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Old 20-05-2008, 18:34   #136
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No thanks, Kevin. Declare yourself the victor by default. But brush up on your reading skills!
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Old 21-05-2008, 01:13   #137
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Ok, on the paint issue, does anyone know how the manufacturers of the Hugo boss Racing boat overcame the issues about having a black hull or does that have the issues and its just because the boat will only have a limited life that they kept the colour.

The loads on a bipod mast are smaller than that of a single mast, that should be basic bending of beams knowledge. The load won't be half that of a single mast but it will be lower. Also the loads on the bulkhead will be lower as a result.

Windage, I will agree that the windage will be higher, I wouldn't think that it would be much higher tho as due to the load being split between 2 masts the mast section can be smaller, also the sail will be more efficient due to not having a mast infront of it.

Please bear in mind this is to be a practical sail boat, I'm not after excessive speed, although it would be nice.

I am not ignoring peoples comments but I'm looking into their points further and then look into ways of either overcoming them or if needs be put the idea back on the shelf for someone else to try.

This boat is not going to get built soon, just don't have the time, money or space to do it. I look at spending at least a year finishing the design of and will then look at making scale models before finally making the actual thing.
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Old 21-05-2008, 05:59   #138
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Originally Posted by sandy daugherty View Post
No thanks, Kevin. Declare yourself the victor by default. But brush up on your reading skills!
Oh Sandy, it's not about victory. You made, what I believed to be, baseless comments - I'm just looking for the reasoning behind them. At least explain how an A-frame "triangulates excessive loads"? And if you think I've misread you, then please elucidate!


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Old 21-05-2008, 09:54   #139
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Catamarans are not rigid structures. Encountering waves or gusty winds, one bow will imperceptably lift before the other. One stern will drop more. The resulting flex is fully accomodated in a tripod rig or a conventional forestay-backstay / upper and lower shroud system. The A frame will undergo exceptional loads because it triagulates this distortion. The loads become massive and are infinitely repeated. You will either have to build in the rigidity of a concrete blockhouse, or accomodate (and predict) the flexibility required with shock absorbers and torsion bars. Its not impossible, its impracticable.
Sandy,

Take this with a grain of salt since I am no naval architect, but if an A-frame mast was set on the extremities of the main crossbeam/bulkhead (as the SMG boat) then I would think that the twisting forces would be negligable since the beam will be rigid.

