Empty oceans before age of discovery
Crown-Horned Snorkack
exploration?
Starting from northwest Europe: Shetlands, with 60 km sea gaps either
side of Fair Isle, have been settled since at least bronze age. St.
Kilda and North Rona had old human settlements, not sure how old.
Faroes, 280 km from Shetlands, were completely desert before Irish
monks (who did not bring any laity/women along) and first permanent
settlers were Vikings. Ditto about Iceland.
South of Rockall, all isles are less than 50 km from mainland/big
islands and all which were big enough to sustain farmers were settled
from times immemorable (and those which were smaller were regularly
visited to fish, herd, hunt birds...). Up to Canaries/Macaronesian
region.
The remotest Mediterranean isles are IIRC Pelagie islands, known since
ancient times.
Canaries were settled by Guanches. Madeira and Azores were desert when
found by Portuguese.
Cape Verde Islands were desert. Bioko was settled, Sao Tome and
Principe desert.
In Indian Ocean, things get funnier. Madagascar was settled - rather
recently. Comoros also were settled - but Seychelles were desert. As
was Christmas Island.
Then there are the mystery islands that have been settled but became
desert. Kangaroo Island, Bass Strait islands.
In Pacific, Polynesians also left a number of mystery islands.
Christmas Island. Campbell Island. Norfolk Island. Henderson and
Pitcairn. Nihoa and Necker.
In northwest Pacific, Izu Islands, Ryukyus and Marianas were long
settled. Daito, Ogasawara and Io islands between them were unsettled,
though plainly big enough to sustain villages.
In East Pacific, Cocos Island, Galapagos and Juan Fernandez stayed
desert, although Galapagos was visited by Indians. In West Atlantic,
Tierra del Fuego was settled, but Indians did not reach Falklands.
Bahamas were settled, but Bermudas were out of reach.
If you want to make a PoD that an island actually exists somewhere,
then we can consider where an island could exist without being
discovered in prehistory and butterflying away the subsequent events
as we know them..
Dixon Hand
wrote:
Madagascar was settled by people speaking a language similar to
languages spoken in the Philippines, Malaysia and elsewhere around
SouthEast Asia. Go figure. Hey, you should take a look at this pic of
Cameron Diaz running around topless:
http://notsafeforkids.com/?page_id=1227
pyotr filipivich
Crown-Horned Snorkack <chorned...@hush.ai> wrote on Fri, 10 Oct
2008 13:00:21 -0700 (PDT) in soc.history.what-if :
Take a look at ocean currents and prevailing winds. Put an island
in the middle "of nowhere", off the trade winds and out of the
currents and until you get either steam or complete daft exploders
(going where there was no rational reason to go) they are "unknown
lands."
tschus
pyotr
--
pyotr filipivich
Most of the intelligentsia haven't studied history, so much
as they've absorbed the Correct Position on "History".
SolomonW
@k16g2000hsf.googlegroups.com>, chorned...@hush.ai says...
> If you want to make a PoD that an island actually exists somewhere,
> then we can consider where an island could exist without being
> discovered in prehistory and butterflying away the subsequent events
> as we know them..
>
Near Antarctica
David Johnson
a499-44e0-9df...@k16g2000hsf.googlegroups.com:
> In Pacific, Polynesians also left a number of mystery islands.
> Christmas Island. Campbell Island. Norfolk Island. Henderson and
> Pitcairn. Nihoa and Necker.
If memory serves (and it often doesn't), Pitcairn *was* inhabited at some
time before the mutineers settled there, but they'd all died off/left for
some reason.
> If you want to make a PoD that an island actually exists somewhere,
> then we can consider where an island could exist without being
> discovered in prehistory and butterflying away the subsequent events
> as we know them..
I think your only real shot is in the South Atlantic, about halfway between
the Falklands and South Africa. As you said, almost every other scrap of
land big enough to support humans in the Pacifc, Indian and North Atlantic,
well, supported humans well before the "Age Of Exploration."
Mind you, we're not going to be talking *tropical* islands here, but you
could have some fair sized ones down there without mucking up this ATL's
history up to said Age of Exploration.
David
Brian Davis
wrote:
> If memory serves (and it often doesn't), Pitcairn *was* inhabited at some
> time before the mutineers settled there, but they'd all died off/left for
> some reason.
Not only Pitcairn but Henderson have signs of resident populations
(from reading Diamond's "Collapse"). It wouldn't surprise me if most
of the rest did at one time or another as well, but due to marginal
resources (& management of same) collapsed and were not resettled.
--
Brian Davis
Crown-Horned Snorkack
wrote:
> Crown-Horned Snorkack <chornedsnork...@hush.ai> wrote in news:454398c4-
> a499-44e0-9df1-b5697bd30...@k16g2000hsf.googlegroups.com:
>
> > In Pacific, Polynesians also left a number of mystery islands.
> > Christmas Island. Campbell Island. Norfolk Island. Henderson and
> > Pitcairn. Nihoa and Necker.
>
> If memory serves (and it often doesn't), Pitcairn *was* inhabited at some
> time before the mutineers settled there, but they'd all died off/left for
> some reason.
>
> > If you want to make a PoD that an island actually exists somewhere,
> > then we can consider where an island could exist without being
> > discovered in prehistory and butterflying away the subsequent events
> > as we know them..
>
> I think your only real shot is in the South Atlantic, about halfway between
> the Falklands and South Africa. As you said, almost every other scrap of
> land big enough to support humans in the Pacifc, Indian and North Atlantic,
> well, supported humans well before the "Age Of Exploration."
>
No, I didn´t say so.
North Atlantic: Iceland, Faroes, Azores, Madeira, Cape Verde, Bermuda.
Indian Ocean: Seychelles, Mascarenes, Christmas.
Pacific: Juan Fernandez, Cocos, Revillagigeido, Daito, Io, Ogasawara
> Mind you, we're not going to be talking *tropical* islands here, but you
> could have some fair sized ones down there without mucking up this ATL's
> history up to said Age of Exploration.
>
> David
Plenty of tropical islands in the above list.
Allen W. McDonnell
> > If you want to make a PoD that an island actually exists somewhere,
> > then we can consider where an island could exist without being
> > discovered in prehistory and butterflying away the subsequent events
> > as we know them..
>
>> I think your only real shot is in the South Atlantic, about halfway
>> between
>> the Falklands and South Africa. As you said, almost every other scrap of
>> land big enough to support humans in the Pacifc, Indian and North
>> Atlantic,
>> well, supported humans well before the "Age Of Exploration."
>>
>No, I didn´t say so.
>
>North Atlantic: Iceland, Faroes, Azores, Madeira, Cape Verde, Bermuda.
>
>Indian Ocean: Seychelles, Mascarenes, Christmas.
>
>Pacific: Juan Fernandez, Cocos, Revillagigeido, Daito, Io, Ogasawara
>
You didn't mention the Kerguelen Islands in the south Indian Ocean.
--
*******************************
Oxygen: - An intensely habit-forming accumulative toxic substance. As little
as one breath is known to produce a life-long addiction to the gas, which
addiction invariably ends in death. In high concentration it causes death
quickly, but even in a 20% dilution few survive more than a 0.8 century.
Isaac Asimov
David Johnson
How are you defining "historical exploration" then? I took it to mean the
"Age of Exploration," which is generally considered to start during the
15th century. If you're using that time frame, cross off Iceland and the
Faroes from your list.
If you're using "pre-history" in the usual sense (before written
records), well first of all, *whose* "pre-history" are we talking about.
And second, you're going to have to *add* a lot of islands to your
list...heck, New Zealand wasn't settled until 1000 AD!
I think you need to clarify...or at least set a definite date here.
David
--
_______________________________________________________________________
David Johnson home.earthlink.net/~trolleyfan
"So many of you come time and time again to watch this final end of
everything which I think is really wonderful and then to return home to
your own eras and raise families and strive for new and better societies
and fight terrible wars for what you know is right, it gives one real
hope for the whole future of lifekind...
...Except of course we know it hasn't got one."
SolomonW
trolleyfa...@earthlink.net says...
> >
> > North Atlantic: Iceland, Faroes, Azores, Madeira, Cape Verde, Bermuda.
> >
> > Indian Ocean: Seychelles, Mascarenes, Christmas.
> >
> > Pacific: Juan Fernandez, Cocos, Revillagigeido, Daito, Io, Ogasawara
> >
> >> Mind you, we're not going to be talking *tropical* islands here, but
> >> you could have some fair sized ones down there without mucking up
> >> this ATL's history up to said Age of Exploration.
> >>
> >> David
> >
> > Plenty of tropical islands in the above list.
>
> How are you defining "historical exploration" then? I took it to mean the
> "Age of Exploration," which is generally considered to start during the
> 15th century. If you're using that time frame, cross off Iceland and the
> Faroes from your list.
Many start the "Age of Exploration," with Prince Henry the Navigator as
many of the Islands in the Pacific were not settled till then so they
do if this definition is adopted.
Quadibloc
wrote:
> Which parts of Earth were unreached by humans before historical
> exploration?
There's always Antarctica...
John Savard
cryptoguy
wrote:
> Crown-Horned Snorkack <chornedsnork...@hush.ai> wrote in news:454398c4-
> a499-44e0-9df1-b5697bd30...@k16g2000hsf.googlegroups.com:
>
> > Christmas Island. Campbell Island. Norfolk Island. Henderson and
> > Pitcairn. Nihoa and Necker.
>
> If memory serves (and it often doesn't), Pitcairn *was* inhabited at some
> time before the mutineers settled there, but they'd all died off/left for
> some reason.
>
> > If you want to make a PoD that an island actually exists somewhere,
> > then we can consider where an island could exist without being
> > discovered in prehistory and butterflying away the subsequent events
> > as we know them..
