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24-03-2010, 10:16
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#151
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Registered User
Join Date: Oct 2008
Location: San Diego
Boat: Farrier f27
Posts: 704
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Quote:
Originally Posted by sailorbyfate
This morning, Abby wrote the following:
I thought AIS was line of sight only. How could she pick up a signal a hundred miles away?
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AIS operates on vhf frequency and that's why it's thought to be useful at line of sight distances. However as with vhf radio transmission range is often considerably greater than that. Also line of sight is referring to antenna height (freighter's antenna is up to 150' and a sailboat's is 45' up to 80' or more). There have been posts relating that in certain geographical areas vhf is reflected off mountain ranges, weather conditons also affect signal propagation so the signal range is variable.
These web sites that display AIS info are not whats used by shipping or AIS to function.
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24-03-2010, 10:47
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#152
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Registered User
Join Date: Jan 2010
Posts: 19
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An antenna 150' high "sees" a horizon about 14 nautical miles away. A sailboat with an 80' mast "sees" a horizon about 10 nautical miles away. So spotting a ship 24 nautical miles away would be no surprise. And since VHF waves will bend a little, 40 nautical miles would sometimes be possible. The nearest mountains are hundreds of miles away, below the horizon, so mountain reflections wouldn't be a factor. Until someone can show me what I'm missing, I'll assume Abby was speaking figuratively when she said "a hundred miles."
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24-03-2010, 11:07
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#153
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Registered User
Join Date: Oct 2009
Location: East Coast
Boat: 382 Diesel Duck
Posts: 1,176
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Quote:
Originally Posted by sailorbyfate
Until someone can show me what I'm missing, I'll assume Abby was speaking figuratively when she said "a hundred miles."
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She wasn't.
I asked the same question here a month or so ago and found out that long range reception is quite possible due to atmospheric and other bounces.
-Sven
__________________
Shiplet
2007 Diesel Duck 382
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24-03-2010, 11:33
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#154
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Registered User
Join Date: Jan 2010
Posts: 19
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That's interesting! Since AIS broadcasts are so short in duration, I would think that a transitory effect might allow AIS where voice would still be ineffective. Thanks for clearing this up.
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26-03-2010, 23:28
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#155
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Registered User
Join Date: Jan 2010
Location: New Zealand
Boat: 44Ft Sloop
Posts: 112
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Quote:
Originally Posted by sailorbyfate
That's interesting! Since AIS broadcasts are so short in duration, I would think that a transitory effect might allow AIS where voice would still be ineffective. Thanks for clearing this up.
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VHF is stranger than strange. I often pick up clear transmits from hundreds of miles away, yet can't get a local station from behind islands. Go figure.
Anyway. Does anyone know where Abby is at the moment?
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27-03-2010, 04:33
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#156
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Registered User
Join Date: Apr 2008
Location: Toronto, Ontario
Boat: 42 Passage CC
Posts: 177
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Here is a little update on Abby through one of my friends blogs Where Next? - More Engine Nonsense
__________________
The Artful Dodger
Passage 42 Centre Cockpit
Toronto, Canada
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27-03-2010, 05:35
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#157
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CF Adviser Moderator Emeritus
Join Date: Dec 2006
Location: Montrose, Colorado
Posts: 9,845
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Quote:
Anyway. Does anyone know where Abby is at the moment?
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I first saw her Day 63 report last night (Pacific Daylight Time), which hadn't been there earlier yesterday. It reports her 722 miles west of Cape Horn.
See: Abby Sunderland | Abigail Sunderland | Wild Eyes | Solo Circumnavigation | Shoecity.com Sponsor for the map of her locations on each of the daily reports.
TaoJones
__________________
"Your vision becomes clear only when you look into your own heart. Who looks outside, dreams; who looks within, awakens."
Carl Gustav Jung (1875-1961)
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01-04-2010, 09:16
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#158
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CF Adviser Moderator Emeritus
Join Date: Dec 2006
Location: Montrose, Colorado
Posts: 9,845
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From today's Los Angeles Times, comes word that Abby Sunderland has cleared a big hurdle by putting Cape Horn in her wake.
* * *
Abby Sunderland rounds Cape Horn
The Thousand Oaks teen is cheered by her progress. But more challenges await as she tries to sail solo around the world.
Abby Sunderland prepares her 40-foot sail boat "Wild Eyes" in the harbor at Marina Del Rey on Jan. 12. (Al Seib / Los Angeles Times / January 12, 2010)
By Pete Thomas
March 31, 2010 | 5:14 p.m.
"Rain driven by freezing wind pelted her 40-foot sailboat, but Abby Sunderland was in remarkably good spirits early Wednesday afternoon.
