Why don't catamarans have boom vangs?

[Tin Tin]

Originally Posted by LeeV

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

Another well known cat

Excerpt from a Leopard 42 review:
"Like other Leopards, the 42 has what looks like a vang, which is unusual on a cat. However, its main function isn’t sail trim, but rather keeping the boom from hitting the cabintop accidentally when the mainsail is lowered without tensioning the topping lift"

[Sand crab]

I think the use of boom brakes should be outlawed. Look at that poor thing, it's terrified.

[markiobe]

[Tupaia]

Originally Posted by John_Trusty

If you want great sail trim, go ahead and add that fancy above-boom vang. I would guess that this mechanism would constantly touch sail cloth and lead to chafe.

Sail cover will be an issue.

[Tupaia]

Not related specifically to a vang but this would severely impinge on the ability to reef downwind by scandalising the main and using the mainsheet and boom to lever the sail down by the leech rather graunching it down by the luff or having to turn upwind.

[GRIT]

I haven't read the whole thread, so if this has been said, then just ignore my post.

Selden would not sell me a vang. I had to fight just to get the boomkicker part of the vang, and had to agree never to install line on the kicker. I wanted a vang to keep the boom from falling on the house when reefing, and because I dislike topping lifts even more than I dislike "turn your head and cough".

They said there would be far too much pressure on the boom, and that they wouldn't warranty the boom with a vang.

We use the kicker to support the boom. It's got a spring in it, so it doesn't just support the boom at it's lowest point, it lifts it when I reef too. We got the strongest spring available for the Selden 30 boomkicker. It supports our 6.1m boom and the 75m2 sail, even when furled. If I sit on it, I can bottom it out, if I bounce. It's a great rig to have.

So, in answer to the OP, I'd say there's just too much pressure on the boom, with most cats.

Cheers.
Paul.

[catsketcher]

Originally Posted by Tupaia

Not related specifically to a vang but this would severely impinge on the ability to reef downwind by scandalising the main and using the mainsheet and boom to lever the sail down by the leech rather graunching it down by the luff or having to turn upwind.

Not a problem with vangs. Not getting the main down on a square is more a problem caused by diamonds. Our supremely well vanged main can be pulled down on a square up to about 25 knots. Only once have I not been able to drop it or raise it on a square. I love not having diamonds. Much easier than my non vanged tri.

The point a poster made quoting the Leopard salesman is something I would disagree with. A well vanged sail is easier to trim and ease past the traveller ends improving safety. Again I would make the comment that sales people who have not sailed a cat with a good vang, which is very rare, shouldn't make statements about them being less safe.

I get that vangs don't make sense on a normal cat boom. But if you want good vanging you certainly can get it and sales people are making excuses about the sailing, but not the engineering, concerns.

[Tupaia]

Originally Posted by catsketcher

Not a problem with vangs. Not getting the main down on a square is more a problem caused by diamonds. Our supremely well vanged main can be pulled down on a square up to about 25 knots. Only once have I not been able to drop it or raise it on a square. I love not having diamonds. Much easier than my non vanged tri.

Can't see what difference diamonds make. I thought your rig has a wishbone. A conventional vang would prevent the boom from being raised beyond a certain point without lots of friction and lines that would be an impediment when reefing by the leech.

[catsketcher]

On closer reading I remembered what scandalizing was. I thought it was something to do with dropping a gaff in a squall. I thought you were explaining pulling the main down on a square using the reef lines. On my old boat the diamonds made doing anything with the main downwind impossible, hence the comment about diamonds.

[fxykty]

Originally Posted by catsketcher

On closer reading I remembered what scandalizing was. I thought it was something to do with dropping a gaff in a squall. I thought you were explaining pulling the main down on a square using the reef lines. On my old boat the diamonds made doing anything with the main downwind impossible, hence the comment about diamonds.

What are you referring to as your diamonds, that you say they impinged on the sail when it was let out for downwind? Did you not have shroud(s) that were located well aft of the mast?

Our mast has two sets of swept back spreaders (plus a forward prod each) for a total of 6 diamond stays in two sets of three, going from the mast to spreader/prod end and back to the mast. We have a single cap shroud on each side that at deck level is about 2m aft of the mast. That’s what our mainsail hangs up on when reefing or unreefing downwind - the diamonds aren’t in the way at all.

Regarding scandalising the main when reefing, that would mean for our boat two people would be needed to reef, as our reefing lines and halyard are at the mast and the mainsheet is in the cockpit. But if all the lines were close to each other in a cockpit that is a way to use the more efficient mainsheet system to manage the leech loads.

We reef downwind by letting out the halyard a metre or so, then grind in the reef clew line a metre, and repeat until we can make fast the reef’s tack line. I believe this is called graunching, due to the loads on and noises of the boom end sheaves. The key is to keep moderate tension on the leech most of the time so that the top half of the sail doesn’t drag on the rigging. We bring the traveller well to windward of centreline and ease the mainsheet only enough so that the boom can rise a bit. Unreefing downwind is the reverse.

Regarding a vang, as others have reported the mast and boom must be designed for them as the loads are huge. But, if used just to support the boom in place of a topping lift, with presumably enough travel so that it doesn’t bottom out under sailing conditions, that sounds like a great idea. We have room and we’ll add that to our upgrade list - phaffing about with a topping lift is not a big deal, but it is just one more thing to check before lowering the halyard to reef or drop the sail.

