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Old Dec 11, 2014, 04:38 PM
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What does the vang do and how?

Can anyone explain the function of the vang? Should it be tightened to keep the boom from lifting? Should it be loose enough to allow the boom to lift? What should the "normal" "start" position/adjustment? I understand the vang is for putting "twist" in the mainsail, but I just cant seem to grasp the concept.
Please help this confused newbie out.
Thanks
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Old Dec 11, 2014, 04:53 PM
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It simply pulls down on the back of the boom and "Controls" twist/tightness of the leech. With no vang the back of the boom would go way up in a breeze and the leech would blow open.

It isn't hooked to the back of the boom but since the front of the boom does not move up or down when the vang is shortened it pulls down on the back. As long as it is over 45 degrees to the boom it tries to pull down and forward but as mentioned the front can't move so the back comes down. You can have a solid rod type vang that pushes up as well and some boats use that to open the leech in light air. Or something as simple as string that only pulls down.
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Old Dec 11, 2014, 05:33 PM
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For the vang to work properly it is important that your mainsheet only controls the position of your boom off of the centreline.
If your main sheet is pulling the boom down any appreciable ammount that could be causing your confusion.
If tihs is happening your vang would have little or no effect, it being overriden by the mainsheet.
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Old Dec 11, 2014, 06:24 PM
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The vang is not used when working to weather or close hauled. It is used on a broad reach and off wind and as noted to pull the boom down and reduce sail twist when the mainsheet is payed out.

The vang is also not used in heavy air, because one wants the ability to quickly twist the mains'l and dump air to avoid becoming overpowered and broaching. The boat is probably near hull speed anyway and thus the vang has no great value compared to a lot of liability

In light to moderate air, the vang is critical to good performance off wind.
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Old Dec 12, 2014, 10:51 AM
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Quote:
Originally Posted by AA5BY View Post
The vang is not used when working to weather or close hauled. It is used on a broad reach and off wind and as noted to pull the boom down and reduce sail twist when the mainsheet is payed out.

The vang is also not used in heavy air, because one wants the ability to quickly twist the mains'l and dump air to avoid becoming overpowered and broaching. The boat is probably near hull speed anyway and thus the vang has no great value compared to a lot of liability

In light to moderate air, the vang is critical to good performance off wind.
Maybe I set my boat different from yours but I use the vang to give the correct shape to the mainsail leech when going to windward.
Without it you would be relying on the mainsheet to control the leech, a recipe for a burnt out winch.
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Old Dec 12, 2014, 11:05 AM
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Quote:
Originally Posted by Psychosis View Post
Maybe I set my boat different from yours but I use the vang to give the correct shape to the mainsail leech when going to windward.
Without it you would be relying on the mainsheet to control the leech, a recipe for a burnt out winch.
I always use the main sheet to control twist going upwind and the vang for off wind. This gives you the ability to not only have two different twist settings, upwind and downwind, but also some twist adjustment going upwind. This is the reason most big boats have a traveler. It allows you to adjust twist with the sheet and angle of attack with the traveler. If controlling twist with the sheet burns out your winch, you need a bigger winch. Also, vang tension going upwind forces the boom into the gooseneck, which bends the mast which flattens the bottom of the main. Sometimes you want that (heavy wind) but most times you don't.
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Old Dec 12, 2014, 11:30 AM
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I wonder if it would make an interesting poll, do you use the vang to set upwind shape or downwind shape?

Using the vang upwind seems similar in my mind to setting the mainsheet and playing the traveler on a big boat. Otherwise you can't ease the angle of the main without also opening the leech. I think it's common on many RC boats that the fastest setup is not to have the main boom centered upwind, but a few degrees out.

