Why don't catamarans have boom vangs?

[markiobe]

Originally Posted by thinwater

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).

OK, I thought it would be obvious what I meant, apparently not. I do understand, I come from a racing background. The point was that the leech tension is NOT required to 'support' the mast. Obviously leech tension pulls the mast backwards and tensions the forestay. In my mind that's not 'supporting' the mast, it's tuning the rig.

And anyway, the point made by the poster:

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.

was that a 'traveller' is necessary to allow the main to act as that 'backstay'. That is evidently not true, the leech tension only provides the pull on the forestay when roughly upwind, in which case the mainsheet attachment point doesn't require a traveller to be in the right place.

The whole point of the traveller is to move the mainsheet attachment point outboard, when sailing more downwind, in order to maintain twist control if you have no other way of controlling twist; the point of my initial post about vangs. At these angles the leech tension is neither sufficient nor in the right direction to provide forestay tension and 'support' the mast, and the rig tune doesn't need it anyway

And finally, rigs with swept back shrouds, as long as mounted on correctly built and braced hulls, absolutely can provide sufficient forestay tension. Your point is true once the boat gets big/heavy enough, hence bigger boats having perpendicular shrouds and back stays.

As a side point, one of the problems of building a swept back stayed rig with no backstay and then mounting it on a poorly built hull (I'm looking at you Lagoon) oddly enough seems to cause structural issues with the bulkheads, I wonder why...

Originally Posted by Sos

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!

It seems that the Lagoon engineers understand this and, rather than fix the fundamental design problem, ask you as the owner to sail a particular way to protect them from the consequences of choices prioritising internal space over good structural design/build quality.

Any well-built boat with no backstay that wants to maintain good forestay tension created by the shrouds, has angled bulkheads along the line of the forces. Look at literally any racing boat with that style rig that needs rig tension to perform. I've only seen one production cruising cat that does that. A good job that most cruising cats owners never want to race and improve their rig setup. I think there would be many more problems as the structures are fighting the physics.

To be clear, this is a different rig from a beach cat style that uses mainsheet tension to create luff tension upwind and lets the rig flop forward downwind.

[catsketcher]

I'll pop up again.

I vang sheet all the time with the wishbone. My forestay is tight enough for me and I am happy with it. Forestay sag is a legitimate way to make genoas fuller when you want it - in winds up to 10 knots or so. I change to my staysail at about 16 knots - so I may have too much sag for about 6 knots of range upwind. But another issue that makes many cats different from beach cats is the use of inner forestays.

My 38ft cat has an inner forestay, which I use with a staysail in moderate to heavy winds. It goes to 8.2 metres up my 14.1 metre mast.

Having an inner forestay is a great thing for a cat with a larger fore triangle. Many cats, like the Seawind 1000, have very small J measurements and a big boom, and mainsheet tension can make a big deal with forestay tension on these boats. My cat has a relatively larger J (which reduces the effectiveness of sheeting to increase forestay tension) and an inner forestay, which does the same again as both forestays have to share the load.

I prefer to use the smaller foresail in just the times that a super tight forestay is also used (when the wind blows up). So I get a tight and straighter forestay because it is much shorter, with a great flat staysail made for heavier breezes that lasts forever because it is used only part of the time. I love my staysail and it makes me feel bulletproof with its great shape in a breeze. The boat loves the centre of effort being pulled back from the bow in a blow - all great facets of the rig.

One thing that we forget about the beach cat rig is that when reefed the mast can bend backwards (or straighten up) below the hounds when the head is brought down to the hounds or even below. In my old tri I would reef and the mast would invert a bit and the main would be fuller that I wanted. It meant the first reef was almost useless. You can get round this a little by making the diamonds sweep back more and increasing tension but this increases compression on the mast and pokes holes in the main when eased.

With my inner forestay and wishbone pushing forward on the mast at 4.1 metres above the base, reefing does not reduce forward mast bend below the hounds - this keeps the main much flatter in bigger breezes. You can't get around inverted mast bend with increased foot tension - you gotta match the mast bend with luff curve and reducing mast pre bend in a breeze is exactly what you don't want to do - like in my tri. I sometimes just went straight to the second reef because the main was so full it almost was as draggy as the unreefed main.

So what little I lose with the lack of forestay tension on the big genoa, I get back with the staysail being a really great shape AND I get a better flatter main than most when reefed. Beach cats are not meant to be reefed so they shouldn't always be used as an example of cruising cat rigs.