>
> I think your only real shot is in the South Atlantic, about halfway between
> the Falklands and South Africa. As you said, almost every other scrap of
> land big enough to support humans in the Pacifc, Indian and North Atlantic,
> well, supported humans well before the "Age Of Exploration."
>
> Mind you, we're not going to be talking *tropical* islands here, but you
> could have some fair sized ones down there without mucking up this ATL's
> history up to said Age of Exploration.
Well, there's South Georgia, which with the South Sandwich Islands
covers
over 1500 square miles. Hope you like snow. Currently the biggest
source of
revenue is postage stamps.
Peter Trei
Crown-Horned Snorkack
> [Default] I missed the Staff meeting, but the Memos showed that
carried away by prevailing currents who find land are unable to go
back to report their discovery and fetch supplies (including women)
for colonization.
Michael Ash
> Prevailing winds are actually a barrier to exploration. Any castaways
> carried away by prevailing currents who find land are unable to go
> back to report their discovery and fetch supplies (including women)
> for colonization.
That would seem to assume that the only mode of exploration is castaways
who are at the mercy of the winds. If your exploration is done by people
in proper ships who know how to travel into the wind then prevailing winds
simply give them an area of reliable travel in which they can essentially
explore at will. Since the art of sailing upwind was well known before the
age of exploration (and one can always row), the only question is whether
people bothered to explore, or whether castaways truly were the only mode
of exploration. It strikes me as extremely doubtful that this would be the
case, but I don't know that much about it.
--
Mike Ash
Radio Free Earth
Broadcasting from our climate-controlled studios deep inside the Moon
pyotr filipivich
-0500 in soc.history.what-if :
Hence my criterion for putting the island out of the prevailing
trades and/or currents.
Par
> > Take a look at ocean currents and prevailing winds. Put an island
> > in the middle "of nowhere", off the trade winds and out of the
> > currents and until you get either steam or complete daft exploders
> > (going where there was no rational reason to go) they are "unknown
> > lands."
Depends. There has been credible claims that at least some of the
Polynesian migrations followed migratory birds. The evidence does not
have to be direct.
> Prevailing winds are actually a barrier to exploration. Any castaways
> carried away by prevailing currents who find land are unable to go
> back to report their discovery and fetch supplies (including women)
> for colonization.
That is why you travel with the toolkit for tranformng your expedition
into a colony. A few families (I know, insufficient genetic variation,
but still), some pigs, a few chickens, some tools.
/Par
--
Par use...@hunter-gatherer.org
Dawkins is the prototypical evangelical fundamentalist atheist
-- Nix
Crown-Horned Snorkack
> Crown-Horned Snorkack <chornedsnork...@hush.ai>:
>
> > > Take a look at ocean currents and prevailing winds. Put an island
> > > in the middle "of nowhere", off the trade winds and out of the
> > > currents and until you get either steam or complete daft exploders
> > > (going where there was no rational reason to go) they are "unknown
> > > lands."
>
> Depends. There has been credible claims that at least some of the
> Polynesian migrations followed migratory birds. The evidence does not
> have to be direct.
>
> > Prevailing winds are actually a barrier to exploration. Any castaways
> > carried away by prevailing currents who find land are unable to go
> > back to report their discovery and fetch supplies (including women)
> > for colonization.
>
> That is why you travel with the toolkit for tranformng your expedition
> into a colony. A few families (I know, insufficient genetic variation,
> but still), some pigs, a few chickens, some tools.
>
small, mountainous, cold or dry for their crops, or a land that is
already settled by people who do not wish more and are sufficiently
numerous and well organized to do something about it. Colonists would
set out after someone has been there and back, and reported that there
is somewhere to go.
Michele
"Crown-Horned Snorkack" <chorned...@hush.ai> ha scritto nel messaggio
news:454398c4-a499-44e0...@k16g2000hsf.googlegroups.com...
> Which parts of Earth were unreached by humans before historical
> exploration?
Really, really, really out of the way: Kerguelen. And I think there's a few
more islets like those a tad closer to Australia, and belonging to it.
ErrolC
> "Crown-Horned Snorkack" <chornedsnork...@hush.ai> ha scritto nel messaggionews:454398c4-a499-44e0...@k16g2000hsf.googlegroups.com...
>
> > Which parts of Earth were unreached by humans before historical
> > exploration?
>
> Really, really, really out of the way: Kerguelen. And I think there's a few
> more islets like those a tad closer to Australia, and belonging to it.
Note that the Maori visited at least Enderby Island (50 South) around
1350AD.
http://en.wikipedia.org/wiki/Auckland_Islands
Errol Cavit | So we have a paradox. The hard way was also the easy
way.
What has always seemed most marvellous about the settlement of the
Pacific
is that it went against the prevailing winds and it now transpires
that, for people
interested in staying alive, it was taking that very direction that
made it possible.
Geoffrey Irwin, 1992
Jack Linthicum
I add my own view that some of the Pacific Islands were settled in
"hope", ie groups got tired of whereever they were and went looking
for something away from"here".
http://www.paulwaters.com/migrate.htm
This traditional association between fishing and the discovery islands
suggests that fishermen, of whatever identities, were perhaps the most
frequent discoverers of islands in ancient times, either while they
roamed the ocean looking for new fishing grounds or chasing schools of
pelagic fish, or after they were driven off course by storms on their
way to known fishing grounds. A poetic way of describing their
discoveries would be to say that the fishermen caught islands, not
fish. Perhaps the name of Maui was given to anyone who discovered an
island, in honor of some ancestral fisherman-explorer noted for
finding islands.
Another intriguing possibility is proposed in Geoffrey Irwin's The
Prehistoric Exploration and Colonization of the Pacific. Irwin
suggests that those who settled Polynesia may have used a deliberate
strategy of exploration that allowed them to find islands without an
inordinate risk to their lives and with a high rate of survival.
(Other scholars have assumed that the exploration of the Pacific was
full of danger and involved high casualties at sea.) This deliberate
strategy of exploration, according to Irwin, involved waiting for a
reversal in wind direction and sailing in the direction that is
normally upwind (i.e. eastward in the Pacific) for as far as it was
safe to go given the supplies that were carried on the canoe. The
return home (westward) would be made easy when the wind shifted back
to its normal easterly direction. Irwin believes that this strategy is
supported by the west to east settlement of the Pacific, from the
islands of southeast Asia and Melanesia to Samoa, Tonga, the Cook
Islands, the Society Islands, the Tuamotus, and Hiva (the Marquesas).
Although no factual evidence would prove that this strategy of
exploration was actually employed by Polynesian navigators, the
strategy would have been obvious to anyone familiar with sailing. The
tradition of 'imi fenua (Hawaiian: 'imi honua), or "searching for
lands," reported from Hiva and other Polynesian islands, supports such
a notion of deliberate exploration. Teuira Henry gives exploration and
discovery as the motivation for the voyages of Ru and Hina, a brother
and sister who circumnavigated the earth in their canoe Te-apori to
locate islands: "After exploring the earth, Hina's love of discovery
did not cease. So one evening when the full moon was shining
invitingly, being large and half visible at the horizon, she set off
in her canoe to make it a visit." She decided to stay there and
remains today as the figure seen in the moon.
http://pvs.kcc.hawaii.edu/hivavoyaging.html
Voyages of Exploration
The people of Hiva left their islands in search of other lands (He
fenua 'imi, "land seeking"; Hawaiian: 'imi honua). Porter reports:
"The grandfather of Gattnaewa sailed with four large canoes in search
of land, taking with him a large stock of provisions and water,
together with a quantity of hogs, poultry, and young plants. He was
accompanied by several families and has never been heard of since he
sailed" (quoted in Handy Native Culture 19).
Porter also says he heard that "more than eight hundred men, women and
children" departed from the islands of Hiva in search of land. One
group ended up on Roberts' Island (Eiao, NW of Nukuhiva). A few days
after the canoes depart on these voyages of exploration, "the priests
come lurking to the houses of the inhabitants of the valley, whence
they sail, and in a squeaking affected voice, inform [the inhabitants]
that [the voyagers] have found a land abounding in breadfruit, hogs,
coconuts, everything that can be desired,and invite others to follow
them, pointing out the direction to sail, in order to fall in with
this desirable spot. New canoes are constructed, and new adventurers
commit themselves to the ocean, never to return" (quoted in Handy
Native Culture 20).
According to one oral tradition, a large double-hulled canoe named
Kaahua from a tribe called Tuoo under the chief Te-heiva voyaged east
from Puamau on the northeast coast of Hiva Oa and landed at a land
called Tefiti. Kaahua had several houses built on its deck and
"carried a great quantity of breadfruit paste." Its gunnels were so
high, the crew had "to climb up the sides from the bottom to pour the
bilge water out." Some of the crew stayed in Tefiti, while others
returned to Puamau (Handy Native Culture 131).
Howard Brazee
island had it great - until they ate all of the easy to find food.
--
"In no part of the constitution is more wisdom to be found,
than in the clause which confides the question of war or peace
to the legislature, and not to the executive department."
- James Madison
Jack Linthicum
Don't be so sure, if a "king" came along you got breadfruit planted,
fish hauled in,
coconuts, young breadfruit-trees, and other such useful products were
so carried in their vessels during their voyages, as also pigs, dogs,
and fowls. In this manner the taro (Colocasia antiquorum), the sweet
potato, the yam, gourd, and likewise the aute, or cloth-plant
(Broussonetia papyrifera), pigs and chickens
Suzanne Blom
"Crown-Horned Snorkack" <chorned...@hush.ai> wrote in message
news:f82dae64-4cab-42c4...@r15g2000prh.googlegroups.com...
If they shared your assumptions.
Par
Depends, IMHO. Perhaps if you pose a society where long sea journeys are
routine, or where the colonizing effort is in real life a refugee
situation ("the Bad Guys will kill us if we do not leave, lets load out
canoes and set sail"), it is perfectly logical to bring your familly. I
wonder what was the maximum sustainable non-supported journey in
pre-contact polynesia?
