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tarmes 04-13-2012 07:52 AM

Vang on a dinghy
 
Hi all,

I've been sailing dinghies for just under a year and I'd like to better understand how the various sail controls will affect the dinghy's performance.

Would someone be able to explain how and when the vang should be used in this context? Note that I did discover this excellent thread that discussed the vang with respect to the main sheet and traveler: http://forums.sailin...owtopic=104559. However, my dinghy doesn't have a traveler so I'm using the main sheet as the primary control for sail angle.

My curiosity was push when I saw a video on the free Volvo sailing app for the iPad. In the video we see the sailor make changes to the vang (or "kicker"', since he's British) as he rounds a buoy and heads upwind.

When can I find some more detailed info about all this?

Thanks,

Tim

deniseO30 04-13-2012 09:22 AM

Re: Vang on a dinghy
 
gotta love youtube! this should help, enjoy
<iframe width="420" height="315" src="http://www.youtube.com/embed/W9cmwySbS2g?rel=0" frameborder="0" allowfullscreen></iframe>

tarmes 04-13-2012 10:12 AM

Re: Vang on a dinghy
 
Quote:

Originally Posted by deniseO30 (Post 858146)
gotta love youtube! this should help, enjoy

Actually, I'm not loving Google because I'm not finding the answers I'm looking for :)

Using Google:
  • I understand that the vang keeps the boom from raising.
  • I understand that tensioning it will flatten the sail.
  • I understand that used in conjunction with the traveler is maintains the boom position, and therefore the sail twist, as the mail sail's angle is changed.

However:
  • I'm not clear on when, and by how much, the vang should be tightened or loosened.
  • I don't understand how the vang's used differently when going up/down wind
  • It seems to me, perhaps wrongly, that it's more important to make more frequent adjustments on small dingies than on keelboats. I'm I right? If so, why?

I've managed to find the Volvo videos that kicked off my curiousity. In this one he's adjusting the vang ("kicker") on the reach:


And here he's releasing the cunningham and the vang as he rounds the marks:


I'd really like to understand what's going on.

Regards,

Tim

MarkSF 04-13-2012 02:46 PM

Re: Vang on a dinghy
 
Here's my take :

Without a vang at all, and with the traveller always centered, this means that as you move from close hauled to a run, the downwards effect of the main sheet gets less and less. The boom then has a tendency to rise, and the more wind, the more it rises. The effect of this rise is to allow air to spill air out of the leach of the sail, losing some power.

A cruiser might not mind this loss of power, in fact it makes the boat easier to handle, as you have a negative feedback effect, the stronger the wind the more air you spill, but if you are racing you definitely do mind.

A good starting point is to sheet in hard on a close reach, then snug up the vang so it's just tight. Then as you go through the points of sail to a run, the vang is keeping the boom level, fighting the rise.

If you feel overpowered from a beam reach to a run, let the vang out. The boom rises and some air spills out.

Roxy405 04-14-2012 06:33 PM

Re: Vang on a dinghy
 
Tarmes,
Quote:

Originally Posted by tarmes (Post 858173)
I'm not clear on when, and by how much, the vang should be tightened or loosened.
I don't understand how the vang's used differently when going up/down wind

In theory, at least, the vang/kicker on a dinghy is pretty much for controlling leech tension and sail twist.

To rather oversimplify, the reason for doing it is that all the "sheeting-in" force on the sail is concentrated along the boom. As you get further away from the boom up the sail, the sheeting-in force decreases and the wind makes the sail begins to twist—reduces the angle of attack. On a blowy day, it can actually be enough to seriously decrease the amount of power generated by the top of the sail.

The kicker is used to apply tension to the leech of the sail, which helps to keep the sail twist down and more power on. In theory, when going upwind, you don't need the kicker at all (N.B. in practice, you really do) as the mainsheet can be used to pull the boom downwards because the boom end is over the boat (particularly in a laser that has bridle/traveller-y thing). Obviously, in real life you don't want a lot of downwards tension in the mainsheet, so you use the kicker instead to make life easier (plus, it means you keep leech tension on when you're spilling wind in the gusts).

Obviously, off wind you need the kicker to keep the boom down and the right amount of tension in the leech. However, there is less sideways force trying to blow the top of the sail off to leeward—so you need less kicker.

In terms of how much, the classic formulation is "so the top-batten telltale is lifting about 75% of the time, up to 100% in heavy winds."

But
In a Laser or any boat with an unstayed rig, pulling on the kicker bends the mast. This flattens the sail, reducing power. I don't sail those kind of boats, so I couldn't tell you how it is different.

Quote:

Originally Posted by tarmes (Post 858173)
I've managed to find the Volvo videos that kicked off my curiousity. In this one he's adjusting the vang ("kicker") on the reach

There are some clever(ish) kicker tricks. One can, for example, loosen the kicker a touch when overpowered offwind to spill a little wind at the top of the mast (where the heeling moment is greatest) to gain a bit more control. A nice trick in boats with kites—less useful if not.

Quote:

Originally Posted by tarmes (Post 858173)
And here he's releasing the cunningham and the vang as he rounds the marks

Well, the kicker tends to pull the draft of the sail backwards, and the cunningham can be used to bring it back forward. (Although it does other stuff too!).

Quote:

Originally Posted by tarmes (Post 858173)
It seems to me, perhaps wrongly, that it's more important to make more frequent adjustments on small dinghies than on keelboats. I'm I right? If so, why?

Don't know precisely—possibly because keelboats are just generally a touch less adjust-y then dinghies. Probably, more to do with the interaction with the traveller, the weight of the boom, and the option of reefing.

Quote:

Originally Posted by tarmes (Post 858173)
When can I find some more detailed info about all this?

Frankly, I'd prescribe time on the water playing with it. You can get mind-numbingly dull texts on sail aerodynamics but....:confused: While turfing it off round the top mark and down the reach with the kicker on tight will not do you any favours there's probably more to be gained by focusing on trim and balance.

Faster 04-14-2012 10:17 PM

Re: Vang on a dinghy
 
You've gotten some good answers already.. you really do need to play with it.

A good powerful vang can take the place of the traveller, ie all the leech tension can be created by the vang if it has enough purchase and if the boom is stiff enough to transfer all that force through to the clew.

Consider the standard, 'traveler down, sheet on' to depower in a breeze.. the traveler adjustment adjusts the angle of attack of the sail, then the sheet provides the required leech tension. Once you get to the end of the traveller, as Mark said above the downward force available from the sheet goes away and the vang is required to limit boom lift, keep the boom under control and prevent a 'goose wing gibe', a dangerous event prevented by any vang, even a fixed strop.

With a powerful vang, upwind, when you 'run out of traveler' easing the sheet now adjusts your angle of attack and the vang prevents any further boom lift. This is sometimes referred to as 'vang sheeting', it mimics having an 'infinitely wide traveler' and is a common small racer/dinghy technique in a breeze. However if you're doing this it's imperative to ease the vang prior to rounding a windward mark.... bearing off can generate such forces as to literally tear the vang fittings out of the mast/deck/boom etc (.... don't ask......)

So sailing a dinghy with no traveler, having a good vang and getting used to using it should be a great advantage.


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