As an aside when I raced Tornadoes we used to have a 10-1 mainsheet system and gave it a really hard tug. Also to get the mast to work well both the crew and I used to heave with everything we had on the 12 to 1 downhaul system to get the mast to bend the correct way. There was more tension on the luff than the total displacement of the boat and crew by a factor of about 2. Hence my reluctance to use beach cats as a model for my rig. I think a 16ft skiff rig is far more comparable to a typical performance/cruiser cat rig in terms of aspect ratio, mast configuration (lack of rotation - mast section type - lower sheet tension) and relative sizes of main and jib. Skiffs love vang sheeting too. As a performance skiff and Tornado sailor, I certainly knew which model I preferred to use as a basis for a cruising boat when I built my cat.

cheers

Phil

[StuM]

Originally Posted by markiobe

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

I presume that is an answer to:
"Your own design, or being designed by a qualified professional? "


What does he say about the idea of a vang on the boat he is designing?

[fxykty]

Our shrouds are relatively not very back of the mast compared to most other cruising cats so we use running backstays to support the mast in moderate and hard reaching/running conditions and to prevent excess forestay pumping upwind. The running backstays don’t have much effect on forestay sag upwind - our boat is stiff enough that it isn’t an issue. Our mast also has a complex set of diamonds to create and maintain a certain amount of prebend in the mast under all conditions - it’s set and forget.

The mainsheet traveller is the conventional solution to mainsail control and is most actively used when sailing upwind. It allows one to precisely position the boom and to control leech tension independently. An a-frame sheet system does not work as well or precisely. But it is a simpler system, and most cruising boats that have that kind of rig are not expected to sail upwind.

For boom control when deep reaching or running the traveller is not long enough on most cruising boats, including our own, as it would impinge on access to the back of the hulls. Bummer. So we do need to use a preventer line to apply down force to the boom. The same problem exists for a-frame systems, as most designers will not want to place mainsail sheets across the hulls and in the way of foot traffic aft.

If a rig is designed for a vang then there really isn’t a drawback to having one. And it’s a definite positive in getting rid of the topping lift, as well of course providing leech tension at wide angles. I’m not sure that it can be safely retrofitted though without modifying or replacing the boom and/or mast. Any boat with a furling boom system will require a vang and of course those sails have plenty of roach, so it is doable.

I’m not familiar with the wishbone rig, though I have seen several in small and medium sized cats from a distance. Is there still a solid boom? How does the wishbone provide a downward force - isn’t the aft end still free to rise up and requires a sheet to provide downward force? Interesting concept, but for a large cat I’m not sure. And it does add a bunch of windage and more shading to bimini and cabin top solar panels.

[catsketcher]

Nathan Stanton bought Songlines - 45 or 48ft long and probably the most beautiful cat I ever saw. My first time I saw her was watching her builder/skipper (Neville Lloyd) gybe her down the Brisbane river with a flick of his wrist to get the main to gybe - on a large and very nice cat. Last I saw of her was in Brisbane.

Nathan then designed the Freeflow cats - I have included a link below. He altered Neville's wishbone idea with the addition of a boom. This gives ulitmate control of the sail shape. You can see in the shots how the sail can be eased off and still be well vanged.

FreeFlow Catamarans

I would recommend a verson of this setup rather than the wishbone itself - although it is more hassle to build. The boom could be a simple tube - I will probably use a sailboard mast if I upgrade my wishbone. I will even use the mast base and universal. It only acts in compression and can be very light for my use.

As for the wishbone riding up - like a sailboard sail, the foot provides the tension to stop the clew rising up. In my main the sailmaker sewed a length of spectra into the foot - so it takes the tension rather than the cloth. The sail swings in and out like a gate - the tension the wishbone places on the sail is dictated by the tackle at the front end of the wishbone - I call it the snotter tackle.

[fxykty]

Thanks catsketcher for posting - that explains a lot. I assume that each clew reef line goes through the end of the wishbone and that it is not hard connected to the primary clew?

So, the mainsheet only needs to control the athwartships position of the clew and the snotter tackle controls the leech tension. Given the amount of vertical tension that I see on our clew (approx 3.5 ton) how is that handled by the wishbone?

If it could work with our diamonds I’m getting very interested.

[markiobe]

Originally Posted by StuM

I presume that is an answer to:
"Your own design, or being designed by a qualified professional? "


What does he say about the idea of a vang on the boat he is designing?

Hasn’t been discussed yet, other stuff in play atm. Is on the agenda for next week when we next sit down

[catsketcher]

Originally Posted by fxykty

Thanks catsketcher for posting - that explains a lot. I assume that each clew reef line goes through the end of the wishbone and that it is not hard connected to the primary clew?

So, the mainsheet only needs to control the athwartships position of the clew and the snotter tackle controls the leech tension. Given the amount of vertical tension that I see on our clew (approx 3.5 ton) how is that handled by the wishbone?

If it could work with our diamonds I’m getting very interested.

This is where it gets harder. Wishbones don't like diamonds. If you look at my boat - the one on the right with me looking shaggy on the port stern, you will see that the wishbone sits just at the lower tangs. There is lots of room for the wishbone to move around. Retrofitting a wishbone to a diamond rig would not be worthwhile in my opinion.

