Boomvang Adjustments

[zirgoth]

Alright,

i have been reading some material on boomvang adjustments and i am confused. I know each boat is different and trimming maybe different but i am looking for either specific adjustments for the boats i sail or general rules for adjusting this convoluted piece of awesome.

Growing up in sailing camps i sailed albacores (current boat i am sailing), 420's, Pirates (in sea cadets), lasers. I learned that when sailing upwind you tighten your boomvang and when going downwind you loosen it completely. Thats basically all they taught us.

Now from sailing around the old dogs and reading about the boomvang, i hear that going downwind its better to tighten the vang rather than loosen it. I also hear that the vang can be loosened upwind as well.

so i don't know what to do with the vang now. I am hoping you guys can help me out with minimal scathing noob remarks

I am looking for answers concerning when to tighten and when to loosen the vang based on wind conditions and points of sail. if you can please explain when twist is optimal for the sail and when it isn;t. finally, if you can explain angles of attack i would greatly appreciate it.

preping for next seasons races,

zirgoth

 

[Bruno]

Good for you to ask this question. It depends on if you are vang sheeting upwind or not, if you are using a traveler then you may put on some vang upwind to control your leech (twist) and pre-bend your lower mast (camber). If you aren't using a traveler then you'll probably use the vang to do the above and keep the requisite leech tension as you ease your boom beyond your bridle, in which case you will usually want the vang to be quite tight (vangsheeting). In the former case you'll likely want to pull on some vang offwind to control the leech unless it's light. In the latter you'll want to ease some vang to allow more twist and let the boom end up for waves and gybes offwind. In extremely strong winds sailing (particularly gybing) with a tight vang can make the boat more difficult to handle and end up with a broken boom. Experiment.

 

[mustang__1]

the very best thing you could do would be to go out with another boat, set them up completely the same, and then start making adjustments and see what happens. However, the vang controls to a large extent the leech tension, and to a smaller extent (depending on the rig design) mast bend.

Basically, in light air, id be hard pressed to use any vang at all. In light air you want the leech to twist off a bit to account for the changing wind speeds up the rig etc. If the top teltale is stalling 100% of the time, you probably have to much vang on in any sort of boat.

In medium air the basic starting guide that i'll use is to go to the mainsheet tension i want and then snug it. From there, it depends on if we;re over or underpowered. If we're feeling stalled, time to ease it off. If we're overpowered, snug it down a bit more. Still sailing to the top telltale.

In heavy air its very much depenedent on any number of factors. Some boats like to start twisting off to spill power, others you just crank it on. I couldnt tell you the reasoning behind it so well, probably depends on how much mast bend (and thus midgirth flattening).

downwind in light air, completely free. More wind, more vang. You do not want the top of the main blowing off downwind in breeze. you're looking to trim the vang to the point where a: the top batten is parallel to the boom. b: the leech is stabilized ie: its not bouncing all over the freaking place.

Then there's vang sheeting. Whereas in a keelboat you would lower the traveler to maintain sheet tension with a lower angle of attack on the boom, you can pull the vang on so that as you ease the sheet the boom doesnt rise and you maintain leach tension. This is useful in breeze or when you're reaching.

this is really pretty basic, some of it is probably wrong, but it should be good enough to get you thinking about the use of the vang in the right way.

 

[Major Tom]

Every class of boat has it's own set of rules regarding how much vang should be used. Within a class there can also be a whole heap of variations such as crew weight, make of sails and spars, deck chocked or strutted etc etc. As has been said above, 2 boat testing or sitting down or going sailing with one of the quick guys in your chosen fleet is the best way to learn the right info as quickly as possible.

 

[Dave89joe]

the very best thing you could do would be to go out with another boat, set them up completely the same, and then start making adjustments and see what happens. However, the vang controls to a large extent the leech tension, and to a smaller extent (depending on the rig design) mast bend.

