Sunday, February 6, 2011

Sextant and Tits on Bulls

I just bought a Sextant today, I had absolutly no intention of getting one, It just sort of happened.

I brushed the cobwebs off the hatch of Snowpetrel and shook the cockroaches out of the sails, then sailed across to Bruny Island for BBQ. The next day I popped in to see a mate who showed me a sextant he had aquired in a garage sale. I checked it and adjusted out the slight errors, and just held it, unlike my old plastic davis mk 15 this had a "Real" sextant feel, so much like the sextants I learnt to use on the ships. Anyway I bought it.. 500 bucks for a virtually new Freiberger with a lovely wooden case. Why are they so expensive asked karen? 500 bucks I could have bought about 4 GPS units, which would do the same job quicker, more accurately...etc.

So are sextants about as much use as tits on a bull? should they be resigned to antique stores with the walker log?
Sent from my iPhone

3 comments:

  1. I just happened upon a piece of news I have long dreaded ...

    the acknowledgement that GPS signals are rather vulnerable to hacking and spoofing, which could be done either out of sheer vandalism, or more likely to gain military or economic advantage.

    Especially troubling given the number of activities which now rely on it...

    Andrew Troup

    ReplyDelete
    Replies
    1. Very Interesting Andrew, thanks for this advice, glad I learnt to navigate the old school way, just got to remember how now! What sort of range does the signal hacking go out to, and will it just disable the GPS or can it give misleading positions? Cheers

      Delete
    2. Ben

      It seems that GPS signal spoofing (ie giving misleading positions) is in its infancy and currently has to be targetted at a particular user, whose position must be precisely known, as described here:
      http://en.wikipedia.org/wiki/Spoofing_attack#GPS_Spoofing

      As such it's not something a cruising sailor is likely to be subjected to (it seems more likely it could be used to target specific commercial carriers or military receivers, drones, etc etc.)

      GPS signal jamming, so far, AFAIK, has generally been observed on land, over short distances (eg by truck drivers to stop 'spy-in-the-cab' tachographs working, preventing their journeys being tracked by their bosses, or by car thieves for obvious reasons, etc)

      But the GPS signal is very weak (supposedly the energy content is comparable with a car headlight beam at a range of 20,000km) and so susceptible to jamming on a larger scale, relatively easily. It's clearly a much more accessible and more widely applicable technology than spoofing.

      The official US govt position is that "Commercial airliners that use GPS are required to maintain alternative means of navigation." The sale of jamming hardware is illegal in the US, but possibly not in North Korea ... if you're thinking of a sailing trip in that direction ;-)

      Here's a snippet from earlier this year:
      "In 2010 ... North Korea had imported truck-based jamming systems from Russia that could jam GPS signals out to a 100 kilometer radius. Since then, there have been at least three GPS-jamming incidents along the border—which is just 60km north of Seoul........public safety experts say that even jamming on a small scale can create a security threat, especially in coastal waters like those west of Seoul.

      In the latest incident... a total of 553 aircraft flying in and out of South Korea’s Inchon and Gimpo airports reported failures of GPS systems, as did hundreds of ships and fishing boats in the West Sea. The jamming signals, which were first detected on April 28 and apparently ended on May 6, were traced to the North Korean border city of Kaeson. "

      Delete