Single main sail with unstayed mast on cruising catamaran?

[valery gaulin]

I was looking at my next project a cruising catamaran in the 30foot range and was wondering why don't we see any single main sail unstayed mast on cruisong catamaran? Is it a tacking issue? A heaving to issue? Or just because people are scarred of it?

Anybody as an answer?

 

[Ilan Voyager]

Weight and efficiency of the main sail are the problems with an unstayed mast on a multi. The multis have too much stability, specially the catas with the very peculiar curve of stability, maximal just when one hull leaves the water.
I won't enter in the detail of the problems induced by a sweeping mast on a multi, and the fast control of the mainsail which is primordial.
Also cost. On a 30 feet cruising cat the principle MISS (make it simple and stupid) is fundamental. A simple stayed alu rig will be less heavy, more efficient with a good fully battened mainsail and far cheaper than a custom carbon mast and experimental sails.
I would spend the money on good hardware. Hardware is the weak point on cruising multis. Cheap bad sails, too small winches, tracks which do not work under load etc...
And last but not the least a solent jib on a cata is very useful for tacking fast and sure while cruising. A gennaker is a pleasure when the wind is weak.

 

[RHP]

That said, I have seen catamarans with single unstayed mains'l masts, one on each hull.

 

[RHP]

and this one

http://dutoityachtdesign.co.za/project/15-06m-49-nordic-490-fast-cruising-cat/

 

[Ilan Voyager]

That said, I have seen catamarans with single unstayed mains'l masts, one on each hull.

The first pic looks nice, sporty fast. The hulls smell the seventies...Imagine now the inertia of the weight of such twin rig balancing front to back, and side to side. Because there are not miracles in engineering. Two mast are always heavier than one and you'll need 2 mainsails and all the hardware.
And the tracks which permit the control of such high aspect ratio mainsail are cruelly missing at least on one side.
Pretty expensive and none of these rigs has showed so great qualities that they became the mainstream of efficiency...
All has been experimented many times since 50 years with the same results. And the result of 50 years of work by a lot of able people on multis is the sloop rig you see now from the beach cata to the maxi trimaran.

The second pic, and the animation show a very mainstream cat with the complication of 2 masts, double hardware, and no tracks to control the sails. Plus 2 sails to tune and twice the work for reefing doing the monkey very close to the water.
I leave you to imagine the stresses induced in the mast by the boom and the probably hydraulic controls. I would prefer a a single mast, a beefy track on the rear beam, with double chariot on rollers so you can open and close the sail in seconds, just one sheet on a 3 speed winch to free in case of problem, a good automatic solent jib on track so you can work it as needed to tack in seconds in the middle of a busy harbor entry...

 

[valery gaulin]

I would only consider single unstayed mast. Carbon fiber mast and boom. It seams that the technology is here now to produce this kind of rig at a descent cost. Of curse the cost of an aluminum extruded mast is really hard to beat on price. You can get an extrusion die for around 3000$!!! Cheap...

 

[Ilan Voyager]

The issues I pointed on my first post remain. That will be more expensive than a classic rig. Even in carbon it will end heavier. it a problem of structural engineering. No hope in the actual state of the materials.
It's also pretty hard to design. To soft and the cata is underpowered with a whipping mast. Too stiff and it's far too heavy, will not dissipate the stresses and will be very hard on its base support.
The design of the sail is also an headache.
Catas have a very perculiar stability curve with an enormous initial stability at 5 degrees which fades totally at 35 degrees. So a mast rigid enough to move the boat with a 5 degrees heeling has no use as security valve later. The security valve resides in a perfect control of the mainsail with the sheet and the track. You can depower a fully battened mainsail in one second.
Monohulls have a very different curve so they can have advantage of a free standing mast.
There is also the problem of the stresses on the beam. On a mono you can go til the keel getting a lighter mast as it as better suport, not in a cata. And last but not the least a cata is a large platform where it's easy to anchor the rig with minimal compression of the mast and on the beam. Why do not use it?
Also good fully battened mainsails dislike free standing masts if you want to have a good control of the shape.
If unstayed masts were efficient on catas, we would see many. There are excellent reasons these masts are so uncommon. I do not see any rational reason to advocate unstayed masts on a cata. On monos and some small beach tris it is a different story.

But what will stop you immediately, it's your wallet and your calculator. You'll discover that the real cost is ridiculously high for a 30 feet cruising cata.

