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Good morning. Do you know somewhere where I could download the project to sew a size 5.7 sail in the classic windsurfing style one design windsurfer

We learned a lot! Thank you, Julian! 🙏

Thanks for your valuable help.

I want to know what it is called when you lower the sail and tie it. It's called trim. That's not what you are saying.

Thank you for sharing your knowledge. One day, I hope to circumnavigate the globe, and this is precisely the type of information I am looking for. As a commercially rated pilot, much of the information in this video is similar to what I have learned in aviation. Of course, some of the terminology is specific to sailing, but the physics principles of an airfoil remain constant. I'm really looking forward to watching more of your videos.

“Sailing Theory” means they’re not going to give you the facts about how a sail boat works.

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!

Awesome

Hi JH, I believe the impact of current to a sailboat speed and direction is not absolute, or 1 to 1. In otherwords, I don't think you can just add up the combined speed and directions to determine a new vessel speed and direction, like you can in a powerboat. When making these calculations in a powerboat we assume a constant amount of power is being applied at the throttle, rpms. But in a sailboat the "rpms" from the wind increase and decrease relative to current, but are constant relative to the ground. Assuming for a second the sailboat is attached only to the wind and not to the water, the boats speed and direction overground would not change at all regardless of the current. The best example I can give is a sailboat sailing directly down wind at 5 knots in 8 knots of wind, that suddenly comes upon 5 knots of current going in the same direction of the boat is not going to being going 10 knots over ground. It's going to struggle getting over 5 knots overground because it's going to run out of power, "rpms" from the wind. Exaggerate the numbers and it becomes more obvious. Like 5 knots of wind and 20 knots of current. Please help me with this, because you're the only sailor I've found online that really understands this stuff and can explain it in a way that is digestible. Thanks!

Great Video to explain sailboat balance!

Very, very good.

Thank you, excellent demonstration.

That was absolutely fantastic, thank you!

It seems like CLR should point forward not aft. It appears CE and CLR are exact opposites at 18:09 which means the boat would not move if CE and CLR were at same spot fore and aft or the boat would just turn in circles if they were separated.

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.

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.

that´s gold my man

Thanks for the informative videos! Any chance you could share what drawing app you are using?

You have a new follower bud

Excellent ! Love the combination of theory and practice explained visually in simple terms.

Hi Julian, I'm trying to solve a weather helm issue in a Flying Fifteen, which is an early Classic fleet boat so doesn't have a particular set of dimensions, the Classic boats all seem to be dimensioned and rig a little differently. The mast foot has 3 positions, the forward and aft positions being about +/-40mm from the central position. I currently have the mast foot in the forward most position and I'm still experiencing weather helm. Previously I extended the shrouds to get the mast rake as far forward as possible. This did produce a neutral helm, however other aspects of the rig were stupid, the boat looked awful with the boom climbing to aft and the gib clew way above the deck. So I have now reverted to a more normal geometry. I believe I cannot sensibly get the CE further forward than the current set up. Neither is it an easy task to move the keel on a Flying Fifteen, well pretty much impossible! I am wondering whether the rudder itself may not balanced. I'm not sure this is a thing in sailboats (but I believe it is in power boats). The Flying Fifteen rudder is very raked backward with the pivot point close to the top leading corner. This suggests to me there is potential that the rudder itself could have a CLR to aft of the rudder pivot point. If so, this would effectively make the rudder bear down and produce a weather helm effect on the tiller, the tiller being on the opposite side of the rudder pivot point. Does this make any theoretical sense?

Great video

Julian, I have just discovered your tutorials on Utube. I am reasonably new to sailing so on a big learning curve. Your video on Sail Trimming Separation and stall is excellent. Really starting to understand what is happening with tell tales, why and what corrective action you need to take. Really appreciated thanks so much.

Pure excellent these explanations. I've been sailing for almost 20 years and I've never received this information as clearly as I have looking at your videos.

This is excellent!

It would be helpful to go over the when boats meet scenarios in a way that specifically focuses on upwind boats meeting downwind boats. I know it's "the same", but it sure doesn't feel the same.

Could you explain how the underwater slipstream affects how the boat holds it's course? For instance, on the Lee side of the hull/fin the water is experiencing high pressure and naturally the windward underwater side of the hull and fin are experiencing low pressure. The opposite of what is happening to the mast and sails.

How does mast rake affect the C/E?

The centre of lateral resistance is also affected be the underwater profile of the hull, not just the keel. The underwater profile of the hull changes as the boat heels.

Very nicely done.

Exceptionally good explanations.

Try adding shorter telltales that are much closer to the jib's luff, like shown in Photo 2 here: gentrysailing.com/pdf-magazines/9-Achieving-Proper-Balance.pdf Also Figures #2 and #3 here: gentrysailing.com/pdf-magazines/10-Sailing-to-Windward.pdf These telltales are much better because they warn of impending luff and stall rather than signal that luff and stall has happened.

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?

Great examples and explanations. Thank you!

Excessive healing

I do have a problem with understanding your conclusion. Perhaps you can clarify it for me and others, please! The problem is that you are referring to Lee Helm and Weather Helm on your drawings without considering that both of the boats are on opposite tacks! Therefore your conclusion on the right drawing is wrong as it is Leeward heel as the boat is on port tack and the heel is to Leeward; therefore, it is Weather Helm also! Well, I hope I explained it clearly, but need to add that scientifically, you explained this fairly clearly, but CE and its relations to the CLR while sailing is not about the boat's heel instead, it is about the position of CE versus CLR in Forward or Aft position, which will establish whether it is beneficial or not beneficial for sailing!

Might I please ask a very ignorant, amateurish question? For the sake of some medieval research I'm doing ... for example, I'm sailing from a port on a tidal river to the open sea, and assuming a boat where hitting bottom is not a concern .... would I want to leave for the sea with a low tide, since it's going OUT and would not fight me? And conversely, when I want to come back into the river from the sea, enter at high tide, which presumably helps push me in? Apologize for this terribly uneducated question.

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

Fantastic explanation of vectors and I have found all your videos very clear and concise. Just one issue here. Nautical miles should be read off the parallels of latitude scale (vertical scale) and never meridians of longitude (horizontal scale) when using a chart. Meridians of longitude converge towards the poles as you travel from the equator.

Wow

This is super helpful, thanks! I'm getting ready to learn to sail, and my math brain insists I understand the physics, too. It is surprisingly tricky to find a video diving into the physics and "why" of sails, there's just so much practical content out there that it swamps the algorithm and theoretical content like this gets hidden.

The current does not affect the performance of the foil. I don't think what this video says it is right

excellent description with very accurate illustrations of sail boat physics..would be extremely useful if these information are compiled in a booklet

how did you do it can you share with me , thank you

Really good go at a thorough explanation of it. Even if I think you may have time to think some things through.

I pronounce you Sir as "Best Physics/Math Teacher" on RUclips!!

how did you do it can you share with me , thank you

Hi Julian, I do read and see a lot of sailing tutorials and books....your vids are one of the best sources of information.Very well made ! Easy to understand and of great value for beginners and professional sailers. Thank you for your time and effort and for sharing it, you did a great job ! Franz Vienna

Great video on sail trim

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.