When not to use the boom vang?

[jimshipsky]

I recently installed a boom vang on my Cal 21. I understand its importance sailing on a run, to keep the boom from lifting. Also on a reach, to prevent the upper part of the sail from twisting out and spilling wind. So I'm left wondering: when and why would I not want the vang tensioned?

 

[Don Guillette]

You almost answered your question -- the boom vang is the primary mainsail trim control used to adjust twist. The secondary control, if you don't have a boom vang,, is the mainsheet. The vang is important to use when you're closehauled. You use the vang to "dial in" the amount of twist for particular wind condition. A chapter could be written about twist and the use of the boom vang. You'd want to tension the vang to eliminate twist and power the mainsail from top to bottom.

 

[SG]

If you are reefing a conventional mainsail (i.e., not an in-the-boom or in-the-mast one), then before you pull down the reef on the clew, you should allow the boom to rise because it will put a lot less strain on the lines, you're back, winches, and sail. That means the vang SHOULDN'T be tensioned then. After you get the reef tied-in, then you tension the vang and tighten the sheets.

Other than that, I think, as Don point's out, it is really to shape the sail. Depending on how your sail is cut and how lumpy the water is, you would adjust the general rules a bit. In heavier air, you generally want to flatten the sail so the vang will be tighter; and conversely in lighter, you let the main sail get a bit fuller. The twist issue varies a bit depending on the wind gradients you might be sailing in. (An example, in some situations there is a difference in the velocity and direction of the wind as you move up from the water.) Also, in variable conditions, you can set the sail so that it works in more effectively as the wind speeds oscillate slightly.

You've noticed that COLD air sometime has a vertical component to the gusts. The pressure is greater with cold air than the same speed in warmer air because the "gas is denser" as temp drops. There are a lot of variables.

I wouldn't fixate on vang first, I'd worry about the overall position of the boom, then the outhaul, then the vang, then (maybe) halyard tension. Like I said, the condition of your sails, how they were originally cut, how much tweaking you really want to be doing (and how distracting those changes are to your maintaining course, etc.) are something that can drive the crew crazy.

 

[Ken Cross]

One more thing. I'm in the bad habit of not loosening the vang at the end of the day. When I host the sail the next time I can't seem to get the sail all the way up. I eventually look around, slap myself and then take care of it.

It happens more frequently when we have witnesses (I mean guests)

Ken

 

[jssailem]

Ken you may need to tie a string around your finger as a reminder to untie the vang.

 

[JRacer]

Used to be a guy on the TX J24 Circuit nicknamed "Boom Vang John". Pretty sure that was a command more than a name. ;-) His responsibility was to control the boom vang and more importantly to release/ease the boom vang when the boat was about to be overpowered off the wind and about to spin out. Releasing (or easing) the boom vang off the wind in overpowered conditions let the top twist off and depowered the main. On the J24, we "vang sheeted" the main on the wind. So, when going to weather, we'd tighten up the main sheet as required then snug up the vang. Then as we took a puff, we could ease the mainsheet or drop the traveler without the resulting twist off induced at the top of the main that would ordinarily result from easing the mainsheet with a loose vang. Fast!

 

[jssailem]

Like the name. Boom bang John.
Good description of the action and outcome.

 

[JRacer]

Yes, the distinction as to name vs command was in the emphasis assigned to the words

 

[jimshipsky]

Thanks everybody! Very helpful info.
Hadn't occurred to me I might want/need to de-power the main going downwind, in gusts, by easing the vang.
My mainsheet attaches to the end of the boom, so I'm unclear if the vang can do anything when close-hauled. I'll experiment with that next time out and learn.
I have a friend new to sailing who recently confessed he thought I was saying "boom bang", and he kinda prefers that term. When he adds one to his boat, I suspect it will be referred to as the boom bang.

 

[SG]

J/24?

I don't think I have ever seen on reefed in a race. They flatten the main, let it out, whatever. It's amazing how a few crew and a good trimmers can keep those boats going fast (and under control) in winds that boats twice their length can't handle with the same relative amount of canvas have.

That's not say that you can drink a cup of tea with a saucer in the other hand in those conditions. ;^)))

 

[Don Guillette]

.
My mainsheet attaches to the end of the boom, so I'm unclear if the vang can do anything when close-hauled. I'll experiment with that next time out and learn.

