Dual lateral rigs

Starting this thread to open a bit of a discussion on better understanding dual lateral rigs. Not all that common but I start seeing them more and not always with one sail feathered, sure rigid wings, like ice yachts outperform boats. I wonder bout racing but cruising as well, masts, sails/wings, rigging, aerodynamics, it’s a broad subject with a lot of aspects and cant find too much on it

Pete Goss http://www.petegoss.com/journey-to-date-team-philips.php had lateral sails on Team Philips but unfortunately the big cat had other problems. Techniques Avancées http://www.ensta.fr/~lecata/ almost as fast as Hydroptere sails a dual lateral rig. http://www.parlier.org/hydraplaneur/index.php and other new cats report advantages with the setup as well.

I wonder bout my ladybird’s design http://www.boatdesign.net/forums/attachment.php?attachmentid=15095&d=1185625951 lateral bi-pod rig without all the rigging versus the straight up sails, all just for fun and http://www.tspeer.com/landyachts/twin/Julian1.html has some good research but still don’t really comprehend what happens aerodynamically when sticking the mastheads together

Side deck stepped trimable tabernacles can keep masts rotateble but what I also like is the possibility to store folded masts out of the way. Sails/wings or combinations thereof should be easier to reef and handle, have lower CE reducing pitching, better stability, lower CF, set a jib windward easy, than again the shorter dual masts miss some of the higher winds and sure have some other shortcomings.

On steering dual lateral soft sails rig I found some pics I saved some time back from a Portugese site I cant find back. Dual straight up free standing or rigged vs bipod, surfsails or wingsails, half solid fwd and soft aft as C class cat miss nylex. Many configurations possible but hard to find info on so maybe this thread may shine some light

Aero and hydrodynamics of sailing from Marchaj mentions that in the fifty’s Barkla came up with a centre based dual rig A shape. Sort of like the Walker wingsail now and illustrates his earlier attempts with a handley-page type vertical lamel type. The book mentions such rigs as untested then though. Who was Barkla and were to find his sail paper? Marchaj’s book is great but are there any newer books on the topic?

 

The material you've presented covers several issues and leaves out some important ones. I think it's best to consider twin rig designs by comparison to a single rig designed to the same requirements. Otherwise you don't really have a basis for understanding the differences.

The A-frame and upright twin rigs are really different animals, with different design objectives. The two reasons for using a upright biplane rig are to get a better match between the loads from the rig and the structure of a catamaran, and to break the sail area into smaller more manageable pieces with a lower center of effort. The main reason for the A-frame rig is to reduce the heeling moment. The A-frame rig also has less induced drag than a singe rig of the same height. The A-frame has as much in common with a single canting rig as it does with the biplane rig.

In my opinion, the A-frame rig is not well suited to soft sails, nor is it a great choice for watercraft. The reason is while there are some modest gains over the single rig when both sails are drawing equally, the A-frame rig really depends on differential sheeting of the sails to realize its benefits. Assuming one sail is operated near maximum lift, reducing the lift on the other sail effectively cants the rig, and when the lift on the opposite sail is zero the A-frame rig is equivalent to a single canted rig. Soft sails are not suitable for this because they luff when sheeted out to far. This limits the benefit one can get, compared to a rigid wings that can be fully feathered or even backwinded (and, yes, best performance may be obtained by backwinding an A-frame sail).

But which sail should be in each role? For sailing on water, the drag penalty for downward force from the rig is high so one would want to be driving with the leeward sail and sheet out the windward sail. But this can be done by mounting the mast foot of a single rig on a track and allowing it to move to leeward. Such a mast would be self-tacking because the loads are in the leeward direction already. But for sailing on land, the penalty for downward force is not so great and the force helps to prevent skidding. Canting a single rig to leeward from the centerline is not as effective as canting to leeward from a windward position. So an A-frame rigid winged landyacht makes sense because sheeting out the leeward wing effectively moves the rig to windward and cants it to leeward. The rigid wing is better able to maintain low drag and be able to stand up to the compression load.

I think the interaction between the sails of a biplane rig have little to do with the boundary layer control of the jib/main interaction. The sails are just too far apart and not positioned correctly for it. So that's a bit of a red herring.

A biplane rig would have less induced drag than a single rig of the same height, but I've not seen a single designer go that route. They all give each individual sail the same aspect ratio as the single rig, making the height 70% of the single rig's. This means at best the biplane rig can equal the induced drag of th single rig, and the interference between the two rigs is adverse.

It's not clear how much standing rigging the biplane rig uses compared to a single rig. For the examples you've shown, the standing rigging is comparable to or greater than a single mast. That adds a significant amount of windage. Other designs, Team Phillips being one, used the catamaran hull to get the bury necessary for a cantilever rig. I think this makes the best sense.

