other than I have no idea how sails are made. The cool part is you got me thinking on how does the leading edge get created. I mean on an airplane there are structural sparse that create the curvature of the wing. Sails don't have that. So I have spent a lot of time trying to visualize in my mind how that is being created given my knowledge of airplane wings and airflow. I was always shown that the air went straight along the bottom of the wing and the air flowing across the top of the wing is weaker and therefore creates a force differential which then creates Lift in the direction of that Force differential which in sailboats we want that lift to be pointed towards the bow.
We are told that if the air flow is not direct then it is stalled and starts to swirl so maybe the airflow that is filling the sail is stalled air on the underside but then you would think the tell tales would also stall so obviously I don't have a good visual on that yet
That’s why a good sailmaker is imperative! They make the sail so that it has a bit of a belly in the front that way it will take the right shape when the sail is in the wind.
When it’s set right the wind flows evenly across both sides. Trimming with the tell tails is the trick to getting the flow perfect!
hey you will confuse people if you say you will generate more power with more curves !!! Thats only when going down wind!!! Going up wind, you need a more rigid curve
Not entirely. The curve develops the power so more curve is more power.
The trouble is the angle of attack increases so you can’t sail as close to the wind.
For serious upwind performance, a flatter sail lets you point higher due to the shallower angle of attack, but it will still generate less power (though still plenty of power) than the same sail with a deeper belly and a deeper angle of attack sailing further off the wind.
@@RiggingDoctor well its amazing you can go slightly forwads INTO the wind LOL... Too much Belly and you will be going backwards heheheh
@@RiggingDoctor Here is a video idea for you, Why Do we need a Boom (down on deck, rather a smaller Gaff up top) and do a simple Wharroom wingsail???
We enjoyed your explanation. For a masterclass in how to teach your child to tell the time (NOT), type - Dave Allen - "Teaching your Kid Time" into TH-cam. He is an Irish comedian. You may find it useful when teaching your own child eventually!
🤣 it’s off to a great start!
The kids internal clock is our time out on the ocean.
Eat when you are hungry and wake up when someone else tells you to.
@@RiggingDoctor Just to say thanks for your videos. My husband finds most sailing couples irritating for one reason or another, but he thinks your videos are extremely good, as do I.
This was a pretty fine tutorial but gosh oh my ya just can’t top that good old how to make popcorn video you made a while back. I’m sorry. I’m starting to tear up here.