Why don't catamarans have boom vangs?

[tamicatana]

the delta-V mainsheet system is nothing new, although Berman has apparently renamed it the 'A-frame.' Interesting; Berman gives Barreau, the guy who began designing Catanas after Loch Crowther died, credit for the concept.

https://www.practical-sailor.com/sai...l-the-mainsail

https://forums.sailinganarchy.com/th...iences.207207/

Google also 'Leneman Delta-V'


The thing I really don't like about mine is the loss of leech control on broad points of sail. IMO the split mainsheet works better to weather. Me, if I had half an inclination, I'd install a curved traveller instead. I expect there's a reason why those floofy French hot-rod trimarans all have curved travellers...

[capn_billl]

Just like cats don't sail well on the main directly down wind, it's very rare that you would want the main directly on centerline going upwind.

You complain about leach tension?

How about pulling the upwind sheet past centerline, and allowing the leach to curve back to center?

Remember this is a fully battened mainsail, it doesn't take much tension to keep the sail straight.

[fxykty]

Originally Posted by capn_billl

Just like cats don't sail well on the main directly down wind, it's very rare that you would want the main directly on centerline going upwind.



You complain about leach tension?



How about pulling the upwind sheet past centerline, and allowing the leach to curve back to center?



Remember this is a fully battened mainsail, it doesn't take much tension to keep the sail straight.

Not much tension?!? We have an 86m^2 mainsail with 6 full battens and very large roach (no square top though) and with 4:1 mainsheet going to 53:1 2-speed winches. When fully loaded that winch is working really hard to get the top batten parallel to the centreline. Our sail maker estimates 3.5 ton of load on the clew.

If we let the boom down from near centreline the mainsail back winds when close hauled. The only time we sail close hauled with the boom down from the centreline is when we’re willing to feather the main to avoid reefing. Usually we just reef and bring the boom back to centreline.

We never sail with the boom to windward of the centreline, other than while reefing downwind.

[catsketcher]

Originally Posted by fxykty

You are getting a performance cruising cat. The amount of time you will sail angles >130* other than near dead downwind will be minuscule - the whole point of a performance cruising cat is to sail the angles. Your aft beam or coach roof will be plenty wide to have a traveller long enough to handle gybing angles.

As others have pointed out, if you really want to mooch dead downwind use a spinnaker, parasail, or really big top-down asymmetric, with no main at all. In heavy air just use the jib on its own - if you keep your boat light you won’t need much sail area.

Of course I have my own opinion based on my sailing, but I often sail angles deeper than 90 apparent, mostly when the wind blows up.

I am often trying to slow my boat down in bigger breezes, so generating more apparent is something I often DON'T want to do. When the wind blows up going deeper and reducing apparent is exactly what I like to do. I often grab the helm and ride the angles, bearing away in gusts to reduce load on the boat and coming up in the lulls, using the apparent to keep the loads on the sheets pretty constant. I really love sailing on flattish water, hotted up and using apparent to keep everything safe, once when we did 150 miles in 15 hours (actually a couple of times) I was bearing away as the gusts arrived and the boat flew along. This is what skiff sailors do all the time, reducing apparent when required (say when gybing and taking kites down).

The wishbone rig is great in these conditions, providing fab vanging for the main all the way out, virtually no chafe and very low sheet loading. Sometimes I even grab the whole system and pump the whole main in and out a metre or two just for fun and to live my old dinghy days, but not over 15 knots of breeze.

Although I also love using a symmetrical dead downwind (without a main) for long periods, I often run square, or almost square, for hours with the main up, because we are going fast enough and we have to alter course in an hour or two to bring the wind more abeam. Also a well vanged main is so much less liable to chafe that you don't mind using it on a square, and you can ease it out all the way to lie on the stays and so the boat helms better. Also a gybe is not a worry because I can easily wind the main in as we bear away for a gybe. Maybe it is because I do lots of shortish day trips (20-50 miles or so) along the coast, and lots of day sails in protected waters, at home or in the Whitsundays, that I like a main that can run deep as well as go upwind well.

Sailing angles can also be problematic in some situations. I spent a year gybing downwind before I learnt that my boat does not go fast enough to warrant the extra distance in many conditions. I even remember a Brisbane to Gladstone where in the very light conditions, the fastest boats were square running to get into the channel - counter intuitive but true. So running deep with a main up is an important option on my boat - and she aint too slow.

cheers

Phil

[tamicatana]

these videos may offer some insight:

https://vimeo.com/336681983

https://vimeo.com/336847059

[markiobe]

Not sure what insight these give, the students really are beginners…

[markiobe]

Originally Posted by tamicatana

The thing I really don't like about mine is the loss of leech control on broad points of sail. IMO the split mainsheet works better to weather. Me, if I had half an inclination, I'd install a curved traveller instead. I expect there's a reason why those floofy French hot-rod trimarans all have curved travellers...

The advantage of having another attachment point on the split mainsheet/A-frame system positioned well outboard, means that you would have better leech control at wide angles than any shaped traveller on the coach roof. Unless your traveller is on the transom and extends across the whole beam of the boat you wouldn’t be able to get the mainsheet attachment point as far outboard so your leech control would be less…

[markiobe]

Originally Posted by TOM-ROLPH

You don't say whether or not you actually own a catamaran (unless I missed it somewhere)
If you do own one what class?

Being built, 51ft performance cruiser, ~5000kgs. A totally new design from an established builder with an existing production brand.

Originally Posted by TOM-ROLPH

I don't know of an ocean going cat which doesn't have a full width traveller. I don't know of an ocean going cat that has a kicking strap (vang to our US EU shipmates). That kind of demonstrates the point.