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Old 21-05-2008, 10:48   #140
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My adult life has been spent investigating fatal accidents; Airplanes, boats, even a spaceship; the Challenger! I'm retired from the NTSB. Eighty percent of all of those accidents were caused by bad decisions. The rest were a lot of fun to figure out.
I don't want to discourage anyone from exploring beyond the walls of convention. Even Mother Nature does it! I'm fortunate to live within a few hours drive of some of the greatest old boat yards and bone yards, where old dreams lie abandoned, rotting. They are witness to our genetic compulsion to "do it my way." I study them. There are ferrocement junks with circles of rusted rebar where one batch of concrete hardened before the next could be mixed. Steel hulls with cracked chines where an over-heated interior bulkhead contracted and wracked too many panels to be fixed without starting over. And yes, a couple of A frame rigs. I know, at a visceral level, these could be a thing of beauty. They solve the complex engineering challenge of designing a bulkhead to carry the ten to thirty ton compression load of a mast supported in mid air. They open up interior space and deck space right where the helmsman should be. They permit creative new approaches to converting wind across the bow to miles beneath the keels.
I omitted an important point in my previous, excessively long treatise. A frames can also eliminate the structural challenge of providing a centerline forestay that needs to originate in midair, be under so much tension that the sail attached to it doesn't bow to leaward to varying degrees, to be anchored aft in an equally robust structure. That can be accomplished by staying the structure to each bow and stern, using existing structural rigidity. Picture two beams or logs, with cross beams lashed as tight as possible. Lift one bow, and the other is relatively undisturbed. Perfect rigidity is not a reasonable expectation, which is OK, the steady hull continues through the water in something like equilibrium rather than trashing its standing waves and slowing down. Now stand an A frame on this raft, supporting the feet on the logs where there is already a lot of strength, and keep it upright with a rope from the top to each bow and stern. This gives you more things to hang sails on, and some very interesting new aerodynamic considerations. The most interesting of these is about the spanwise flow from three pyramid sails converging at the apex. Can it be converted to miles behind you?
Gone are the huge engineering challenges of building three truss bridges or cantilevers to support a conventional fore-and-aft sailplan, whose principle reccommendation is "that's what we do on half-a-marans!"
One nagging problem remains: this structure is now fully triangulated. Its a pyramid. A little wave goes under the port bow, trying to lift it. The port stern goes down because it hinges at the mast base on that side. This loads up the port backstay, jerking the apex aft and to port, snapping the starboard forestay, trying to lift the starboard bow, depressing the starboard stern, pulling the starboard backstay which cracks the port forestay like a whip, and starts all over again. As the second lookout on the Titanic is reported to have said, "this could be bad."
Putting this A frame on a monohull or trimaran accomplished only one thing. It eliminated the side stays. Instead of a single stick (or seven) that only had to be kept in column to hold up for a long time, you've created a complicated engineering challenge that costs more than twice as much to build, can't be found on the shelves of your local boat builder's super store, and created twin towers that must not only deal with the local breezes, but with the disturbances created by the other tower. Putting this A frame on a catamaran is even harder, because there's nothing but air where you would want to anchor that whole fore-and-aft thing!
An aside: A sail, like a wing, benefits from a thick cross section at the leading edge. A wingsail is more efficient than a single surfaced foil because the air going over the outside of the curve has farther to go than the air on the inside, so it goes faster there, creating a greater pressure differential. A mast is not a bad thing if it has a foil shape and pivots to form the best shape. And the air behind a fixed mast is not dead. Its still working, just not as well.
History speaks to those who chose not to repeat it. The cantilever wing on airplanes in the 1930's was a major breakthrough. The flying wires and struts (the masts and shrouds) of earlier aircraft created drag that increased exponentially with wind speed and circumference (sort of.) so fewer wires, further apart meant more speed, less gas, smaller tanks, more speed, more passengers or bombs, etc.. The closer together these wires were, the greater the drag. Hold your hand out the window at fifty miles per hour with your fingers closed. Now open your fingers wide. the same frontal area has more drag because of the interaction of the flow around each obstruction. Lesson: keep the aerodynamic complexity of your rig to a minimum. It is what moves you, and great care reaps small but valuable rewards.
But the A frame rig still appeals to me; I'll keep doodling, and I hope someone solves this conundrum.
Now about black boats: Thanks for the opportunity to have fun with this one, Steven. Paint it any color YOU want, and repaint it whenever YOU want. Or figure out a way to marinize that digital billboard and have it change colors continuously, like an octopus in heat! (now there is a creative divergence from Mother Nature's conventional practices!) I apologize for the Winebago crack.
Kerry: Reread everything I wrote after "More suggestions, serious ones this time." I'm not demanding anything; I'm asking for solutions, inspiration, and serendipity. The first is about the mainsail. It doesn't have to hang on a rigid luff. In fact, It doesn't have to stay in the middle of the boat all the time. You could have two or three set aside for various wind conditions or combinations, that only need to be raised with a single halyard, flying free. By letting the boom pivot forward of the CEP, it could be self balancing, permitting a single sheet to control it. It could be set close to perpendicular to the longitudinal axis of the boat in a run, or even used to back the boat. And who says you couldn't run a sail up each leg of the A frame?
I'm very serious about regenerating electricity. My present boat is outboard powered, and the gear reduction of the lower ends, combined with the the prop being optimized for thrust rather than being driven, means I can't experiment with regeneration (and still have something to sail at the same time.) Somebody get to work on this; I've got to get that 700# generator out of my aft stateroom!
HenryV: I am very excited about the SMG A frame cat. The legs are set inboard enough to permit easy access fore and aft. The rig looks great. But I was crushed to see that they chose to do without boards or even mini keels. Bummer! History spoke with the Catalac 42's.
I don't see you on the PDQ Forum. I had a 32 (hull #30) for several years. It was a very fine sailing boat, and one I would have recommended to Steven.
Finally: has everybody noticed that there aren't a lot of little Procyons running around local hangouts?
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Old 21-05-2008, 11:14   #141
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Sandy,

