A frame mast concept

[Norman Brown]

Amoco Procyon was a interesting experiment. But as a new concept was not the best or common sence answer for a 'A' frame mast system. The spars were not to correct beam theory so were over weight. On a correctly sparred system they would taper at both ends of each mast (windage down). No heavy system is neaded for chainplates for lower shrouds as they are gone. Lighter compression plates under the masts. No mast compression post (all weight !)The 'A' frame is scantled lighter as it is stiffer as 2 beems are cross joined. If you count it all up with loosing so much steel wire (sg. of 7.2). With a more efficient main I would like to know what's bad !?
Norman

[tspeer]

Amoco Procyon was a interesting experiment. But as a new concept was not the best or common sence answer for a 'A' frame mast system. The spars were not to correct beam theory so were over weight. On a correctly sparred system they would taper at both ends of each mast (windage down). No heavy system is neaded for chainplates for lower shrouds as they are gone. Lighter compression plates under the masts. No mast compression post (all weight !)The 'A' frame is scantled lighter as it is stiffer as 2 beems are cross joined. If you count it all up with loosing so much steel wire (sg. of 7.2). With a more efficient main I would like to know what's bad !?
Norman


The main and jib help to reduce the drag of the mast. A Karman vortex street cannot form behind the mast because the sail acts like a splitter plate. The jib reduces the angle of attack of the mast, changing the apparent wind direction to coming more from ahead, and there can be a favorable pressure gradient toward the jib leech that helps to stabilize and reduce the lee-side separation bubble behind the mast. The rounded leading edge of the mast also provides a generous front-facing area for leading edge suction.

The exposed A-frame mast gets none of these benefits. The mast legs are totally bluff bodies that get more of the full variation in apparent wind direction. The mainsail has a thin leading edge with very little area for leading edge suction. These factors more than make up for the reduction in windage from not having shrouds.

[alan white]

I think the A frame has a chance with a rig where the main working plan is in the mains'l. The two shorter masts angle back enough to allow a vertical mains'l luff to backstay the jibstay.
This allows the omission of any backstay to the stern. Now you can carry a full roach main on a foil gunter yard, so there's a clean leading edge all the way to the top.
The two masts are now far shorter (about 33%, say) and the overall rig windage is improved, as the "center of parasitic drag" is far lower.
If a rig like that performed well enough, it might well be the perfect rig for lowering in minutes for bridges, maintainence, or hauling.

[Norman Brown]

Tom Speer's coment on the sail acting as a splitter plate behind the mast is right. But only part of the answer as vortice's are induced and do spoil the entry of the wind.
The mast legs must be small foil shaped. Circular section will induce drag. Too large a foil and she will sail to windward and have problems in high winds. So correct calc's on the beams and shapes is critical.
I have found a small article on a yacht called 'Kolika' Unfortunatly little info on her sailing capabilities. Does any one know more about this ?
Norman Brown

[Squidly-Diddly]

googling the name didn't bring up anything.

[Paul Scott]

http://www.tspeer.com/landyachts/twin/top.jpg

One direction the A frame idea could lead for sailboats, at least, would be something like Tom's sketch (link above), and designing the A frame for (say) 2 single foiled 3' chords for 20+ K, then use the 2 3' chords as wingmasts for fully battened mainsails (hoisted on them) for 8-20K, and then put a free flying jib in between them (in front of them?) for the light stuff, and a variety of (certainly interesting) downwind sails when needed. The tension for code zeroes might be a bit easier to achieve?
Might be a bit of a nightmare at mooring, but hey, no pain, no gain...

Paul

[Fanie]

got any pics of this A-frame?

Look under aft mast.

[Norman Brown]

For a look at a new type 'A'frame. (Double wishbone 'A' frame) Go to the boat design gallery and put. Lionhart. (Lionhart of Hartlepool). It takes some working out !

[gggGuest]

Tom Speer's coment on the sail acting as a splitter plate behind the mast is right. But only part of the answer as vortice's are induced and do spoil the entry of the wind.

Have you read Mikko Brummers CFD piece on rig behaviour here? You probably should.

http://www.wb-sails.fi/news/Ad_aerodynamics

It seems to me that the more we learn about what's going on the better a conventional round spar looks, and the advantage to be gained by using anything less conventional looks smaller and smaller. As a long standing enthusiast for the idea of using over-rotating wing masts I'm not entirely comfortable with this, but it does help explain why they've so rarely seemed to work as well in practice as I've thought they ought to.

