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Old 19-03-2008, 15:54   #1
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Sailing "uphill"

Last summer, I had a very strong sensation of going "uphill" while sailing toward the SE coast of Newfoundland. Has anyone experienced anything like this? I was pretty tired, but still lucid, and couldn't shake the sensation of steadily climbing up.
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Old 19-03-2008, 15:58   #2
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Last summer, I had a very strong sensation of going "uphill" while sailing toward the SE coast of Newfoundland. Has anyone experienced anything like this? I was pretty tired, but still lucid, and couldn't shake the sensation of steadily climbing up.
Incredibly clear day with no pollution caused you to sense the curvature of the Earth?

That's why I moved up toward that way. The fresh air is niiiice.
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Old 20-03-2008, 09:27   #3
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<couldn't shake the sensation of steadily climbing up…>

Not having taken enough extended cruises out of sight of land to matter, I’ve only had something like you describe happen on the water when coming down the Bay at night and spending too long at the helm… usually I associated such spatial disorientations to growing fatigue…

However, I’ve run into it often enough when motorcycling for extended periods (usually somewhere around twenty-plus hours…) that I’ve gotten used to it as a sign I need to dismount and freshen up a tad before motoring on… I’m told this is more under the heading of “road hypnosis” (as a professional chauffeur friend calls it) than the simple disorientation an aviator may experience when visual references are lost during instrument flying conditions…

Perhaps not the same you experienced, but sure sounds similar…
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Old 20-03-2008, 09:32   #4
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When on a long ocean passage, on a relatively calm, sunny day, I've always had the sensation that I was in a ''bowl". When I scanned the horizon, it looked like it was a bit higher than where the boat was. Uphill in all directions. Weird!
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Old 14-04-2008, 15:40   #5
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I've experienced a sensation of one side of the ocean being higher than the other. I hope it's due to being oriented to the heel of the boat more than the earth. This has happened a couple of times while sailing to Hawaii.
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Old 14-04-2008, 16:03   #6
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there are dips in the ocean

When I was involved with the design and manufacturing of SATNAV navigational equipment for TRACOR I became aware that the ocean is not all at sea level. There are numerous depression through out the planet caused by local magnetic anomalies. IF I remember correctly, a big if as this was 25 years ago, the largest dip is over 3 meters and is located off the Florida coast.

Why did I learn all this? Because the SATNAV relied on doppler shift of the incoming signal from the sat to figure out the distance off and height of sea level was important. SATNAV weren't stationary but orbited and the nav equip used the range changes of three or more sats to get three or more LOPS based on distance from each.

GPS is worlds better, yea ha@!
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Old 14-04-2008, 18:42   #7
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Quite often just standing on a beach gives the sensation that the water is higher than you are.
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Old 14-04-2008, 21:55   #8
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When I was involved with the design and manufacturing of SATNAV navigational equipment for TRACOR I became aware that the ocean is not all at sea level. There are numerous depression through out the planet caused by local magnetic anomalies. IF I remember correctly, a big if as this was 25 years ago, the largest dip is over 3 meters and is located off the Florida coast.

Why did I learn all this? Because the SATNAV relied on doppler shift of the incoming signal from the sat to figure out the distance off and height of sea level was important. SATNAV weren't stationary but orbited and the nav equip used the range changes of three or more sats to get three or more LOPS based on distance from each.

GPS is worlds better, yea ha@!
I read there were differences in sea level because there are gravitational differences caused by the Earth not being uniformly dense. Whichever it is, that's really neat stuff.

I found this question here: Frequently asked questions
4. Why is the sea level higher off the coast of Bermuda than New York?

Any current which flows for longer than a day is, effectively, turning in circles as the Earth rotates. In the same way that an object moving in circles requires a force at right angles to its motion, like the Moon orbiting the Earth, any mean current in the ocean also requires a force (to the left, in the northern hemisphere) to balance its steady motion. This balance, between motion and a pressure force to the left, is known as geostrophy. It as also the reason why winds tend to blow along isobars, rather than directly from regions of high to low pressure, as you see every day on the weather.
The strong northward current, the Gulf Stream, which flows between Bermuda and New York results in sea level at Bermuda being about 1 metre higher than say Charleston (that is to say 'higher' with respect to a surface called the 'geoid', see 1. above).

