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Old 24-07-2018, 16:44   #1
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Sail manipulation: a concise description please?

So, I've read a few books, and listened to some lectures, and at some point in each I find myself looking at words that seem to contradict the other guy.

I don't know if it's me or perhaps they are speaking of differently equipped vessels--something I see many not mention.

Without going into details about 'when' these features are employed, I'm just looking for a good description--a one liner if you will--for the following as they relate to draft size, draft position, twist and so forth.

I've got over 20 years in professional aviation so the ideas of airflow, attack, foils, and centers of pressure are not new to me. That being said, I'm just needing to get over this hump; are their uses so intricate that it's more intuition than scenario based?

Thanks for the patience.

1. outhaul
2. main sheet
3. cunningham
4. boom vang
5. traveller

bonus question: why would a center board be retracted on a beam reach? It would seem the most amount of slip would be had there.
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Old 24-07-2018, 19:41   #2
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Re: Sail manipulation: a concise description please?

Richard Bach, in his novel "Illusions," wrote that learning is the process of realizing how much you already know, and teaching is the process of showing other people how much they already know.


I know very little but offer these words for what value, if any, they may have.


First of all, it is important to realize that you can sail the boat around without much consideration of sail shape. Changes to sail shape are optimizations used to get the last 10% or 15% or whatever out of the boat.


You use the outhaul to tension the foot of the sail, I see it more as a static line that you set once and forget, I suppose racers tweak it.


Mainsheet, is a primary sail control that mainly controls how far away from the centerline of the boat the boom (and sail) are, you let it out the farther off the wind you are. When close hauled it tends to pull the boom down, flattening the sail, the more you tighten it.


Cunningham, my boat has one. Boats with a Cunningham use it to tension the luff. The same thing can be accomplished with the halyard (but due to friction it may not be feasible to tension the luff this way), or with a downhaul (if the gooseneck allows the boom to be pulled down enough to matter), or with a vang (if equipped and if the boom can be pulled down enough to matter).


Boom vang, I don't have one of these, they serve as an alternative to the downhaul and Cunningham as a means to tension the luff while also pulling some of the fullness out of the belly of the sail at the same time. The idea being that a vang is supposed to set the sail shape in a way that will not require as much fiddling as a downhaul would to maintain the proper shape when changing from one point of sail to another.


Traveler, you may have one, or several, or not, I don't have any. A mainsheet traveler is a way of adjusting the geometry of the mainsheet so that the downward force it applies is appropriate at a wider range of points of sail than would otherwise be the case. Sometimes adjustable using stops. Less often, used as a way to get a self-tacking jib, or as a means of adjusting the relative foot and leech tensions on a genoa.


This is probably all wrong and someone will be along shortly with true facts.



Enjoy the voyage..
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Old 24-07-2018, 20:47   #3
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Re: Sail manipulation: a concise description please?

Everything said above is correct. I'm going to try to add on with an aviation perspective since I also have a little background in that field.

Outhaul: Increasing tension on the outhaul will flatten the sail, particularly the bottom portion (the foot). Think of a Mooney wing (flat) vs a Super Cub (deep). The outhaul is adjusted based on wind speed - the faster the wind, the flatter your sail. Just like a plane.

Main sheet: Increasing tension of the main sheet will increase the angle of attack of the sail. If you pull it in too tight, the sail will stall and you will loose a lot of speed. However, main sheet must be kept tight enough to keep the sail filled since it doesn't have a rigid structure like a wing. The main sheet is adjusted to keep the sail at a constant angle to the wind.

Cunningham: Increasing tension on the cunningham tightens the front of the sail (the luff) and generally moves the draft forwards. Cunningham is adjusted based on wind speed - the faster the wind, the more cunningham (because increased wind forces the draft back, so you must correct for it). I suppose adding cunningham is similar to deploying leading edge slats but that's a bit of a stretch.

Boom Vang: Increasing tension on the boom vang tightens the back of the sail (the leech) and is primarily used to control shape at the top of the sail. You want the entire sail to have the same angle of attack to the wind, not have the bottom stalled and the top luffing. Increasing tension on the boom vang will generally increase angle of attack at the top of the sail and is adjusted based on wind speed.

Traveller: The traveller, when used in conjunction with the main sheet, will perform a similar function as a boom vang. The traveller is used to adjust the angle of the main sheet relative to the boom to facilitate that usage.

Bonus: The centerboard is used to reduce leeway, but it adds drag. When you are sailing upwind, the sails are sheeted as tight as possible so the board stays 100% down to counteract that. On a beam reach, with the wind mostly behind you, the sails are eased so you can bring the board up to around 60% without adding leeway. When sailing dead downwind, you can reduce the board to 10% or even less depending on stability of the boat etc.

Hope that helps,
Sawyer
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Old 24-07-2018, 20:53   #4
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Re: Sail manipulation: a concise description please?

Neat summary, Mediator!

Quote:
Originally Posted by Mediator View Post
Main sheet: Increasing tension of the main sheet will increase the angle of attack of the sail. If you pull it in too tight, the sail will stall and you will loose a lot of speed. However, main sheet must be kept tight enough to keep the sail filled since it doesn't have a rigid structure like a wing. The main sheet is adjusted to keep the sail at a constant angle to the wind.
Hmm ... but depending on where your boom is (outboard of the traveller, inboard of the traveller), the functions of the main sheet also include: changing the leech tension, in other words open or closing the leech, changing twist in the leech.

I don't know how to relate that to aeronautics ...
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Old 24-07-2018, 20:59   #5
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Re: Sail manipulation: a concise description please?