That is good stuff. Keep it coming!
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Old 21-05-2008, 18:34   #142
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Originally Posted by sandy daugherty View Post
One nagging problem remains: this structure is now fully triangulated. Its a pyramid. A little wave goes under the port bow, trying to lift it. The port stern goes down because it hinges at the mast base on that side. This loads up the port backstay, jerking the apex aft and to port, snapping the starboard forestay, trying to lift the starboard bow, depressing the starboard stern, pulling the starboard backstay which cracks the port forestay like a whip, and starts all over again. As the second lookout on the Titanic is reported to have said, "this could be bad."
Putting this A frame on a monohull or trimaran accomplished only one thing. It eliminated the side stays. Instead of a single stick (or seven) that only had to be kept in column to hold up for a long time, you've created a complicated engineering challenge that costs more than twice as much to build, can't be found on the shelves of your local boat builder's super store, and created twin towers that must not only deal with the local breezes, but with the disturbances created by the other tower. Putting this A frame on a catamaran is even harder, because there's nothing but air where you would want to anchor that whole fore-and-aft thing!
I fail to see how you don't consider a conventional rig to be a pyramid also? Assume that your catamaran does twist, that twisting will cause one shroud/stay axis to be tensioned and the opposite axis to relax. That tension translates into compression of the mast. The A-frame does more than remove the shrouds - it removes that stick down the centre. No stick down the centre; no compressive stress on the structure. With the A-frame, when the cat twists, the rig rotates, so there is no loading and unloading of stays.

Quote:
An aside: A sail, like a wing, benefits from a thick cross section at the leading edge. A wingsail is more efficient than a single surfaced foil because the air going over the outside of the curve has farther to go than the air on the inside, so it goes faster there, creating a greater pressure differential. A mast is not a bad thing if it has a foil shape and pivots to form the best shape. And the air behind a fixed mast is not dead. Its still working, just not as well.
A sail does not necessarily benefit from a thick cross-section at the leading edge. If the mast/sail combination could have an aerofoil-shaped cross-section then you would have ideal lift-generation with minimal turbulence. As it stands, the mast creates a large area of turbulence behind it. I'm sure you'll agree that most planes are designed with full aerofoils, rather than the mast and sail profile of Lilienthal's gliders.

Quote:
Finally: has everybody noticed that there aren't a lot of little Procyons running around local hangouts?
Like most concept cars, Procyon's many innovations will likely never see the light of day. That's not to say that the ideas don't have merit. As you can see in the Procyon link, the rig was envisioned with specific qualities that could be considered ideal for a cruiser. The world does not always beat a path to your door if you invent a better mousetrap - pity.


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Old 21-05-2008, 18:40   #143
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How about using the A frame with this aft-rig?

What about a tripod?

Sail Propulsion - Revisiting a Mast-Aft Sailing Rig
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Old 21-05-2008, 19:18   #144
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No thanks, Kevin. Declare yourself the victor by default. But brush up on your reading skills!
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Old 21-05-2008, 21:30   #145
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Wingsails and whatnot

"a conventional fore-and-aft sailplan, whose principle recommendation is 'that's what we do on half-a-marans!'...A sail, like a wing, benefits from a thick cross section at the leading edge. A wingsail is more efficient than a single surfaced foil because the air going over the outside of the curve has farther to go than the air on the inside, so it goes faster there, creating a greater pressure differential. A mast is not a bad thing if it has a foil shape and pivots to form the best shape....The cantilever wing on airplanes in the 1930's was a major breakthrough. The flying wires and struts (the masts and shrouds) of earlier aircraft created drag that increased exponentially with wind speed and circumference (sort of.) so fewer wires....the mainsail. It doesn't have to hang on a rigid luff. In fact, It doesn't have to stay in the middle of the boat all the time". This is all part of the chain of reasoning that led to the rig you will find on my website-
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Old 27-06-2008, 23:14   #146
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Sail Aerodynamics

Quote:
Originally Posted by Sandy
An aside: A sail, like a wing, benefits from a thick cross section at the leading edge. A wingsail is more efficient than a single surfaced foil because the air going over the outside of the curve has farther to go than the air on the inside, so it goes faster there, creating a greater pressure differential.