I don't think it matters where the mainsheet is attached. A lot of folks think the main function of the vang is to keep the boom from rising while sailing down wind and that's true but the vang comes into play while closehauled also. I don't know what brand of vang you installed but I'd like to speak about the Garhauer Rigid Vang, which I sold & installed when I lived in So Ca. I installed it so that the boom was 10* above horizontal while at rest. The reason for that is if the vang was installed flat horizontally you's have no where to go to induce twist. In other words, half the twist would be already eliminated. So, when you started your sailing day you had to crank down a little on the vang or your sail would be twisted off to much. To induce twist you just eased the vang. To flatten the sail, you just cranked on the vang past horizontal.

The vang should be released before lowering the main.

Jim: on your next sail, after you raise the main, look up the sail to see how much twist you've induced due to your installation. What brand of vang did you install??

Some folks on this forum may not know what twist is - once you've seen it you'll remember it. To see it at your computer, form your right hand vertically as if you were saluting. That's "zero twist". Now turn your fingers only gradually to the right -- you're inducing twist and power is spilling off of your fingers.

 

[JRacer]

J/24?

I don't think I have ever seen on reefed in a race. They flatten the main, let it out, whatever. It's amazing how a few crew and a good trimmers can keep those boats going fast (and under control) in winds that boats twice their length can't handle with the same relative amount of canvas have.

That's not say that you can drink a cup of tea with a saucer in the other hand in those conditions. ;^)))

We never even had reef points put in the main sail. No Need for them. ;-) You are correct. Our main sail depowering tools were backstay (flatten), outhaul (flatten) mainsheet (dump a puff) with the vang honked down so as not to allow the top to twist off - vang sheeting, and dropping the traveler. Doesn't get much better than "The Ultimate One-Design". Nothing like a ride downwind with a lot of breeze and the chute up but your "Boom Vang John" better have that boom vang line in his hand at all times and the good ones know when and how much to ease without being told!

 

[jimshipsky]

What brand of vang did you install??

No brand, I had a spare Ronstan block (40 mm, fiddle, becket, adjustable cleat, universal head) and a similar-size double sheave block. My Cal 21 was not built with attachments for a boom vang. I found a food service stand at Goodwill made of 5/16" stainless rod. Cut out two lengths, bent them into hoops, forged flats on the ends, drilled holes for attachments. Bought some 5/16" yacht braid at Hamilton Marine.
RE: vang when close-hauled
While I'm going to experiment with this today, it seems to me that when close-hauled the mainsheet can pull the boom directly downward more forcefully than the vang, due to its far longer lever arm--my mainsheet attaches at the end of the boom.

 

[Scott T-Bird]

You are right that the mainsheet has far greater mechanical advantage than the vang. Actually, the traditional vang IS a slightly ridiculous set-up for attempting to adjust twist. The geometry is all wrong. You have limited length between the bottom of the mast and the gooseneck, so that severely limits your ability to attach the boom end of the vang at a location on the boom that is effective. Make the angle too steep and you significantly reduce the lever arm to pull the boom down. Make the angle too shallow and you are just pulling the boom against the mast, potentially bending or damaging the mast, if you had enough force, and not really applying much force towards bringing the boom down. There really is NO optimum position for the vang because it is really nothing but a big compromise with regard to the application of force.

That is why, when you are sailing close hauled, the most advantageous way to adjust twist is with the combination of mainsheet to adjust twist and traveler to adjust angle of attack. Your vang only does something useful when sailing off the wind and the traveler car is all the way out.

 

[Stu Jackson]

Your vang only does something useful when sailing off the wind and the traveler car is all the way out.

That is not my experience. Even when close hauled, the vang does make a difference in the sail shape. That's one of the reasons it is there. I have mid-boom sheeting and a Garhauer rigid vang. I used to have a Catalina 25 with end boom sheeting and a soft vang. Also worked as described. Same with my Catalina 22.

 

[Don Guillette]

I thought it might be a soft vang, which as Scott describes, is a problem. A rigid vang is much more efficient -- that's why they were invented. The only twist you have is the amount the sailmaker built into the sail and even with your setup you can take most of that twist out with your setup but you can't induce anymore than what you have. You don't even have to be sailing to see what twist you have. Raise the main sail at the dock and lift & pull down on the boom by hand and look up the sail to check it out. As boat size (mainsail area) increases the soft vang becomes less & less efficient.

