Boom Vang

[Don Guillette]

Tadd5181: Sorry about the delay in answering your question. I don't like to jump in on these threads and prefer to let them rum to see how others are thinking.ED (Alameda) is correct in that it bugs me when I go on boats and realize the skipper is not using all the controls that GOD put on the boat for the mainsail and jib. The first control I look at whe I step on board is the jib fairlead and many times they look like they are frozen in place. It is obvious the skipper never used it. Another one, especially on a C30, is the outhaul. Generally that is frozen in place also which means it is like the broken clock and right only for one point of sail and wind speed and wrong for all others. Sometimes, within 5 minutes of looking around, I know where the skipper is from a sail trim standpoint and it gives me a good starting pointAnyway, here is the Readers Digest version of the boom vang. First, ALL THE CONTROLS FOR THE MAIN AND JIB ONLY effect 4 things and they are DRAFT DEPTH, DRAFT POSITION, TWIST and ANGLE OF ATTACK. Some of the controls effect 2 or 3 of those elements and one, the traveler, only effect 1 and that is the angle of attack. The boom vang effect 2 elements.The boom vang effects primarily TWIST. Secondarily, it effect DRAFT POSITION and thirdly it is used to prevent the boom from rising when the boom it outboard of the rail. The problem there is that the further the boom goes out over the rail the less mechanical advantage the mainsheet has due to the pulling angle and without the boom vang to pull down the boom it would tend to rise up.That is one of the reasons I prefer the rigid vang.So, say your sailing along in 10 to 12 knots of wind and you want to power up the mainsail. Crank on the boom vang. What you have just done is reduce TWIST in the top 1/3 of the sail. You are harnessing all the power the sail can give you. Say your over powered and you want to depower the main and bring the boat back on its feet. You would release the boom vang. The effect is the top of the main sail open up (twists off) and spills air.The problem with all this is that the controls for the main and jib are like the carbs in the V8 engine - you can't just mess with one and expect to get 100% performance.The last thing I will leave you with is that unless a mate COMPLETELY understands DRAFT DEPTH, DRAFT POSITION, TWIST and ANGLE OF ATTACK sail trim will never make any sense. Additionally, if a mate does not know which controls on the main and jib are used to adjust those 4 elements of sail trim they will never progress past the beginner lever. On the other hand, if they master those concepts they are in the high intermediate level.Tadd5181 - any questions - if so just fire away.

 

[T37 Phil]

Which vang?

I'd be interested in comments on how people use a rigid vs soft vs combo vang differently in the context of sail trim.

 

[John24107]

Good Old Boat

Interesting article about vangs in Good Old Boat March/April edition. Page 44.

 

[Don Guillette]

Good Old Boat

John: What did the article say?

 

[Stu Jackson]

Difference between rigid and soft vang in context

of sail trim? Other than the lack of a topping lift, there is no difference. You want the sail flat and the boom down, you pull in the vang. Since they are both attached at essentially the same points, the only difference is the material of the equipment that's performing the function.

 

[T37 Phil]

Vang line stretch

Stu - Let me put it this way. A PO had put a Boomkicker rigid vang on my C27. This held the boom up slightly above horizontal. The 4:1 soft vang would not bring it down. If I pulled down on the end of the boom, the kicker would flex and the boom would drop, but the vang wouldn't hold it there (but the mid-boom mainsheet would if the boom was centered). In thinking about this post it occured to me that the control line was Sta-set and that little bit of stretch was enough to make it useless for sail trim. So for the boomkicker style rigid vang anyway, the upward force can create a problem. I wonder if other styles of rigid vang have their own peculiarities.

 

[jimq26]

You need a much more powerful vang with Boomkicker.

I know from experience on my past two boats that a minimum of 12:1 or even 16:1 purchase is required for the system to work right. You must also use proper lines that will not stretch.The link explains it.

 

[George B]

Vang in Very Light Air

I have a light air question. (We have a C34 with mid boom sheeting and a wide traveler beam.) In very light air (3-10kts – hey, I sail in SF Bay) and I move the traveler up to centerline the boom, will I gain power applying vang? At what point will my main be too flat? In our “normal” light air conditions (10-15kts), I control twist mainly by keeping constant mainsheet tension and moving the traveler up and down. Above 15ks the traveler is mostly down.

 

[Bilbo]

Boom kicker

Phil fromGenevaThe Boomkicker device isn't a rigid vang. It's primary function is to replace the topping lift and to provide some boom support with some added control of the sail shape. I have one on my C22 and it's working fine. The problem with your 27 may be that either the kicker was not the correct one for that boat or it was misadjusted. I would say that your vang lines will stretch to a point and then eventualy break if this was the case but I suspect that your cleat was not holding the line well. The Good Old boat Mar. / Apr. article talks about a few things.They are advocating having two vangs in a different setup. A quick skimmed summary. 1)The angle that a vang represents reduces it's effectiveness. It is attached at the base of the mast and it should be attached to a point below the mast attachment. The metal bails used for traditional vangs often are a weak point and the stress on the gooseneck where the boom attaches to the mast is high.2) They advocate having strap attachements at the mid-point of the boom (loose-footed main) and then using two 8:1 vangs where one attaches to this strap setup on the boom and the other attaches to a point on the rail area of each side. The webbing straps used on their Mason 43 are 1" wide and have a load of 3,200 lbs. This gives a few advantages. A) The vang underneath the boom is a more efficient purchase on the boom. B)It also helps to prevent accidental jibes. and C) the vang on the alternate side can be used to help bring in the boom or help to keep the boom down to reduce twist. D)This also serves as a boom preventer and they feel is more safe than a preventer. It doesn't appear that the boat is rigged with a main sheet. Just these two vangs that are acting in a triangular fashion.The author doesn't recommend rigid vangs because they can break. ANd they prefer topping lifts.The author's web site:http://www.madeonmomo.com/You can see the blocks and straps to the vang setup on the mod right of that page where the caption to the jpg reads, "British Columbia & Alaska, Summer 2006"

 

[Bob Moretti]

upwind on a C30 with midboom mainsheeting

Don,As you are well-experienced on the C30, could you say a bit about upwind sailing and the vang? Ny C30 has midboom sheeting, and it is difficult for me to imagine that the vang can do much in terms of reducing twist that isn't already accomplished by the mainsheet. Am I wrong?

 

[Don Guillette]

C30 (or any boat) Upwind

Bob: Yes, you are wrong and here is why. I'm going to go into more detail tomorrow but here is a preview. I've said this so many times since I started this forum that the following (the 4 elements of sail trim)could be my middle name.There are 4 things that ALL the sail trim controls for the main and jib are adjusting and they are draft depth, draft position, twist and angle of attack. The boom vangs primary function is twist and secondarily draft position. The mainsheets funtion is also twist but only secondarily. It's primary function is adjusting the angle of attack. Its third function is adjusting draft position. So here is what happens when you rely on the mainsheet and crank on it to take the twist out when your sailing upwind - you increase the angle of attack which powers up the boat, you also move the draft position forward which slows you down but you do take out a little twist. Next time your out sailing, crank on the mainsheet and check out the twist in your sail. Then crank on the boom vang and see what happens to the twist. You'll see it is reduced. If you had a rigid vang it would almost disappear.Also, lets say you wanted to ease the mainsheet while sailing upwind. If you were relying on only the mainsheet then the twist would go back in the sail. Had you applied the boom vang, the twist would remain the same as you eased the sail out.All of this gets worse on other points of sail when you rely only on the mainsheet to reduce twist. It is at its absolute worse when the boom goes over the side of the boat and the mainsheet angles out and all mechanicanical advantage is lost.