/Par
--
Par use...@hunter-gatherer.org
It provokes the desire, but it takes away the performance.
-- William Shakespear, Macbeth
cryptoguy
> Suzanne Blom <sueb...@execpc.com>:
>
>
>
>
>
>
>
> > "Crown-Horned Snorkack" <chornedsnork...@hush.ai> wrote in message
> > news:f82dae64-4cab-42c4...@r15g2000prh.googlegroups.com...
> > On 14 okt, 12:10, Par <use...@hunter-gatherer.org> wrote:
> > > > Prevailing winds are actually a barrier to exploration. Any castaways
> > > > carried away by prevailing currents who find land are unable to go
> > > > back to report their discovery and fetch supplies (including women)
> > > > for colonization.
>
> > > That is why you travel with the toolkit for tranformng your expedition
> > > into a colony. A few families (I know, insufficient genetic variation,
> > > but still), some pigs, a few chickens, some tools.
>
> > But they wouldn´t dare. There might be no land, or land that is too
> > small, mountainous, cold or dry for their crops, or a land that is
> > already settled by people who do not wish more and are sufficiently
> > numerous and well organized to do something about it. Colonists would
> > set out after someone has been there and back, and reported that there
> > is somewhere to go.
>
> Depends, IMHO. Perhaps if you pose a society where long sea journeys are
> routine, or where the colonizing effort is in real life a refugee
> situation ("the Bad Guys will kill us if we do not leave, lets load out
> canoes and set sail"), it is perfectly logical to bring your familly. I
> wonder what was the maximum sustainable non-supported journey in
> pre-contact polynesia?
Depends when - the tech developed as time went by.
By the time they had double hulled canoes, a long way indeed:
From
http://www2.hawaii.edu/~adamson/vol43a1.html
"After testing for sea worthiness of boat and crew by sailing around
the Hawaiian Islands, the Hokule'a set sail for Tahiti, a distance of
2,500 miles, on May 1, 1976, as the State of Hawaii's bicentennial
project. Without charts or instruments, the navigator Mau Piailug,
from the Satawal atoll in the Caroline Islands of Micronesia, guided
the Hokule'a to Papeete where the canoe and crew were greeted by the
largest crowd ever assembled in Tahiti. On July 26 the Hokule'a sailed
into Kewalo Basin, Honolulu, met by an impressive regatta of boats of
every size and watched by people gathered at vantage points from
Diamond Head to Magic Island. The actual distance traveled round trip
was 5,400 miles."
Peter Trei
Edward Green
> In rec.arts.sf.science Crown-Horned Snorkack <chornedsnork...@hush.ai> wrote:
>
> > Prevailing winds are actually a barrier to exploration. Any castaways
> > carried away by prevailing currents who find land are unable to go
> > back to report their discovery and fetch supplies (including women)
> > for colonization.
>
> That would seem to assume that the only mode of exploration is castaways
> who are at the mercy of the winds. If your exploration is done by people
> in proper ships who know how to travel into the wind then prevailing winds
> simply give them an area of reliable travel in which they can essentially
> explore at will. Since the art of sailing upwind was well known before the
> age of exploration (and one can always row), the only question is whether
> people bothered to explore, or whether castaways truly were the only mode
> of exploration. It strikes me as extremely doubtful that this would be the
> case, but I don't know that much about it.
In regard of sailing upwind, I note its absence in C.S. Lewis's*
fantasy "The Voyage of the Dawn Treader". The sailors begin to
grumble that they have been sailing with a prevailing wind so long
they can't get back. I've wondered if it was the Narnians who hadn't
discovered tacking into the wind, or C.S. Lewis.
Not a sailor, I've worked out the vector diagram for tacking several
times, and though I can make it work, I can't make the intuition
stick. What's the history of this invention, anyway?
*if I read E.B. White correctly, that's correct.
Michael Ash
> In regard of sailing upwind, I note its absence in C.S. Lewis's*
> fantasy "The Voyage of the Dawn Treader". The sailors begin to
> grumble that they have been sailing with a prevailing wind so long
> they can't get back. I've wondered if it was the Narnians who hadn't
> discovered tacking into the wind, or C.S. Lewis.
>
> Not a sailor, I've worked out the vector diagram for tacking several
> times, and though I can make it work, I can't make the intuition
> stick. What's the history of this invention, anyway?
I can't answer the question about the history. But I've found that the
intuition works a lot better if I stop thinking of them as sails and start
thinking of them as wings. Sails are just inflatable airfoils of varying
degrees of performance.
> *if I read E.B. White correctly, that's correct.
If you're referring to the apostrophe, I'm pretty sure that's right, even
though people seem to feel very uncomfortable putting 's after an s.
Ilmari Karonen
>
> Not a sailor, I've worked out the vector diagram for tacking several
> times, and though I can make it work, I can't make the intuition
> stick. What's the history of this invention, anyway?
I've no idea, but I'll note from personal experience that there's no
sharp transition between sailing slightly downwind and slightly
upwind. Sailing at an angle to the wind requires a different
technique (and equipment) than sailing (almost) dead downwind, but
once you've got the hang of going sideways, it's just a matter of
gradual refinement until you suddenly notice that you can actually
reach a wind angle of over 90 degrees.
Then it's just a simple matter of reasoning: "Okay, so I can't sail
straight there, since the wind is against me, but what if I first sail
some distance sideways and then turn around...?"
Mind you, the refinement isn't necessarily trivial, particularly if
you're starting with primitive sails and hull that aren't very good at
going sideways in the first place. But the incentive is very much
there, since just being able to reliably sail sideways to the wind
makes sea travel _much_ more convenient.
--
Ilmari Karonen
To reply by e-mail, please replace ".invalid" with ".net" in address.
Juho Julkunen
@v15g2000hsa.googlegroups.com>, spamsp...@netzero.com says...
> In regard of sailing upwind, I note its absence in C.S. Lewis's*
> fantasy "The Voyage of the Dawn Treader". The sailors begin to
> grumble that they have been sailing with a prevailing wind so long
> they can't get back. I've wondered if it was the Narnians who hadn't
> discovered tacking into the wind, or C.S. Lewis.
Or possibly beating into the wind all the way home would take longer
than their supplies would last.
> Not a sailor, I've worked out the vector diagram for tacking several
> times, and though I can make it work, I can't make the intuition
> stick. What's the history of this invention, anyway?
"To Harness the Wind: A Short History of the Development of Sails"
by Leo Block seems to give a fair account. Apparently Phoenicians,
building on Minoan designs, had ships capable of sailing upwind around
700 BCE.
It was a step in the process of learning to sail further from straight
downwind, which requires steering and dealing with heeling and leeway.
Egyptians over time added steering oars, lowered sail to reduce
heeling, and moved the mast from forward nearer to middle. Minoans
provided the mast with supporting shrouds and stays and developed
methods for trimming sail which enabled them to sail across the wind.
Phoenicians added a long straight keel for increased lateral
resistance, which allowed them to sail upwind. Lateen sail was
developed probably in the fifth century BCE and had quite good windward
performance.
Chinese had junk sails capable of upwind sailing at least around
300BCE. Polynesian had vessels capable of upwind travel before they met
Europeans, possibly a good while before.
--
Juho Julkunen
Jack Linthicum
Probably back to before there are any written articles about sailing.
Some bishop n 404 AD described the event but anyone with a ship and a
sail that can be moved to change its angle to the wind could decide
that tacking is the best way to beat into the wind. The Polynesians
had triangular sails in the far BCs and lateen rigs were around in the
period of the 4th or 5th century BC.
Look up I. C. Campbell, "The Lateen Sail in World History", Journal of
World History (University of Hawaii), 6.1 (Spring 1995),
Rich Rostrom
>
> In regard of sailing upwind, I note its absence in C.S. Lewis's*
> fantasy "The Voyage of the Dawn Treader". The sailors begin to
> grumble that they have been sailing with a prevailing wind so long
> they can't get back. I've wondered if it was the Narnians who hadn't
> discovered tacking into the wind, or C.S. Lewis.
Sailing upwind by tacking is possible, but a lot slower
than sailing downwind. The tacking course is a zigzag
track, which covers a lot of extra distance, especially
for a square rigger which can't sail close to the wind.
A long voyage downwind into open ocean could easily
become a one-way trip.
Michael Ash
> On Oct 25, 2:36 am, Edward Green <spamspamsp...@netzero.com> wrote:
>>
>> In regard of sailing upwind, I note its absence in C.S. Lewis's*
>> fantasy "The Voyage of the Dawn Treader". The sailors begin to
>> grumble that they have been sailing with a prevailing wind so long
>> they can't get back. I've wondered if it was the Narnians who hadn't
>> discovered tacking into the wind, or C.S. Lewis.
>
> Sailing upwind by tacking is possible, but a lot slower
> than sailing downwind. The tacking course is a zigzag
> track, which covers a lot of extra distance, especially
> for a square rigger which can't sail close to the wind.
Probably true in practice but not necessarily in theory. A sailboat can
sail faster than the wind, but only if it's going at least partially
upwind. I believe a theoretically optimal sailboat will be able to sail
arbitrarily fast at angle angle into the wind except directly into it.
Real sailboats obviously can't. I know that with good technology the
optimal angle is definitely not straight downwind, but I don't know enough
about sailing to really say more.
Eivind
> A sailboat can sail faster than the wind, but only if
> it's going at least partially upwind.
Nonsense. Unless by "partially upwind" you mean any direction whatsoever
except directly downwind and directly upwind. That's for your
"theoretical" sailboat, of which there are none. Real sailboats can
however easily sail faster than the wind when going for example
sideways, relative to the wind. That's not "partially upwind" in my book.