Regarding trimming the boom beyond the traveller, it depends on the type of cat and the angles that are typically sailed. We are very rarely sailing much wider than 130* AWA as we like to sail VMG angles, and at 130* our boom is just barely past the end of the track. Any less than 130* and we use traveller and sheet to manage the sail shape - I don’t know how a vang would help as I assume we’re not talking about dinghy vang sheeting?

If we want to go any deeper we rig a line from the end of the boom to a midship pad eye and back to a primary winch. The gear is big and the loads are immense to keep the big roach from twisting off in any decent breeze. But it’s pretty rare for shape control; much more often the line is there to keep the main from flogging back and forth in lighter winds and bigger swells. A vang wouldn’t help for that.

[thinwater]

• My cruising cat. I seriously thought about it, but the cabin got in the way. Sometimes (rarely) I would winch the boom down with a line to a mid-ships cleat, going deep with no chute.
• Rotating masts. Would have to be released to tack or jibe; the forward pressure would prevent rotation. But not most cruising cats.
• F-boat. The designer assumed that they would be raced, and with a chute or reacher up you never ease the main that far, generally not even to the end of the track. When you are not using downwind head sails (strong winds) you probably want some twist. Also, some are fitted with roller furling booms, which makes fitting a strong vang impractical.
• Bendy masts (like the 49r) and vang sheeting. Vang sheeting allows the leach to open more in gusty conditions than traveler sheeting. Not as relevant to cruising boats, and square top sails also provide some of that function.

You see a lot of performance ocean racing boats, mono and multi, without vangs. They use big head sails and go faster than the wind. But cruising cats aren't that fast. I would have like a vang on my Cruising cat... but not that often. Only specific wind angles and strengths, only without the chute up. Square top sails further reduce this advantage.



I think it is just a matter of compromise and simplicity. The need on multis is less, so the compromises are a little less attractive. But I sure would not say they are useless, just "used less."

[Houston450]

I didn’t read all the answers, so this may have already been stated; I started sailing on JBoats and learned quickly about band and creating leach tension for downwind performance. Now I sail a Lagoon 450F and often wished for an adjustable boom vang. Even better I could get rid of the topping lift that keeps the boom off my bimini. But it would sacrifice the big sunpad I have forward of the helm. You end up using the long traveler to get the leach tension and keep all the guests happy. Maybe a removable vang, but now you’re adding work . I’m sure performance cats have them, but remember your goal.

[markiobe]

I think we need some definitions of terms as clearly there's a lot of misunderstanding about what a vang is and by extension what I'm actually asking!!

I used the term 'vang' where normally I'd use 'kicking strap' or 'kicker' as I think vang is used more geographically widely. A vang/kicker is designed to apply a downward force to the boom in order to control mainsheet twist and leech tension. Depending on how bendy the mast is it may also flatten the sail. 'Vang sheeting' is using the vang to control twist/leech tension and only using the mainsheet to control sheeting angle. This is often used in windy conditions upwind on boats where the mainsheet is being continually played (sheeting angle adjusted). It lowers the mainsheet load and ensures that the mainsail remains the correct shape regardless of sheeting angle.

Certain vang/kicker systems with a strut or combination strut/lever arm can, as a byproduct, be used to support the boom like a topping lift. Most can't as they are simply a system of cascading blocks and lines with no rigid component. The struts on certain boats (Leopard I think?) are not vangs/kickers as they are simply there for boom support. For clarity I was NOT asking about this use-case.

The reason for the question was then; why do catamarans not use vangs/kickers and instead use a travellers, when they are:

- heavier and more complicated
- don't accomplish the goal as effectively as a vang/kicker especially at wider angles. This is an efficiency and also potentially a safety issue.

Based on what people have posted it seems to me that the reasons are some combination of:

- not enough space between coachroof and boom to create a system with sufficient leverage
- given the lower leverage the forces required create the potential for breakage on larger cats
- 'it's what we've always done' inertia. Initially caused maybe by the issues above and/or the fact that previously the blocks and systems weren't good enough to build vangs/kickers that worked well enough.
- Most cruisers either don't know how to use, or care enough about mainsail control to that extent anyway and builders are very conservative/not innovative.

Thanks for all the responses and thoughtful answers . I think that we'll aim to have a vang/kicker and not have a traveller if possible. Obviously we'll defer to the builder and rig designer's expertise however!

[WantTo]

Manta catamarans have boom vangs, a boom brake, and dinghy davits. We went wing and wing for 7 days USVI to Miami. Used autopilot to keep wind at 160°. Had 2 unintentional gybes, but the boom gently changed sides thanks to the brake. Great boat.

[dwightsusan]

Depends on the cat. No vang on our 47'x28' performance cruising cat with an end sheeted boom and a very wide traveler. We sheet with the traveler and vang with the mainsheet. This gives us total 2 axis control of the location of the end of the boom, and total control over leech tension. Our higher boat speeds typically bring the apparent wind well forward. Even on a broad reach our boom end is still directly over the car somewhere on the leeward traveler track. We usually tack when running directly downwind typically keeping the apparent wind near or just abaft beam. Running close to directly downwind on a course constrained by channel or shoals we run out of traveler and the boom closes on the slacked leeward running backstay. Time to launch a spinnaker appropriate for the wind velocity.