Interesting that this sea level difference is caused by currents.
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Old 25-06-2008, 02:03   #9
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Ayup, it's called geostrophic currents if memory serves me right. Conceptually pretty much the same thing as low and high pressure areas in the atmosphere, and good ol' Coriolis makes the water flow perpendicular to the slope of the "hill" or "trough" - or 'follow the isobaric surface' as an oceanographer would put it. It's the major driving force behind the great ocean currents.

In the northern hemisphere, the current would move anti-clockwise in a "trough", and clockwise around a "hill" - in exactly the same way the wind moves around a low and high pressure respectively.

Thermohaline currents are the other "biggie" when it comes to moving major amounts of seawater. As opposed to geostrophic currents, which are, for all practical reasons, parallell to the surface, thermohaline currents move water vertically and are triggered by density differences as the temperature - thermo - and salinity - haline - properties of the water changes. This is the driving force behind the great ocean conveyor caused by the cooling of the water in the Norwegian sea, which makes the water to sink due to its greater density. The cold water then moves south along the bottom of the atlantic, turns west around the Cape of Good Hope and into the Indian ocean and the Pacific, where it slowly heats and resurfaces for its return trip to the Atlantic.

It is this latter phenomena which is causing most worries wrt global warming, as higher sea temperatures may cause a disturbance in the formation of deep water in the Norwegian sea, triggering a complete or partial shutdown of the great ocean conveyor.

OK, I'm not an expert in this area, just something I remembered from an introductory course in physical oceanography way back when at university. Unfortunately, and oftentimes to my regret, I ended up majoring in information sciences instead
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Old 26-06-2008, 06:50   #10
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One time tuna fishing about 250NM out from Sydney, we came across a current that was about 5-6C warmer than the surrounding ocean. The sea was silky smooth and you could actually see a little step in the water at the interface. . Lots of turtles and manta rays in it.
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Old 26-06-2008, 09:49   #11
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Originally Posted by Oyvind View Post

Thermohaline currents are the other "biggie" when it comes to moving major amounts of seawater. As opposed to geostrophic currents, which are, for all practical reasons, parallell to the surface, thermohaline currents move water vertically and are triggered by density differences as the temperature - thermo - and salinity - haline - properties of the water changes. This is the driving force behind the great ocean conveyor caused by the cooling of the water in the Norwegian sea, which makes the water to sink due to its greater density. The cold water then moves south along the bottom of the atlantic, turns west around the Cape of Good Hope and into the Indian ocean and the Pacific, where it slowly heats and resurfaces for its return trip to the Atlantic.
Well, almost. The colder water moving south along the bottom of the Atlantic turns east around the Cape of Good Hope to enter the Indian Ocean, at which point it splits. A significant portion circulates through the Indian Ocean south of the sub-continent. The major portion continues across the depths of the southern ocean before turning north below Australia, moving north through the Pacific up to the Aleutians before warming and rising, swinging south again down through the eastern Pacific, then turning west across the top of Australia and rejoining the Indian Ocean circulation about half-way between Australia and southern Africa.

Here's a visual reference:

Great ocean conveyor belt - Climate Change

TaoJones

PS: Don't know what the deal is with the quote above, as nothing was changed other than extracting the non-applicable portion.

[ed: You'll have to place the ellipsis]
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Old 26-06-2008, 18:48   #12
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Here is a nice write-up and diagram of the Earth's Geoid Height:

Earth radius - Wikipedia, the free encyclopedia

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Old 27-06-2008, 06:24   #13
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TaoJones,
you are, of course, perfectly right. And it would be a funny thing, indeed, to turn west around the Cape of Good Hope when you are coming from the Atlantic Ocean

The illustration shown on the link you posted isn't entirely correct, though, as the deep water formation primarily takes place in the Norwegian Sea, north of Norway, not in the North Atlantic.
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Old 28-06-2008, 01:30   #14
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I wonder if the "up-hill" phenomena Bill is suggesting is more to do with distortion due to a layer of cold air on th water surface. The colder air is denser and thus has a magnifying affect which gives the effect of the water being higher.
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Old 28-06-2008, 10:09   #15
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TaoJones,
you are, of course, perfectly right. And it would be a funny thing, indeed, to turn west around the Cape of Good Hope when you are coming from the Atlantic Ocean

The illustration shown on the link you posted isn't entirely correct, though, as the deep water formation primarily takes place in the Norwegian Sea, north of Norway, not in the North Atlantic.
Here's a more detailed representation of the thermohaline circulation patterns, Oyvind. I note that the other graphic, while "generalized," does mention the Norwegian Sea in the text.

Image:Thermohaline Circulation 2.png - Wikipedia, the free encyclopedia

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