I must say that I find these threads on AIS and other high tech items
fastinating. But I wonder if we easily become too dependant on these
electronic wonders.
We are still in the "dark ages"--Since we still plot our position on the
charts, even though we have at least 3 GPS's aboard. The reason is that I
have had GPS go down--near military ships, military bases, and have heard of
times it was down in specific areas.
As for digital transmissions of VHF and AIS range--it may be that some of
these long AIS captures is due to trophosphereic ducting, rather than superior
techology (although I did find it most interesting that the soldered
connections gave better signal returns than the crimped and pierced
connectsion--long a contention I have held).
The plus of in-expensive VHF is that every boat can have one and
proportionally increases safety. The baine of this, is that in areas which
have many recreation vessels, the VHF is practically useless, because of the
abuse of the system. The limited range of VHF is a real plus there!
It is too early to see how well DSC will work, because the full system is not
operational, and many boats which have a DSC compatable radio have not gotten
the number or hooked up the NMEA data stream.
Where do you draw the line in expendatures? When we went cruising, it was a
real strugle to decide if we could afford the $3000 for a Magnavox Sat Nav
(which were just being released to the public) ($3000 was more than $10,000 in
todays world, but it was a significant part of our budget, when we were world
cruising at $1000 a month) For example: Flir--great technology--but the few
dozen times you might really need it, may not justify the $8,000 cost.
I don't think you can compare the response from tug boats to that of ocean
freighters. We know, and have known, a number of
Tug boat skippers. Their world is closer to ours, than the 1000 foot tanker.
Many of the tug skippers own recreational vessels. I suspect that a smaller
percent of merchant ship skippers own recreational vessels. We found that
virtually 100% of tug skippers would respond to a VHF contact--and about 80%
of Merchant ships would respond.
I am sure I would have an AIS reciever--since they are relitatively cheap.
When the Transponders come down in price, I am sure that we will see many more
recreational vessels which have them--but then you will find the merchant
vessels filtering them out because of the "clutter".
Thanks for the insight into the issues. I alerted Ben Ellison (Panbo) about
this thread, and I don't know if he has contacted you all or not, but there
are a number of issues which need to be discussed on a much broader level.
Regards,
Bob Austin
Bob commented inthe above thread on the reliability of GPS.
I have a Northstar GPS that has always worked well EXCEPT for one occasion.
I was north of the eastern portion of Sicily near Vulcano Island searching
for an appropriate anchoring site. Suddenly (>5 seconds) the location of my
boat on the chart plotter moved sideways about 1/2 mile. About 1 minute
later it moved sideways again about 1/2 mile and was now showing on land and
traveling inland.
I stopped, started up my backup GPS and compared LAT / LON the ships GPS was
off by about 1 mile but still acting like it knew where it was with proper
speed and heading data.
I turned off the ships GPS and restarted it. It came back with all the
errors corrected.
The purpose of the story is only to emphasis that sometimes the GPS is
WRONG.
Sail safely, John Harris
World Odd @ Sea
Don't we have bases in Sicily?
Ron Rogers
Yes we do have bases in Sicily - but then how did the backup GPS have the
correct data and the ships GPS not ?
Incidentally, the ship GPS has worked perfectly for 14 months since that
incident.
John Harris
World Odd @ Sea
Are they both averaging position over the same time period?
Ron Rogers
----- Original Message -----
From: "John Harris" JohnPH@Comcast.net
| Yes we do have bases in Sicily - but then how did the backup GPS have the
| correct data and the ships GPS not ?
|
| Incidentally, the ship GPS has worked perfectly for 14 months since that
| incident.
The backup GPS was turned on, found reference satellites and gave a reading
over a period of about 60 seconds, the boat was standing still i.e. < 1/4
knot of speed.
The difference of location was approximately 1 mile which was similar to the
2 sideways steps in the route shown by the chart plotter connected to the
ships GPS.
John Harris