Why don't catamarans have boom vangs?

[sowwaninii]

Many cats don’t have travelers, but rather two main sheets lead to blocks port and starboard. By tensioning the leeward sheet one gets somewhat of a bang effect.

[celle2000]

The width and lack of heeling allows a different set up - as per attached PDF file

[meirriba]

Usually there is not enough space on a cat between cabin roof and boom for a vang with good length and angle to be effective.
Wrong angle and/or attachment point on the boom will cause breakage.
Z-spars told me very clearly that I will lose the warranty if I would install an after market vang.
The answer of wide traveler is good only up to the point of traveler's end. After that there is still an angle where the boom is out but still sail is not on the shrouds.
We live with this most of the time, or install something like a preventer from an one of the extra eyes we have under the boom (behind the middle of the boom) to a middle deck cleat.

[contrail]

Another thing in favour of the wide traveller is that even in the small gap between where the traveller effectively controls twist by being all the way to the end of the track, and the limit to easing the boom caused by the tripod rig and its aft mounted shrouds, the mainsheet is still pretty well sheeted in, so that an unintended gybe only involves a manageable movement of the boom, rather than a slam right across the boat. Having sailed dozens of kinds of boats, I actually find the long traveller on a cat to be very easy to use.



Another safety reason that used to be cited is that, in the case of a very strong gust, and impending capsize, pretty rare for today's heavy cats, assuming some rational amount of sail up, simply letting go the main not only allows it to ease out, but up, as well, "scandalizing" the main and depowering it. A boom vang is another line to release, and the thinking went that the fewer lines to release, the better. A capsize on a 49er is an easier thing to deal with, should it happen!

[Montanan]

Physics. Huge difference in lever arm when the traveler is pulling down the end of the boom compared to the above boom vang. Dramatic difference between the push and the pull.

[JasonS]

Manta catamarans have rigid boom vangs. The first ones were solid and not easily adjustable. After that they came with US Spars or Garhauer adjustable boom vangs. They work well.

[Apollo19.5]

Good discussion to have. Have raced and cruised on both and find one with a traveller and vang the most useful for getting decent sail control. Always annoys me to have the main sheeted so close in going downwind due to too much twist and sweeped back stays/spreaders. Yes a preventer helps but still a PITA. Think the main reason for not having a vang is simplicity for owners that dont come from a sailing back ground (and also the charter market).

[catsketcher]

Gday Mark,

I don't agree with many of the comments in the thread - because I love my vanged main. As for extra weight or cost, no it can be cheaper and lighter, and far less effort to sail. Also having a vang makes the main safer, with less sheet load and much better on the mainsail in terms of chafe.

I was a super competitive dinghy sailor and most cats make me cry with the inability to properly maintain sail shape at deep angles with the main. It as if the designers said "We will help you sheet the sail well to a beam reach, but from then on deeper you are on your own" So owners have to use downhauls led to the rail or just over sheet the main when running on a square or a broad reach.

There are many good reasons not to use a typical vang and your idea of a pusher vang is a good one - it is just not big enough. You have to get the pusher all the way to the end - you gotta get a wishbone.

I went the wishbone route 22 years ago for my cat. I was a racer who had raced Lasers, Tornados, 420s, 16ft skiffs, IOR boats and more and love tweaking a boat. Tweaking a mainsheet with over a tonne of sheet load doesn't appeal. So my cat has almost no sheet load.

In the 22 years of ownership of my cat I have rebuilt the cockpit dodger into a bridgedeck cabin, moved the cockpit, changed the motor setup three times, added an aft deck, changed the steering three times - I don't mind trying things. getting them wrong and rebuilding. But the wishbone is gold.

I can throw the winch handles overboard and sail upwind in 20 knots. My wife can trim the main easily, the sail is beautifully vanged downwind (which is the majority of your cruising orientation) and you can let the sail out further than a typical sail because it is so well vanged it just doesn't move. My main is 22 years old and still works well (the wishbone never lets of flog or chafe).

There will be a lot said about wishbones by people who don't use them but I could never have a large cat without a wishbone. It satisfies the racer in me because it allows me to trim as much as I want with a flick of my wrist. The cost is way less than a boom, traveller and winches, you go faster downhill and even upwind because of better vanging and increased downwind leech tension and the sail is protected from chafe. I sheet mine from a composite pedestal which does the same job as a bridle.

You do need to use a two or three stay a side rig, to get rid of the diamonds which are not suitable for the wishbone. For me that was another benefit. Because I made my own boat, composite chainplates were easy but buying diamonds from a rigger was pricey. Altogether the wishbone probably saved me about $10- 15 000 AUD and I got a safer, faster and easier to sail boat too.

The photo attached is one I have posted before but it shows the wishbone well.

[Scott bouchie]

I put a boom vang on my cat it helps keep the wind in the sail going downwind.

[Montanan]

Originally Posted by catsketcher

Gday Mark,

. . .

There are many good reasons not to use a typical vang and your idea of a pusher vang is a good one - it is just not big enough. You have to get the pusher all the way to the end - you gotta get a wishbone.

I went the wishbone route 22 years ago for my cat. I was a racer who had raced Lasers, Tornados, 420s, 16ft skiffs, IOR boats and more and love tweaking a boat. Tweaking a mainsheet with over a tonne of sheet load doesn't appeal. So my cat has almost no sheet load.