 

[Corley]

As Ilan notes it's hard to beat a stayed mast. I went through the design spiral on my F40 trimaran project and everything led back to a stayed mast. Carbon is nice but aluminium works out cheaper. I had a friend who built a Schionning cruising cat with a carbon birig wingmasts it worked out quite a bit heavier than expected needed lots of fairing and horrified the mooring contractor who had a hard time setting a mooring that would hold it.

At one stage it broke out my double ended mooring and dragged the mooring blocks upstream before the boat thankfully beached without damage. The owner believed my mooring wasn't strong enough but it had held other cruising cats up to 40' previously with standard rigs with no problems through gales, so make you own mind up on that.

 

[Ilan Voyager]

As Ilan notes it's hard to beat a stayed mast. I went through the design spiral on my F40 trimaran and everything led back to a stayed mast. Carbon is nice but aluminium works out cheaper. I had a friend who built a Schionning cruising cat with a carbon birig wingmasts it worked out quite a bit heavier than expected needed lots of fairing and horrified the mooring contractor who had a hard time setting a mooring that would hold it.

At one stage it broke out my double ended mooring and dragged the mooring blocks upstream before the boat thankfully beached without damage. The owner believed my mooring wasn't strong enough but it had held other cruising cats up to 40' previously with standard rigs with no problems through gales, so make you own mind up on that.

Corley, I forgot the mooring problem. I'm getting old...Or you leave the mast free and it will flap until destruction, or you block it and the whole boat will run like a wild mustang on it's mooring, hitting everything.
Like you I do not see the interest of carbon when alu do the job at a fraction of the cost, unless you are in up to date racer fighting for the world cjampiomship.
I hate to have the mainsail cut and recut, and cut again because the bending of the mast is uncontrollable.
I have seen a rotating unstayed wing mast ending with spreaders....lol. After spending the price of a new Mercedes, the owner of this catamaran, throwed the unstayed rig in the garbage, asked to his old dad some money and installed a used rig and sails. Not glorious but at least he could sail again with some peace in mind.

 

[Mr Efficiency]

Can you gents explain this unstayed mast mooring problem for the uninitiated ?

 

[Corley]

Even without sail up the wingmasts generate a large amount of lift. The greater the chord the larger the problem seems to be. The same sort of problems were experienced with the plywood wingmast on Pacifica another racing cat that is in the same place in strong wind it used to sail on it's mooring so badly it kept wearing out bridles and was always at risk of breaking out the mooring. To solve the problem they just kept adding weight and increasing the size of the bridle and mooring lines until they could hold it still it's quite a sight in a strong wind it still snatches a bit but nothing too serious by comparison.

The mooring ground where my mooring is set is pretty protected but wingmasts stick well above the mangroves and generate a stack of lift in a gale. The owner of the boat in question who was using my mooring now sets his rigs opposed to attempt to stall them and apparently it at least reduces the problem.

Just to illustrate the magnitude of the lift they can generate the racing trimaran Steinlager crossed the Great Australian Bight with not a stitch of sail up just sailing on the wingmast. On a racing trimaran you would be inclined to live with some of the issues for the performance but on a cruising boat I cant see them being anything but a huge pain.

 

[UpOnStands]

Can you gents explain this unstayed mast mooring problem for the uninitiated ?

the problem is actually with wingmasts or strongly elliptical mast that develop "lift". Stayed or unstayed.

Unstayed by itself is not a mooring problem.

 

[Corley]

That however is also is part of the dilemma increasing the section size reduces the amount of material to achieve adequate section stiffness so wingmasts are a better fit for the requirement. If you go for a thin mast it has to be very heavy to get adequate section stiffness. Birig helps with some of the problems as plenty of bury in the hulls for the mast base. Here is a photo of the cat that was on my mooring it has since had the rig height shortened.

 

[UpOnStands]

ah, Bi-Polar.
So far only initial sea trials have been posted to youtube.
Very interested to see how well the new shortened masts power the boat.

Power -- if OP wants a cruiser the design problem is eased significantly. IIRC, Shuttleworth feels that a 2:1 profile is adequate and not aerodynamically active. 10% bury so 10m above deck and 1 m bury. Total weight of 45 kgs?

 

[Mr Efficiency]

the problem is actually with wingmasts or strongly elliptical mast that develop "lift". Stayed or unstayed.

Unstayed by itself is not a mooring problem.

OK, thanks.