Dynarig system

[Miquel Viver]

I'm a student of navigation on the university of Barcelona (Spain)and I need information about dynarig.
After two weeks I found some articles but there are some things that i can't understand.
First of all, how much efficient is the dynarig than the tradicional sails?
What is the power of the motors of each mast? They are electric motors?
And the last one, is true that the mast can resist the wind without any rope between the top of the masts or the deck?¿ I can't understan how the base of the mast can resist force without break.

Sorry for my mistakes but I need to improve my english level. ejjeje

Thanks for your answers.

PD: if there are somebody who speak spanish and know about it, can send me a private message.

[Eric Sponberg]

The Dynarig as on Maltese Falcon has got to be an engineering marvel (if not a nightmare, depending on your point of view). Certainly, a lot of thought and calculation went into its design. I do not have any inside knowledge of the rig or the yacht, and I have no notions about whether or not it is more efficient than a conventional. One would have to look at model test results or comparative CFD calculations to give an opinion. I have not seen or heard anyone discuss that in engineering detail.

But I want to speak to the idea of the free-standing masts. Think of a flagpole--it is the same engineering model, a cantilever beam. Flagpoles typically don't fall over, so neither do free-standing masts. Obviously, the strength of the mast itself is great enough to withstand the loads from the wind, and the stiffness is such that it will not bend too much. The support for the mast is the hull girder (hull and deck) which floats freely in the sea. The stability of the boat limits the load on the mast. If the load from the wind is very high, the boat will heel over until the righting moment equals the heeling moment. The boat sails at the resulting heel angle. Such righting moment loads are easily calculated. Also, it is easy to calculate the strength and stiffness required for the mast which are dependent on the size and shape of the mast section and the materials from which it is made.

In free-standing rig design, carbon fiber is the best choice of material because it is very stronq, quite stiff, and lightweight. It is also fairly expensive, but is used increasingly in rig design of all types. Maltese Falcon's masts are made of carbon fiber.

Eric

[marshmat]

Hi Miquel,

Sailors are an inherently conservative lot. That's why we still have wires holding masts up- it's always been that way, the racing rules assume you have shrouds and stays, so everyone designs skinny masts that need a quarter-mile of spaghetti to keep them up.

Eric's a bit of a rebel this way, having designed a number of free-standing rigs that, from what I've heard, did pretty well. I'm surprised he didn't mention this, so I will: Go to your airport. Look at whatever jet happens to be taxiing out to the runway. If it's an Airbus 320, it'll weigh around 77 tonnes at takeoff and be supported by a wing 34 metres wide. Turn that on its side and the structural mechanics isn't much different from a sailboat with a 17-metre freestanding mast. (Actually, the boat has it a heck of a lot easier, as far as loads are concerned- even in a storm, its mast is dealing with only a tiny fraction of the load the plane's wing is sustaining.) When was the last time you saw a jetliner with wires holding the wings to the belly?

[Zilver]

Here are two articles about the rig. You might already have found them....


http://www.araneus.it/PDFs/Boat%20In...e%20Falcon.pdf

and

http://www.waddiloveyachts.com/maltesefalcon.pdf

Cheers, Hans

[ancient kayaker]

The Dynarig makes me think of the junk rig.

Matt, I would rather design the plane wing than the sail, it does not have to handle wind from any direction, just an alpha range of a few degrees. Outside of that, it's dead and the pilot gets the blame.

[tom28571]

On a large boat, I'd guess that the Dynarig's main appeal is that it reduces the number of expensive crew needed. Spend a million and get rid of a cheap crewman. Looks very mechanically complex to me but that's probably my curmudgeonly nature. Kind of how computers have reduced the workload and simplified our lives.

[dskira]

The Dyna rig of the Maltese Falcon can't twist like the real square rig. The twisting make all the difference. The M.F. seams to heel a lot with rather little wind. A twinsted square sail will adapt better to a wide range of wind.
I find the Dyna rig very stiff, without much way to play with.
But free standing mast is surely the way to go, and far less strainuous for the hull. But that is my own opinion!

[ancient kayaker]

The Maltese Falcon is undoubtedly a remarkable craft, but it's hardly new. I wonder what concept it would have if it were being built today. I'm guessing a wave-piercing catamaran with rotating sectional wing sails, which would provide serious beat-the-wind speed with reduced heeling.

[Eric Sponberg]

Originally Posted by ancient kayaker

The Maltese Falcon is undoubtedly a remarkable craft, but it's hardly new. I wonder what concept it would have if it were being built today. I'm guessing a wave-piercing catamaran with rotating sectional wing sails, which would provide serious beat-the-wind speed with reduced heeling.

Maltese Falcon is brand new, just over two years since launch. Although the concept for the rig goes back to the 1960s, MF's is the biggest and most advanced version that has ever been built, to my knowledge. The Walker Wingsail trimaran with rotating rigid wingsails was built about 10-15 years ago and was not much of a success. Alternatively, the Little America's Cup is probably the most visible arena for advance rigid wing and multihull design. But such rigs as those, which are not reefable, would be most impractical on yachts, which typically cater to luxurious lifestyles, and that means carrying a lot of weight. The LAC boats are exceedingly lightweight. Technological advances are everywhere, and much depends on the whims of the owner and the size of his wallet as to which one to follow.