> Real sailboats obviously can't. I know that with good technology the
> optimal angle is definitely not straight downwind, but I don't know enough
> about sailing to really say more.
Straight downwind no sailboat can go faster than the wind. This is
inituitively obvious, consider a sailboat that is going downwind exactly
as fast as the wind. At this point its sails are experiencing zero
force, regardless of what shape they are, so obviously they can do
nothing more for you.
The answer is that the more streamlined, more keeled, more advanced a
sailboat is, the higher it can go into the wind, and the higher the
optimal angle for speed is. The optimal angle for speed is not the same
as the highest-possible-angle though.
It also depends on the wind, the angle isn't the same in low and in high
winds.
Eivind
Michael Ash
> Michael Ash skreiv:
>
>> A sailboat can sail faster than the wind, but only if
>> it's going at least partially upwind.
>
> Nonsense. Unless by "partially upwind" you mean any direction whatsoever
> except directly downwind and directly upwind. That's for your
> "theoretical" sailboat, of which there are none. Real sailboats can
> however easily sail faster than the wind when going for example
> sideways, relative to the wind. That's not "partially upwind" in my book.
You're right, my bad. I was mixing up "faster than the wind" with "no
theoretical limit on maximum speed". The latter requires the boat to be
sailing in the hemisphere that would be designated as "into the wind". If
the wind is coming from any angle from behind, then there is some fixed
maximum limit which depends on the angle and the wind speed. However you
are correct that the maximum speed will be greater than the wind speed if
the angle is not directly downwind.
ErrolC
Hence my sig down-thread. Irwin was a major force in developing
theories of Polynesian expansion, and realised that a planned
exploration approach up(prevailing)wind made a lot more sense than
'spread by accident'.
--
Errol Cavit | "It is not clear to everyone that a few paragraphs
fudged up by a bunch of mediocre, biased and possibly deceitful
British Maori-language scholars in 1840 is a suitable bible for Maori-
Pakeha relations in the 21stC, infallible and omnipotent." James
Belich, <Making Peoples>
JimboCat
> Michael Ash skreiv:
>
> > A sailboat can sail faster than the wind, but only if
> > it's going at least partially upwind.
>
> Nonsense. Unless by "partially upwind" you mean any direction whatsoever
> except directly downwind and directly upwind. That's for your
> "theoretical" sailboat, of which there are none.
Two morons decide to race downstream on a wide river in sailboats on a
windless day. [These are "theoretical" sailboats, the current in the
river is perfectly uniform, and there is absolutely no air moving
anywhere whatsoever (spherical cow territory).] They untie from the
dock and begin drifting downstream.
The first moron detects a relative headwind and ducks down in the
cockpit to cut the drag.
The second moron says, "Aha, finally a wind," and puts up the sails
and begins tacking back and forth.
Who wins the race?
Jim Deutch (JimboCat)
--
"Do you have a cite for that? Most wall-plugs don't have that wall-
plug
efficiency." - David M. Palmer
Eivind
> Two morons decide to race downstream on a wide river in sailboats on a
> windless day. [These are "theoretical" sailboats, the current in the
> river is perfectly uniform, and there is absolutely no air moving
> anywhere whatsoever (spherical cow territory).] They untie from the
> dock and begin drifting downstream.
>
> The first moron detects a relative headwind and ducks down in the
> cockpit to cut the drag.
>
> The second moron says, "Aha, finally a wind," and puts up the sails
> and begins tacking back and forth.
>
> Who wins the race?
The choice of frame is free.
It makes no difference to a sailboat if the water is moving and the air
stands still (relative to the earth) or if the water stays still and the
air is moving.
The second moron wins.
Eivind
cryptoguy
I'm not convinced. Yes, Moron 2 moves faster relative to the water,
in the direction he is tacking, but that's at an angle, not directly
downstream. But I don't think he can be moving down the river
faster than Moron 1.
Can you give a cite that shows that it is possible to sail against
the prevailing wind faster than with it? Tacking back and forth
is called 'beating' if you need a search term.
Peter Trei
Jack Linthicum
http://www.physclips.unsw.edu.au/jw/sailing.html
http://wings.avkids.com/Book/Sports/intermediate/sailing-01.html
The sail in a tack is using the shape of the sail as an airfoil,
sailing with the wind the sail is actually decelerating the effect of
the wind pushing on the sail.
cryptoguy
wrote:
>
> The sail in a tack is using the shape of the sail as an airfoil,
> sailing with the wind the sail is actually decelerating the effect of
> the wind pushing on the sail.
Hmm... in this artificial scenario, I can see this, but in the larger
context of this thread, it's clear that 'favorable trade winds' are
always following winds.
Modern, high performance boats, tacking continuously, might
be able to sail upwind faster than downwind, but I'm curious
whether any ship used during the peopling of the world could
sail upwind with sufficient efficiency to do this.
Peter Trei
Jack Linthicum
>
> > The sail in a tack is using the shape of the sail as an airfoil,
> > sailing with the wind the sail is actually decelerating the effect of
> > the wind pushing on the sail.
>
> Hmm... in this artificial scenario, I can see this, but in the larger
> context of this thread, it's clear that 'favorable trade winds' are
> always following winds.
>
> Modern, high performance boats, tacking continuously, might
> be able to sail upwind faster than downwind, but I'm curious
> whether any ship used during the peopling of the world could
> sail upwind with sufficient efficiency to do this.
>
> Peter Trei
Ask the 'nesians, Poly, Micro and Mela
JimboCat
I though Evind was very clear, but let me rephrase.
Change the premises of the problem slightly, and the answer is
obvious:
You are in the middle of the ocean, the waters calm as far as the eye
can see. A very gentle breeze is blowing. Your boat is light and
responsive, so you put up your sails and start tacking slowly into the
breeze.
Does it really matter that you happen to be in the middle of the Gulf
Stream, and as far as the meteorologist is concerned, it's a calm day?
Jim Deutch (JimboCat)
--
"Pirates? Nonsense! We're Preemptive Nautical Salvage Specialists."
Wayne Throop
: You are in the middle of the ocean, the waters calm as far as the eye
: can see. A very gentle breeze is blowing. Your boat is light and
: responsive, so you put up your sails and start tacking slowly into the
: breeze.
Is there a minimum speed of breeze (for a given ship) which can be
effective for going upwind in such a situation? My guess is that there
is, and that it's not totally insubstantial; more than walking speed or
so, maybe.
Wayne Throop thr...@sheol.org http://sheol.org/throopw
JimboCat
> : JimboCat <103134.3...@compuserve.com>
> : You are in the middle of the ocean, the waters calm as far as the eye
> : can see. A very gentle breeze is blowing. Your boat is light and
> : responsive, so you put up your sails and start tacking slowly into the
> : breeze.
>
> Is there a minimum speed of breeze (for a given ship) which can be
> effective for going upwind in such a situation? My guess is that there
> is, and that it's not totally insubstantial; more than walking speed or
> so, maybe.
IANASailor, but I wouldn't be surprised. We were explicitly talking
about spherical cows, however...
Jim Deutch (JimboCat)
--
"Nothing is perfect. Nothing is precise and certain (except the mind
of a pedant). Perfection is the mere repudiation of that ineluctable
inexactitude which is the inmost quality of being."
ergj...@gmail.com
> In rec.arts.sf.science Rich Rostrom <rrostrom.21stcent...@rcn.com> wrote:
>
> > On Oct 25, 2:36 am,EdwardGreen<spamspamsp...@netzero.com> wrote:
>
> >> In regard of sailing upwind, I note its absence in C.S. Lewis's*
> >> fantasy "The Voyage of the Dawn Treader". The sailors begin to
> >> grumble that they have been sailing with a prevailing wind so long
> >> they can't get back. I've wondered if it was the Narnians who hadn't
> >> discovered tacking into the wind, or C.S. Lewis.
>
> > Sailing upwind by tacking is possible, but a lot slower
> > than sailing downwind. The tacking course is a zigzag
> > track, which covers a lot of extra distance, especially
> > for a square rigger which can't sail close to the wind.
>
> Probably true in practice but not necessarily in theory. A sailboat can
> sail faster than the wind, but only if it's going at least partially
> upwind. I believe a theoretically optimal sailboat will be able to sail
> arbitrarily fast at angle angle into the wind except directly into it.
> Real sailboats obviously can't. I know that with good technology the
> optimal angle is definitely not straight downwind, but I don't know enough
> about sailing to really say more.
Ice boats can sail _very_* fast into the wind.
*(the underscore means "I don't really know how fast, but I want it to
look impressive :)
ergj...@gmail.com
>
>
>
> > JimboCat skreiv:
>
> > > Two morons decide to race downstream on a wide river in sailboats on a
> > > windless day. [These are "theoretical" sailboats, the current in the
> > > river is perfectly uniform, and there is absolutely no air moving
> > > anywhere whatsoever (spherical cow territory).] They untie from the
> > > dock and begin drifting downstream.
>
> > > The first moron detects a relative headwind and ducks down in the
> > > cockpit to cut the drag.
>
> > > The second moron says, "Aha, finally a wind," and puts up the sails
> > > and begins tacking back and forth.
>
> > > Who wins the race?
>
> > The choice of frame is free.
>
> > It makes no difference to a sailboat if the water is moving and the air
> > stands still (relative to the earth) or if the water stays still and the
> > air is moving.
>
> > The second moron wins.
>
> I'm not convinced. Yes, Moron 2 moves faster relative to the water,
> in the direction he is tacking, but that's at an angle, not directly
> downstream. But I don't think he can be moving down the river
> faster than Moron 1.
I am convinced. The comment about frame is key.
