Do you need a Vang?

[mtompson]

I have been watching a few of the Skip Novak's videos on YouTube ( very good! ) and notice the boats, Pelagic & Pelagic Australis don't have vangs fitted. ( at least I can't see any ).
The boom preventer will help, and a big heavy boom, and his sails are cut fairly flat.
But I just wondered if any of you have thoughts on this?
thanks

[Hydra]

The boat on picture is sailing close hauled. Then, a vang isn't needed: the mainsheet pulls the boom down. A vang is useful when reaching: in this situation, the sheet pulls obliquely. Without a vang, the boom could rise, twisting the sail too much.

Alain

[roverhi]

Before the days of the boom to mast rod vangs, sailors used tackle from the boom to the deck to keep the boom from kiting when the sheets were eased. It looks that is what the boat in question uses.

You cannot sail off the wind without a vang on the main unless you are happy with a crappy trimmed mainsail. Once the sheets are eased beyond the range of the traveler, the boom is going to kite intoducing significant bag in the leech of the sail. That twist reduces effective sail area, increases healing moment, and reduces the forward driving force of the sail. It DDW and broad reaching conditions it could ruin the sail through chafe on the stays and spreaders.

Boom on current boat is low and long which makes the angle from the base of the mast to a possible rigid boom attachment point very shallow. Did not want to risk a gooseneck failure with the very high compression loads the shallow angle would necessitate. Went with on four part tackle from the deck to the boom on each side to act as a vang and preventer. It's worked fine but could result in a bent boom if the boat was to role the boom end into the water. Have used very light cam cleats to secure the bitter end of the block lines hoping that will fail releasing the line. Don't rig the vangs when there is an obvious possibility of the boat dipping the boom.

[mtompson]

Thanks guys. This shot shows the boat going downwind ( with a very famous landmark in the background! ) still no vang, she is reefed heavily, and not much twist so with the long heavy boom and the preventer, maybe a vang is not needed?

[Ex-Calif]

What those other guys said...


In the downwind photo they are using a downhaul on the leward side that goes to a turning block on the rail.


I suppose it is doing double duty as a boom preventer.

[Suijin]

Keep in mind there are different kind of vans. There are hard vans and then there are running rigging vangs and there are sheeting arrangements that can give you much of the same function as a vang.

Hard vangs have the unfortunate possibility of blowing up on you in squalls or other circumstances where a hard accidental gybe can happen. I've seen some pretty serious hardware broken in those circumstances.

Valiant originally sold their boats with a hydraulic vang, but when they updated the rig in the 42 they put on a preventer rig that acts as vang when off the wind, based on a few blown up hard vangs.

They both have their strengths and weaknesses. I have a hard vang and I like it, but you have to be careful with it. On a bigger boat a hydraulic vang can really help you going to weather, getting the right sail shape, so it's not just for off the wind.

[savoir]

No boat needs a vang but there is a proviso. Without a vang the boat absolutely must have a downhaul that can be connected to the toe rail on either side. Such a downhaul is easy to see in the photos above.

[roverhi]

Originally Posted by savoir

No boat needs a vang but there is a proviso. Without a vang the boat absolutely must have a downhaul that can be connected to the toe rail on either side. Such a downhaul is easy to see in the photos above.

So what is a downhaul if it's not a vang???? To me they have a vang to the rail that probably goes to a winch to tension it.

[Adelie]

Originally Posted by mtompson

Thanks guys. This shot shows the boat going downwind ( with a very famous landmark in the background! ) still no vang, she is reefed heavily, and not much twist so with the long heavy boom and the preventer, maybe a vang is not needed?

The strap around the boom about where a vang would attach is one form of preventer that also serves the same function as vang when sailing off the wind. When I raced a Cal40 in Seattle that was the system we used.


Adelie

[savoir]

Originally Posted by roverhi

So what is a downhaul if it's not a vang???? To me they have a vang to the rail that probably goes to a winch to tension it.

A vang is permanently attached to the mast just above the collar.


I agree that the rope in the pics goes to a winch.

[xeon_tsd]

On my boat the rigid vang holds the boom at rest and keeps the topping lift from singing in the wind. That alone is worth it, add in the sail shaping help, it's a no brainer.

[savoir]

That is the best feature of a rigid vang. You can reef without worrying about the boom hitting the deck. It also takes the load off the leech in light air.

[Adelie]

See the attached sketch showing the distinction between vang, cunningham and downhaul.

The purpose of the vang is to control leech tension and leech twist once the mainsheet is eased. It also prevents the boom from 'skying' once the main sheet is eased enough that it provide little down force to the boom. For boats with bendy booms, attached foot and no 'shelf', it can also help a little bit to flatten the sail, though this effect is rather minimal.

The cunningham and downhaul both serve to tighten the luff of the main which has the secondary effect of moving draft. Because the downhual also moves the boom (the goose neck slides) is is also tightening other parts of the sail in a vertical direction and the effect on draft is subtly different. In racing classes where the maximum height of the head and the minimum height of the tack are rigidly enforced, the gooseneck will often the be fixed in place so that error can not accidentally be made that would disqualify the boat. In that case a cunningham would be used. It is also used on some boats with loose footed mains such as the Laser.

Going back to vangs, on some boats where there boom is very low to the deck, a normal vang would make such a small angle to the boom as to have little effect. In those cases it is sometimes possible to install a radiused track on the deck with the center of the radius as the back face of the mast. An adjustable line or wire drops straight down from the boom to a traveling car on the track and in this way the leech twist can be adjusted. See attached photo of a Star where this system is used.

[mtompson]

I do like the simplicity of Palegic's set up, and where they sail you can understand the philosophy to keep things simple, and easy to fix. The fact that you could slide the strap along the boom also adds another nice tuning method.
Thanks for the comments.

[Suijin]

Originally Posted by mtompson

I do like the simplicity of Palegic's set up, and where they sail you can understand the philosophy to keep things simple, and easy to fix. The fact that you could slide the strap along the boom also adds another nice tuning method.
Thanks for the comments.

That is the arrangement that a lot of offshore boats use. It's a preventer, but serves the function of a vang when the main is eased out.

There is one risk associated with that design, which is of breaking your boom if you bury it in a wave. The use of a strap vs. a fixed attachment diminishes it but does not eliminate it. As with all things there are pros and cons to every approach.