Your explanation is not necessarily wrong, it just leaves a bad impression that has lead to incorrect explanations of ‘aerodynamic lift’…..
The second description we will call the Popular Explanation which is based on the Bernoulli principle. The primary advantage of this description is that it is easy to understand and has been taught for many years. Because of its simplicity, it is used to describe lift in most flight training manuals. The major disadvantage is that it relies on the "principle of equal transit times" which is wrong. This description focuses on the shape of the wing and prevents one from understanding such important phenomena as inverted flight, power, ground effect, and the dependence of lift on the angle of attack of the wing”.
“Students of physics and aerodynamics are taught that airplanes fly as a result of Bernoulli’s principle, which says that if air speeds up the pressure is lowered. Thus a wing generates lift because the air goes faster over the top creating a region of low pressure, and thus lift. This explanation usually satisfies the curious and few challenge the conclusions. Some may wonder why the air goes faster over the top of the wing and this is where the popular explanation of lift falls apart.
In order to explain why the air goes faster over the top of the wing, many have resorted to the geometric argument that the distance the air must travel is directly related to its speed. The usual claim is that when the air separates at the leading edge, the part that goes over the top must converge at the trailing edge with the part that goes under the bottom. This is the so-called "principle of equal transit times".
As discussed by Gale Craig (Stop Abusing Bernoulli! How Airplanes Really Fly., Regenerative Press, Anderson, Indiana, 1997), let us assume that this argument were true. The average speeds of the air over and under the wing are easily determined because we can measure the distances and thus the speeds can be calculated. From Bernoulli’s principle, we can then determine the pressure forces and thus lift. If we do a simple calculation we would find that in order to generate the required lift for a typical small airplane, the distance over the top of the wing must be about 50% longer than under the bottom
“So, why has the popular explanation prevailed for so long? One answer is that the Bernoulli principle is easy to understand. There is nothing wrong with the Bernoulli principle, or with the statement that the air goes faster over the top of the wing. But, as the above discussion suggests, our understanding is not complete with this explanation. The problem is that we are missing a vital piece when we apply Bernoulli’s principle”

For a more correct explanation of how an airplane wing develops lift I suggest this paper:
How Airplanes Fly: A Physical Description of Lift
http://www.allstar.fiu.edu/AERO/airflylvl3.htm


The reason I act to correct this impression is because I’ve had to defend the correct explanation of the ‘slot effect’ on so many occasions in the past. The slot effect between the headsail and the following sail (most often the mainsail) is much misunderstood and misquoted in many textbooks. This slot-effect is very important to my justification of a ‘cutter like’ headsail arrangement on my mast aft rig.
How Sails Work, the slot effect
http://www.boatdesign.net/forums/showpost.php?p=5685&postcount=3
Arvel Gentry's slot explaination
http://boatdesign.net/forums/showpost.php?p=51730&postcount=19

Regardless of whether you can accept my efforts to find a way to physically support this rig, or a variation of it, I don’t think you can dispute the explanations concerning the effectiveness of the sails in relation to one another.


Quote:
Originally Posted by Sandy
…a sail, like a wing, benefits from a thick cross section at the leading edge. A wingsail is more efficient than a single surfaced foil…

Again, partial true. From that same document above:
There are many types of wing: conventional, symmetric, conventional in inverted flight, the early biplane wings that looked like warped boards, and even the proverbial "barn door". In all cases, the wing is forcing the air down, or more accurately pulling air down from above. What each of these wings have in common is an angle of attack with respect to the oncoming air. It is this angle of attack that is the primary parameter in determining lift
If one then changes the angle of attack both up and down one finds that the lift is proportional to the angle….. A similar lift versus angle of attack relationship is found for all wings, independent of their design. This is true for the wing of a 747 or a barn door. The role of the angle of attack is more important than the details of the airfoil’s shape in understanding lift.”

So yes a thicker cross section at the leading edge of a single-surfaced foil is advantageous for providing a ‘less sensitive’ leading edge to the attack angle of the incoming airflow, but the thickness of the foil section of the sail is not a major determinate of lift generation.

I’ve suggested that all of my furling sails be attached to round-sectioned furling foils as this could decrease their sensitivity to a narrow band of attack to incoming airflow, and besides, round foils furl more evenly than asymmetric ones.



Quote:
Originally Posted by Sandy
A mast is not a bad thing if it has a foil shape and pivots to form the best shape. And the air behind a fixed mast is not dead. It’s still working, just not as well.