As for reefing, this is where Neville (who designed Songlines) was very clever. Originally reefing required gymnastics and hooks but Neville mounted a flat plate on the end of the wishbone. All the reefing lines originate there and double back, then proceeding through a clutch. I winch on the reefing lines using a mast winch and it cleats itself. It works pretty well but the second reef and beyond do pull back hard on the main so it needs to be strong. A laminate sail needs a reinforcing patch led forward at the second and third reefs.

cheers

Phil

[CaptainRivet]

Originally Posted by Sos

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!

Having additional backstays and a 2nd forestay is a wise decision if you seriously wanna sail a Lagoon other then a 380
Lagoon prohibits everything that has to do with sailing...designedaround the berths, as habour queen and charter motor vessel... The rigg and sails are there for decoration
Your warranty is not much worth anyhow with Lagoon as alot owners figured outthe hard way...
Lagoon will soon have to change 180 complete riggs due to a court decision. Curious how this will be executed, just given the history and the way they deal with these misconstructions in the past...

[smj]

Originally Posted by CaptainRivet

Having additional backstays and a 2nd forestay is a wise decision if you seriously wanna sail a Lagoon other then a 380

Lagoon prohibits everything that has to do with sailing...designedaround the berths, as habour queen and charter motor vessel... The rigg and sails are there for decoration

Your warranty is not much worth anyhow with Lagoon as alot owners figured outthe hard way...

Lagoon will soon have to change 180 complete riggs due to a court decision. Curious how this will be executed, just given the history and the way they deal with these misconstructions in the past...

Why additional backstay’s and 2 forestay’s on all Lagoons with the exception of the 380?

[CaptainRivet]

Originally Posted by smj

Why additional backstay’s and 2 forestay’s on all Lagoons with the exception of the 380?

To support the underdimensioned and undercanvased rigg. To get this heavy condos seriously sailing you need to add a lot canvas... Eg the 420 is loaded for bluewatercruising around 17t and has. a genua of 37sqm, to sail in 12kn you need min 80sqm and if you don't want to furl it in at 16kn it needs to be thicker then a spinacker one... Well a spinnaker need to be a huge one...

[markiobe]

Originally Posted by CaptainRivet

To support the underdimensioned and undercanvased rigg. To get this heavy condos seriously sailing you need to add a lot canvas... Eg the 420 is loaded for bluewatercruising around 17t and has. a genua of 37sqm, to sail in 12kn you need min 80sqm and if you don't want to furl it in at 16kn it needs to be thicker then a spinacker one... Well a spinnaker need to be a huge one...

To add to that, the hulls are so bluff pushing them through the water requires some serious horsepower!! To be fair to Lagoon, they're not the only brand that fits this description...

[markiobe]

Originally Posted by fxykty

Thanks catsketcher for posting - that explains a lot. I assume that each clew reef line goes through the end of the wishbone and that it is not hard connected to the primary clew?

So, the mainsheet only needs to control the athwartships position of the clew and the snotter tackle controls the leech tension. Given the amount of vertical tension that I see on our clew (approx 3.5 ton) how is that handled by the wishbone?

If it could work with our diamonds I’m getting very interested.

Phil kindly took the time to chat with me about his rig and, although he thinks its fantastic, one of the ideas to improve on his layout was to have the aft end of the wishbone attach to a traditional boom via a short track. That way you could have a line running through a block system pulling aft, then forwards to the mast to be led wherever. Pulling the line would push the wishbone down, tensioning the leech. It would provide an elegant way to adjust leech tension.

One of his other points was that nowadays you'd make the wishbone out of carbon to ensure that you have the stiffness to not distort under the load.

[AKA-None]

Ok so in this thread I see people referring to a vang to hold the boom up but I always thought a kicker held the boom up and a vang pulled the boom down
But a single device may do both
Please correct me if I’m mistaken

[fxykty]

Originally Posted by AKA-None

Ok so in this thread I see people referring to a vang to hold the boom up but I always thought a kicker held the boom up and a vang pulled the boom down
But a single device may do both
Please correct me if I’m mistaken

Vang and Kicker are synonyms - they both mean the same thing. Different places use different words.

A soft vang/kicker may be simply a block and tackle arrangement - its only job is to pull down on the boom. A topping lift is required to hold the boom up.

A hard or solid vang/kicker will put the block and tackle arrangement inside a spring loaded pair of tubes. The block and tackle provides the downward pull, while the spring provides the lifting force. The tubes hold everything in line. No topping lift is required. Instead of a block and tackle and spring, larger boats will use vangs with hydraulic cylinders.

Finally you can have a hard vang with a spring but no block and tackle that only is meant to hold the boom up. It is not designed to provide any downward force.