Eric

[Miquel Viver]

Thanks for our answers.

Another question... are more cheaper the motor to rotate the mast than the motor for a propeller?

It is posible to use this sistem to reduce the fueloil on the shipping industry.
What do you thing about it?
Do you imagine a 300 lenght ship with four mast?

[ancient kayaker]

Originally Posted by Eric Sponberg

...advance rigid wing ... But such rigs as those, which are not reefable ...
Eric

Since a rigid wing can be allowed to feather with very little drag, is it generally necessary to reef it? Certainly for a hurricane or in port but one gets notice if such events. The MF is indeed a special craft, it's nice to see outside-of-the-box thinking.

[Stumble]

Miquel,

Using the sails is much cheaper than turning an engine, and yes the rig from the MF could be used on shipping vessels. However it would require a redisign of the vessels and the way they carry cargo, since current shipping vessels are not designed to heel to any significant degree.

There are some prototype applications of sails on shipping vessels, that have been very sucessfull so far. However they are using Kites not rigs since it allows the sail to be flown much higher, entering the much stronger and steadier winds at over 500 feet.

[Tcubed]

<<<<<<The Dyna rig of the Maltese Falcon can't twist like the real square rig.>>>>>>>

Hooray for someone who noticed exactly my first objection to the M.F. rig!

Mix wind that varies in strength with height, with a rig that moves forward all as one piece and you get twisted apparent wind.

All sails must twist correspondingly along their height to present the same angle of attack at each section to the twisted apparent wind. In the tea clippers and other square rigged ships great care was taken to adjust each and every pair of braces to get just the right amount of twist, and rightly so.

The dynarig is a neat method of drastically reducing the manpower required for a square rig, at the expense of extra mechanical complication and obligatory power assist (fuel burning) but that is not my objection. My objection to it is that the way it is set up does not allow for twist, which is a serious blow to this rig's hopes of efficiency. Were it not for this one crucial detail it would in fact be very efficient.

[Eric Sponberg]

Miguel--The drawback with multiple masts, particularly when sailing on the wind, is that each mast/sail forward creates a downwash to the next mast/sail aft. Usually, by the third mast, there is so much downwash and disturbance in the airflow that the sail cannot draw lift well and its efficiency is greatly reduced. Adding a fourth mast on a hull long enough would not necessarily be a feasible move.

I think the record for number of masts is the Thomas W. Lawson, a seven-masted schooner. She was a commercial vessel, and for one reason or another, was not a successful ship.

Ancient K--Unfortunately, you cannot let a rigid wing rig weathervane while sitting on a free-floating boat, whether anchored or tied to a dock. In any kind of wind, a weathervaning rigid rig will start to oscillate to alternating angles of attack, first to one side, then the other. This sets up a rolling motion that gradually increases to a dangerous amount as the rig changes lift from side to side. I heard of one instance of a 36' sailing yacht with wingmast rig (soft sail, which was stowed) almost capsize at her anchor because the owner thought that weathervaning would be the most stable way to leave the boat. He almost lost the boat. Another was a similar experience on a 25'er with quite a large wingmast that sailed all around her mooring at about 4 knots with a weathervaned mast. A similar experience occured with a wingmasted cat ketch of about 37' that would sail around her anchor if the wingmasts were left to weathervane.

What you have to do is tie the masts in position so that they don't move. On a single-masted boat, set the mast at an angle to centerline of at least 45 degrees so that the mast naturally stalls. On a cat ketch, set the forward mast 45 degrees one way and the after mast 45 degrees the other way. The boat will sit absolutely still at anchor. In fact, other boats in the anchorage, from my experience, will swing more.

So on a rigid, non-reefable wing, you are stuck with a lot of lift and windage in the air. This is totally impractical. In the 1988 Americas Cup, when Dennis Conner raced his rigid wing 60' catamaran against the 90' New Zealand maxi, his crew had to take the whole boat out of the water and lay it on its side when they were done racing--one ama on the ground, the tip of the rigid wingmast on the ground, and the other ama sticking up in the air. That is the only way they could keep control of the boat when not using it.

Eric

[ancient kayaker]

Eric: good point about the oscillation. I actually made a kite once that was shaped like a vertical wing; it worked by oscillating rapidly sideways. Not very efficient but it fascinated onlookers.

I was thinking of the type of wingsail that has a stabiliser mounted a short distance behind to control the angle of attack (alpha). These wingsails pivot freely and are not constrained by sheets. The alpha is controlled automatically and they do not oscillate. The angle of the stabiliser is reversed for tacking, and it can be set in "neutral" for feathering or adjusted to increase or decrease lift. A number of these could be arranged up the mast so each could find its own best alpha for optimum "twist" per Tcubed comments. A control would be needed for each stabiliser but the amount of power is negligible as the stabiliser itself does the work of controlling the wing and it could be pivoted at its center of lift. After all, before servos and autopilots were introduced airplanes weighing many tonnes were controlled for hours by the limited strength of the pilot's arms.

Since thrust can be changed from side to side, it should also be feasible to steer a slow-moving multimast vessel using the power of the wingsails.

Having said all that, it would be a sensible precaution before a storm or after mooring to lower some or all of them. If that engineering problem can be solved I think the idea has merit, at least for a primarily wind-powered craft if not as an auxiliary propulsion to reduce fuel consumption.