Vang Sheeting

[FecklessDolphin]

It is my understanding that the usefulness of vang sheeting is for when you do not have an effective traveler and need to release the main in a gust. If you just release the mainsheet with a loose vang, you will not only allow the boom to go to leeward, but also will allow the boom to rise, powering up the main by opening up the leech, countering your primary goal of managing the gust. So to prevent that, you keep the vang super tight when you release the main and the boom moves to leeward but does not rise and you maintain tension in the leech. You just have to remember to ease the vang when turning downwind so you so not snap the boom. I would think this would have a role on a cruising boat in high winds going to windward.

[Jman]

Vang sheeting can be effective in higher wind speed even when fairly close hauled. You can keep the leach powered up, but bubble, or effectively loose a lot of the healing power caused by the main, but maintain some pointing ability. This also presumes that the main at this point is outboard of the traveller, if still inboard you can do the same thing with sheet and traveller. This is racing, main either can't be reefer, or the next mark is so close that reefing would cost more time than luffing all but the leach of main.

Cruising, just put the reef (or reefs) in. Almost every cruising boat I have seen (and a great many racing boats), unless hydraulic, have no where near the purchase power to effectively control the loads generated on the vang in any way that resembles trimming.

Once off the wind too much vang can cause the catastrophic events noted if the boom hits the water while rolling or broaching. Large powerful racing boats actually have a foot pedal at the helm(s) to blow to hydraulic vang as the helmsman sees that a roll or broach may cause such an event. This can also be used to prevent the broach if done early enough.

In lower wind speeds, once boom is outboard of the traveller, trim the vang to keep top batten parallel to the boom. The loads are still huge, glancing at a bunch of cruising boats around us, in the 35-42' range the sheets are multi-purchase and then run to winch. Or cascading purchase systems, yet the vangs are just 4:1 setups. Unless set before easing the main, or luffing the main, there is no way any one will be able to "trim" these under load.


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[Jman]

Originally Posted by FecklessDolphin

It is my understanding that the usefulness of vang sheeting is for when you do not have an effective traveler and need to release the main in a gust. If you just release the mainsheet with a loose vang, you will not only allow the boom to go to leeward, but also will allow the boom to rise, powering up the main by opening up the leech, countering your primary goal of managing the gust. So to prevent that, you keep the vang super tight when you release the main and the boom moves to leeward but does not rise and you maintain tension in the leech. You just have to remember to ease the vang when turning downwind so you so not snap the boom. I would think this would have a role on a cruising boat in high winds going to windward.

Allowing the boom to rise will depower it. Keeping the leach tight keeps it powered up. The leach opens so much with no vang that the main just spills air.


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[svTOTEM]

Originally Posted by FecklessDolphin

If you just release the mainsheet with a loose vang, you will not only allow the boom to go to leeward, but also will allow the boom to rise, powering up the main by opening up the leech, countering your primary goal of managing the gust.

This is wrong. The boom rising allows the upper section of main to twist and spill wind - depowering the main and reducing load thus "managing the gust". Keeping the vang on has the opposite affect, requiring the mainsheet to be eases much more until the mainsail flogs to depower.

[svTOTEM]

Jman - I agree that many cruising boats don't have vang control with 4:1. I have 16:1 (4:1 with 2 cascading 2:1) - easy to setup and offers great control.

When wind is on, racing boats have a person constantly trimming the vang. That person watches gusts and the helm for slight signs of rounding up to dump the vang - then when trim back in when steering is stable.

[MarkSF]

I have no traveller so the vang is the primary control over sail twist. Normally I just set it so the boom is level. This means that as I go from close hauled to beam reach, the vang is doing increasing work vertically, keeping the boom level. Apparently, on a J105 this would have snapped the boom. Thankfully, my Bristol is no J105.

The vang has lots of purchase (Garhauer solid one) so fine adjustments to sail twist can be made easily.

If the weather helm on a beam reach gets out of hand I release the vang, allowing the top of the leech to spill air.

[FecklessDolphin]

Originally Posted by svTOTEM

This is wrong. The boom rising allows the upper section of main to twist and spill wind - depowering the main and reducing load thus "managing the gust". Keeping the vang on has the opposite affect, requiring the mainsheet to be eases much more until the mainsail flogs to depower.

"If you don’t vang sheet, one problem you have is that when you ease your mainsheet in a puff, you allow the leech to twist and you make the mainsail fuller (because less leech tension means less mast bend). This is not good in a puff" quoted from "Play your vang around the course" By Dave Dellenbaugh

[OldFrog75]

Originally Posted by FecklessDolphin

"If you don’t vang sheet, one problem you have is that when you ease your mainsheet in a puff, you allow the leech to twist and you make the mainsail fuller (because less leech tension means less mast bend). This is not good in a puff" quoted from "Play your vang around the course" By Dave Dellenbaugh

Dellenbaugh is introducing another variable into the equation - mast bend. I would say most sailors/racers adjust mast bend by easing or tightening the backstay not the vang or mainsheet. It's true that if you ease the backstay and straighten the mast the draft will move forward and the depth of the sail increases which should power up the sail but I can't see where easing the mainsheet would have that pronounced an effect on mast bend unless the backstay was very loose and the mainsheet was on really hard prior to easing, such that you were using the mainsheet rather than the backstay to control mast bend.