Look at the rest frame of the water, with a wind going overhead equal
and opposite in speed to the current. The guy who ducks in the
cockpit lessens the rate at which he is blown downwind, but he is
still blown downwind. The other guy is moving _upwind_. Translate
back into the rest frame of the shores, and he is moving faster
downriver.
ergj...@gmail.com
>
> The sail in a tack is using the shape of the sail as an airfoil,
> sailing with the wind the sail is actually decelerating the effect of
> the wind pushing on the sail.
This is partially, if you will excuse my usage, a fixation on the
magical properties of "airfoil". Tacking into the wind (I've
recovered my vector diagram now) can be understood purely in terms of
a sail acting like a slat, resulting in a specular reflection of the
wind.
I see by looking at the same diagram (which unfortunately I can't
sketch here), as well as the valuable change of frame concept
mentioned earlier, that as the boat accelerated, the effective wind
would swing around towards the bow.... damn...!
I think the effective limits would be wind resistance of the rest of
the above water hull, and hull resistance in the water, but it looks
to me like there is no other theoretical limit on the speed of the
hull. Oh yeah, side slip of the keel, also. It actually looks like
other that these factors, there is a kind of self-amplifying effect of
sailing into the wind -- the head wind becomes faster, and you can
therefore extract even _more_ energy from it.
I know it sounds like a tale told by a moron, but I think it's
correct. As I said, I think ice boats can travel ridiculously fast
into the wind ... all but eliminate hull friction and side slipping --
drag is your only remaining enemy. The seemingly impossible non-
intuitive feature of the unlimited speed must be the power implicit
between the wind and the water (ice), which you can seemingly exploit
more quickly by moving more quickly...
Yeah, I know, it still sounds like a tale told by an idiot... but I
still think it's correct.
Larry Caldwell
(Michael Ash) says...
In the USA, when a word ends in s, you just add the apostrophe without
the s to create the possessive, so the correct usage would be C. S.
Lewis' fantasy.
Your insight about sails being airfoils is correct, but you also need a
water foil (center board) for effective tacking. That keeps the boat
from being blown sideways through the water.
--
For email, replace firstnamelastinitial
with my first name and last initial.
Michael Ash
> In article <12249408...@web1.segnet.com>, mi...@mikeash.com
> (Michael Ash) says...
>> In rec.arts.sf.science Edward Green <spamsp...@netzero.com> wrote:
>> > In regard of sailing upwind, I note its absence in C.S. Lewis's*
>> > fantasy "The Voyage of the Dawn Treader". The sailors begin to
>> > grumble that they have been sailing with a prevailing wind so long
>> > they can't get back. I've wondered if it was the Narnians who hadn't
>> > discovered tacking into the wind, or C.S. Lewis.
>> >
>> > Not a sailor, I've worked out the vector diagram for tacking several
>> > times, and though I can make it work, I can't make the intuition
>> > stick. What's the history of this invention, anyway?
>>
>> I can't answer the question about the history. But I've found that the
>> intuition works a lot better if I stop thinking of them as sails and start
>> thinking of them as wings. Sails are just inflatable airfoils of varying
>> degrees of performance.
>>
>> > *if I read E.B. White correctly, that's correct.
>>
>> If you're referring to the apostrophe, I'm pretty sure that's right, even
>> though people seem to feel very uncomfortable putting 's after an s.
>
> In the USA, when a word ends in s, you just add the apostrophe without
> the s to create the possessive, so the correct usage would be C. S.
> Lewis' fantasy.
Not how I was taught. I was taught that you add an apostrophe without a
trailing s for a *plural* word which ends in s. Singular words which end
in s still get 's at the end. So you have abscess's and abscesses' and, of
course, children's. I could be wrong on this though, but I'm pretty sure
that's at least how I was taught to do it.
> Your insight about sails being airfoils is correct, but you also need a
> water foil (center board) for effective tacking. That keeps the boat
> from being blown sideways through the water.
An excellent point. One which is often ignored simply because the water is
about three orders of magnitude denser makes a good keel, making it much
easier to have than a good sail, but still critical to the thing working
properly.
Edward Green
> In rec.arts.sf.science Larry Caldwell <firstnamelastinit...@peaksky.com> wrote:
>
>
>
> > In article <1224940835.768...@web1.segnet.com>, m...@mikeash.com
> > (Michael Ash) says...
> >> In rec.arts.sf.science Edward Green <spamspamsp...@netzero.com> wrote:
> >> > In regard of sailing upwind, I note its absence in C.S. Lewis's*
> >> > fantasy "The Voyage of the Dawn Treader". The sailors begin to
> >> > grumble that they have been sailing with a prevailing wind so long
> >> > they can't get back. I've wondered if it was the Narnians who hadn't
> >> > discovered tacking into the wind, or C.S. Lewis.
>
> >> > Not a sailor, I've worked out the vector diagram for tacking several
> >> > times, and though I can make it work, I can't make the intuition
> >> > stick. What's the history of this invention, anyway?
>
> >> I can't answer the question about the history. But I've found that the
> >> intuition works a lot better if I stop thinking of them as sails and start
> >> thinking of them as wings. Sails are just inflatable airfoils of varying
> >> degrees of performance.
>
> >> > *if I read E.B. White correctly, that's correct.
>
> >> If you're referring to the apostrophe, I'm pretty sure that's right, even
> >> though people seem to feel very uncomfortable putting 's after an s.
>
> > In the USA, when a word ends in s, you just add the apostrophe without
> > the s to create the possessive, so the correct usage would be C. S.
> > Lewis' fantasy.
>
> Not how I was taught. I was taught that you add an apostrophe without a
> trailing s for a *plural* word which ends in s. Singular words which end
> in s still get 's at the end. So you have abscess's and abscesses' and, of
> course, children's. I could be wrong on this though, but I'm pretty sure
> that's at least how I was taught to do it.
My recollection agrees with yours, for what that's worth. And anyway,
E. B. White was a 'murcan. And also way, I would _say_ "Lewis's",
pronounced "Lewises" fantasy. But I wouldn't get too testy about it:
we're losing the battle to keep the apostrophe out of the pronoun its,
and indeed out of (non-possessive) plurals, which foretells the coming
collapse of western civilization more than global warming, even.
> > Your insight about sails being airfoils is correct, but you also need a
> > water foil (center board) for effective tacking. That keeps the boat
> > from being blown sideways through the water.
As I mentioned, I think airfoils in general are overrated. At best,
they are slightly peculiar and more efficient modified slats, but
qualitatively, they do nothing an angled slat does not do: deflect
air. I've argued a lot about this on Usenet, so I must be an
expert. :^}. "Lift" is just Newtonian deflection of air, whether done
cleverly or crudely. Airfoils do it somewhat cleverly, sometimes.
I'm not sure why Google sometimes posts my name and sometimes my gmail
address, but I'm not trying to be cute.
Eivind
>>> The first moron detects a relative headwind and ducks down in the
>>> cockpit to cut the drag.
>>> The second moron says, "Aha, finally a wind," and puts up the sails
>>> and begins tacking back and forth.
>> The choice of frame is free.
>>
>> It makes no difference to a sailboat if the water is moving and the air
>> stands still (relative to the earth) or if the water stays still and the
>> air is moving.
>>
>> The second moron wins.
> I'm not convinced. Yes, Moron 2 moves faster relative to the water,
> in the direction he is tacking, but that's at an angle, not directly
> downstream. But I don't think he can be moving down the river
> faster than Moron 1.
No, he actually moves *upwind* by tacking. That's not only for a
theorethical perfect sailboat. Even an actual, existing sailboat manages
this, sailing against the wind.
Moron 1 ends up following the stream down at the speed of the water.
Since these are theorethical perfect sailboats his air-drag is zero when
he aims to minimize it.
Really, it's perfectly obvious. Allow the frame to shift in your head
and you see it clear as day.
Consider the PERFECTLY analogous situation: Who is better at traveling
north in a wind coming from the north; moron 1 who ducks down, drops his
sails, or moron 2 who is tacking northwards ?
You agree in this situation tacking is beneficial, yes ?
Then, in your head, change frames: It's no longer air moving south over
still water. It's water moving north in still air.
To the sailboats this really really makes zero difference (aslong as
they interact only with water and air), all they care about is the
relative motion of the two media.
Frames being freely choosable is pretty basic physics, I don't know what
kinda reference you want for that. Try any intro-level physics-textbook
whatsoever.
Eivind Kjørstad
Eivind
> Is there a minimum speed of breeze (for a given ship) which can be
> effective for going upwind in such a situation? My guess is that there
> is, and that it's not totally insubstantial; more than walking speed or
> so, maybe.
Not that I've noticed windsurfing, no. There's offcourse a minimum
windspeed under which it gets *boring*, but even the ligthest of ripples
will work.
The change of *apparent* wind-direction and *apparent* wind-speed due to
your own speed is very well-known and plenty noticeable for any sailer.
If the wind is really 10m/s from the north, but you're going 10m/s to
the east, your *apparent* wind is going to be 14m/s coming from the
northeast.
Eivind
Eivind
> Ice boats can sail _very_* fast into the wind.
>
> *(the underscore means "I don't really know how fast, but I want it to
> look impressive :)
It's impressive enough; up to 80 mph and an angle up to aproximately
35%-40% into the wind.
It's generally better to go only 25% into the wind though, because at
the extreme angles your speed-loss is larger than your gain from the
increased angle.
Eivind
Michael Ash
> On Nov 2, 7:11?pm, Michael Ash <m...@mikeash.com> wrote:
>> Not how I was taught. I was taught that you add an apostrophe without a
>> trailing s for a *plural* word which ends in s. Singular words which end
>> in s still get 's at the end. So you have abscess's and abscesses' and, of
>> course, children's. I could be wrong on this though, but I'm pretty sure
>> that's at least how I was taught to do it.
>
> My recollection agrees with yours, for what that's worth. And anyway,
> E. B. White was a 'murcan. And also way, I would _say_ "Lewis's",
> pronounced "Lewises" fantasy. But I wouldn't get too testy about it:
> we're losing the battle to keep the apostrophe out of the pronoun its,
> and indeed out of (non-possessive) plurals, which foretells the coming
> collapse of western civilization more than global warming, even.
