r we being PULLED or PUSHED??
- Thread starter gudiss
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Aerohydrodynamics of Sailing
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I'd say it depends on your point of sail. Sailing on a reach or upwind, pulling. On a downwind run, pushing.
Interesting philosophical question. I'm not so sure that it does depend on the point of sail. In either case there's low pressure on the leeward side and high pressure on the windward side. The pressure differential drives the sail toward the lower pressure side.
Does a fan pull air or push it?
Does a fan pull air or push it?
Depends which side you're on.
Also an interesting engineering question. The aircraft I worked with in the Air Force would convert from a jet turbine at speed and altitude to a ramjet. The engineers would say the turbine supplied 15% of the thrust, and the inlet of the engine supplied the other 85%. I just nodded, and said, yeah but that afterburner is awfully loud.
I am no physicist and this is how I see it: I don't think this is a philosophical question. Physics are in play in all points of sail. Dead downwind we are being pushed - no lift involved. Exactly where the line is when lift is no longer a factor is not something that is clear to me. I suspect that even a broad reach involves lift as is evidenced by the speeds one can attain on that point of sail as opposed to dead downwind. I think the fan analogy is an entirely different principle, which I see as an issue of every action has an equal and opposite reaction. There is no such opposite reaction to the wind we sail off of. 
More food for thought - Someone suspended by a parachute falls slower than gravity would otherwise suggest. Is that because the person is being pulled up or pushed up? Is the parachute itself being pushed up or pulled up by the air?
Wind produces two different forces, lift and drag Lift is reasonably considered pull, and drag is push. This video seems to covers both:
If someone really wanted to be pedantic (certainly not me ) they could point out that the OP’s question was whether our sails push or pull us, not whether the wind pushes or pulls us. One could probably argue that the wind pushes and/or pulls. But the sails are only ever in tension. They’re cloth, so they really can’t be in compression. So I think that regardless of what the wind is doing the sails are only pulling us.
) they could point out that the OP’s question was whether our sails push or pull us, not whether the wind pushes or pulls us. One could probably argue that the wind pushes and/or pulls. But the sails are only ever in tension. They’re cloth, so they really can’t be in compression. So I think that regardless of what the wind is doing the sails are only pulling us.
the op asked about the "sails". the sails always are pulling the vessel. the wind is another discussion.
example: the sheets are never pushing anything, always pulling.
example: the sheets are never pushing anything, always pulling.
Is a plane pulled up or pushed up? IMHO I'd say pulled up against the force of gravity. On any point of sail except a run or very broad reach the sail acts like a wing. The boat, fuselage, is being pulled forward against the counter force of the keel, gravity, which makes it go forward instead of sideways. If my analogy is incorrect, please do not hesitate to correct me. I am not a pilot but I think I have at least a rudimentary understanding of the physics at play. At least enough to be dangerous.
LoL... a physicist would want to know where the person asking the question is sitting on the boat.... relative to a person sitting on the high pressure side of the sail you are being pulled... if you are lounging on the bow on the leeward side of the main sail, ... you are being pushed
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