Basically, in light air, id be hard pressed to use any vang at all. In light air you want the leech to twist off a bit to account for the changing wind speeds up the rig etc. If the top teltale is stalling 100% of the time, you probably have to much vang on in any sort of boat.

In medium air the basic starting guide that i'll use is to go to the mainsheet tension i want and then snug it. From there, it depends on if we;re over or underpowered. If we're feeling stalled, time to ease it off. If we're overpowered, snug it down a bit more. Still sailing to the top telltale.

In heavy air its very much depenedent on any number of factors. Some boats like to start twisting off to spill power, others you just crank it on. I couldnt tell you the reasoning behind it so well, probably depends on how much mast bend (and thus midgirth flattening).

downwind in light air, completely free. More wind, more vang. You do not want the top of the main blowing off downwind in breeze. you're looking to trim the vang to the point where a: the top batten is parallel to the boom. b: the leech is stabilized ie: its not bouncing all over the freaking place.

Then there's vang sheeting. Whereas in a keelboat you would lower the traveler to maintain sheet tension with a lower angle of attack on the boom, you can pull the vang on so that as you ease the sheet the boom doesnt rise and you maintain leach tension. This is useful in breeze or when you're reaching.

this is really pretty basic, some of it is probably wrong, but it should be good enough to get you thinking about the use of the vang in the right way.

+1 on all the above.

Ill add that a good rule of thumb is to make sure that the top leach telltail is stalling about 50% of the time up wind. You will progressively add more vang as the wind picks up until you get very over powered. When it is survival conditions it will actually help to twist off the main by letting off on vang when you are going up wind. Some one correct me if I'm wrong but when it is blowing the dogs off chains you want some vang going down wind. The added vang will stabilize the boat some so the boom isn't flying around.

In very light wind it is nice to pull the vang so that it is just slack when you are going up wind but still tight enough that the sail catches wind when you roll tack. If it is too loose the boom bounces all over the place and the sail can back wind.

You can adjust the vang going up wind as the wind strength changes. You will want to pull the vang on in the puffs and ease in the lulls.

In all fairness I can't stress the importance of a tuning partner.

Most of this knowledge is based on sailing 420s/ FJs so some of it may not apply to other boats.

 

[knobblyoldjimbo]

my tuppence worth is that you'll need some vang off the wind once the mainsheet traveller loses it's impact, if you get a puff of wind or gust you want the leech to be firm (not tight of course) but firm so that the main keeps its shape and pushes the boat forward instead of just bowing and absorbing the wind.

I had one on my beachcat until I changed the gooseneck configuration and I'm sure it made a big difference. Gybing also was easier and more powerful as the boom didn't lever upwards, just came across - also pulled the boat forward as you pulled the boom towards the centreline.

 

[Steam Flyer]

... ... ... ...

I learned that when sailing upwind you tighten your boomvang and when going downwind you loosen it completely. Thats basically all they taught us.

... ... ...

That's not only wrong, it's crazy. If there is any weight in the wind at all, you must have some vang tension downwind or the boat becomes difficult to steer as well as slow.

Vang tension has it's own logic. The vang controls how much the boom rises, allowing the maisail to twist. If you lat all tension off the vang, and sail a beam reach in whatever a decent powered-up breeze is for the boat, you will observe that the upper 1/3 of the main is not working very hard, the lower 1/3 is trimmed in too tight, and only the middle section is driving efficiently.

Having the lower section of the mainsail overtrimmed makes the leverage of the boom fight the rudder (unless you heel to windward) and is slow. Pull on some vang tension, as you pull the leach of the main straighter you will feel the tiller ease up and the boat will go faster.

When borad reaching, or going DDW, the effect is not quite as dramatic BUT having the vang too loose can lead to death-rolling (capsize to windward) as well as making it more difficult to steer... especially if the wind is gusty, and/or there is much chop.