Quote:
Originally Posted by Alan Mighty View Post

I don't know how to relate that to aeronautics ...
Good point, forgot to mention twist.

If anyone is familiar with the Wright Flyer and other very early aircraft, they did not use ailerons but instead twisted the end of the wing to induce roll. I suppose adding twist to the top of the sail is the same premise

When cruising I use the traveler to induce twist when sailing upwind in strong conditions because it's easier than going on deck and adjusting the vang. But when dinghy sailing we only use the vang, no traveler.
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Old 24-07-2018, 22:51   #6
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Re: Sail manipulation: a concise description please?

Quote:
Originally Posted by Mediator View Post
... If anyone is familiar with the Wright Flyer and other very early aircraft, they did not use ailerons but instead twisted the end of the wing to induce roll. I suppose adding twist to the top of the sail is the same premise..
No, it is not related.

The reason for twist is two fold:
1. In light to moderate winds, because the wind speed is greater aloft. This causes the apparent wind to blow at different speeds at different elevations. Had you not noticed this, through the tell tales?
2. Depowering in stronger winds. Obvious enough.


Something that has been skipped over is HOW the Cunningham moves the draft. The sail cloth can be stretched, changing the shape of the sail in a complex way. This is communicated through rules of thumb that overlook the underlying reasons. It is important to understand the reasons if you wish to understand different sail cloths and sail designs.



Really, it's all in books. You just need to get the right ones and read them closely.
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Old 24-07-2018, 23:50   #7
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Re: Sail manipulation: a concise description please?

I can't add much that hasn't been said, except the traveller: Great to minimize the force from accidental gybes when sailing downwind. Of course, you should have a preventer, but for short legs, put the traveler to leeward and any accidental gybe will not be as crashing....
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Old 25-07-2018, 00:10   #8
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Re: Sail manipulation: a concise description please?

ONLY one you'll ever need, superb, best and most understandable descriptions EVER written on the subject.


https://shop.sailboatowners.com/prod...im+Users+Guide
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Old 25-07-2018, 06:51   #9
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Re: Sail manipulation: a concise description please?

Whoa great responses. Thanks everyone. I'll be looking into that book too.

I had a question that should have been in the first post. It's kind of loaded.

Cunninghams, Vangs, Travellers, outhauls, et al.

How often are they included in a boat? I'm guessing larger = more components.

But, what are the common combinations? Meaning, for example, if there was a Cunningham would there most likely be a vang and traveller? Would you ever find a vang and not a traveller, or the reverse?

Or, does this just go down the rabbit hole of boat designs and the whims of the designers?
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Old 25-07-2018, 07:51   #10
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Re: Sail manipulation: a concise description please?

Quote:
Originally Posted by thirtywest View Post
...
How often are they included in a boat? I'm guessing larger = more components.

But, what are the common combinations? Meaning, for example, if there was a Cunningham would there most likely be a vang and traveller? Would you ever find a vang and not a traveller, or the reverse?

Or, does this just go down the rabbit hole of boat designs and the whims of the designers?

Read the books. Look at boats. Do the homework.



The first book probably showed all of these on a racing dinghy. Some larger boats are missing important adjustments, and often sailors add them. Many sailors have adjustments they don't understand how to use.
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Old 25-07-2018, 08:02   #11
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Re: Sail manipulation: a concise description please?

Youve done enough reading...go sailing and it will start to make sense.
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Old 25-07-2018, 08:12   #12
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Re: Sail manipulation: a concise description please?

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Originally Posted by belizesailor View Post
Youve done enough reading...go sailing and it will start to make sense.
^^^
This
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Old 25-07-2018, 08:31   #13
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Re: Sail manipulation: a concise description please?

Quote:
Originally Posted by thirtywest View Post
Whoa great responses. Thanks everyone. I'll be looking into that book too.



I had a question that should have been in the first post. It's kind of loaded.



Cunninghams, Vangs, Travellers, outhauls, et al.



How often are they included in a boat? I'm guessing larger = more components.



But, what are the common combinations? Meaning, for example, if there was a Cunningham would there most likely be a vang and traveller? Would you ever find a vang and not a traveller, or the reverse?



Or, does this just go down the rabbit hole of boat designs and the whims of the designers?


Traveller varies with boat design. Lots of cruising boats don’t bother with a traveller. Larger racing boats do have them. Racing dinghies are aided by scale effects and can get by with vang and mainsheet. My Cal20 doesn’t have a traveller but was and still is a heavily raced class.

Some boats with very low booms don’t have a vang but most do. I raced on a Cal40 where the owner elected to not have a vang, on the wind he had main and a fairly short traveller. Off the wind he had double rubber strops to the leeward rail that acted as both bang and preventer.
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Old 25-07-2018, 08:33   #14
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Re: Sail manipulation: a concise description please?

Quote:
Originally Posted by Adelie View Post
Traveller varies with boat design. Lots of cruising boats don’t bother with a traveller. Larger racing boats do have them. Racing dinghies are aided by scale effects and can get by with vang and mainsheet. My Cal20 doesn’t have a traveller but was and still is a heavily raced class.

Some boats with very low booms don’t have a vang but most do. I raced on a Cal40 where the owner elected to not have a vang, on the wind he had main and a fairly short traveller. Off the wind he had double rubber strops to the leeward rail that acted as both bang and preventer.
And how did it go to windward
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Old 25-07-2018, 08:36   #15
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Re: Sail manipulation: a concise description please?

On the wind he was just as fast as all the other Cal40s.
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