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View Poll Results: Blue Water- is a Sextant Necessary?
Absolutely essential 24 18.90%
Desirable, but not essential 52 40.94%
Good fun, but little practical use these days 39 30.71%
Don't waste your money and time on this 11 8.66%
Sextants make excellent dingy anchors. 3 2.36%
Multiple Choice Poll. Voters: 127. You may not vote on this poll

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Old 05-11-2012, 16:39   #151
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Re: Poll-Blue water. Is a Sextant Necessary?

Quote:
Originally Posted by 44'cruisingcat View Post
The reason would be - training. In a war, it's possible the GPS satelites could be targeted.
It's got nothing to do with training, you do the same on my ship or find another job......
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Old 05-11-2012, 17:24   #152
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Re: Poll-Blue water. Is a Sextant Necessary?

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Originally Posted by Don Lucas View Post
Amazing the lengths some here will go to try to make the sextant sound needed.

But 84% of poll takers still say ............. NO!
Most of them (unlike you, it would seem) are probably not saying

"Nobody needs it", they're saying "I don't need it".


And most of those who do need it, don't pretend everybody needs it.

So I think (actually I hope) that your message, and the polarisation of opinion you seem to relish, is lost on most of us.
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Old 05-11-2012, 17:29   #153
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Re: Poll-Blue water. Is a Sextant Necessary?

Quote:
Originally Posted by 44'cruisingcat View Post
The reason would be - training. In a war, it's possible the GPS satelites could be targeted.
In a limited way it probably is training, but it is probably for a whole host of other reasons too, such as:

1) Limited accuracy of the maps as regards basic relative positions of items on the map and also the Lat/Lon of said items. The following quote is straight from NOAA's website on the page for downloading RNC's (Raster Navigation Charts):

"Any inaccuracies due to old methods of collecting, processing and displaying data on the paper chart were transferred to the RNCs. As a result, the accuracy of modern positioning systems such as GPS may exceed the positional accuracy of the RNC. The impact of positioning accuracies can be minimized by not zooming an RNC beyond the scale of the original NOAA chart.

While NOAA has accuracy standards for each step in the data collection and chart production process, much of the depth information found on NOAA charts is based on surveys conducted before 1940, the shoreline is more than 20 years old, and paper charts used to be compiled manually."

RNC Downloads


2) There are also issues with degradation of GPS signals from sources such as jammers (as mentioned by micah719) and solar storms which could disable the whole GPS constellation if bad enough.
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Old 05-11-2012, 17:37   #154
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Re: Poll-Blue water. Is a Sextant Necessary?

Quote:
Originally Posted by Andrew Troup View Post
Most of them (unlike you, it would seem) are probably not saying

"Nobody needs it", they're saying "I don't need it".


And most of those who do need it, don't pretend everybody needs it.

So I think (actually I hope) that your message, and the polarisation of opinion you seem to relish, is lost on most of us.
Seems that for you there must have been a lot more words in my post than the ones I actually typed! Which "us" do you speak for?
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Old 05-11-2012, 18:02   #155
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Re: Poll-Blue water. Is a Sextant Necessary?

Quote:
Originally Posted by 44'cruisingcat View Post
The reason would be - training. In a war, it's possible the GPS satelites could be targeted.
My take would be that it's for the increased situational awareness.

Looking out the window and thinking to self - "that rock looks f#cking close" has much to commend it.......no matter the size of the vessel .
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Old 05-11-2012, 18:32   #156
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Re: Poll-Blue water. Is a Sextant Necessary?

I think the bigger problem with growing up on GPS is that navigators, and I use the term loosely, are no longer learning the art of dead reckoning. (That's how we used to keep our position between fixes when you didn't have a constant GPS fix.)

Prior to the advent of GPS, I kept a boat in Moss Landing. I'd often return to port in the fog, and although I didn't have radar, I could alway find my way back into the harbor because I had a depth sounder. If my dead reckoning was good enough that I knew what direction to turn once I reached the 10-fathom line, I could follow it until I could hear the bell buoy, and then run a compass course straight into the harbor. No worries.

I've noticed, however, that a lot of GPS-only navigators don't know how to run a compas course these days, especially under sail.
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Old 05-11-2012, 18:57   #157
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Re: Poll-Blue water. Is a Sextant Necessary?

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Originally Posted by westsail374 View Post
Here's a possible issue:

Many weapons that could be used by terrorists for stand-off attacks use GPS for guidance. Similarly, some aircraft that may be used by hostiles use GPS for the same purpose. That's why the Feds have the capability to shut down the system at any time, with no notice whatsoever.
...

Maybe the Feds will never need to turn off GPS.

...
I only know of one time that they have shut it off -- and I was about half way between Massachusetts and Bermuda at the time. The main chart plotter lost signal and we pulled out hand-held back-ups...oops...nothing worked because there was NO signal.

