Originally Posted by UpOnStands
sounds like a classic strawman argument.
OP wants a single unstayed mast. No mention of wing.
Lets imagine a single unstayed mast, regular sail arrangement works? well, poorly, not at all. Why?
The strawman is a retired naval engineer, worked on fast patrol boats and frigates for the French navy, also fishing boats in wood and composites until 160 feet and closer to sail boats worked on the procedures of the definition of representative norms for naval composites. Thus "he engineered" for some NA who designed a big bunch of racing multihulls of the French Flying Circus. He was part also in the technical team of two Class C and also has been consultant in the aerospace field.
And some decades ago before resuming studies for being engineer, the strawman was a naval carpenter, who earned his master from the Compagnons Du Devoir et Liberté after 4 years touring in Europe in six different shipyards.
So the strawman is beginning now after a few years of zen meditation during his retirement to have a global idea how works a boat, specially multis, field he had worked in for 18 years at the highest level.
Take care of what you write, there are a few guys in the forum who are more qualified than I am. Some did the America's Cup and not once, some are very experienced builders. Some are excellent NA with many successful designs. At least 2 are Phd engineers. Beware they could be less gentle than me.
Please think twice before writing something like your last post. But I'll be a nice old daddy and I'm going to give in simple words the factual reasons why an unstayed mast it's a false good idea on a catamaran, so you will learn something.
I'll write it for the the third time in this thread. Catamarans have a peculiar curve of stability. The max stability is when one hull just barely leaves the water. Something like a meager 5 degrees of heel. After the righting moment diminishes sharply and you can say that at 35 degrees the cata will capsize on flat sea. More the rig is tall and heavy, the angle of capsize will be smaller. So the stability starts maximal, that the important point. Add the fact that multis have fast reactions. Keep that in mind.
Monos and tris have very different curves. Monohulls are "tender", and the max righting moment is very grossly at 90 degrees on a old fashioned mono. Note that the curve is very soft, gradual, gently rounded.
So you can calculate for a mono an unstayed rig rigid enough for example until 20 degrees, and having such a bend that he will empty the sail at 25 degrees for example to stay in a comfortable zone of sailing. Monos have slow reactions thus being more forgiving for the sleepy skipper.
Inevitably you'll need a very rigid mast on a cata to take advantage of its initial stability, unless you sacrifice badly the performances of the boat by spilling out the wind from the sail each time the cata tries to accelerate. You'll get a floating pontoon not a sailing cata.
Rigid means heavy even with carbon fiber. And this rigidity is useless as security valve, the righting moment is already going down fast, but the weight of the mast hastens the capsize. the angle of no return is smaller.
In short words you have lost and performance and security. Not a good bargain.
The true security on a catamaran is a fast release of the main sheet. To be more subtle you can work on the angle of the sail and the tension on the sheet. That needs a beefy hardware, blocks on ball bearings, big track with double chariot on rollers even on a modest 30 feet.
With this good investment in hardware, you can command fast the main sail and open it within 2 seconds. That's efficient, you have the power and the security.
For me it's just enough to discard an unstayed mast on a catamaran, but there are more complications, a genuine Mexican telenovela.
Catamarans are strange boats where the mast is placed at the worst place, structurally speaking, ie the middle of a beam.
Happily a stayed mast works mainly in compression on its base, cats are wide so the rigging is largely open thus minimizing the compression on the mast. And as you have plenty of place between the cables you can use very large spreaders. You get something rather light, highly tunable and if well designed very reliable.
As it's rather rigid (we won't talk of differential bendings controlled by the "arthur" lever of rotation, variable angulation of the spreaders etc... on a cruising boat) the shape of the sail is well defined and its fullness can be easily tuned. These masts are very easily tunable.
You can even change the rake. With a little tweaking you'll get a rigging perfectly adapted to your cata, with a light and responsive helm and good tacking ability. They are not cheap, but within the possibilities of a 30 feet catamaran owner.
It's not the case on a unstayed mast. Almost nothing can be changed easily. Any mistake of conception is almost impossible to fix unless spending a lot of money...He bends too much, buy a new one, The sail is too full, change it. You would like yo move a bit farther the center of the sail plan, it's a major refit of the base of the mast,
But I have not finished. I told you that was a bad telenovela. It's indecently expensive for a 30 feet cruising catamaran, whose owner is not a billionaire.
If you have read all the posts of the thread and if you have a some engineering knowledge, explain to me how to put a free standing mast in the middle of nowhere, ie a beam, or a roof designed to receive only the compression of a stayed mast. The means a major recalculation of the stresses induced by a free standing mast which has to be embedded in the cabin to minimize the shear efforts and most important to get a decent weight. But remain the torsional effects of such a formidable lever. Plus the materials and the work. That is pretty heavy, expensive and it's not 100% guaranteed...
Add the cost of a custom made carbon mast ( do not forget that this mast must have a conic tapered shape, it's not a simple pipe) plus the "experimental" sail compared to an ali mast and its rigging...The result is frightening for most wallets.
And the telenovela goes on inexorably into the worst. After all that, the catamaran is slower, less sure because of the weight of the mast, cannot be tweaked by simple means, but you'll always need the hardware for controlling the main sail because your life depends on.
Nobody has never seen a unstayed mast catamaran with truly appreciable performances.
And the only mean to know is to make the accurate VPP of the boat...I would like to see precise VPP and VMG polars. That must be sadder than a Spanish Crucifixion painting.
If you have good rational arguments in favor of a single unstayed mast on a catamaran, I'll be happy to read it. Have a nice day from the strawman.
PS Unstayed single and twin masts have been closely examined by serious NA and NE several times since 35 years. Not worth.