Do I need this boom vang? - SailNet Community

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  #1  
Old 07-27-2009
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Do I need this boom vang?

Is the boom vang redundant if I have a boom sheet traveler that attaches to the boom just forward of the vang? The gooseneck is firmly held in place with a down haul line and a boom stop. The only thing I do with the vang now is release it to get out of the way to put the cabin top up and then take the slack out when I put the top down.

I want to get it off if it's not needed or I want to use it if it's going to give me better performance.
Mike
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  #2  
Old 07-27-2009
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that depends on a few factors the boom vang would be really nice when the winds get nasty, which means the pop top would be down. if you only sail in nicer weather and dont race you probably dont need it.
my 27 foot boat does not have a vang, or even a travler the main sheet attaches to both sides of the companion way.
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  #3  
Old 07-27-2009
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What do you use to hold the outboard end of your boom down on a broad reach or run?
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Old 07-27-2009
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You probably should keep the Vang

Quote:
Originally Posted by MtHopeBay View Post
Is the boom vang redundant if I have a boom sheet traveler that attaches to the boom just forward of the vang? The gooseneck is firmly held in place with a down haul line and a boom stop. The only thing I do with the vang now is release it to get out of the way to put the cabin top up and then take the slack out when I put the top down.

I want to get it off if it's not needed or I want to use it if it's going to give me better performance.
Mike
Mike,
the vang and the traveler system control two different aspects of the sail trim. The traveler controls the horizontal angle of the boom relative to the centerline of the boat while the vang controls the vertical angle of the boom relative to the mast.
When running, you'll probably need to let your boom go almost 90 degrees to the centerline which will give you little control over the vertical angle no matter how you set the blocks on the traveler. To keep the free end of the boom down you'll need the vang whether in light air or heavy. In light air the vang will also lessen the bouncing of your boom which spills what wind you have and slows your boat.
I'd keep the vang

Last edited by bloodhunter; 07-27-2009 at 07:33 AM.
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Old 07-27-2009
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Just to clarify Bloodhunter's comment..the traveler adjusts both the vertical and horizontal position of the boom through a comparatively narrow angle, (typically around 35 to 45 degrees either side of the centerline of the boat. After that the traveler is at its stops and so the forces of the mainsheet become increasingly horizontal allowing the boom to rise. A boom vang controls twist at these wider angles.

The following is a discussion from an earlier thread that includes a description of the proper use of the traveler and boom vang....

Amongst non- racing sailors, frequently there seems to be a misunderstanding of the term de-powering (reducing the power of the sails) resulting in the term being mistaken for shortening sail (reducing sail area by reefing or partially furling sails). De-powering a sail generally is easier and quicker than reefing, but still results in less weather helm and heeling while moving faster than a reefed sail would permit.