[Paul Scott]

I was obsessing about this a while ago- some stuff I found interesting

"Reduction of fluid forces acting on a single circular cylinder and two circular cylinders by using tripping rods" Mahmbub, Sakamoto and Moriya

"Flat plate drag reduction by turbulence manipulation" Narasimha and Sreenivasan

"fluid mechanical issues of the flow around a bluff body" Akhilesh - this one is a power point presentation, so easiest

Paul

[fishwics]

some stuff I found interesting

"Reduction of fluid forces acting on a single circular cylinder and two circular cylinders by using tripping rods" Mahmbub, Sakamoto and Moriya

"Flat plate drag reduction by turbulence manipulation" Narasimha and Sreenivasan

"fluid mechanical issues of the flow around a bluff body" Akhilesh - this one is a power point presentation, so easiest

URLs? or are they paper-only
Cheers
Simon

[Paul Scott]

[QUOTE=Paul Scott;259603]I was obsessing about this a while ago- some stuff I found interesting

"Reduction of fluid forces acting on a single circular cylinder and two circular cylinders by using tripping rods" Mahmbub, Sakamoto and Moriya

http://cat.inist.fr?/aModele=afficheN&cpsidt=15272519

"Flat plate drag reduction by turbulence manipulation" Narasimha and Sreenivasan

http://www.springerlink.com/content/a7514400p341477g/

"fluid mechanical issues of the flow around a bluff body" Akhilesh - this one is a power point presentation, so easiest

my printout of this one does not have the web address on it, but I'll try to get it.



Paul

[Paul Scott]

"fluid mechanical issues of the flow around a bluff body" Akhilesh - this one is a power point presentation, so easiest to look at


http://www.leb.eei.uni-erlangen.de/winterakademie/2007/results/content/course01/pdf/0116.pdf

[Norman Brown]

The unstable vortice's of a round body are avoided by having a egg or slight wing form set of masts. This drops the unstable element. Cross spars are made smaller and flatter. It has to be remembered that a standard rig has all the wire holding it up that has exactly this problem. Listen to the rigs of yachts in harbour during a strong wind, Oscilating. With a 'A' frame most of this is gone.:cool:

[Russell_Miller]

It'd be interesting to conduct the experiment again with a skin around the frame to help the aerodynamics out. When people home build carbon spars they'll build round sections (cause its easiest) and then add a better leading edge from a less expensive material that won't affect the spars bend characteristics.

[Norman Brown]

The new masts (inverted whishbones set as 'A' frames) on my boat are slight wing form made from a former as clam shells. Then externaly wrapped in carbon. A drawing was posted in feb. if you look up Lionhart.

[brian eiland]

Amoco Procyon was a interesting experiment.
Did you happen to visit this subject thread,

http://www.boatdesign.net/forums/sailboats/procyon-project-bold-experiment-10771.html

[Norman Brown]

Yep. Got all that Brian. Could do with more from the people who sailed her as a comparison for windward performance. But I am sold on the idea and the figures look good so the masts are being built at the moment. The hull is going in the water in 3 weeks time. All I want now is a morgage on the morgage on the morgage on the morgage........ I think you get the picture. Sailing will not take place until late in the year.

[brian eiland]

If I remember correctly there are some sailing comments within that thread by Olaf Harken himself, and his captain ??

[Norman Brown]

Yes. I have been through the threads. Olaf has a few words but it does not do justice to the boat. A sailing comparison with other yachts of standard rig would be a useful tool. A polar diagram. What the feel of the boat was like in both light and heavy air's. Handling in a gale. As a experiment all sorts of info must have been put together. Who has it ! ? Randy West would be interesting to talk to !:cool:

[tspeer]

It'd be interesting to conduct the experiment again with a skin around the frame to help the aerodynamics out. When people home build carbon spars they'll build round sections (cause its easiest) and then add a better leading edge from a less expensive material that won't affect the spars bend characteristics.

What apparent wind angle will the skin be based upon? I believe this question, more than simple easy of manufacture, is what drives round sections.

[Russell_Miller]

Tspeer

It all depends on the type of boat and what you reckon the upwind speed you're designing for will be. It really wouldn't matter what the shape of the skin is, as long as you're ok with the aerodynamics of it i guess, i think anything would help to keep the advantages of an "a-frame" type mast and address the disadvantages.

[CT 249]

Yes. I have been through the threads. Olaf has a few words but it does not do justice to the boat. A sailing comparison with other yachts of standard rig would be a useful tool. A polar diagram. What the feel of the boat was like in both light and heavy air's. Handling in a gale. As a experiment all sorts of info must have been put together. Who has it ! ? Randy West would be interesting to talk to !:cool:

I saw some results years ago that did not show the speed in a flattering light. The only "outside" perspective I can see on the net is this one;

"With all respect to Olaf and Harken's far-sighted
Procyon project I recall seeing that boat from the Pied Piper's rail, Dick
Jennings' six-time Chicago Mac line honors holding Santa Cruz 70. We were
sailing off Milwaukee before the Queen's Cup and saw the intriguing
Procyon. Pied Piper hardened up and closed with them on a parallel upwind
course. After a few minutes sailing slowly backwards, Procyon broke off
this interesting comparison. We did get a laugh at their course change. I
don't ever recall completing a port-port race and finding Procyon in and
tied up to the bar ahead of us. Maybe they hadn't gotten their numbers
worked out yet. It was an interesting collection of ideas."