"That's because the 16-year-old from Thousand Oaks, while friends back home were coming off a refreshing spring break, had just rounded Cape Horn between South America and the Antarctic Peninsula.
"She had safely traversed a passage known as the Mt. Everest of the yachting universe, a mariners' graveyard fraught with unpredictable gales and gargantuan waves.
" 'It's the milestone I've been waiting for,' the budding adventurer said, when reached via satellite phone, minutes after she had crossed from the Pacific into the Atlantic."
* * *
To read the rest of the story, go to:
Abby Sunderland rounds Cape Horn - latimes.com
TaoJones
__________________
"Your vision becomes clear only when you look into your own heart. Who looks outside, dreams; who looks within, awakens."
Carl Gustav Jung (1875-1961)
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01-04-2010, 23:04
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#159
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Registered User
Join Date: Oct 2008
Location: Puget Sound
Boat: Irwin 41 CC Ketch
Posts: 2,878
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Atta way lass!
__________________
"Go simple, go large!".
Relationships are everything to me...everything else in life is just a tool to enhance them.
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06-04-2010, 11:55
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#160
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CF Adviser Moderator Emeritus
Join Date: Dec 2006
Location: Montrose, Colorado
Posts: 9,845
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I certainly don't want to seem harsh, but it seems to me that either Abby or her router(s) have been correcting a little navigation boo-boo over the past few days. It appears that she was headed for the wrong end of the Falklands / Malvinas after rounding Cape Horn, then got sorted out to take the islands to port. This appears to have wasted two days.
See: Abby Sunderland | Abigail Sunderland | Wild Eyes | Solo Circumnavigation | Shoecity.com Sponsor
TaoJones
__________________
"Your vision becomes clear only when you look into your own heart. Who looks outside, dreams; who looks within, awakens."
Carl Gustav Jung (1875-1961)
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06-04-2010, 12:08
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#161
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Registered User
Join Date: Oct 2008
Location: San Diego
Boat: Farrier f27
Posts: 704
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Yeah it seemed like they weren't actually looking at the weather forecasts. Often it's a survival or at least prudent thing to head north asap.
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06-04-2010, 16:18
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#162
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Registered User
Join Date: Feb 2009
Location: A real life Zombie from FL
Boat: Gulfstar 53 - Osiris
Posts: 5,416
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Actually according to her blog the winds died and she was not able to keep on the northerly planned course, so she switched and went the long way around the south of the islands. Here is her post on it.
Quote:
Had a bit of a slow day today with no more than 4 knots of wind for most of the day. But at least it was warm and sunny! It got all the way up to 63 degrees today!! I had been routed to go west of the Falkland Islands and just get north fast. But with the wind angle I ended up with and my position I wasn't able to. I could have waited for the wind to shift but that wasn't going to be for awhile and then, not for long. So I decided it would be better to head back and go south of them. It's a longer way to get around them but at least I wouldn't be stuck too close to shore. Wild Eyes does not go to weather and being too close to shore can be very dangerous.
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06-04-2010, 16:51
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#163
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CF Adviser Moderator Emeritus
Join Date: Dec 2006
Location: Montrose, Colorado
Posts: 9,845
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Thanks for clarifying that, osirisail. I hadn't been reading her blog.
I know she has a couple of month's cushion in her quest to take the record from Jessica Watson (Jessica, born May 18, 1993 and Abby, born October 19,1993). She lost three of those five months she "was born with" by leaving on her record attempt some three months later than Jessica. The two months she has in hand are in addition to having a faster vessel, but if something breaks that will cost her time while effecting repairs, the loss of a day or two here and there could add up to a complete loss of her cushion.
If Jessica closes the circle by early May, Abby will need to sail back into Cabo San Lucas by early July to claim the record. This could be close.
__________________
"Your vision becomes clear only when you look into your own heart. Who looks outside, dreams; who looks within, awakens."
Carl Gustav Jung (1875-1961)
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07-04-2010, 18:54
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#164
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Registered User
Join Date: Jan 2010
Posts: 19
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You're overthinking the math. Abby is 5 months younger than Jessica, so if she finishes less than 5 months after Jessica, she'll have the (unofficial) record. Assuming Jessica finishes by around May 1, Abby could finish as late as Oct 1 and still claim the record. Finishing by Oct 1 is the least of Abby's worries. If she does finish without stopping or getting assistance, it is near certain she'll have the record.
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07-04-2010, 19:12
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#165
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Registered User
Join Date: Mar 2009
Location: Houston
Posts: 149
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Quote:
Originally Posted by TaoJones
I certainly don't want to seem harsh, but it seems to me that either Abby or her router(s) have been correcting a little navigation boo-boo over the past few days.
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Quote:
Originally Posted by TaoJones
I hadn't been reading her blog.
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An interesting combinations of posts.
~
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