Is a Vang Really Useful on a mid to Large Boat? - Page 2 - SailNet Community
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post #11 of 64 Old 01-30-2014
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Re: Is a Vang Really Useful on a mid to Large Boat?

I have a solid vang on my 42 footer, and I really think that all it does that is useful is to hold up the boom (even thought I have a topping lift, too).

Maybe a racer would get another .001 knots by using it somehow, but I think it's dead weight on my boat.

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Re: Is a Vang Really Useful on a mid to Large Boat?

Thanks for the assessment, Rich. Some clarifications:

Quote:
1. the vang's connection to mast is higher than the absolute base of the mast
The attachment point is just above the mast collar. In the photo, the vang is loose and you can see the lower set of blocks just above the bowline in the jib sheet. It's as low as it can go.

Quote:
2. From the pic, and I may be wrong, but I see a 5:1 vang being used
I was wrong when I wrote 4:1, that was the original configuration. In the photo, it's 6:1.The 2nd set of blocks are obscured in the photo.

Quote:
the 'tail' of the vang seems to be running along parallel to the mast; and if so, the 'tail' is generating NO 'down' force
That's true and could be reconfigured to go to the mast collar turning blocks. The manufacturer ran the lines that way for neatness, I suspect. Good idea.

Quote:
A vang that makes a 45 angle with its boom will generate 40% more 'downforce' than a vang that makes a 30 angle intercept.
Agreed. The angles are horrendous. But if I move the boom attachment point forward to get 45 degrees, then the moment arm on the boom will be reduced. So I think that I will solve one problem and create another.

Your last paragraph is the most helpful. I'll look at when and how I apply vang. Thanks.

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Quote:
I really think that all it does that is useful is to hold up the boom
True. The spring in the rigid vang is fighting the 4:1 or 6:1 block arrangement, reducing the down power. Rigid vangs are poor "vangs", IMO. They're mostly boom holder-uppers.

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post #13 of 64 Old 01-30-2014
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Re: Is a Vang Really Useful on a mid to Large Boat?

The vang isn't that useful close hauled. Your mainsheet has more downward force on the boom.

It should be useful when you are on a beam reach or deeper. In those conditions you would have traveled down to the limits of your traveler and the mainsheet can no longer be used to control downward force on the boom.

My first boat didn't have an effective traveler, so I used the vang all of the time. My current boat has a traveler that has a lot of travel and I don't get to sail on a beam reach that often (Puget Sound is long and skinny), so I there are many days of sailing where I don't touch the vang. However I'm still glad that it is there for those days when I need it.

My vang leads back to a clutch and cockpit winch. I don't use the winch with the vang very often, but it is there should I need it. The same winch is shared with the main halyard (it's primary use), outhaul, and first reef line.

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post #14 of 64 Old 01-30-2014
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Re: Is a Vang Really Useful on a mid to Large Boat?

Quote:
Originally Posted by Sabreman View Post
True. The spring in the rigid vang is fighting the 4:1 or 6:1 block arrangement, reducing the down power. Rigid vangs are poor "vangs", IMO. They're mostly boom holder-uppers.
Well, I've gotta disagree with that one...:-) I rate an effective vang as being pretty essential, and although rigid vangs can be pricey, I consider mine to be worth every penny...

The preventer arrangement you describe is a poor substitute for a vang in anything more than light to moderate conditions, in my view... I'm not a fan of mid-boom preventers taken vertically to a sail track or the rail, especially when the breeze comes up... An effective preventer needs to be led from the end of the boom to a point well forward of the mast, in my opinion, and when it's led back to the cockpit, it's an arrangement easily adjusted on any point of sail off the wind...


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post #15 of 64 Old 01-30-2014
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Re: Is a Vang Really Useful on a mid to Large Boat?

those are the preventers I was talking about at least...jajaja anything mid boom for example is an easy way to break stuff

I like snubbers on preventers too...you know just in case! jajaja

again vangs are boat dependant definitely NOT mandatory on all boats

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post #16 of 64 Old 01-30-2014
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Re: Is a Vang Really Useful on a mid to Large Boat?

I wouldn't consider sailing without a vang.
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post #17 of 64 Old 01-30-2014
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Re: Is a Vang Really Useful on a mid to Large Boat?

I am reading this thread and shaking my head at some of these responses. I would have expected some of these responses back in the 1960's but not today. Like my estemed colleagues Ron, (Faster), Bob Perry and Jon Eisberg noted, to me a boom vang is a very critical piece of safety equipment that prevents the boom from rising up and taking out the backstay and rig in an accidental jibe. Those kinds of boom hitting backstay and taking down the rig or breaking a boom incidents were a pretty frequent occurances back in the day when boom vangs were not all that common.

A traveler is no substitute for a vang except perhaps when close reaching. A traveler only impacts the leech tension when the boom is perhaps 45 degrees of less off the centerline (especially with a coach roof mounted traveler). Beyond that the sail is free to develop too much twist. At that point you have a collection of over trimming or under trimming which implies a mix of bad trade offs; too much abrasion as the sail saws up and down on the rigging, too much twist making you more prone to jibing, broaching and rolling and too much weather helm. And a traveller does not come into play in the accidental jibe senario descibed above.

While you can rig a tackle to the rail that will act pull down on the boom and control twist, doing so is considered a very dangerous practice in heavy air, when you are more likely to dip a boom end from rolling or a knockdown and break something dramatically. Itwas extremely strongly discouraged at the safety at sea seminars that I have attended.