There is a reason IOMs have a mast ram on the other side of the boom connection.
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Old Dec 12, 2014, 01:29 PM
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RW if you were confused before!!!!!!!!!!!!
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Old Dec 12, 2014, 01:33 PM
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I should clarify that my comments are from a perspective of full size sailing rather than from my limited RC sailing. No doubt the two don't always gehaw.
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Old Dec 12, 2014, 02:55 PM
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I've sailed "big" boats all my life, and model boats for the last 10 years or so. The statement below is totally wrong in my experience. In heavy air downwind, you need the vang to control main twist. Too much twist causes the mainsail to push the masthead to windward, causing oscillations and "broaching" to windward. When reaching, easing the vang can reduce weather helm.

On my models, I use the "rigid" vang to set and maintain twist both upwind and down. I've seen and heard of models with "spring loaded" vangs that allow some twist control upwind with the mainsheet. I'm not convinced they're worth the weight and complexity...but that's just me.

Of course there are also servo controlled vangs in some classes that allow them. Those are probably optimum except for the weight and complexity.

Kevin
C-J #551

[QUOTE=AA5BY;30175800

The vang is also not used in heavy air, because one wants the ability to quickly twist the mains'l and dump air to avoid becoming overpowered and broaching. The boat is probably near hull speed anyway and thus the vang has no great value compared to a lot of liability

QUOTE]
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Old Dec 12, 2014, 10:05 PM
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I think everyone is bouncing on different sides of the same idea. The vang controls mainsail twist. Its usefulness varies per the conditions. Gusty verses shifty. And as the sheet brings the boom in those forces may over ride the vang settings. And some boats react differently than others.
I usually set the vang a little looser on gusty days to depower a bit. The boat is big and heavy, so it doesn't squirt out in a puff like an ultralight displacement type (or cat). I can always control the sheet via tx.

Dave
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Old Dec 13, 2014, 01:05 PM
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Dear Posters,
While I thank you all for your input on my questions I am now more confused than ever. The opinions given here tend to counterdict each other. I still have no clear understanding of the concept. Should I loosen the adjustment ring on the vang so that the boom flops up and back slightly? How much? Should I tighten the adjustment so that the boom does not move up at all? When should I do either of these adjustments and why? Forgive my ignorance, but I am an old guy and I dont have 20 plus years of RC sailing left to figure this stuff out by trial and error.
Thanks, R/W
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Old Dec 13, 2014, 01:54 PM
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OK, first, what does the vang do?
The vang primarily pulls the outboard end of the boom down. This increases the length from the head of the sail to the clew, which tightens the leech. A tight leech is called "closed" and puts very little twist in the sail. Easing the vang allows the boom to rise, shortening the distance from the head to the clew, allowing the leech to "open." See picture, two boats, one leech open and one closed.

When do you want the leech open or closed?
Typically, going to weather you want it closed. This allows you to sail closer to the wind or point higher. However, if the boat is overpowered (heeling too much) you may want to open the leech to bleed off some of the heeling force. Also if your speed is down and you want to accelerate quickly, opening the leech gives you more power, but slightly less point.
When you are off the wind, you want the twist to give you more power since you are not interested in sailing close to the wind.

How do you use this?
The easy answer is to trim the vang for the closed leech all of the time. This gets you 90% of the way there, but does not give you the ability to "shift gears," or accelerate quickly when your speed is down. Nor does it allow you to open the leech up when you are off the wind. This is all fine for cruising, but it is not racing fast.
If you adjust the vang for a reach, with some twist, and then use the main sheet to control the leech when you are close hauled you have much more control and flexibility to adjust for conditions.

So, either way is OK, it just depends on what you want to do.
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Old Dec 13, 2014, 10:34 PM
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Thanks Greg28... I am less confused now!!

Cheers;
Eric
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Old Dec 14, 2014, 01:36 PM
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Here is another question about the vang. How many use a ridged vang, one that holds the boom from going up or down. Yesterday when I was sailing the new boat the leach of the main was closing too much when pointing and pulling the sheets all the way in. I assume it is due to the vang allowing the boom to lower (closing the leach) with the main sheet. I had to loosen the sheets a little to get some twist back into the main. After reading Greggs reply I guess I'm right where I should be.
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