In general, set the vang tension so that the lower leach telltales stream steadily and the upper leach telltale flips behind the sail somewhere between 10% and 75% of the time... how much, depends VERY much on the type of boat and the conditions. In general, the heavier & slower the boat, the more you want it flipping behind the sail (generating a "starting vortex" for the whole sail, working as a foil). The choppier the conditions, the less you want it flipping behind the sail.

FB- Doug

 

[BalticBandit]

A lot of good feedback here. But the most important thing to realize is that the vang is just another tool for shaping the sail. And one of the reasons why there is a "different rule for different boats" is that it is an indirect control that affects TWO DIFFERENT aspects of the sail at the same time.

The first one - is the tension in the leech of the sail. lots of folks have commented on this effect.

the second is bending the mast.

This is a bit less obvious and this is ALSO the part that is THE MOST VARIABLE boat from boat. Consider the following three boats:

29er - with what is popularly called a GNAV (because it is a solid lever ABOVE the boom)

Laser - which is a traditional rope triangle below the boom

Star -which has a vang on a circular track about 2' behind the mast

In the star, the majority of the pull is STRAIGHT DOWN with very little force pushing the boom forward. So there is very little mast bending effect. Hence vang is used purely to control the amount of twist in the sail (ie how much the angle of attack of the upper part of the sail has vs. the bottom. EXCEPT that the top of a star mast is very very very flexible, so just pulling on the leech of the sailcloth, bends the tip aft. And as you bend the tip of the mast,the upper middle gets pushed forwards, which in turn pulls some of the sailcloth forwards and hence takes some curvature out of the sail (ie flattens it)

So upwind in a star the vang is almost never used. Off the wind on a reach or downwind, the vang is used to get the right amount of curve in the upper batten

On the laser (and other traditionally vanged boats), part of the force of the vang pulls the boom downwards, but because it also pulls the boom towards the mast, it also bends the bottom of the mast forwards. This in turn bends the the whole mast into a bow and like with the star flattens the sail a bit

ON the 29er, the GNAV has even more impact on the curvature of the mast because the forward force is where the lever pushes into the mast - about 4' up from the deck. This means that when initially set (say at 25%) the vang closes the leech, but if you really really really crank the GNAV on, it bends the tip of the mast aft and starts to open up the leech.

It is this impact on the shape of the mast itself that is what makes vang settings vary so much from boat to boat.

 

[halfcolours]

A lot of good feedback here. But the most important thing to realize is that the vang is just another tool for shaping the sail. And one of the reasons why there is a "different rule for different boats" is that it is an indirect control that affects TWO DIFFERENT aspects of the sail at the same time...

...

ON the 29er, the GNAV has even more impact on the curvature of the mast because the forward force is where the lever pushes into the mast - about 4' up from the deck. This means that when initially set (say at 25%) the vang closes the leech, but if you really really really crank the GNAV on, it bends the tip of the mast aft and starts to open up the leech...

+1

and thanks for finally explaining to me something that I found very strange when I've had a drive of a 29er, was a bit of an out of sight, out of mind thing for me I suppose.

 

[mustang__1]

well, i think the main reason (and im sure people will disagree...) for the GNAV is to clear up space for the crew. It makes the 29er a really ergonomic (aside from the placement of the vang/cunno) and easy boat for the crew.

 

[BalticBandit]

well, i think the main reason (and im sure people will disagree...) for the GNAV is to clear up space for the crew. It makes the 29er a really ergonomic (aside from the placement of the vang/cunno) and easy boat for the crew.

Well I think partly it was to mimic the 49er for which the 29er was supposed to be a Junior's training boat. And yes on the 49er it was an ergo thing.