In a general sense, there are a lot of factors in powering up or down a sail but the two biggies are the depth of its camber and the angle of attack. The deeper the camber (curvature of the sail) the more drive the sail develops, but along with drive (which is the forward component of the force generated) with increased camber comes a higher side force as well. This side force causes heeling and leeway. In really light air, the airflow lacks sufficient energy to flow around a sail with too deep a camber so the sail may actually be slightly flattened. As the wind picks up, you can introduce deeper camber which is how you 'power up' a sail. Powering up involves and easing of halyards, outhauls, and backstays. >>
> >
As the wind builds, so does drive but at some point hydrodynamic drag becomes the limit on speed, and at this point additional drive is not necessary. As this point is approached, heeling and weather helm become excessive. As the boat approaches this point, the sails need to be de-powered. To begin to de-power the sails, halyards, outhauls, and backstays are tightened. This pulls fabric out of the body of the sail, flattening the sail. The sail produces less forward drive, but it also produces less side force. >>
> >
The second aspect of this discussion is angle of attack (the angle between the direction that the wind hits the sail and the sail itself). For any given wind and sail shape, at any point on the sail, there is an ideal angle of attack. If the angle of attack is too flat, the sail luffs, and if the angle of attack is slightly too steep, the sail generates less lift and more drag and greater side forces causing more heeling and leeway. In the extreme case of too steep an angle of attach, the airflow stalls and very little drive is generated, and side forces go up dramatically.>>
> >
Because of gradient wind effect, (air moving slower near the water than higher in the air due to the friction between the water surface and the air above) in light air, the apparent wind angle felt by the sail will be different at the head of the sail than at the foot. The apparent wind at the foot of the sail will appear to be more forward than the air at the masthead. To allow the sail to have a proper angle of attack twist is introduced into the sail so that the upper part of the sail has a different angle of attack than the bottom of the sail. Here is where the traveler, backstay, and the boom vang come into play.>>
> >
By bringing the traveler to windward, the pull of the mainsheet becomes more horizontal than vertical. In doing so, the boom is held inward toward the centerline, but the boom is allowed to lift a little, and that lifting eases the tension on the leech of the sail allowing more twist to develop. >>
> >
As the wind builds, gradient effect generally becomes insignificant, so the whole leading edge of the sail wants the same angle of attack and in general, that angle of attack needs to be much flatter than it would be in moderate winds. To unify the angle of attack, the traveler is lowered to leeward and the mainsheet tightened, which increases the downward force on the leech of the sail. This increased leech tension removes the twist from the sail. As the wind builds the angle of attack can further be lessened by lowering traveler further to leeward. As you bear off on a reach, the traveler can be further lowered to maintain the proper angle of attack without powering up the sail, but at some point the sail needs to be eased broader off than the length of the traveler can permit while still generating the proper downward force, at that point the Vang takes over the main role in controlling twist and the sheet then simply controls the overall angle of attack of the sail.>>
> >
Simply easing the mainsheet in a strong breeze does allow the head of the sail to twist off and reduce heel, but it comes at a price. In easing the sheet the boom rises and allows more fabric into the body of the sail increasing power just when you need to reduce power, and also in order to obtain enough drive, the lower portion of the sail is over trimmed developing a lot more weather helm than would occur with proper sail bladed out sail trim. >>
> >
The backstay tension (especially on a fractional rig) can be used to de-power the rig further. On any rig, even one with a stiff mast, tensioning the backstay removes sag from the forestay and is doing so, draws fabric out of the sail in a horizontal direction, flattening the jib and de-powering it. As the forestay is tightened the mast moves aft and that also changes the relationship between the jibsheet lead and the head of the sail, allowing the leech of the jib to open slightly, reducing the angle of attack of the upper portion of the sail. On a boat with a bendy rig, and more dramatically and controllably on a fractionally rigged boat, as backstay tension increases the mast bows forward, in doing so it also draws fabric out of the sail de-powering the sail in the same manner that tightening the forestay flattens and de-powers the jib. Also similar to the jib, the masthead moves aft as the backstay is tightened and that opens the leech slightly at the head of the sail, easing the angle of attack and further reducing heeling, weather helm and leeway. >>
> >
There is a tendency to dismiss this as 'racer stuff' but these kinds of subtle sail trim adjustments can make for a much more comfortable and controllable passage as well as adding significantly to the speed of the boat. >>
> >
Lastly, really disagree with the idea that "if your sails are basically trimmed correctly, and you are making the kind of fine adjustments that a skilled racer would use, those fine adjustments can't be measured by your knotmeter". Small adjustments to backstay or traveler positions can tremendously reduce weather helm and heel angles. On my prior 28 footer, these fine tuning items were good for a half-knot or more, and on bigger boats or in higher winds, these kinds of minor adjustments can yield enormous gains in speed and comfort.>>

Jeff
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  #6  
Old 07-27-2009
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Why is your vang aft of your mainsheet ? Before you do anything you might want to go to the class association website for your particular boat and look at the rigging diagram there...
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Old 07-27-2009
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I wish

Quote:
Originally Posted by Sailormann View Post
Why is your vang aft of your mainsheet ? Before you do anything you might want to go to the class association website for your particular boat and look at the rigging diagram there...
I wish there was an association and rigging diagram.

I misspoke: boom vang is forward of the mainsheet.

I'll read more about it when I'm not at work, but I get the gist. I do race informally and want to get better performance than I am currently. It's my first season sailing so I'm still figuring out sail shape basics but getting better. I now have things under control enough that I can actually look over the sails and rig while sailing and see what they're doing.
Mike
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Old 07-27-2009
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Quote:
Originally Posted by MtHopeBay View Post
I wish there was an association and rigging diagram.

I misspoke: boom vang is forward of the mainsheet.
I was gonna say: That's some odd rigging that boat has

I do race informally and want to get better performance than I am currently. It's my first season sailing so I'm still figuring out sail shape basics but getting better.[/QUOTE]Recommend Ivar Dedekam's Sail and Rig Tuning. Easily one of the best, and least-expensive, sailing-related purchases I've made to date

And yes: You'll be wanting that vang. It has a wide range of uses. Basically: Just about any time the boom's wanting to bounce, the vang is handy

Jim

Last edited by SEMIJim; 07-27-2009 at 12:25 PM.
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Old 07-27-2009
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Look up. If you are reaching or running and a portion of the sail is beyond perpendicular to your course you are spilling air and need a vang.

Keep it simple.
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