The preferred method of rigging a preventer is to take it forward to a turning block and then back to a quick release in the cockpit. The line should be stretchy enough to absorb an impact should the boom hit the water, but no so stretchy that it will allow the boom to reach within 30-40 degrees of the centerline of the boat.

Frankly, as I read Sabreman's description, it sounds like the problem is the geometry of the vang, and not that there is a vang in itself. Rich H is right that a vang should ideally be rigged at a 45 degree angle. Sabreman's vang appears to be at an angle approaching 30 degrees. Moving the attachment point forward on the boom to a 45 degree angle would increase the downforce by something like 20-25% while the lost leverage on your boom would decrease the mechanical advantage at the leech by 12-15%, overall a net gain. But the biggest advantage to changing the geometry is the massive reduction of load parallel to the boom on your gooseneck.

The good news is that an experiemental fix is cheap and easy. You should be able to rig a strop that wraps around your boom using either webbing or line at the right position and try it for a while. You will probably need to run a tight retainer line from the strop back to the original boom vang mounting position to prevent the strop from sliding up the boom under load.

I would also note, that my boom vang with 400 square feet of sail on an 18 foot boom, is 12:1 and is led back to a winch. I originally had second cascade which resulted in a 24:1 but still found myself using a winch in heavy air.

Jeff
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Last edited by Jeff_H; 01-30-2014 at 10:48 AM.
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post #18 of 64 Old 01-30-2014
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Re: Is a Vang Really Useful on a mid to Large Boat?

Quote:
Originally Posted by Alex W View Post
The vang isn't that useful close hauled. Your mainsheet has more downward force on the boom..
The prime function of the vang is to control 'twist' in the main. Unless you have a radial traveller that goes from rail to rail and you dont touch the mainsheet pressure ... when the boom is moving across the traveller, the amount of twist in the main will be changing. Twist sets the angle of attack for all levels (up from the deck) of the sail; If the twist becomes variable and changeable, the efficiency of the sail becomes less, usually much less ... even in some cases to become subject to sudden 'power-ups' when in very gusty conditions. Also too a sail with a inadequate vang system will require constant 'trimming' as the wind pressure varies; and, its very rare to have constant wind pressure.

A sail that is 'twisted' to match the gradient wind is easy to 'blade out' (the entire luff 'breaks' instantaneously) when overpowered; a sail that doesnt have reasonably good matching twist can either 'power-up' or will be 'unattached' at the head and overtrimmed at the foot with only the mid panels 'working'. If you attempt to luff-up with a grossly mal-twisted sail, something aloft is 'going' to 'power-up' when you do.
The easiest way to keep 'constant twist' is via a 'good' vang system ... and especially when the boom is no longer directly above the traveller (thats why 'vang sheeting' works so well). Even when the boom is more or less directly above the traveller, sail pressure will cause the mainsheet to not be perfectly 'vertical' ... and the vang is indeed helpful to keep the 'tack angle' of the sail (or boom to mast angle) more or less constant, and without much change in mainsheet tension (that tack angle being held constant also results in constant fore/aft position of maximum draft in the sail).

A sail whose twist is 'variable' with wind pressure will be changing its 'aerodynamics' up and down along the vertical (luff). in the high speed planing hulled sport boats with inadequate vangs ... we call those folks: 'swimmers'.
In long distance sailing I feel its always better to be 'on' with trim and shape as a 22 hour day is usually more satisfying than a 24 hour day, especially when 'getting out of the way of stink'.

Simply put, no vang = increased vulnerability to a 'goose wing' gybe. A 'goose wing' gybe can easily change a mainsail into a spinnaker when all the slugs on the luff break free from the mast.

;-)
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Last edited by RichH; 01-30-2014 at 11:10 AM.
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post #19 of 64 Old 01-30-2014
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Re: Is a Vang Really Useful on a mid to Large Boat?

Quote:
Originally Posted by RichH View Post
The prime function of the vang is to control 'twist' in the main. Unless you have a radial traveller that goes from rail to rail and you dont touch the mainsheet pressure ... when the boom is moving across the traveller, the amount of twist in the main will be changing.
You quoted me saying "The vang isn't that useful close hauled. Your mainsheet has more downward force on the boom."

Nothing that you've written disagrees with that. When close hauled the mainsheet on his boat has greater purchase and better leverage on the leech of the sail then the vang does on his boat. I'm not surprised that he can't control twist better with the main than the vang. Once the main sheet has the boom where he wants it he can tighten the vang to hold it there.

The traveler position hasn't made a gross change in sail twist as you travel across the range on the boats that I've sailed on. On my Pearson 28-2 it closes twist slightly at the extreme ends of the range, but typically by the time I'm there I've also switched to using the vang to control leech twist. I have little experience on boats over 30' and perhaps the geometry there does make a bigger difference.

I am pro-vang and added the missing one back to my boat. I just don't think it is likely to be that effective compared to the main sheet for controlling leech twist when close hauled, as shown in the photo at the start of this thread.

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Last edited by Alex W; 01-30-2014 at 11:53 AM.
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post #20 of 64 Old 01-30-2014
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Re: Is a Vang Really Useful on a mid to Large Boat?

I am with Rich, Jeff, Bob, Jon and Ron.

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