Personally, I prefer to use the rigid vang for the purpose it was designed for -- to adjust twist. You can use the mainsheet, if you don't have a functioning vang but when you use the mainsheet to adjust twist you're also messing with draft position and angle of attack and maybe for the point of sail & wind condition you don't want to be messing with those 2 items because you have them set for 100% efficiency..

Actually, your vang looks nice for a DIY build. You could get a bit more efficiency by moving it father aft on the boom..

 

[Kings Gambit]

If you read Peter Nielsen (September 2017 Sail p. 56) you find: "On boats equipped with mainsheet travellers, the vang is not used when going to windward because the mainsheet applies sufficient tension to the mainsail leech..." He goes on to say, however, that when sailing to windward in the absence of a traveller: "... it [vang] must be used to keep the leech tensioned when the mainsail is eased in gusts." It's hard to imagine how the vang on my boat (Rodkicker) could do much more to affect sail trim going to weather with the traveler raised to windward, the mainsheet properly sheeted, and the mainsail leech lines properly tensioned. Are we saying that easing the vang in that trim configuration and point of sail will ease the heeling force on a 38-ft boat?

 

[jimshipsky]

Raise the main sail at the dock and lift & pull down on the boom by hand and look up the sail to check it out. As boat size (mainsail area) increases the soft vang becomes less & less efficient.

Thanks Don.
I'll give that a try. Altho it seems to me that as I pull down on the boom the leech will be drawn taut and there will be zero twist. I keep my boat on a mooring, so as I lift up on the boom the sail will be in irons and I don't think any twist can appear. You must mean when the boat is secure at a dock I could turn the boom to close-hauled or reach (if the wind isn't very strong!) and then twist would appear.
My original Q was "when don't I need to be applying vang tension?". I've learned the answer is mostly when I want/need to de-power the sail. Now I've learned a rigid vang can de-power a sail far more than a soft vang. New territory for me!
BTW, my photo of my vang was shot at an angle, making the actual angle appear steeper than it is. I aimed for 45 degrees.

 

[Scott T-Bird]

That is not my experience. Even when close hauled, the vang does make a difference in the sail shape. That's one of the reasons it is there. I have mid-boom sheeting and a Garhauer rigid vang. I used to have a Catalina 25 with end boom sheeting and a soft vang. Also worked as described. Same with my Catalina 22.

Well, yes, maybe I am overstating my opinion. I do keep the vang snugged down when close-hauled because if you do ease the main, the vang does go to work.

Actually, my comments are more about the geometry of the vang itself. Even a rigid vang, while able to apply more control, is an inefficient use of force. All that horizontal force is applied just to get a fraction of vertical force applied to the inboard end of the boom to hold it down, where the leverage is simply awful. It's a ridiculously inefficient set-up. As Don says, you could get a bit more leverage by moving the attachment further down the boom, but way more force is directed horizontally, pushing the boom into the mast. Most of the force is simply wasted. But that's sailing, and is one of the reasons why we go so slow!

 

[Ross S]

Thanks Don.
I'll give that a try. Altho it seems to me that as I pull down on the boom the leech will be drawn taut and there will be zero twist. I keep my boat on a mooring, so as I lift up on the boom the sail will be in irons and I don't think any twist can appear. You must mean when the boat is secure at a dock I could turn the boom to close-hauled or reach (if the wind isn't very strong!) and then twist would appear.
My original Q was "when don't I need to be applying vang tension?". I've learned the answer is mostly when I want/need to de-power the sail. Now I've learned a rigid vang can de-power a sail far more than a soft vang. New territory for me!
BTW, my photo of my vang was shot at an angle, making the actual angle appear steeper than it is. I aimed for 45 degrees.

For your original question: Ease the vang to de-power as you said. I don't understand why you said a rigid vang can depower more than a soft vang. If anything the opposite is true. Also ease the vang in light winds, you'll need the twist to get that top mainsail leech tell tale to stream. Sometimes just the weight of my boom and sail take too much twist out in light winds and I'll tighten up the topping lift to put some twist back in.

When not in light wind or not overpowered? I adjust the vang to get my top mainsail batten approximately parallel to the boom. Sometimes, I find that my soft vang doesn't give me enough mechanical advantage to get as flat as I like, so I just pull down the back of the boom by hand while a crewmate tightens the vang.