I’ve certainly experienced many a ‘dead zone’ behind fixed mast, particularly larger sections…..and zones that have absolutely NO pressure differential across the sail cloth.
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Old 28-06-2008, 09:53   #147
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The role of the angle of attack is more important than the details of the airfoil’s shape in understanding lift.


All these years when I was taught how wings "fly" I just could not understand how bernoulli's principle was "the" reason. The angle of attack on my models seemed to me to make the difference, plus speed.

Now I know I was not wrong.
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Old 28-06-2008, 10:33   #148
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What causes lift?

I have read the debate about what principles cause lift in sails and in wings, and I agree that the Bernoulli must be a relatively minor effect. Two cases convince me-the ability of upside down airplanes to fly when the Bernoulli explanation should have them plummeting to the ground faster than a flung stone, and the ability of an old-fashioned flat (versus the newer cambered designs) junk sail to sail to windward. These cases prove to me that the 'direction change' aka 'Newtonian' explanation must be the major cause of lift. I do note that camber has an effect, but it seems to me that its major effect is to reduce turbulence and stalling, causing more of the direction change to be turned into lift than would occur if more of the force were to be lost in eddy making. The Bernoulli effect probably increases the lift somewhat in a well trimmed sail.

Of course, arguments by real scientists like Tom Speer go right over my head-I am reduced to looking thoughtfully at the drawings, mostly, and trying to make my rigs look as much as possible like his drawings. That is what I did when designing the BigCat 65 rig that most people think looks so odd and traditional, and of course, I did the same when designing the BigCat Sport rig. He uses the 'Clark Y' foil shape for the first part of his mast/sail combination, and so I do, too. See: Aerodynamics of Teardrop Wingmasts
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Old 28-06-2008, 14:06   #149
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Yep,
Inverted flight of my models worked to confuse me. They flew while I remained confused, but like the rest of life, confusion takes a back seat when one is having fun!
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Old 29-06-2008, 08:37   #150
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I did alot of work on model aircraft wings as a younger man. Main problem for low speeds is to prevent or delay stalling of the airflow particularly at the leading edge. The translation to sail leading edges is obvious but the other place a wing can stall is at any discontinuity to the air flow. The transition from the back of the mast or the rigid front section of a wing mast onto the flexible sail must be smooth on the backside (upper of a wing). Neither wing edged sails or masts do much to help this. Lumps on the pressure side (underwing) just add a bit of drag and don't damage lift too much.
With round masts it would help if the sail could be slung smoothly from the back lee edge of the mast rather than the centre but it's really not that practical. Foresails are worse in that front edges are very sharp and therefore prone to stalling but trimming is much easier because we can see whats happening and adjust the sail angle to suit. The 'belly' in the sail allows the leading edge to split the wind while the curve displaces it's direction. The air will try to follow the back face of the sail if it's not interrupted or too heavily loaded.
The other difference on a sailing craft is that drag is not as important. Water is 100 times better than air at generating lift from motion and keels are a better shape as well. Note attention to the leading edge of keel shape is still important to prevent turbulence / stalling!
WING TIPS. By adding fences at the wing tip to model aircraft the books said we added half a chord (front to back edge distance) to the span as it prevents air spilling over the end of the wing. This seemed about right on our models.
I'm surprised sails don't do this more often. Sealing or just closing off the foresheet to the railing or deck will markedly improve performance. No good for can racing with frequent sail changes but long distance and cruising?
Needs a bit of sorting but I will be trying this as soon as I have a boat to play with.
THE MAINSAIL. A broad boom will hold the sail (lazy jack) better, catch rain water better with an easy transfer to tanks at the mast end, provide more shade from rain and sun, improve mainsheet lower level performance.
If you've got a hand held wind-o-meter do me a favour and look at windspeed over the bow (or uncluttered deck), then windspeed under the sail.
If there's no difference I withdraw all the above.
FLAP EFFECT. That little pressure bulge on the mainsail where the flow from the foresail seems to be is probably holding the airflow onto the back of the main generating better main performance. For best effect it should probably be visible but not pronounced. Comments please?
There are some who take trimming seriously and understand their own boat, and most others, almost instinctively. Please let me know if this makes any sense? Does it actually work in practice? I do wish so much I could prove it myself. This bloody house is a hell of an anchor and the boat remains at the top of the wish list way above buying another house.
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