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post #11 of 85 Old 02-15-2019
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Re: sailing past close hulled?

I find it difficult to determine exactly what the question is. I think that a boat can be sailed very close to the wind but the closer you go the less drive in the sails and a point is reached where the resistance of the hull overcomes the forward drive. I think a boat forereaching illustrates this...points really well but slow. Take away the resistance and things change, ice boats can sail really close and very fast. Does this help?
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post #12 of 85 Old 02-15-2019
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Re: sailing past close hulled?

Start by pondering a vertical air foil and consider a vector drawing of the forces involved ..wind, drag ...lift and the angle at which things happen. Then the vectors are applied to the Center of Lateral Resistance of the hull .Lift is smallest vector
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post #13 of 85 Old 02-16-2019
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Re: sailing past close hulled?

I don't really think the keel has much to do with this it's mostly a function of the sail. The keel has a bit to do with it as a more efficient keel a deep racing keel vs a shallow full keel will point significantly higher. The deep well-designed racing keel is a better lift producing surface.

As a pilot I will try to explain lift with explanations using aviation principles.

To understand lift look at the Bernoulli's Principle. This is the theory driving why a sail can go beyond the point angle where wind pushes the sail to a point where the wind is pulling the boat forward against its own forces.
https://en.wikipedia.org/wiki/Bernoulli%27s_principle

Eventually the sail will reach the "critical" "angle of attack". Angle of attack is the angle of the wind to camber of the sail. When you are close hauled the boat is at optimum angle of attack to make progress to make progress against the wind give or take. The sail is pulling as much as it can as close to the wind as it can.

As you point higher the wind no longer flows over the sail in a way that produces lift. At first the sail starts getting disturbed air aft of the center of the draft, shown by telltales flicking backwards. Eventually the sail begins to luff. In a plane this is where the wing stalls. In a plane the wing stops producing lift and the plane stalls the plane falls out of the sky for just a second. As the nose drops the angle of attack increases and the wing starts producing lift again if all goes well. If it doesn't go well spin....splat.

In a boat you can exceed the angle of attack by pinching (pointing closer to the wind than optimum) it looks like you are heading closer towards the wind but you are literally stalling the sail. Because gravity is not working against you the boat does not fall out of the sky like an airplane. It may look like you are sailing at 30 degrees into the wind, but you are likely stalling the sail and sliding sideways.

https://en.wikipedia.org/wiki/Angle_of_attack

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post #14 of 85 Old 02-16-2019
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Re: sailing past close hulled?

Pity people were saying "Sailing 101" as it sounds irritating and diminishing.

Most people who read a thread dont know the forum its in is "Learning to Sail" so this forum IS Sailing 101!!!!!!!

Maybe some people will be a bit nicer to a new sailor asking difficult questions..

Now to your qustion about 30 degrees and going to 20 degrees. YES! It can occur and occur easily! The people who said it cant clearly need to re-do their Sailing 101!!

An aircraft has the same airfoil as a sailboat except its horizontal. It flies much closer to the wind than 30 degrees, flaps up. Closer than 20. Because it has the engines as well. If it didnt have them it would Stall.

Exactly the same on a sailing boat, there gets to be a time that the boats sails stall. Its not as catastrophic as a plane, but you will stop dead in the water, the sails flap, and the boat falls off the wind until the sails fill again.

The *Exact* point you are looking for is when the sails begin to Luff and the boat speed drops off. When this happens its a degree or 2 above what your boats best angle it. That may be 45 degrees, 40, 35, 30 etc, each boat is individual.

So, when you test and experiment, yes, certainly wind the main track to windward (in different wind conditions) theres a precise time when the sail is working and when it ceases to work properly and boat speed drops.


Have fun learning. We all did it. However some have forgotten how they learned so some simple things they intrinsically now know are very difficult for them to explain so they yell: " Its sailing 101!"

Mark

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post #15 of 85 Old 02-16-2019
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Re: sailing past close hulled?

Quote:
Originally Posted by MarkofSeaLife View Post
Pity people were saying "Sailing 101" as it sounds irritating and diminishing.

Most people who read a thread dont know the forum its in is "Learning to Sail" so this forum IS Sailing 101!!!!!!!

Maybe some people will be a bit nicer to a new sailor asking difficult questions..

Now to your qustion about 30 degrees and going to 20 degrees. YES! It can occur and occur easily! The people who said it cant clearly need to re-do their Sailing 101!!

An aircraft has the same airfoil as a sailboat except its horizontal. It flies much closer to the wind than 30 degrees, flaps up. Closer than 20. Because it has the engines as well. If it didnt have them it would Stall.

Exactly the same on a sailing boat, there gets to be a time that the boats sails stall. Its not as catastrophic as a plane, but you will stop dead in the water, the sails flap, and the boat falls off the wind until the sails fill again.

The *Exact* point you are looking for is when the sails begin to Luff and the boat speed drops off. When this happens its a degree or 2 above what your boats best angle it. That may be 45 degrees, 40, 35, 30 etc, each boat is individual.

