.....depends which tack you're on.

I love messin' with Jay!

I can't envision an area of low pressure sucking. I can put a dime on my desk and push it with my finger, but no matter how hard I try the dime just won't follow my finger when I move my finger away.

See if you can envision this.

http://www.snopes.com/risque/penile/pool.asp

Boy, that must have...Sucked!

I was in the UK when Parliament decided not to improve the rail system between London and the Chunnel. Reporters were asking people for their reaction. A pastor responded, "I am against the Chunnel because the high speed trains will force the smell of garlic through the tunnel and envelop England."

That's one more fool I can ignore. As my list gets longer, this site becomes more enjoyable.

awesome! thanks guys!

what i got out of this:
1. i read correctly, they do get "sucked" forward
2. don't fly with Timbo
3. math hurts my head

Timbo, you said 'downwind you're being blown'

On our cats downwind, especially with a spin up, it's still being drawn along by lift on the various sails.

Yeah I know, I was just trying to get the word Blown into the discussion somehow...

We still have not answered the question, Would you rather be sucked or blown? And can there be any Sucking, without it also Blowing? How fast do you go on a zero wind day? I submit that in order to be sucked, you must first be blown.

Thanks again for the input...

ok, here is why i posted this... i mentioned that we are being sucked upwind... and was met with this as resistance:

Sorry Andrew, you have it mixed up. Nothing is sucked, or pulled. We don't actually "pull" a wagon, it is pushed. If you analyze the loads involved you realize that the palm of your hand is pushing on the rear edge of the wagon handle. This increased pressure forces the wagon forward.
Our shrouds are under tension, follow the loads from the hound to the pin at the hull & you find the same thing happens. There is no sucking that shroud downwards.
A sail is much the same as an aircraft wing, which operates on Bernoullis Therom. Airflow meeting the leading edge of a wing, or sail, is forced to split. To simplify greatly, lets think of two air "packets", "A" is forced to travel around the front side, "B" the rear. The two packets want to meet at the same time at the trailing edge.
A wing generally has a degree of camber,(again simplifying, the greater the camber, the greater the potential lift) this camber results in a greater distance along the top edge. "A" is forced to speed up to go the greater distance in the same time. We never added any energy to packet "A" or "B", so the total energy must not change. To achieve this, the pressure of faster moving packet A decreases. We now have a low pressure on top of the wing, & a relatively higher pressure underneath. You have heard since grade 4 science that Nature abhors a vacumn. The higher pressure area tries to get into the lower pressure & equalize it. Result, the wing is forced upwards,(lift) by this higher pressure. We need the higher pressure to obtain results.
Our cars engine does not "suck" air, it is pushed in by higher outside pressure, hence the decrease in power at higher altitudes as atmospheric pressure decreases. To regain that power we turbo charge, or super charge. TC or SC do not create more "suction", they create more pressure on the intake side. It is important to understand this principle, it is not just a matter of semantics.
This differential of pressure is responsible for quite an amazing repertoire in our everyday lives, carburetors, forcing solvent up the tube (notice I didn't say "suck") of the gizmo we attach to our air compressor for cleaning things, & most importantly breathing. Take a breath, our diaphragm drops creating a lower pressure in the lung cavity. Higher atmospheric pressure pushes air into our lungs. Jump off your Cat with a piece of hose in your mouth, then use it as a snorkel. Floating on the surface it is easy to breathe, about 16" down, you die. At that point the water pressure squeezing your chest cavity has equaled the air pressure trying to push into your lungs. No amount of "sucking" can refute the laws of physics and allow you to draw breath. If you could increase the atmospheric pressure it could overcome water pressure to a greater depth & allow you to breathe. This is one reason a SCUBA tank must be pressurized.
Back to sails, now that we understand it is a higher pressure driving the sail,(and skegs or boards converting this push into forward motion). To get more lift(power)we need greater total pressure,which can be obtained by more area, higher wind velocity, denser air, co efficient of lift that is determined by wing shape (CL), or some combination of these. Air velocity has a "squared" function in the equation, & so has the greatest effect. We can't do much with air density, but we can alter the CL by changing sail shape.
A wing,(aircraft or sail) can increase/decrease camber several ways, flaps being the most common way to increase. As they move rearwards & down, they increase both chord & camber. Same is true for leading edge devices,(slats). Increasing chord results in an increased wing area. If you couple the larger area with an increase in CL ie greater camber, the result is greater lift, (power). Of course nothing comes free, greater lift results in greater induced drag. As long as we increase lift more than the resultant increase in drag, we are ahead of the game. A tall narrow sail results in what is called a high aspect ratio,(chord vs span) very efficient...think of a gliders wing, or any soaring bird. This is where the sail trimmer comes in. Modern rigs allow us to change the sail shape to suit the conditions. A hard wing sail will be more tunable, & powerful, but the cost & complexity will also be greater.
And you thought college physics was a waste of time

Yeah,

I figured you knew that. I also agree it must blow before you can be sucked.

With all the talk of getting s..ked or getting bl.wn it sounds as though we are in JW's words "Circling the drain"

As mentioned above, it's really just a question of differential pressure. What you label it is pointless. It's just as correct to say "pushed" as "sucked" because you have the high pressure on one side and the low pressure on the other. Going downwind, the same principles are in play.

As an aside, I made the mistake of using the word "sucked" in an explanation in a high school science class, the teacher nearly ripped my head off (not because the word was objectionable, but because I didn't use the correct explanation regarding the pressures).

Mike

Kudos to you for discussing it at a HS class!

I mean discussing the forces at work for the boat to 'go'

Keep in mind, this was a very long time ago...

The discussion involving sucking had more to do with how a vacuum worked, or something like that.

Honestly, the guy just liked to ridicule us. He cracked himself up asking questions that should have been aswered with "boron" and when no one spoke up, he would drop "helpful hints" like, "Rhymes with MORON..."

We did discuss airfoils, wings, sails, etc. in a later high school physics class, with a much better teacher.

All things being equal, my high school education was probably the best money that I ever spent. Well, that and my Hobie Cats.

Mike