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Old 09-06-2010, 22:27   #16
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OK...Hypothetical question.

We are all aboard a boat headed for Hawaii....we left San diego on a heading to intercept our fist way point somewhere 100 miles at sea to or first turn picking up the trade winds ( Or what ever winds they are)

After the turn onto your rhumb line we loose GPS for 7 days...We know the basic current pattern...we know our course heading, we know the deviation, the wind direction and speed, we know our speed through the water.

How far off in 7 days can we really get?

If we never get GPS back are we at a huge risk of missing the islands completely? Next stop main land China?
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Old 10-06-2010, 02:54   #17
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Don't use a metal sextant in a thunderstorm, because if it gets struck by lightning, it will melt, warp, or otherwise malfunction.
Can you see the horizon in a thunderstorm?
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Old 10-06-2010, 02:58   #18
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OK...Hypothetical question.

We are all aboard a boat headed for Hawaii....we left San diego on a heading to intercept our fist way point somewhere 100 miles at sea to or first turn picking up the trade winds ( Or what ever winds they are)

After the turn onto your rhumb line we loose GPS for 7 days...We know the basic current pattern...we know our course heading, we know the deviation, the wind direction and speed, we know our speed through the water.

How far off in 7 days can we really get?

If we never get GPS back are we at a huge risk of missing the islands completely? Next stop main land China?

I sailed for years without a log (back in the days of sextants) .After the morning site I would go let's see 5 kn for a few hours, then it died a bit, cranked along at 7 for a couple of hours during the night then 5 again since dawn, that's about 110 miles, yesterday we picked up 10 miles from surface drift and should get the same today so 120 sounds good.
I was geberally within 5 miles.
So after 7 days lets say 35 miles, round it up to 50 to be safe and there you are, the Big Island is visible at that range - no problems.
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Old 10-06-2010, 03:39   #19
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< electronics navigation only.

I actually wouldnt' mind having a sextant aboard but considering i have 3 gps units aboard atm, the cost of a sextant makes it a luxury item.

besides.. those continents are kinda hard to miss anyways...
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Old 10-06-2010, 03:54   #20
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I actually wouldnt' mind having a sextant aboard but considering i have 3 gps units aboard atm, the cost of a sextant makes it a luxury item. besides.. those continents are kinda hard to miss anyways...
We have just picked up one of those plastic Mk 15 sextants. Probably more for fun than anything less, but if it gives me a position within 10 miles once a day that will do for us.

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Old 10-06-2010, 04:14   #21
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Oh nice call pete7, just had a quick look and there is some pretty affordable plastic models.

cheers mate.
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Old 10-06-2010, 09:01   #22
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Yes, mine is sat on my desk at work at the moment, another ebay bargin. Shame I can't see the horrizon, oh and its raining too. Did someone ask how to take a sight in a thunderstorm

Whilst its probably 20 years old, I don't think its ever been used, has the plastic box and even cardboard outer cover in tact. Chap at work came into my office and said "I have a book at home how to use one of those, I'll bring it in" and he did.

So whilst its not taking many sights at the moment, it is a conversation piece. Oh and the boss asked am I planning on sailing off somewhere? my reply left him worried

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Old 10-06-2010, 09:39   #23
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Paraphrasing history

I wonder if they had these conversations after John Harrison's nvention of the chronometer. Before 1440 and the drawing of a map with latitude on it sailors sailed using land siteings, soundings from continental shelves and the compass rose. Drift out of site of land and the off the shelf and you fell off the earth.

Once the the means to calculate latitude was understood you could find the latitude of the object you were seeking and use the compass to travel the line of latitude - hoping winds and currents played ball and the chart you were using put the island in its correct location. In the 1500's the Portugese understood longitude but it was based on time and a clock that would keep accurate time while at sea didn't exist. In the early 1700's England put forth a prize to whomever solved the problem a British clockmaker John Harrison invented the marine chronometer. In the early days the chronometer was a third of the cost of the ship but at least you could find your way out there!

The world is now a known place but in Columbus' day it was different. He went to his grave convinced he had been to India, China and Japan though he'd only been to the Carribean. His navigation skills weren't very good but his stubbornness was unrivalved!

I sure hope those GPS sats keep ticking away! I worked in telcom for about 10 years. We monitored solar activity because flares would wreak havoc on our computers. Love those northern lights though!
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Old 10-06-2010, 12:46   #24
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Hey, hang on, I just had a thought.... (don't laugh)... the folks that use a metal-shine-it-at-the-sun-doodad do you use a calculator or computer to work out the maths??????????????????

Or a pen and paper?

Admit it.


So a power outage will stuff the pro-sexytant people just as much as the mythical problems with a single gps...
Tables, almanach, if you can add 2 + 2 = ? you be right.
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Old 10-06-2010, 12:57   #25
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Hey, hang on, I just had a thought.... (don't laugh)... the folks that use a metal-shine-it-at-the-sun-doodad do you use a calculator or computer to work out the maths??????????????????

Or a pen and paper?

Admit it.


So a power outage will stuff the pro-sexytant people just as much as the mythical problems with a single gps...
Solar flares take out satellites, not the box in your boat. You can have 10 GPS receivers on your boat, if you don't have satellites transmitting you have electronic boxes that do nothing. And solar flares have caused the GPS system to go down for a short time in the 90s.

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Old 10-06-2010, 13:04   #26
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Navigation without electronic aids is a completely different cup of tea than with electronics aids. Greater care is taken in choosing time and destinations and requires real Mariners.
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Old 10-06-2010, 13:31   #27
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Navigation without electronic aids is a completely different cup of tea than with electronics aids. Greater care is taken in choosing time and destinations and requires real Mariners.
Not sure if I would use the term "real Mariners".........but certainly a different way of navigating, in both courses and attitudes. GPS says I could something. It doesn't say that I should.

But Astro Navigation? pah! waste of time How hard is it really to find a Continent?? If you can't find a Continent you shouldn't be allowed on the sea ..........it's when you have "discovered" a Continent that the real navigation starts and everyone can then tell who the real Mariners are. They are the ones not swimming ashore
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Old 10-06-2010, 14:49   #28
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I use pen, paper and slide rule or printed logarithm tables and trig functions when working a sextant to find my position. You can even use a sextant to find distance if you have a landmark of known height in sight.
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Old 10-06-2010, 15:30   #29
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Don't use a metal sextant in a thunderstorm, because if it gets struck by lightning, .
---it becomes an electrical navigation device--doesn't it ??
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Old 10-06-2010, 15:45   #30
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In response to Hummingway ( who I hope to see in July)- I am all for GPS and electric naviagation..but I think navigation based on electrons running across a semiconductor which has to stay dry and pristine and relying on a weak signal from another piece of electonic equiptment hundred of miles away probably deserves a backup. Not an electronic backup, but one that uses your common sense and looking around you. On coastal waters- it is running fixes on paper charts. On the ocean- it is the sextant and knowing how to use it.
What happens when you loose the sextant- if you understand the principles you can construct crude tools and at least take noonsites...
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