Thanks a lot for the illuminating answers. I read somewhere that the
"sail-as-airfoil" trick is a rather recent one, and that formerly
people would just let the wind push them around. Is that true, and if
yes, how recent is the invention?

Thanks,
Axel

sails always worked as sails work. the thinking about them has changed, but
airfoils are airfoils, and have been since birds learned to fly a bit back.

Thanks a lot for the illuminating answers. I read somewhere that the
"sail-as-airfoil" trick is a rather recent one, and that formerly
people would just let the wind push them around. Is that true, and if
yes, how recent is the invention?

Thanks,
Axel

Axel Boldt wrote:
Thanks a lot for the illuminating answers. I read somewhere that the
"sail-as-airfoil" trick is a rather recent one, and that formerly
people would just let the wind push them around. Is that true, and if
yes, how recent is the invention?

Thanks,
Axel

umm... it's probably a "AD" date rather than a "BC" but there are
designs of sails which are pretty ancient that do run as proper
airfoils, not just a drag device. The Arab Lateen rigs are I think
pretty old, as an example.

Remember what Cook found in the south seas? The native canoes "went
about three miles to our two" - European rigs were not the hottest thing
at the time.

Andy.

Square-rigged boats could sail no higher than a beam reach. However, the sails
were not flat, and they were trimmed appropriately to allow the boats to be
sailed other than dead downwind.

I don't recall the date triangular sails were invented, but they were the dawn
of upwind sailing in the west; junk rigs enabled upwind sailing in the east.

"Axel Boldt" wrote...
Thanks a lot for the illuminating answers. I read somewhere that the
"sail-as-airfoil" trick is a rather recent one, and that formerly
people would just let the wind push them around. Is that true, and if
yes, how recent is the invention?

John,

This is a common mis-conception.

The truth is that most merchant vessels could do only do 160 deg between
tacks, but many other square sails could do well better than that. It
just took a lot of manpower and money to handle the extra rigging that
would tighten the luff. Vikings with wool sails reports taht they could
manage about 120 and that was not equaled until the fore and aft
rigged schooners appeared in the early nineteenth century.

Matt Colie
Lifelong Waterman, Licensed Mariner and Perpetual Sailor


John Weiss wrote:

Square-rigged boats could sail no higher than a beam reach. However, the sails
were not flat, and they were trimmed appropriately to allow the boats to be
sailed other than dead downwind.

I don't recall the date triangular sails were invented, but they were the dawn
of upwind sailing in the west; junk rigs enabled upwind sailing in the east.

"Axel Boldt" wrote...

Thanks a lot for the illuminating answers. I read somewhere that the
"sail-as-airfoil" trick is a rather recent one, and that formerly
people would just let the wind push them around. Is that true, and if
yes, how recent is the invention?

Axel

First please realize that the brother Wright had to reinvent
aerodymanics whent hey found out the all the material that they had
collected was junk. (Mr. langley didn't like them very much.) They
were also the first people to build and used a wind tunnel (they built
three in total) to any advantage.

The "sail as a foil" convention can not really be tied down easily, but
the oldest paper in my library is from the mid-teens and contains some
things that are now known to be in error. A book that I have was
written in the mid-twenties and it is hard to tell the difference
between the going to weather part of this book and my newer ones.

From the things that I was taught by much older people about a half a
century ago, the understanding of the function both square and
fore-and-aft rigged sails is not recent, but the language to describe it
is (realiviely).

Matt Colie
Lifelong Waterman, Licensed Mariner and Perpetual Sailor

Axel Boldt wrote:
Thanks a lot for the illuminating answers. I read somewhere that the
"sail-as-airfoil" trick is a rather recent one, and that formerly
people would just let the wind push them around. Is that true, and if
yes, how recent is the invention?

Thanks,
Axel

The invention goes back at least as far as the "Boomarang", Chinese Junk
Rig, Lateen Rig, Polynesian Claw Sail; All before the time of Common
Age. The Europeans didn't have knowledge of it until 1000's of years
later

Ole Thom

The answer to your question, is yes. Sails are made from dacron for ease of
handling & shortening, and cost. Many examples of rigid-wing vessels exist,
I suggest doing a search on that. They often use fairings at the leading
edge, or movable trailing edges to fine tune the foil.

An aircraft can fly inverted, because its angle-of-attack changes to suit
the correspondingly lower efficiency of the foil in this position. As others
have noted, acrobatic craft often employ nearly symmetrical foils for this
reason. A normally profiled foil will fly inverted, but inefficiently, and
at a much lower VMG due to the increased drag from the higher angle of
attack.

Try some "Bernoulli experiments for kids",and you will reach a better
understanding.

"Axel Boldt" wrote in message
m...
Hi,

I'm trying to understand how a boat can sail against the wind.
Explanations on the internet usually go like this: "The sail has an
airfoil shape, the air goes faster on one side than on the other,
creating lift by Bernouilli's principle." But I know that for flying
planes, the wing's airfoil shape is not essential (otherwise planes
couldn't fly on their back): it's the angle of attack that matters. So
I'm wondering if the same is true for sailing: would it be possible to
sail against the wind with a sail that's a rigid flat surface, not an
airfoil-shaped piece of cloth?

Thanks,
Axel

ac, you lack totally and utterly ANY understanding of what is going on --
airfoilwise -- on either or, same same, a sailboat sail.

ac, the ng askes that you NEVER post on this subject again. for the obvious
reason.

From: "AC"
Date: 8/21/2004 5:50 PM Eastern Daylight Time
Message-id:

The answer to your question, is yes. Sails are made from dacron for ease of
handling & shortening, and cost. Many examples of rigid-wing vessels exist,
I suggest doing a search on that. They often use fairings at the leading
edge, or movable trailing edges to fine tune the foil.

An aircraft can fly inverted, because its angle-of-attack changes to suit
the correspondingly lower efficiency of the foil in this position. As others
have noted, acrobatic craft often employ nearly symmetrical foils for this
reason. A normally profiled foil will fly inverted, but inefficiently, and
at a much lower VMG due to the increased drag from the higher angle of
attack.

Try some "Bernoulli experiments for kids",and you will reach a better
understanding.

"Axel Boldt" wrote in message
om...
Hi,

I'm trying to understand how a boat can sail against the wind.
Explanations on the internet usually go like this: "The sail has an
airfoil shape, the air goes faster on one side than on the other,
creating lift by Bernouilli's principle." But I know that for flying
planes, the wing's airfoil shape is not essential (otherwise planes
couldn't fly on their back): it's the angle of attack that matters. So
I'm wondering if the same is true for sailing: would it be possible to
sail against the wind with a sail that's a rigid flat surface, not an
airfoil-shaped piece of cloth?

Thanks,
Axel

JAXAshby wrote:

ac, you lack totally and utterly ANY understanding of what is going on --
airfoilwise -- on either or, same same, a sailboat sail.

ac, the ng askes that you NEVER post on this subject again. for the obvious
reason.



Jax,
Do you intend to annoy people, or is it just by accident?