 

[J Buoy]

Most Albacores these days have a split tail mainsheet which can centre the boom but also tighten the leech. This combined with the rig tune allows you to not need much boom vang upwind until the wind is more than moderate. Insofar as the leech is concerned in light stuff we prebend the mast upwind to open it and ram it aft in medium wind to tighten it. As mentioned above, keep the telltales streaming. Off the wind on runs you want your mast fully aft and your vang on only enough to keep the sail from spilling. On reaches you will need to play the vang constantly and as a rule of thumb you will want to keep the vang just tight enough to have the telltale second from top flowing constantly.

I am still working my way up the fleet so do not take it as gospel but there are lots of tuning guides out there for the Albacore that explain the setup and effects in more detail.

 

[Sneaky Duck]

Another thing to keep in mind is that vang is played differently for each cut of sail too. I know that in thistles the Proctor sails like it when you play the traveler but the Fishers like you to Vang sheet.

I know I've been taught in the Thistle that you want to crank on more vang when going upwind as the breeze increases. This not only holds the leach tight but also bends the boom and helps flatten the sail. Around the top mark we ease it a bit to let the sail be more full but taunt enough to not let the boom pop up in a puff. Lesson I learned this year however is when it's really blowing make SURE someones got their hand on the vang going down wind. Blowing it can be the thing that keeps you upright... Oops.

 

[mark1234]

Another small subtlety that's been missed is it depends more on where the wind is from than where the boat is going - for instance, downwind in some boats, the main's still working in a very upwind (apparent-wind) mode (49ers, moths), whereas in others it's working as a barn door rather than an aerofoil (laser, etc). That has quite an impact on vang use.

I'm not convinced two boat tuning is entirely necessary at this gross (coarse, rather than unpleasant!) a level. Simply sail for a few minutes and try something significantly different. You'll soon get an idea for what makes the boat feel right, and vice versa.

 

[BobBill]

A lot of good feedback here. But the most important thing to realize is that the vang is just another tool for shaping the sail. And one of the reasons why there is a "different rule for different boats" is that it is an indirect control that affects TWO DIFFERENT aspects of the sail at the same time.

The first one - is the tension in the leech of the sail. lots of folks have commented on this effect.

the second is bending the mast.

This is a bit less obvious and this is ALSO the part that is THE MOST VARIABLE boat from boat. Consider the following three boats:

29er - with what is popularly called a GNAV (because it is a solid lever ABOVE the boom)

Laser - which is a traditional rope triangle below the boom

Star -which has a vang on a circular track about 2' behind the mast

In the star, the majority of the pull is STRAIGHT DOWN with very little force pushing the boom forward. So there is very little mast bending effect. Hence vang is used purely to control the amount of twist in the sail (ie how much the angle of attack of the upper part of the sail has vs. the bottom. EXCEPT that the top of a star mast is very very very flexible, so just pulling on the leech of the sailcloth, bends the tip aft. And as you bend the tip of the mast,the upper middle gets pushed forwards, which in turn pulls some of the sailcloth forwards and hence takes some curvature out of the sail (ie flattens it)

So upwind in a star the vang is almost never used. Off the wind on a reach or downwind, the vang is used to get the right amount of curve in the upper batten

On the laser (and other traditionally vanged boats), part of the force of the vang pulls the boom downwards, but because it also pulls the boom towards the mast, it also bends the bottom of the mast forwards. This in turn bends the the whole mast into a bow and like with the star flattens the sail a bit

ON the 29er, the GNAV has even more impact on the curvature of the mast because the forward force is where the lever pushes into the mast - about 4' up from the deck. This means that when initially set (say at 25%) the vang closes the leech, but if you really really really crank the GNAV on, it bends the tip of the mast aft and starts to open up the leech.

It is this impact on the shape of the mast itself that is what makes vang settings vary so much from boat to boat.

Bandit and Major Tom +1

 

I could add that "what the sail(s) look like counts. You sail long enough, you begin to have a gut feeling about sail shape, and it is usually good 'nough, but some sailors are techy and never or have yet to encounter that wisdom. Sorta like, if it looks good, it probably is good, but you also have to know your boat...so sail is a lot ...it comes.