So, when you test and experiment, yes, certainly wind the main track to windward (in different wind conditions) theres a precise time when the sail is working and when it ceases to work properly and boat speed drops.


Have fun learning. We all did it. However some have forgotten how they learned so some simple things they intrinsically now know are very difficult for them to explain so they yell: " Its sailing 101!"

Mark
This does get complicated when current direction and speed is considered as it adds another vector which will impact on the optimal angle you can sail to windward.

And of course there is leeway... the boat going to windward will *slip* sideways and this too impacts the apparent wind angle... higher wind speed, more heel, more leeway.

As the boats moves the apparent wind is felt (measured)... both its direction and speed. Sails need to be trimmed to the apparent wind angle... so as boat speed increases you need to trim your sails to match the angle of the wind.

Sailing (trim) in apparent winds is more forgiving as the wind angle moves from close to the bow to dead down wind. All the aforementioned force *vectors* are more critical and determining how close to the wind you can sail (well). You *pinch* higher decreasing the apparent angle of the wind to the bow... bow speed will fall off until you no longer make forward way. Course calculators in some integrated systems can show a value of VMG... velocity made good to windward. You will find that pointing higher does not always get you there sooner.

So pointing ability depends on several factors not simply the true angle of the wind.

If you want to experiment with this, find a day with a consistent breeze and a place of no current and discover how you boat performs at different angles to the wind at THAT true wind speed. If the wind speed goes higher or lower your best VMG angle to sail will vary. Footing off for speed will send you on a longer course to sail to your upwind destination.

My B&G instruments boat speed reads to .01 accuracy of a knot and will show a trend in speed - up or down. If you hold a compass course you can optimize sail trim because the speed reading is so sensitive. For those who use GPS for speed you cannot trim to the same level of precision. But for many this hardly matters.

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post #16 of 85 Old 02-16-2019
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Re: sailing past close hulled?

Quote:
Originally Posted by serpa4 View Post
What is the point of your statement, "This should be taught this in ASA 101"?
My point was that this topic should be addressed in ASA 101 as part of the lecture and on the water exercises. In fact, there are at least two ASA test questions on the ASA 101 test (64 and 99) that cover the term "close hauled." Your signature file suggests that you have attended 101, 103 and 104. By mentioning the specific course, you could refer to the book that you should have received as part of ASA 101, or your notes - if you have any. When I teach 101 I talk about this topic and introduce Bernoulli's principle and the Coanda effect. The fact that you have mis-spelled the term and are asking questions that should be covered in class suggests that you do not have a firm grasp of this topic.

Therefore, I am left to conclude that either: a) it wasn't covered, and the school did a poor job - this is one of the reasons why I do not like 1-week "Fast-Track" courses, b) it was covered and you didn't get it -- this is another reason why I do not like 1-week "Fast-Track" courses, c) your signature is overstating your credentials.

This is the internet - you are going to get some snark, and you should be able to deal with it, or you should go read a book in a corner. The guys over at SailingAnarchy would have chewed you up and spit you out if you posted this over there (and it would have been hillarious to the rest of us ).

Most of the people on SailNet try to help others when we can. Mark's post above is a particularly good one, and echoes the article that I linked to when I mentioned the wingsail in my earlier post above. Unlike when I teach, we aren't paid to do this, and we can therefore pick and choose whom we wish to share our experience with. It is not a matter of being "snobby," it is a matter of trying to help those that are willing to learn, and are appreciatve of our effort. Your post #6 suggests that you've got your panties in a twist, so I'll offend you no more with my experience / advice. Welcome to "the list"
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post #17 of 85 Old 02-16-2019
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Re: sailing past close hulled?


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post #18 of 85 Old 02-16-2019
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Re: sailing past close hulled?

A sailboat's ability to point and it's boat speed are inextricably linked. As it's speed increases, apparent wind increases and moves forward. As apparent wind velocity increases, the wind's power (i.e., it's ability to drive the boat) increases. But, the speed of a sailboat's displacement hull is limited by it's waterline length. For these reasons, a conventional displacement sailboat is incapable of generating enough speed to enable it to sail closer to the wind than 30-45 degrees. Because a conventional displacement sailboat is limited by it's speed in it's ability to point, it's sails are cut more full, to maximize their efficiency at a pointing angle between 30-45 degrees.

By comparison, the potential speed of an iceboat isn't limited by it's waterline length. In addition, an iceboat isn't affected nearly as much as a sailboat by friction and by the speed-killing effect of waves crashing against it's bow. Accordingly, it is capable of achieving much higher speeds, and it's sails are cut much flatter, which enable it to point much higher.

Cutting the sails flatter for a conventional, displacement hull sailboat wouldn't enable it to point higher, because that would reduce the power of the sails and reduce it's ability to achieve it's maximum potential speed. Reducing speed reduces pointing.