. . . But the wishbone is gold.

I can throw the winch handles overboard and sail upwind in 20 knots. My wife can trim the main easily, the sail is beautifully vanged downwind (which is the majority of your cruising orientation) and you can let the sail out further than a typical sail because it is so well vanged it just doesn't move. My main is 22 years old and still works well (the wishbone never lets of flog or chafe).

There will be a lot said about wishbones by people who don't use them but I could never have a large cat without a wishbone. It satisfies the racer in me because it allows me to trim as much as I want with a flick of my wrist. The cost is way less than a boom, traveller and winches, you go faster downhill and even upwind because of better vanging and increased downwind leech tension and the sail is protected from chafe. I sheet mine from a composite pedestal which does the same job as a bridle.



The photo attached is one I have posted before but it shows the wishbone well.

[gezza]

I'm not sure how much value my reply may provide, but it may provoke further discussion.
A number of years ago I bought a Voyage 440 and was busy buying some new parts. I spoke to somebody senior at the factory in Cape Town and asked why there is no vang (the Voyage has a boom strut - supports the boom but does not restrain or control it). His response was that cats do not have vangs as an overtightened vang was the a potential cause for a pitchpole situation; obviously very undesirable in a cat as there is no heeling or broaching to alleviate the problem.

At the time I was brand new to cats and did not have sufficient cat understanding to take the conversation any further with him. So food for thought ???

[markiobe]

Originally Posted by capn_billl

I just had a detailed discussion with a US Spars engineer on this very topic.

A couple features on MY boat (Leopard-44), YMMV.

My Boom is around 8,000MM long, or nearly 30 ft. with a square top fully battened main sail that looks like half an acre from the helm.

I have a boom topping lift, run to a clutch, and a rigid what looks like a boomvang, but is just a fixed support to keep the boom from dropping to the deck if a tourist forgets the boom topping lift.

I was told by the enginer "under no circumstances should any obstruction or resistance be applied to the Vang".

The reason is the upward force of the mainsail is to great for the area under the goosneck to handle, and it will break.

The ONLY place that had enough leverage to counteract this force is the mainsheet at the end of the boom.

For example if the wind exerts 10,000 Newtons on the mainsail, which is tied at the Clew to the end of the boom, a boomvang attached to the boom 5 ft from the mast will have 30/5=Ratio of 6, = 60,000 TIMES the angle 1/SIN(5/2), yields 100,000lbs of sheer force at the point of connection.

That's bolt shearing, mast bending deck shredding, cable snapping levels of force.

With the center of effort at the middle of the boom, and the mainsheet at the end, you get less than HALF that force, or 3,500 lbs, divided by a 4 to one block, which is why we use 1/2 inch Dacron rated at 8,000lbs, instead of smaller rope for our mainsheets.

The force required to move a 30,000lb boat through the water at 10 knots is exerted on the frame by the gooseneck, the main halyard, and the mainsheet added together.

SO for a smaller boat, a boomvang is cool, I like them myself, but for a larger CondoCat, they simply aren't practical.

One big reason for the insane mainsail width, is the mast is moved way forward so it doesn't obstruct the Salon leaving a really long boom that runs 3/4's the length of the boat.

Which does cause some sail handling issues.

My suggestion for other boats is to call the manufacturer of your mast, and boom, and talk to their engineer before any modifications.

Really interesting and useful, thanks! This will definitely be included in the conversations with builder and rig designer

[markiobe]

Originally Posted by gezza

I'm not sure how much value my reply may provide, but it may provoke further discussion.
A number of years ago I bought a Voyage 440 and was busy buying some new parts. I spoke to somebody senior at the factory in Cape Town and asked why there is no vang (the Voyage has a boom strut - supports the boom but does not restrain or control it). His response was that cats do not have vangs as an overtightened vang was the a potential cause for a pitchpole situation; obviously very undesirable in a cat as there is no heeling or broaching to alleviate the problem.

At the time I was brand new to cats and did not have sufficient cat understanding to take the conversation any further with him. So food for thought ???

Definite food for thought, thanks

[markiobe]

Originally Posted by contrail

Another thing in favour of the wide traveller is that even in the small gap between where the traveller effectively controls twist by being all the way to the end of the track, and the limit to easing the boom caused by the tripod rig and its aft mounted shrouds, the mainsheet is still pretty well sheeted in, so that an unintended gybe only involves a manageable movement of the boom, rather than a slam right across the boat. Having sailed dozens of kinds of boats, I actually find the long traveller on a cat to be very easy to use.

Makes sense, thanks

Originally Posted by contrail

Another safety reason that used to be cited is that, in the case of a very strong gust, and impending capsize, pretty rare for today's heavy cats, assuming some rational amount of sail up, simply letting go the main not only allows it to ease out, but up, as well, "scandalizing" the main and depowering it. A boom vang is another line to release, and the thinking went that the fewer lines to release, the better.

Again that's a good point

Originally Posted by contrail

A capsize on a 49er is an easier thing to deal with, should it happen!

Capsizes? Nope, never happened on ours...

[LeeV]

https://www.leopardcatamarans.com/si..._rendering.jpg

Another well known cat