Interesting that the claimed 15% increase in upwind speed certainly didn't work out. It seems that the reality fits closer to the views demonstrated by wb sails and Tom Speer, and that a single mast is better.

Interesting too that the world's fastest boat; the world's fastest windsurfer; the world's fastest offshore yachts; the world's fastest dinghy and the world's fastest skiff all have big mains and all bar one (the very specialised MI) have a mast in front of that big main. The "no mast" idea has been around for many decades and it has yet to be successful.

As Gggguest says, the interesting thing about wing masts is that they generally don't seem to provide anything like the performance advantage in reality that they do in theory. They have, after all, been around since the 1930s and in all that time, their success has been pretty much limited to a few cat classes.

When theory (or at least a theory held by some) is disproven time and time again by practice, maybe the theory is wrong?

[Norman Brown]

Maybe she just did not perform as a hull. Info from people who sailed her would be interesting. I am comitted :o ( I should be !) to this type of rig.
It offers me what I want from the boat.

[Brent Swain]

There is an aluminium fishboat on the BC coast, which as an A frame mast with a roller furling main , vertical betwen the frames, and a roller furling jib foreward. Called "George" something. Looks slick.
Brent

[brian eiland]

Quite a few more bi-podded, A-frame, wishbone mast discussions here:

http://www.boatdesign.net/forums/boat-design/wishbone-sailing-rig-1999-3.html

[Norman Brown]

Now the interesting point is: Should the wing shapes point outwards or inwards. when going to windward the most exposed mast is the windward so they should have the pressure drop facing outwards inorder to pull the boat upright.
But the fastest air is coming off the genoa on the down wind side of the boat. So the pressure drop should face inwards in order to pull the boat upright.
Ho. It's a quandry !

[Number One]

Hi, my name is Gerhard. Iam living in Cape Town at the moment, but i am an austrian. Yes austrian - not australian. I designed some years ago for me and my wife a "easy to use" conzept for a 50ft Cat. Because i like fast sailing, and me wife is worried about that, i must find a solution. It must be possible to sail alone with the boat, to reef the sails in all condition and al courses witout stress. I think you know what I mean. The solution war for me was the A frame Mast. I made it - together wit a spezial hull design, we call it ULDP hull (ultra low draft performance) with only aprox 800mm draft. Now after tree years, i must say, it was the best idea of my boatbuilding life. The idea war so god that I must start two Years ago with a prof. boatbuliding here in SA.
You ca find some arguments for the A frame mast on my Web site; www.sail-the-difference.com . If you have some questions to the mast or the concept, ask me.
I also sailed with some editor from sailing magazine in europe, but they didnt wrote properly about the concept. An editor said to me behind the hand. "If we write the reality about your performance, then we get a Problem with the big companies in the Multihull industrie, which pay every month a lot of advertising!?That was the reason that we sailed a race some weeks ago. With a skipper which learnd to sail two years ogo with the "number One" . It was also his first race! The cat class was easily won by Number One. In the tree longer Distances(all together about 9 hours) she was 1h24 min in front of the next cat. Much more important for me was, Number One was able to tack better than many of the fast monohulls taking part of the race. Reaching in 18 Knots of true wind she achieved 11-12 knots up wind and whilst beating her VMG was 6.5 Knot!!! That with a 17,3m Mast with 90m²sailaera and no daggerboard! Best regards Gerhard

[Norman Brown]

Thanks very much for that info. The pic's don't realy show the size and details of your rig. Have you any ?
I am glad to here from someone who has actualy done this instead of pontificating.
Have you come across any mono hulls with this rig ?

[brian eiland]

Hi, my name is Gerhard. I am living in Cape Town at the moment, but I am an Austrian.

The idea war so good that I must start two years ago with a prof. boatbuliding here in SA.

You can find some arguments for the A frame mast on my Web site; www.sail-the-difference.com . Gerhard
I believe I've referenced your website in several of my other discussions on this forum. You might consider posting your observations over on one of these other discussions where there are a greater number of folks that have made contributions to the subject matter; ie,
http://www.boatdesign.net/forums/boat-design/wishbone-sailing-rig-1999.html

...and the reference to SMG
http://www.boatdesign.net/forums/boat-design/wishbone-sailing-rig-1999-8.html#post275713

...you might have been referenced under 'boomless' subject as well



But I do have one question for you. Why did you find it necessary to have a forward cockpit now that you have a furling mainsail??

[yipster]

compliments on your number one A boat we all gazed over before here
ever considered lateral sails on the rig for your cat?

[Manie B]

Hi Gerhardt

it sure looks very good

best of luck with the new venture

obviously a HUGE investment of time - money - and effort