To summarize, a sailboat's ability to point is primarily affected by the maximum speed that it is capable of generating. Once it is sailing at the maximum speed that it is capable of generating, then moving the traveler farther to windward doesn't generate more power. On the contrary, it makes the sail less efficient and reduces it's power. The goal is to optimize boat speed by optimizing the sail's power and minimizing the boat's drag as it moves through the water.
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post #19 of 85 Old 02-16-2019
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Re: sailing past close hulled?

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Originally Posted by Sailormon6 View Post
A sailboat's ability to point and it's boat speed are inextricably linked. As it's speed increases, apparent wind increases and moves forward. As apparent wind velocity increases, the wind's power (i.e., it's ability to drive the boat) increases. But, the speed of a sailboat's displacement hull is limited by it's waterline length. For these reasons, a conventional displacement sailboat is incapable of generating enough speed to enable it to sail closer to the wind than 30-45 degrees. Because a conventional displacement sailboat is limited by it's speed in it's ability to point, it's sails are cut more full, to maximize their efficiency at a pointing angle between 30-45 degrees.

By comparison, the potential speed of an iceboat isn't limited by it's waterline length. In addition, an iceboat isn't affected nearly as much as a sailboat by friction and by the speed-killing effect of waves crashing against it's bow. Accordingly, it is capable of achieving much higher speeds, and it's sails are cut much flatter, which enable it to point much higher.

Cutting the sails flatter for a conventional, displacement hull sailboat wouldn't enable it to point higher, because that would reduce the power of the sails and reduce it's ability to achieve it's maximum potential speed. Reducing speed reduces pointing.

To summarize, a sailboat's ability to point is primarily affected by the maximum speed that it is capable of generating. Once it is sailing at the maximum speed that it is capable of generating, then moving the traveler farther to windward doesn't generate more power. On the contrary, it makes the sail less efficient and reduces it's power. The goal is to optimize boat speed by optimizing the sail's power and minimizing the boat's drag as it moves through the water.
This is important when sailing a boat at or close to its limiting hull speed. Good post sailormon. Mono hull sailboats are displacement hulls and when they move forward they create a bow wave and this wave grows longer and long. At hull speed the hull is "supported" on two wave crests... if it could push past hull speed it would be trying to sail UP the back of the first wave crest.

The observant sailor will, if not taught in school or from a book will learn how to get their boat to sail its max speed for different wind directions usually by trial and error and seeing what sail controls do what. And we haven't even discussed weather and lee helm and the lift a keel provides, hull form and wetted surface.

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post #20 of 85 Old 02-16-2019
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Re: sailing past close hulled?

A proper answer to Sherpa's question has a lot of parts that come into play to fully understand the answer. The ASA 101 book does have a good, albeit simplified answer to the question, and Sailormon 6's answer provides a major portion of the explanation.

Another part of the question asked whether pulling the sail to windward of the center would allow the boat to point higher. The answer to that starts with the way a sail generates forces. Like any wing, as long as the airflow remains parallel to the surface of the sail for the entire surface of the sail, a sail generates it's forces over the entire surface of the sail, with the highest proportionate forces occuring near the leading edge of the sail, and the relative lower forces per square area occuring near the trailing edge. As a slight simplification, those forces at any point on the sail will be perpendicular to the surface of the sail cloth.

So for any angle of attack, (the angle of the sail relative to the apparent wind) there will be drive(forward forces), side forces, and drag(forces resisting forward motion). As the angle of attack is reduced, the side forces and drag increase relative to drive.

This occurs for a variety of reasons. To begin with, drive is diminished at flatter angles of attack. This occurs because at flatter angles of attack, if left unadjusted, the sail will luff.

Luffing is the opposite of stalling. Stalling (adjusting the sail to far to windward) occurs when the angle if attack is too steep so that the apparent wind is too perpendicular to the surface of the sail which in turn results in the air flow separating from the surface of the sail, and stops generating lift.

Luffing occurs when the angle of attack is too flat, and the wind is able to get to the leeward side of the sail and collapse the wing shape of the sail. To prevent the sail from luffing, the sail shape needs to be flattened and that in itself reduces drive.

But also as the angle of attack of the sail is rotated closer to the center line of the boat, a larger percentage of the area of the sail is pointed sidewards, and some of the sail is pointed slightly towards the back of the boat, so that the amount of side force and drag is increasing.

This slows the boat, and since the keel's ability to resist side force is proportionate to speed, and side forces are increased, the boat makes more leeway.

So, More specifically to the question about rotating the boom to windward, if the angle of attack is rotated above the center line of the boat, more of the former side forces are aimed astern and effectively become drag, greatly slowing the boat, and a larger percentage of the drive becomes side forces, causing a rapid increase in leeway, until the boat eventually has no forward motion, and only has leeway. That is effectively what happens when a boat is have to, but that is another topic for another day.

Jeff


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Last edited by Jeff_H; 02-16-2019 at 11:47 AM.
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