So true. The apostrophe is descending to the point where it essentially
just means "Look out, here comes an S!"
>> > Your insight about sails being airfoils is correct, but you also need a
>> > water foil (center board) for effective tacking. ?That keeps the boat
>> > from being blown sideways through the water.
>
> As I mentioned, I think airfoils in general are overrated. At best,
> they are slightly peculiar and more efficient modified slats, but
> qualitatively, they do nothing an angled slat does not do: deflect
> air. I've argued a lot about this on Usenet, so I must be an
> expert. :^}. "Lift" is just Newtonian deflection of air, whether done
> cleverly or crudely. Airfoils do it somewhat cleverly, sometimes.
As a pilot, I view this differently, although with the same end results.
Slats are airfoils too! They happen to be poor airfoils, as their L/D
ratio is very low, but they are airfoils.
What people are trying to say when they say "good sails are actually
airfoils" is that they produce lift. That is, they produce a force that is
perpendicular to the velocity of the oncoming air. A boring crappy square
sail produces no lift, only drag, and therefore can only sail downwind. A
good sail will produce lift and will therefore have the ability to sail
upwind. The L/D ratio of that sail along with the drag characteristics of
the hull will tell you just how fast and at what angle. The flat slat is
an airfoil just like the others, it just doesn't perform as well.
It's the lift, not the airfoil-ness, that really counts and makes a
difference. With that intuitive leap the rest becomes (I think) pretty
obvious, and without it sailing upwind makes no sense.
Eivind
> What people are trying to say when they say "good sails are actually
> airfoils" is that they produce lift. That is, they produce a force that is
> perpendicular to the velocity of the oncoming air. A boring crappy square
> sail produces no lift, only drag, and therefore can only sail downwind.
This is factually incorrect.
A perfectly flat, perfectly square sail can, infact, sail upwind.
Not as well as a more sophisticated sail, granted, but there's nothing
magically separating 1 degree downwind from 1 degree upwind.
Eivind
Michael Ash
>
>> What people are trying to say when they say "good sails are actually
>> airfoils" is that they produce lift. That is, they produce a force that is
>> perpendicular to the velocity of the oncoming air. A boring crappy square
>> sail produces no lift, only drag, and therefore can only sail downwind.
>
> This is factually incorrect.
>
> A perfectly flat, perfectly square sail can, infact, sail upwind.
Implicit in my description of the "boring crappy square sail" is that it
produces no lift. Of course any sail can produce lift, but the boring
crappy square sails don't produce lift because the people who handle them
don't make them do that. Without lift you cannot sail upwind.
> Not as well as a more sophisticated sail, granted, but there's nothing
> magically separating 1 degree downwind from 1 degree upwind.
Actually there is. 1 degree downwind requires only drag. 1 degree upwind
requires your sail to produce lift.
Jack Linthicum
The Vikings created the beitass (good name) which we call a "whisker
pole" now, to stiffen the luff of the sail and point the sail into the
wind.
To Harness the Wind By Leo Block
http://books.google.com/books?id=ezgq0VnV5XQC&pg=PA51&lpg=PA51&dq=sail+shapes+history&source=web&ots=1BnGe9Jh_7&sig=_RqIUtu5_RF3x0_IzuLX4cXUAt0&hl=en&sa=X&oi=book_result&resnum=6&ct=result#PPA26,M1
page 26
Before the beitass the square sail was tilted and brailed to create a
"near lateen" shape. above reference page 20
Eivind
>>> A boring crappy square sail produces no lift, only drag, and
>>> therefore can only sail downwind.
>> This is factually incorrect.
>> A perfectly flat, perfectly square sail can, infact, sail upwind.
> Implicit in my description of the "boring crappy square sail" is that it
> produces no lift. Of course any sail can produce lift, but the boring
> crappy square sails don't produce lift because the people who handle them
> don't make them do that.
Perhaps that's what you mean, but it's not what you said. You stated
categorically that a "boring crappy square sail" "con only sail
downwind", when I call you on this, pointing out that actually, a
flat-square sail is perfectly capable of sailing upwind you now change
your statement. Now you claim the sails can't "because the people who
handle them don't make them do that".
That's just silly.
Eivind
Michael Ash
I was hoping that "boring", "crappy" and "produces no lift" were clues
that I was talking about a sail that produced no lift, and therefore could
not sail upwind.
Crown-Horned Snorkack
> >>> Michael Ash skreiv:
>
> >>>> A boring crappy square sail produces no lift, only drag, and
> >>>> therefore can only sail downwind.
>
> >>> This is factually incorrect.
> >>> A perfectly flat, perfectly square sail can, infact, sail upwind.
>
> >> Implicit in my description of the "boring crappy square sail" is that it
> >> produces no lift. Of course any sail can produce lift, but the boring
> >> crappy square sails don't produce lift because the people who handle them
> >> don't make them do that.
>
> > Perhaps that's what you mean, but it's not what you said. You stated
> > categorically that a "boring crappy square sail" "con only sail
> > downwind", when I call you on this, pointing out that actually, a
> > flat-square sail is perfectly capable of sailing upwind you now change
> > your statement. Now you claim the sails can't "because the people who
> > handle them don't make them do that".
>
> > That's just silly.
>
> I was hoping that "boring", "crappy" and "produces no lift" were clues
> that I was talking about a sail that produced no lift, and therefore could
> not sail upwind.
>
cylindrical (or conical, spherical etc.) sail. Cylinder, because of
its axial symmetry, is the only airfoil, or waterfoil, that through
all angles of attack is for symmetry reasons incapable of producing
lift and only produces drag.
The performance of a ship depends on two foils. Airfoil and waterfoil.
If you have a ship which has a perfect waterfoil (like iceboat) and
airfoil only capable of drag (cylindrical one), it can move only
downwind - but it can move arbitrarily close to right angles to the
wind.
If you have a ship which has a perfectly incapable waterfoil, with
axial symmetry so it only creates drag, but a perfect airfoil, it also
can only sail downwind - but it again can move arbitrarily close to
right angles to the wind.
So, in order to sail upwind, one needs both a waterfoil and an
airfoil.
But with airfoil and waterfoil both with limited effectiveness, you
can very well find that you cannot sail upwind either. The combined
efficiencies of waterfoil and airfoil will give you a sum somewhere
between 0 and 180 degrees.
Edward Green
> In rec.arts.sf.science Edward Green <ergjo...@gmail.com> wrote:
> > As I mentioned, I think airfoils in general are overrated. At best,
> > they are slightly peculiar and more efficient modified slats, but
> > qualitatively, they do nothing an angled slat does not do: deflect
> > air. I've argued a lot about this on Usenet, so I must be an
> > expert. :^}. "Lift" is just Newtonian deflection of air, whether done
> > cleverly or crudely. Airfoils do it somewhat cleverly, sometimes.
>
> As a pilot, I view this differently, although with the same end results.
> Slats are airfoils too! They happen to be poor airfoils, as their L/D
> ratio is very low, but they are airfoils.
>
> What people are trying to say when they say "good sails are actually
> airfoils" is that they produce lift. That is, they produce a force that is
> perpendicular to the velocity of the oncoming air. A boring crappy square
> sail produces no lift, only drag, and therefore can only sail downwind. A
> good sail will produce lift and will therefore have the ability to sail
> upwind. The L/D ratio of that sail along with the drag characteristics of
> the hull will tell you just how fast and at what angle. The flat slat is
> an airfoil just like the others, it just doesn't perform as well.
Ok. I'll buy into your definition of an airfoil, since you buy into
my advocacy of the slat. I feel compelled to point out cantankerously
then that a square sail _can_ produce lift too, if the wind is at an
angle to the yard. Now, maybe that is not possible, considering the
torque on the yard. I don't know enough about square rigging to
answer that.
> It's the lift, not the airfoil-ness, that really counts and makes a
> difference. With that intuitive leap the rest becomes (I think) pretty
> obvious, and without it sailing upwind makes no sense.
Alright, buy that: sailing up wind requires lift (force at right
angles to wind direction) and a keel, which also supplies "lift", by
this definition, relative to the hull flow. Whoa... heavy insight
here man: a sailing ship is simultaneously sailing in two media, one
much denser than the other, and (one hopes) in relative motion. Once
in relative motion the skillful sailor is able to exploit that power
source to go pretty much wherever he or she wants.
Is there any "two media relative flow" analogue in outer space one
could tack with? One could always use the cosmological background
radiation vs. stellar winds, near stars, if one had spectrally
differentiating sails? Or maybe the star's radiation would swamp the
background even in the low frequency spectral ranges.
Edward Green
wrote:
> There is only one type of sail that does not produce lift. And that is
> cylindrical (or conical, spherical etc.) sail. Cylinder, because of
> its axial symmetry, is the only airfoil, or waterfoil, that through
> all angles of attack is for symmetry reasons incapable of producing
> lift and only produces drag.
>
> The performance of a ship depends on two foils. Airfoil and waterfoil.
>
> If you have a ship which has a perfect waterfoil (like iceboat) and
> airfoil only capable of drag (cylindrical one), it can move only
> downwind - but it can move arbitrarily close to right angles to the
> wind.
>
> If you have a ship which has a perfectly incapable waterfoil, with
> axial symmetry so it only creates drag, but a perfect airfoil, it also
> can only sail downwind - but it again can move arbitrarily close to
> right angles to the wind.
>
> So, in order to sail upwind, one needs both a waterfoil and an
> airfoil.
Nice analysis!
I suppose it would be cheating to spin the cylinder?
> But with airfoil and waterfoil both with limited effectiveness, you
> can very well find that you cannot sail upwind either. The combined
> efficiencies of waterfoil and airfoil will give you a sum somewhere
> between 0 and 180 degrees.