With respect, I think this demonstrates only that the cruising sailing world is very conservative. Not a criticism, I understand why, but I don’t think proves in any way that the traveller is necessarily the best solution. I’m also not saying it isn’t, I’m questioning the status quo, that’s all.

Originally Posted by TOM-ROLPH

The vang system on the 49er is a dinghy solution on an ocean going vessel it's going to be huge, hugely expensive and place huge strains on the mast.

Agreed and maybe that’s the main reason it isn’t done. I’m no engineer and maybe what’s not feasible on an 45ft FP might be on something half the weight and more easily driven. People who understand the maths will tell me and we’ll obviously take the experts’ advice.

As I said, I have no dog in this fight, simply asking questions and defaulting to the simplest answers. I don’t like accepting received wisdom without asking why, and since the boat is being designed with first principles front and centre, everything is being questioned.

[markiobe]

Originally Posted by foufou

I believe there is another reason for travelers that has not been mentioned. The sail, with main sheet attached to the traveler act as a back stay. While catamarans have swept back shrouds that take loads from astern the leech of the main and the main sheet also take those loads. It is all part of the mast support system.

No, I cannot believe that this is true.

Firstly, to design a rig that requires a movable ‘stay’ to remain upright is nuts.

Secondly, a huge number of cruising boats sail downwind with no main up at all, and by this logic masts would fall over the handlebars all the time.

Thirdly, you need the ‘backstay’ support downwind and that’s exactly when the main would provide virtually zero support as it’s trimmed at a wide angle.

[StuM]

Originally Posted by markiobe

Being built, 51ft performance cruiser, ~5000kgs. A totally new design from an established builder with an existing production brand.

Your own design, or being designed by a qualified professional?

[belizesailor]

Originally Posted by CarlF

Coming from monohull racing myself, I found many of the rigging decisions on a cat perplexing at first. Most so the swept back shrouds that keep you from letting the boom out. I also said "Where's the vang?"

But I've concluded that cats rigs are well thought out - most certainly not done this way because cat sailors don't know how to sail.

Performance cats spend a larger percentage of the time close hauled than monohulls. There just isn't a lot of time that you want the boom out beyond the traveler length. I strongly urge the OP to consider an Oxley parasailer with a furled mainsail for those relatively few times when a performance cat has the wind aft of the beam.

The swept spreaders and wide shroud base make the mast stronger than a narrow monohull. This allows designers to reduce the size/weight of the mast section and shrouds. Not having a backstays allows the large roach of cat mainsails which greatly improves mainsail power due to the longer cord in the upper half of the sail.

But all this power in the mainsail means that a boom end traveler is the best system for leach control. A boom vang would require a heavier boom section and either raising the gooseneck or lowering the cabin top to not have the vang at too shallow an angle.

The traveler also allows you to adjust the leach with a powerful mainsail sheet winch. Most cat sailors (and mono sailors) sail with the leach far too open. It takes a lot of winch power to tighten the leach enough to get the battens parallel to the boom on these huge sails. To create the same force with a boom vang would require hydraulics. Block and tackle would not suffice.

If the OP must have his boom vang, then he should go all the way and use a monohull rig on his cat - with unswept spreaders, a backstay, and larger fore triangle. Picking a few things from column A and a few things from column B is not good engineering.

And unfortunately almost all cruising cat rigs evolved from performance cat rigs...thus most current cruising cat rigs are not great cruising rigs and the performance aspects of them have very little relevance on must modern cruising cats.

[thinwater]

Originally Posted by markiobe

No, I cannot believe that this is true.

Firstly, to design a rig that requires a movable ‘stay’ to remain upright is nuts.

Secondly, a huge number of cruising boats sail downwind with no main up at all, and by this logic masts would fall over the handlebars all the time.

Thirdly, you need the ‘backstay’ support downwind and that’s exactly when the main would provide virtually zero support as it’s trimmed at a wide angle.

A little cat experience might help. You may not be understanding the point.



One of the functions of the backstay, in addition to keeping the mast up, is providing forestay tension. Angled shrouds are not good at this, the forestay tends to sag if the main is not tight, and the jib becomes full and draft-aft. Racers pay a LOT of attention to keeping the forestay tight with mainsheet tension. This is a really big deal on beach cats and some dinghies.



Off they wind this does not matter. No main needed (but still a good idea).

[thinwater]

Originally Posted by belizesailor

And unfortunately almost all cruising cat rigs evolved from performance cat rigs...thus most current cruising cat rigs are not great cruising rigs and the performance aspects of them have very little relevance on must modern cruising cats.

And there is a LOT of truth in this. Cool looks can be more important to sales than function. The beach cat design evolved, in part, for precise heel control (flying a hull), something that has little relevance to cruising boats.

[Sos]

Originally Posted by markiobe

No, I cannot believe that this is true.

Firstly, to design a rig that requires a movable ‘stay’ to remain upright is nuts.

Secondly, a huge number of cruising boats sail downwind with no main up at all, and by this logic masts would fall over the handlebars all the time.

Thirdly, you need the ‘backstay’ support downwind and that’s exactly when the main would provide virtually zero support as it’s trimmed at a wide angle.

I believe that Lagoon advice that you don't sail with just the jib in higher wind strengths so the mainsheet/topping lift are working hard. Also applies to flying just a spinnaker.
Not a problem on our cat since we have backstays but then we have no roach in the mainsail!

[markiobe]

Qualified professional, designer/builder, with lots of experience and successful boats on the water.