A cantilevered biplane rig on a catamaran with the same height as a single rig would have a sail chord half that of the single rig. With a strong vang, this would mean the sheeting loads would be as little as a quarter of the sheeting load for a single rig. This would make the sails easier to trim. It would also mean almost twice the un-reefablewingmast area - not a trivial consideration for an off-shore racer.

Bottom line is, there's no sense talking about the rig itself. It's only meaningful in the context of the whole design, and when compared to other more conventional alternatives.

 

Tom thanks and here my novice aero dynamicus reply that sees why you consider the A rig more suited for landyachts.
The A rig in its basic form however is as old as the pyramids and attractive to various other design objectives as well,
like striking, storage, rigging, stability and more, provided ofcourse its performing well.

In Marchaj’s book I handed back to the library Barkla questioned his own airflow at the top of his single based A
but that made me think of 3d flows in feathering dual maybe even fwd raked A based systems,
where the windward sail does not so much function as a jib but may give a contribution in cupping adjustable camber
in a than combined, say single wing system

I like your flipover / under / mast base movement idea witch could also set the windward forward as jib in an A
but feel it takes some of the simplicity away as it needs extra rigging and more and still think the extra sail can do good.
The drag penalty for sailing the A rig in water is a point and interesting to calculate as is your math on the vang.
Team Phillips had freestanding masts and if I did read Pete Goss site right he was doing 32 knots on just the masts
so belive there is something to say for a simple striking system. I also remember you and others mentioning sailing a rigid wing
on open water may result in sick sailors, any thoughts on strikable half rigid fwd and soft reefable aft?

Doubt much more lateral cat techno is going to be shared but I still like to get a deeper understanding on all sorts of bi-plane set-ups.
Maybe a little windtunnel testing but first stop over and seek papers at the national air and space laboratory, they may be friendlys ;-)

 

doing some reading i found the purple pics shown above site back
also have some quotes marked from books on the biplane and A rig to scan
a pic of team phillips made me wonder if besides flawed construction wavepiercing was perfect
meanwhile, see my gallery, i imagined a flotation flying soucer crows nest winglet in top
of an A mast where the biplane foils should be at least a chord lenght apart
silence is golden but i'm learning and cant stop dreaming out loud

some biplane links that give a good read
http://fabbrovichyachtdesign.com/en_progetti_ccm_armo.html
http://www.seglermagazin.de/Orma-Termine-Parlier-mischt.3474.0.html
http://www.schionningdesigns.com.au/www/page.cfm?pageID=271
http://www.multihull-maven.com/Boats/Radical_Bay_8000
http://www.desktopaero.com/appliedaero/configuration/multiplesurfaces.html
http://aero.stanford.edu/Reports/VKI_nonplanar_Kroo.pdf
http://www.parlier.org/hydraplaneur/bateau/caracteristiques.php?lang=eng
http://www.wingo.com/multihulls/ensta/
http://forums.boatdesign.net/showthread.php?t=4020
and wonder if the, i think it was $15 contribution to
http://www.dcss.org/ayrs/14B.html
is good for some more up to date insight information

 

There is a nice write up of the A frame pyramid rig in the book High Speed sailing. Pretty interesting stuff. There seems to be a lot of advantages to that rig; I wonder why it isn't more common.

 

good to hear and thanks mentioning rapscallion, my request is out to the library
i read all i can find on bi-rigs and its time getting some numbers to my sketch

 

New bi-rig cat design with cantilevered masts

Sorry Yipster, I did not intend to attempt t Hijack your thread, so have moved the whole lot

Alan

 

YA,

the nice thing about the book is the inclusion of equations. Lots of equations. It's a great book. I had to buy it.

 

I've looked at the A-frame rig a bit. You can find the predicted aerodynamic characteristics of a wide range of different geometric variations here.

If you compare the A-frame rig with a single sail of the same height, the A-frame has better performance once the wind increases to the point at which the craft becomes stability limited with regard to how much sail it can carry. However, it's not necessarily well suited for sailing on water compared to sailing on land.

That's because you have to choose between producing an upward force from the rig without substantially reducing the heeling moment, vs getting a reduction in heeling moment accompanied by a downward force from the rig. A landsailor can actually benefit from the downward force, but the watercraft cannot.

Of course, most people do not compare twin-sail rigs (including A-frames) on the basis of equal height. They tend to keep the panel aspect ratio similar to the single sail rig and go for a reduction in height. If you do that, there may not be any performance advantages at all.

 

That link looks interesting. The A frame rig discussed in the book, (which is my only source of info on the subject) is a bit different. The span between the two sails is equal to the chord length all along the wing itself. If I remember right, one of the advantages was the lower center of effort for a given amount of sail area, I think it was 1/3 lower. The rig was also supposed to generate more lift because you could carry more sail area longer - but that seems to echo what you were saying.

It also was supposed to be easier to handle, one sheet for the whole rig, and no winches even for larger boats. The rig itself it also self tensioning. The hull of the boat does not have to take tension from the rig - so the boat could be lighter - which was one of his big selling points.