Not sure what you are getting at here, and what your angles mean.
Surely if you can travel arbitrarily close to perpendicular to the
wind with no waterfoil and a good airfoil, even a crummy waterfoil can
propel you a few degrees into the wind. By "sail upwind" do you mean
directly into the wind?
I think the only way to sail directly into the wind is to cheat: to
use the sea floor as a reference when there is a current. You can
never sail directly into the wind in the frame of still water (except
maybe by indulging in some higher order cheating involving Coriolis
forces).
Wayne Throop
: Is there any "two media relative flow" analogue in outer space one
: could tack with? One could always use the cosmological background
: radiation vs. stellar winds, near stars, if one had spectrally
: differentiating sails? Or maybe the star's radiation would swamp the
: background even in the low frequency spectral ranges.
Well, iirc, in the solar ssystem, the solar wind and light pressure has
a slight angle between them, which is visible in comet tail structure
among other things. However, I'm not sure you can get much out of that.
http://www.windows.ucar.edu/tour/link=/comets/tail.html
Of course, then again, you can just look at light pressure and whatever
the local gravity is, though "left" wrt gravity is... hrm... not really
possible, quite.
Michael Ash
> angles to wind direction) and a keel, which also supplies "lift", by
> this definition, relative to the hull flow. Whoa... heavy insight
> here man: a sailing ship is simultaneously sailing in two media, one
> much denser than the other, and (one hopes) in relative motion. Once
> in relative motion the skillful sailor is able to exploit that power
> source to go pretty much wherever he or she wants.
Yep, that's exactly it. This is why a sailboat can mostly decide where to
go, whereas neither a sail-less boat nor a hot-air balloon can.
> Is there any "two media relative flow" analogue in outer space one
> could tack with? One could always use the cosmological background
> radiation vs. stellar winds, near stars, if one had spectrally
> differentiating sails? Or maybe the star's radiation would swamp the
> background even in the low frequency spectral ranges.
Within the solar system, a combined light and magnetic sail (for solar
radiation and solar wind) could give you something sort of similar.
Note that you don't necessarily need two media, one medium and a force can
do it too. For example, sailplanes can go where they want (when conditions
are right) due to moving air and gravity. (And, surprise, the reason the
sailplane can pretty much do as it please while the balloon is *mostly* at
the mercy of the atmosphere is because the sailplane has an airfoil.)
Likewise, a solar sail ship can go where it likes (slooooowly) throughout
the solar system using simply light and gravity. I assume that using a
magnetic sail in addition to a light sail will expand its possible
manuevers but I haven't worked it through.
Eivind
> I think the only way to sail directly into the wind is to cheat: to
> use the sea floor as a reference when there is a current. You can
> never sail directly into the wind in the frame of still water
Why not ? I think it depends on how you define "sail".
If it means just maintaining a passive, constant shape and being pushed
directly against the wind by the sail-and-keel then you are correct,
that's not possible.
But if it just means "being windpowered" then it is perfectly possible.
For example, a large vehicle could in principle have two hulls that tack
oposite of eachother so the the vehicle itself moves directly against
the wind. The vehicle could look like a telescoping katamaran. (I didn't
say it'd be PRACTICAL, just theorethically possible)
Or you could simply drop a large keel to not drift, then use a
windturbine to charge a battery, after the battery is full, haul the
keel up and start your electrically powered propeller. repeat until
you've arrived.
Eivind
Edward Green
I concede. Good thinking.
Wayne Throop
: Or you could simply drop a large keel to not drift, then use a
: windturbine to charge a battery, after the battery is full, haul the
: keel up and start your electrically powered propeller. repeat until
: you've arrived.
Actually, couldn't you just run the wind turbine and propeller
simultaneously and continuously? I think that should work; your wind
turbine (as an ideal) would be set up to push the blades/airfoils sidways,
with minimum drag, while the propeller/waterfoils would be set up to push
the water back. Basically, counting on the ability to have lower drag
from the air medium, and higher thrust from the denser water, and so in
effect deflecting the wind forces sideways, but the water forces pointing
straightways. Hrm. Feels like it should work, but I'm not at all sure.
Hrm. Ah, think of it with the wind turbine and propeller mechanically
linked, and conceive of the propeller as a keel "tacking" in a circle,
"microtacks" or whatever. Think of the propeller as a keel that the
wind pushes on via mechanical linkage. Same concept as the telescoping
katamaran, but going round and round rather than back and forth.
Edward Green
> : Eivind <eivindor...@gmail.com>
> : Or you could simply drop a large keel to not drift, then use a
> : windturbine to charge a battery, after the battery is full, haul the
> : keel up and start your electrically powered propeller. repeat until
> : you've arrived.
>
> Actually, couldn't you just run the wind turbine and propeller
> simultaneously and continuously? I think that should work; your wind
> turbine (as an ideal) would be set up to push the blades/airfoils sidways,
> with minimum drag, while the propeller/waterfoils would be set up to push
> the water back. Basically, counting on the ability to have lower drag
> from the air medium, and higher thrust from the denser water, and so in
> effect deflecting the wind forces sideways, but the water forces pointing
> straightways. Hrm. Feels like it should work, but I'm not at all sure.
It might work, but it's hard to distinguish it intuitively from
pushing a boat forward in still air, turning the wind turbine, hence
powering the water propeller, and... viola! perpetual motion! I'm
not saying it is perpetual motion in the case you have air movement,
just that intuitively it feels about the same.
> Hrm. Ah, think of it with the wind turbine and propeller mechanically
> linked, and conceive of the propeller as a keel "tacking" in a circle,
> "microtacks" or whatever. Think of the propeller as a keel that the
> wind pushes on via mechanical linkage. Same concept as the telescoping
> katamaran, but going round and round rather than back and forth.
I think we have to run the numbers, and show that when there is a
breeze, the induced drag in the water propeller is smaller than that
in the air propeller, so that we just _might_ make parasitic drag
small enough to go forward: whereas in still air, we should find the
numbers are just the same ... i.e., there is no margin for
unproductive drag, so practically (as we expect), the think cannot
work. At least that is the sane answer.
Eivind
> : Eivind <eivin...@gmail.com>
> : Or you could simply drop a large keel to not drift, then use a
> : windturbine to charge a battery, after the battery is full, haul the
> : keel up and start your electrically powered propeller. repeat until
> : you've arrived.
> Actually, couldn't you just run the wind turbine and propeller
> simultaneously and continuously? I think that should work; your wind
> turbine (as an ideal) would be set up to push the blades/airfoils sidways,
> with minimum drag, while the propeller/waterfoils would be set up to push
> the water back.
That would be possible I think. Consider the situation on land. You have
a vehicle with wheels and a wind-turbine on the rood, headed directly
into the wind.
It can turn on the brakes, stand still and generate power. But it seems
to me it could also connect the wind-turbine to the wheels and go
forward, provided the gearing was low enough. (seems to me that a
infinitely low gearing should be no different from putting the brakes
on, so I don't see why a -almost- infinitely low gearing shouldn't cause
us to creep forward)
I *think* the situation on water is analogous, when we're talking
spherical-cow-territory propellers and keels. (a wheel is a really good
keel: It has very low friction in one direction, and incredible high
friction in any other direction)
Eivind
Edward Green
> Wayne Throop skreiv:
>
> > : Eivind <eivindor...@gmail.com>
> > : Or you could simply drop a large keel to not drift, then use a
> > : windturbine to charge a battery, after the battery is full, haul the
> > : keel up and start your electrically powered propeller. repeat until
> > : you've arrived.
> > Actually, couldn't you just run the wind turbine and propeller
> > simultaneously and continuously? I think that should work; your wind
> > turbine (as an ideal) would be set up to push the blades/airfoils sidways,
> > with minimum drag, while the propeller/waterfoils would be set up to push
> > the water back.
>
> That would be possible I think. Consider the situation on land. You have
> a vehicle with wheels and a wind-turbine on the rood, headed directly
> into the wind.
>
> It can turn on the brakes, stand still and generate power. But it seems
> to me it could also connect the wind-turbine to the wheels and go
> forward, provided the gearing was low enough. (seems to me that a
> infinitely low gearing should be no different from putting the brakes
> on, so I don't see why a -almost- infinitely low gearing shouldn't cause
> us to creep forward)
That's some good analytical thinking there (he said in frank
admiration).
> I *think* the situation on water is analogous, when we're talking
> spherical-cow-territory propellers and keels. (a wheel is a really good
> keel: It has very low friction in one direction, and incredible high
> friction in any other direction)
Of course (and I'm neither arguing pro nor con, just commenting) in
water we can't put the brakes on. An analogy might be the difference
between required power to stand on the ground, and to hover 10 ft. off
the ground. The latter, given the absence of brakes, requires power
to constantly move fluid, while the former does not. Similarly, given
a body sticking into both the water and the air (otherwise known as a
"boat"), with the wind blowing (which takes the role of gravity), it
takes no power to ride at anchor, but it does take some power merely
to hold our place against the wind otherwise.
It doesn't seem to me to be a slam-dunk that we can get more than this
minimum power into a screw by sticking up a windmill, but maybe I'm
just not being clever enough.
Maybe two very large counter-rotating screws would look enough like
large keels to act like brakes? Or how about paddle wheels? You make
the blades large enough, they start to look very much like road
wheels. Or how about a "paddle tread" ... the whole contraption looks
like a WWI tank tread with huge paddle blades: the turbine car (as
above) rides forward inside the tread, which can be made to have an
arbitrarily small terminal velocity in the water...
Aha! There's the ticket. Since we can in fact make a hull with
athwartships "keels" draggy enough to have an arbitrarily low terminal
velocity in the water when driven by a fixed wind velocity, we can
mount one of your low-geared turbine cars inside, and drive forward.