[cwyckham]

Originally Posted by savoir

You guys are jumping between two topics - vang sheeting and vang easing.

The two are not the same thing. The boom on the J105 snapped because the vang was not eased when the boat bore away and that has nothing to do with vang sheeting.

The vang on every boat should be eased when bearing away whether vang sheeting or not.

Why should the vang be eased when bearing away?

The vang is usully only used when the boom is outside the traveler. Let's say that I'm beam reaching and have the vang on so that the top batten is parallel to the boom. Now I bear off to a deep broad reach. The apparent wind drops off and the sail is now in a drag rather than lift configuration (sail is stalled).

I don't believe the forces have increased much. I want the vang on to keep the top of the sail off the shrouds. Why would I want to ease the vang?

In my case, I do use vang sheeting a bit. It's just easier since I don't have much purchase on my mainsheets for heavier winds. I can basically set the vang at "a bit over twisted" and then just center the boom with my twin mainsheets (in an inverted "v" configuration).

If I need to move the boom around, then I can ease the windward sheet and the sail maintains its shape. This is equivalent to dropping the traveler.

I have a smallish main and a largish boom. I have mid-boom sheeting and the sheets are only a couple of feet forward of the traveler. I would guess I there's 30-50% more force on the vang than the sheets, but the convenience factor is pretty high for a twin sheet configured boat.

[OldFrog75]

Originally Posted by cwyckham

Why should the vang be eased when bearing away?

There's a video earlier in the thread that sort of addresses that question.

[Blue Stocking]

With a loose-footed main, all the load is on the clew fitting. Tremendous bending load on the boom. In the film you can see the boom starting to flex before folding.

[svTOTEM]

FecklessDolphin - The context of Dave Dellenbaugh's article is small boat racing, and has nothing to do with cruising boats. Most cruising boats have 1-1/2" to 3" of prebend, no backstay adjuster, and a stiff mast section so that vang tension has no affect on the mast; and so is irrelevant to how a vang works on cruising boats.

Blue Stocking - Loose foot or not the clew takes all of the load. An attached main foot do not change how a boom bends under load - except with dinghies.

[Nicholson58]

Originally Posted by svTOTEM

This is wrong. The boom rising allows the upper section of main to twist and spill wind - depowering the main and reducing load thus "managing the gust". Keeping the vang on has the opposite affect, requiring the mainsheet to be eases much more until the mainsail flogs to depower.

Absolutely correct. Twisting off the top of the main not only dumps wind but dumps the wind where it will do the most good - high up, lowering the center of effort as well as de-powering. This is the only way I can operate my Tornado Cat in moderate to high wind since there is no reefing.

On our Camper 58, in-mast roller furling means no battens & negative roach. It is almost a moot point for us & I rarely touch the vang. Our vang is a manual tackle operated from the mast. Everything else is in the cockpit so one other reason to ignore it. I occasionally use it as a preventer but never in big wind. My main sheeting is spread along the boom and from port to starboard at the deck in a way that prevents a hard snap on a jibe. The traveler is on a winch in the cockpit. Our boom is 10" tall X 6" wide. It can only be lifted by two people or a winch. Seldom need vang. I don't think much about breaking it although, the vang attachment is in the perfect place to concentrate stresses.

On the Heritage I raced (a lifetime ago) we only used the hydraulic vang to fine tune the sail shape. Trimmers moved the main sheet & traveler on gusts. This was faster and more accurate than pumping & releasing. I imagine that on the insanely light race boats today this may not be the case.

[cwyckham]

Originally Posted by OldFrog75

There's a video earlier in the thread that sort of addresses that question.

A boom broke in a video. That honestly doesn't address any of my questions. If a vang can't take stresses from being used off the wind, then why do boats have vangs? They aren't needed on the wind.

[svTOTEM]

cwychham - Booms should be engineered to take vang loads without problem: some will flex and others not. Excessive flex can mean poor engineering or that a vang was added later and the boom wasn't designed for it.

There are 2 concerns using a vang: 1) not easing in higher winds can lead to excessive heel, knockdown, and losing steerage (because main sail forces overpower the rudder, especially when well heeled and the upper rudder may be out of the water). 2) boom hitting the water, usually when broaching will often enough lead to a broken boom.

If the vang is on tight and your heeling 20 degree or more, it's time to ease it a bit unless there is a skilled vang trimmer. I rarely let the vang off altogether because excessive twist plasters the upper main against the rigging, causing chafe. At that heel it's probably time to reef and then trim with moderate vang -fast, less heel, less load, less chafe.