Fortunately, we had been practicing our celestial just for grins....continued with DR and celestial all the way to Bermuda. The GPS signal came back up just as we were making our approach at 4AM (that was re-assuring...sure don't want to screw that one up).

We got ashore and discovered that George Sr had launched Dessert Storm a couple of days before.

While it is probably unlikely, yes the civilian signal can be turned off.

So, no matter how many GPS enabled devices you have aboard, having a plan "C" is a good idea. For coastal cruising (which is really what most cruisers do in fact anyway...despite all this talk of "blue water"), I'm fine with good old DR and coastal piloting. But, well of shore, it sure would be handy to have a sextant aboard.

Personally, for typical cruising, I do not usually carry my sextant (unless I plan to practice...which of course I rarely actually get around to anyway). We normally only make relatively short coastal hops anyway. Our longest run (by far) last season was just under 400nm near coastal and most of our runs were much shorter. I don't need a sextant, or a GPS, for that....and I NEVER leave port without my traditional nav tools and paper charts.

But, seriously offshore (like trans-oceanic), I would still pack mine along just for piece of mind...because a land fall like Bermuda is a pretty small target to hit using DR alone.
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Old 05-11-2012, 19:09   #158
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Re: Poll-Blue water. Is a Sextant Necessary?

Quote:
Originally Posted by Bash View Post
I think the bigger problem with growing up on GPS is that navigators, and I use the term loosely, are no longer learning the art of dead reckoning. (That's how we used to keep our position between fixes when you didn't have a constant GPS fix.)

Prior to the advent of GPS, I kept a boat in Moss Landing. I'd often return to port in the fog, and although I didn't have radar, I could alway find my way back into the harbor because I had a depth sounder. If my dead reckoning was good enough that I knew what direction to turn once I reached the 10-fathom line, I could follow it until I could hear the bell buoy, and then run a compass course straight into the harbor. No worries.

I've noticed, however, that a lot of GPS-only navigators don't know how to run a compas course these days, especially under sail.

I remember when I had a Magnavox Satnav. About every 20-60 minutes...Kachunk!...a fix. However you had to figure the time that elapsed from when you got the fix to where you were in the moment. GPS had just come out for the public at a price of $2800.
I too was in Moss Landing in the North and South Harbor. You're right about the fog and feeling your way in. There are a few markers to help you in and once close, you can use the compass and lo and behold the markers on the bridge of Highway 1.
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Old 06-11-2012, 00:30   #159
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Re: Poll-Blue water. Is a Sextant Necessary?

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Originally Posted by belizesailor View Post
I only know of one time that they have shut it off -- and I was about half way between Massachusetts and Bermuda at the time. The main chart plotter lost signal and we pulled out hand-held back-ups...oops...nothing worked because there was NO .
Very interesting case.
Reports of long term gps jamming are very rare, although I don't doubt the military has the capability, even car theives can cuse short term jamming. However, some of reports are due to failures of the GPS units rather than the GPS system.

A common problem is when failure of the primary GPS unit occurs people resort to a HH that has not been used for a long time.
The HH takes a very long time to get a fix because it has lost its almanac data.
Another mistake is to set the units to SD fix only. Loss of the SD signal means the GPS units will stop displaying a fix.

I am not saying that is the case here but some details would help rule out these sort of possibilities.
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Old 06-11-2012, 05:04   #160
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Re: Poll-Blue water. Is a Sextant Necessary?

while this debate is amusing we do need to scratch some nonsense about GPS and GNSS in general. ( The GPS system isnt the only one up there you know).

The US can not in reality turn the GPS system off, Its far too embedded in civilian life. Its like saying they could turn the power off. it isnt going to happen.

In some sort of total war situation, one against an adversary that has the military technology to degrade a significant proportion of the GPS constellation, its still a far-fetched idea that the GPS system can fail ( or be taken down). Only a few military groupings like some EU combined states, Russia, maybe china and or Japan have the ability to do so. Does anything really think that they be sailing anywhere in the context of such a war!!!.

The coarse acquisition code C/A is an instrinic part of the overall GPS signal methodology its also used in military receivers that decode P(Y) codes. There is no "civilian" part of GPS, merely a coarse and fine code, with the higher precision code encrypted. Switching off the C/A code would render the P(Y) cide very difficult to use with long time to first fix, Again the GPS cant really be restricted by turning of that code. ( Selective avavilabilty could be turned on).


With many countries or grouping building GNSS systems, it is likely within the next 20 years that we will see several fully operational GNSS systems, GLONASS is already be refurbished , Gallileo will launch eventually and China will do its own thing.