We then merely take the aft hull sections out of the water and place
them in again at the bow (hence the tread). :-)
Well, _I'm_ convinced (proof of concept). And I think your analysis
of the wind driven car is spot on: since we can charge the battery
with the brakes engaged, we have enough power available continuously
to creep forward at _some_ velocity over ground.
The large bladed screws would serve the same purpose, but the concept
seems more bloody obvious with the paddle wheel... heck, we can drive
around inside a huge paddle wheel like a treadmill! Best yet. We know
we can drive forward at some velocity, and we merely have to make the
terminal velocity of the wind driven underwater hull smaller than that
velocity.
Wayne Throop
: It doesn't seem to me to be a slam-dunk that we can get more than this
: minimum power into a screw by sticking up a windmill, but maybe I'm
: just not being clever enough.
You can pretty much continuously deform the one case into the other.
As an intuition pump, consider two sailing ships tacking into the wind
on mirror-symmetric courses. Now yolk them together. As they separate,
wind lift is being used to drive them apart, and keel lift is being used
to lift them upwind. Then they reverse and come together, changing keel
and sail angle as necessary.
Now, just imagine the waterfoils that are the two keels in isolation,
and suppose that when leftwards-moving, they sink down a bit and
rightwards-moving they rise up a bit so they can move past each other,
and move the whole length of the yolk before reversing, instead of just
half way. Now, at the ends of a pass, rotate these waterfoils rather
than insisting on keeping them one-side-up; that just makes the turn
occur easier. Now, just regularize that trajectory a bit, and you've
got waterfoils moving in a circle, ie, a propeller.
Eh. Seems fairly clear to me. Exact shape of the
wind-(mill/turbine/whatnot) and propeller blades left as an exercise
for the designer, but if the one works, I don't see why the other could
be workable. You've started with two ships tacking upwind, and that
definitely works, then added a yolk, then modified the "keel"s paths
through the water a bit, so you're just varying the exact trajectory
of the waterfoil, and exactly how the airfoil pushes on the waterfoil.
Is all. But you're keeping the same angle of attack of both airfoils and
waterfoils as what was working to start with. And no particular stage
of the deformation adds anything that should make it stop working, naict.
Eivind
> On Nov 6, 3:25 am, Eivind <eivindor...@gmail.com> wrote:
>> I *think* the situation on water is analogous, when we're talking
>> spherical-cow-territory propellers and keels. (a wheel is a really good
>> keel: It has very low friction in one direction, and incredible high
>> friction in any other direction)
> Of course (and I'm neither arguing pro nor con, just commenting) in
> water we can't put the brakes on.
Sure we can. In spherical-cow-land we can create arbitrarily large
friction with the water, which is equivalent to putting brakes on.
(atleast it's arbitrarily close to that) Even in real life, a large keel
standing 90 degrees on the direction of the force can be a pretty darn
good brake.
> An analogy might be the difference
> between required power to stand on the ground, and to hover 10 ft. off
> the ground. The latter, given the absence of brakes, requires power
> to constantly move fluid, while the former does not.
Not in spherical-cow-land it doesn't. You just make your drag/mass ratio
high enough, and your fall-rate is inifintely low.
> Similarly, given a body sticking into both the water and the air (otherwise
> known as a "boat"), with the wind blowing (which takes the role of
gravity), it
> takes no power to ride at anchor, but it does take some power merely
> to hold our place against the wind otherwise.
It takes zero power to get arbitrarily close to holding your place
though. And with a perfect spherical-cow keel it takes zero power.
> It doesn't seem to me to be a slam-dunk that we can get more than this
> minimum power into a screw by sticking up a windmill, but maybe I'm
> just not being clever enough.
Since the minimum power is zero I think it's pretty slam-dunk. (in
spherical-cow-land I mean)
Eivind
Eivind
> As an intuition pump, consider two sailing ships tacking into the wind
> on mirror-symmetric courses. Now yolk them together. As they separate,
> wind lift is being used to drive them apart, and keel lift is being used
> to lift them upwind. Then they reverse and come together, changing keel
> and sail angle as necessary.
Yeah. The telescoping catamaran. I'd pay to see that thing sail, it'd be
an interesting "not because it's useful, but because it's possible"
thing to build. Something for which I have a lot of sympathy.
Consider this thing:
http://video.google.com/videoplay?docid=1166410532864021843
Is it practical ? Hell no !
Is it cool ? Yes !
Eivind
Ilmari Karonen
> On Nov 5, 2:53 pm, thro...@sheol.org (Wayne Throop) wrote:
>> : Eivind <eivindor...@gmail.com>
>> : Or you could simply drop a large keel to not drift, then use a
>> : windturbine to charge a battery, after the battery is full, haul the
>> : keel up and start your electrically powered propeller. repeat until
>> : you've arrived.
>>
>> Actually, couldn't you just run the wind turbine and propeller
>> simultaneously and continuously? I think that should work; your wind
>> turbine (as an ideal) would be set up to push the blades/airfoils sidways,
>> with minimum drag, while the propeller/waterfoils would be set up to push
>> the water back. Basically, counting on the ability to have lower drag
>> from the air medium, and higher thrust from the denser water, and so in
>> effect deflecting the wind forces sideways, but the water forces pointing
>> straightways. Hrm. Feels like it should work, but I'm not at all sure.
>
> It might work, but it's hard to distinguish it intuitively from
> pushing a boat forward in still air, turning the wind turbine, hence
> powering the water propeller, and... viola! perpetual motion! I'm
> not saying it is perpetual motion in the case you have air movement,
> just that intuitively it feels about the same.
Actually, this has been done. A bit of Googling turns up
e.g. http://www.treehugger.com/files/2007/02/windmill_sailbo.php .
Another, even more counterintuive example I came across while looking
for this was http://www.youtube.com/watch?v=aJpdWHFqHm0 . It's a
video of a wind-powered cart that can move downwind faster than the
wind(!). Links to a nice PDF article explaining the design.
The trick, of course, being that, instead of using wind power to push
yourself against the ground, you use power from the wheels to drive a
propeller pushing you against the air. In principle, there should be
nothing stopping you from doing the same on water just as well.
--
Ilmari Karonen
To reply by e-mail, please replace ".invalid" with ".net" in address.
Edward Green
> On 2008-11-06, Edward Green <ergjo...@gmail.com> wrote:
>
>
>
> > On Nov 5, 2:53 pm, thro...@sheol.org (Wayne Throop) wrote:
> >> : Eivind <eivindor...@gmail.com>
> >> : Or you could simply drop a large keel to not drift, then use a
> >> : windturbine to charge a battery, after the battery is full, haul the
> >> : keel up and start your electrically powered propeller. repeat until
> >> : you've arrived.
>
> >> Actually, couldn't you just run the wind turbine and propeller
> >> simultaneously and continuously? I think that should work; your wind
> >> turbine (as an ideal) would be set up to push the blades/airfoils sidways,
> >> with minimum drag, while the propeller/waterfoils would be set up to push
> >> the water back. Basically, counting on the ability to have lower drag
> >> from the air medium, and higher thrust from the denser water, and so in
> >> effect deflecting the wind forces sideways, but the water forces pointing
> >> straightways. Hrm. Feels like it should work, but I'm not at all sure.
>
> > It might work, but it's hard to distinguish it intuitively from
> > pushing a boat forward in still air, turning the wind turbine, hence
> > powering the water propeller, and... viola! perpetual motion! I'm
> > not saying it is perpetual motion in the case you have air movement,
> > just that intuitively it feels about the same.
>
> Actually, this has been done. A bit of Googling turns up
> e.g.http://www.treehugger.com/files/2007/02/windmill_sailbo.php.
>
> Another, even more counterintuive example I came across while looking
> video of a wind-powered cart that can move downwind faster than the
> wind(!). Links to a nice PDF article explaining the design.
>
> The trick, of course, being that, instead of using wind power to push
> yourself against the ground, you use power from the wheels to drive a
> propeller pushing you against the air. In principle, there should be
> nothing stopping you from doing the same on water just as well.
Explain why that won't work in still air. :-) :-) :-)
Dave Typinski
There's no velocity, momentum, or energy difference between still air
and the ground. If there's a difference, something situated at the
interface can exploit that difference.
In fact... thinking about it in broader terms... doesn't most life
exist at such energy interfaces for precisely that reason?
--
Dave
Ilmari Karonen
As Dave points out, it's because, without wind, the ground won't be
moving relative to the air. Thus, you can't get more energy from the
motion of the ground under your wheels than you must spend pushing
against the air to maintain your speed.
Edward Green
> On 2008-11-09, Edward Green <ergjo...@gmail.com> wrote:
>
> > On Nov 7, 9:10 am, Ilmari Karonen <usen...@vyznev.invalid> wrote:
>
> >> Another, even more counterintuive example I came across while looking
> >> for this washttp://www.youtube.com/watch?v=aJpdWHFqHm0. It's a
> >> video of a wind-powered cart that can move downwind faster than the
> >> wind(!). Links to a nice PDF article explaining the design.
>
> >> The trick, of course, being that, instead of using wind power to push
> >> yourself against the ground, you use power from the wheels to drive a
> >> propeller pushing you against the air. In principle, there should be
> >> nothing stopping you from doing the same on water just as well.
>
> > Explain why that won't work in still air. :-) :-) :-)
>
> As Dave points out, it's because, without wind, the ground won't be
> moving relative to the air. Thus, you can't get more energy from the
> motion of the ground under your wheels than you must spend pushing
> against the air to maintain your speed.
I was being slightly ironic, but thanks for your answers. It
_sounded_ as if you hadn't excluded that case. I agree with you, it
is at least as counter-intuitive as the first case. In fact, I'm
still not convinced what I'm seeing in that video! I'm not sure it
doesn't work oppositely to your explanation.