Hence GPS itself will not be the only game in town

The trend in GNSS is to increase positional accuracy, so the thing is only going to get better. The encrypted P(Y) code is rapidly being eclipsed by GPS modernisation anyway and Gallileo will simply sell resolution as required for example. I expect in time the P(y) code will become simple P code. ( non encrypted). Space based augmentation systems have largely removed its usefulness and carrier phase systems have got around the ionosphere propagation issues

What is apparent is that many countries have invested in selective GPS jamming systems ,as GPS is easy to selectively jam, however as far as we are concerned this stuff is irrelevant as again we are not going to be sailing in a area where conflict based military GPS jamming is ongoing ( not without a death wish).

Accuracy of charts has nothing to do with position fixing metrologies, charts are inaccurate irresptive of whether we resolve our posiiton using land based LOPs, constellatioin based LOPs or in effect satellite based LOPs. In the chart is wrong , all will show us in the wrong place.,


The Sextant debate cant be won , by running down GPS, that now tilting at windmills. Its like saying you should carry a backup steam engine in your gas powered car. The technology works, is reliable , easy to use and effective.

The sextant is a historical piece of equipment, as it surpassed other position fixing equipment, its is today itself surpassed.

However, If you like me, enjoy using such older "technology" much like we enjoy using pseudo canvas sheets to propel us around , then great . But less leave anti-GPS arguments go.


Its worth noting that during desert storm the US moved the GPS constellation to provide better DOP figures as the US military didnt have enough military ( P code) receivers and relyed on 000s of civilian receivers. This isnt the case today, the constellation is sufficient and more P code receivers are around. Thats is what many users especially in the altantic saw as a poorer DOP figures or some degradation in accuracy during that time,( 16 Block II birds were active at that time).

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Old 06-11-2012, 11:28   #161
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Re: Poll-Blue water. Is a Sextant Necessary?

Quote:
Originally Posted by Bash View Post
I think the bigger problem with growing up on GPS is that navigators, and I use the term loosely, are no longer learning the art of dead reckoning. (That's how we used to keep our position between fixes when you didn't have a constant GPS fix.)

Prior to the advent of GPS, I kept a boat in Moss Landing. I'd often return to port in the fog, and although I didn't have radar, I could alway find my way back into the harbor because I had a depth sounder. If my dead reckoning was good enough that I knew what direction to turn once I reached the 10-fathom line, I could follow it until I could hear the bell buoy, and then run a compass course straight into the harbor. No worries.

I've noticed, however, that a lot of GPS-only navigators don't know how to run a compas course these days, especially under sail.
My experience agrees with this.

I took a coastal pilotage course prior to taking a celestial navigation course.

Imagine my pleasure when I learned I could use the sextant to closely determine my distance offshore to known-height shore marks. It was like getting a magic trick right.*

These methods are only redundant to the prudent mariner if you figure one source of information (the GPS/plotter) is necessary, and not all sources (eyeball, sea state, compass, depth, etc.)

I wonder how many advocates of GPS only would chuck their depthfinders and glass over the superfluous transducer hole in the bottom? After all, if you know your lat/lon., surely the depth is on the plotter, right?

*When I learned the "sextant on its side" method (basically a finer grade of hand-held compass bearing angle measurement), I took my salvaged optical rangefinder off the boat. I don't sail a museum, after all.
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Old 06-11-2012, 12:10   #162
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Re: Poll-Blue water. Is a Sextant Necessary?

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Looking out the window and thinking to self - "that rock looks f#cking close" has much to commend it.......no matter the size of the vessel .
Lol. Give that man a beer!
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Old 06-11-2012, 13:39   #163
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Re: Poll-Blue water. Is a Sextant Necessary?

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Originally Posted by Don Lucas View Post
Amazing the lengths some here will go to try to make the sextant sound needed.

But 84% of poll takers still say ............. NO!
Gosh Don, a few years ago there was a national poll in the States, and some large fraction of respondents said they didn't believe that the Moon landings were real. I won't get into how many folks believe that the universe was formed around 6000 years ago over a period of seven days... so do you really think that this number (84%) has any real meaning?

But seriously, I suspect that the 84 % that you note is closely equal to the percentage of respondents who never really sail offshore. For coastal or harbour sailing, many of us who do carry sextants and know how to use them would agree that they are not necessary.

Cheers,

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Old 06-11-2012, 13:49   #164
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Re: Poll-Blue water. Is a Sextant Necessary?

well you know the poll is the poll, just because a more "vocal" group of posters says otherwise it doesn't change the results
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Old 06-11-2012, 14:12   #165
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Re: Poll-Blue water. Is a Sextant Necessary?

Yep.

Would be valuable data to know how the votes of actual blue water sailors split.

Then it would be valuable too to know what the naysayers understood under 'blue water' ...

;-)

I think that 17% of 'definitely yes' votes is indeed an extremely good result.

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