I recently removed a Sitex 767c from my small sailing boat with the
intention of putting it into long-term storage. I typically run one of 3 GPS
units which have met my needs in varied situations. They all feed a laptop,
send 0183 data to the radar display, the autopilot, etc., via various
switching methods. They all run on the ship's mains, and 2 of the 3 run on
batteries also. My cruising area has at various times covered the area from
the Maritimes to the northern Caribbean and that's likely to remain the
case. I have read that the US is considering eliminating funding for LORAN
despite the recent buzz about eLORAN and other innovations and this factored
into my removal decision.

I am currently investigating a potential cruise along the southern coast of
Newfoundland and it has been pointed out to me by experienced visitors there
that the charts in many cases do not correspond to the coordinates supplied
by GPS (independent of datum and the fact that I have the latest charts
corrected to the most recent Canadian Notices). In some cases the charts
differ from GPS readings by a mile or so according to some reports. For a
person like me who really enjoys the convenience of GPS-supplied piloting
information, this adds an additional but certainly not insurmountable
complication. It just means something more to think about and attend to.

While I was thinking about this I was recalling the old tricks we used to
use in the Bahamas prior to GPS and some of the very good privately
published charts such as the Explorer series and Steve Pavlidis' material.
We would simply use the offset feature of the LORAN to get a relatively good
position, and we would update the corrections as often as possible while in
harbor to give the best rendering of LORAN data on the chart. None of my GPS
units has a provision for entering an offset or correction. In fact I am not
certain this feature is available in any GPS unit, although it may be.

However this feature is certainly still available with my trusty Sitex 767c,
and from what I have read the LORAN chains available on the south coast of
Newfoundland are reasonably good. So here I sit wondering if I should bother
re-fitting the Sitex (which really only means plugging in a few cables and
the antenna into the existing coupler). I would then have the option of
using the corrected LORAN when the GPS gives unsatisfactory information.

Has anyone tried this in a similar situation (i.e., specifically where the
GPS does not correspond to the latest charts)? Is this a good idea in the
first place?

--
Good luck and good sailing.
s/v Kerry Deare of Barnegat
http://home.comcast.net/~kerrydeare

Armond Perretta wrote:
I recently removed a Sitex 767c from my small sailing boat /snip/
Has anyone tried this in a similar situation (i.e., specifically where the
GPS does not correspond to the latest charts)? Is this a good idea in the
first place?

I have a loran in my toy airplane. Arnav R21. It gives bearing to
waypoint, cross track error, distance, ground speed. When it stops
working, I'll remove it. I don't expect that to happen soon.

Brian W

On Thu, 26 Nov 2009 11:32:40 -0500, "Armond Perretta"
wrote:

Has anyone tried this in a similar situation (i.e., specifically where the
GPS does not correspond to the latest charts)? Is this a good idea in the
first place?

I have tried it but I'm not sure that I'll do it again. The
corrections typically apply only to a limited area since they are the
result of charting error, not GPS lat/lon error. In my experience it
is all too easy to forget that you have applied an offset. That leads
to trouble when you go to some new area where the charting error is
either different or non-existent.

I'm planning a cruise to the same area (southern Newfoundland) so I
appreciate the intelligence. I would use the private charts you trust
to enter the general shoreline as a route you can call up on one of
the chartplotter units. A good winter project. It will give you a
visible constant offset from the charted line that you can apply to
courses and navigational dangers. In some areas you might want to
simply enter a line to remain offshore from. The route names could be
used to indicate which method applies.

If you are a Garmin Bluecharts user, you could save this work in a gdb
file to share with others (like me It doesn't sound like you are
using Bluecharts but, if so or something else that can load gdb or gpx
files, contact me privately. I have the means to load and scan charts
into AutoCad so that lines can be traced and their properties printed
out in text files which would give you lat long points to enter. Gpx
files are in ASCII format so, given some time, I could write a program
to process the text output from AutoCad into gpx files that could be
read directly by a number of GPS plotting programs. I used to do a
lot of this text file string manipulation. There may be simpler and
more direct approaches but this is just what occurs to me off the top
of my head. I might have plenty of time this winter to work on
something like this and it would be well worth my while as a way to
become more familiar with the area and the charts.

BTW if I had a functioning Loran on my boat, I would keep it as a back
up considering the things that could shutdown GPS although I wouldn't
go out and buy one for that purpose. I also used Loran in my airplane
because it worked well enough that I couldn't justify the cost of a
GPS. Aircraft navigation, VFR at least, is a lot less precise than
marine navigation however. When you get within 3 about miles, you
switch to eyeballs.

--
Roger Long

There is also another way to check this out. I load the GPS tracks
from my cruises into Google Earth as you can see here (click the image
it see the GE version):

http://www.rogerlongboats.com/2009September.htm

Going back over my trips I can see that, in Maine at least, there is
almost perfect correspondence between the Bluecharts and Google Earth.

Here is a bit of the shoreline of the southwestern tip of Newfoundland
traced in Bluecharts and then transferred to Google Earth. It's
clearly not as accurate as in Maine. However, I don't have the
detailed charts for Newfoundland unlocked and this is a trace from the
larger area chart that serves as the basemap. I would have unlock the
chartset for Newfoundland and redo it to see what the actual
correspondence is but it will give you an idea of what can be done.

http://www.rogerlongboats.com/images/GErock.jpg

I've found the Bluecharts generally very accurate around the coast of
Maine but on stunning error in a very well traveled channel right in
Portland Harbor came to light recently when the brand new fireboat
tore a shaft off and damaged most of its centerline.

Here is how Bluecharts shows a section of Whitehead Passage:

http://www.rogerlongboats.com/images...eadGarmin1.jpg

and here is how NOAA shows it on their most detailed chart:

http://www.rogerlongboats.com/images/Whitehead.jpg

On Fri, 27 Nov 2009 06:18:52 -0800 (PST), Roger Long
wrote:

There is also another way to check this out. I load the GPS tracks
from my cruises into Google Earth as you can see here (click the image
it see the GE version):

http://www.rogerlongboats.com/2009September.htm

Going back over my trips I can see that, in Maine at least, there is
almost perfect correspondence between the Bluecharts and Google Earth.

Here is a bit of the shoreline of the southwestern tip of Newfoundland
traced in Bluecharts and then transferred to Google Earth. It's
clearly not as accurate as in Maine. However, I don't have the
detailed charts for Newfoundland unlocked and this is a trace from the
larger area chart that serves as the basemap. I would have unlock the
chartset for Newfoundland and redo it to see what the actual
correspondence is but it will give you an idea of what can be done.

http://www.rogerlongboats.com/images/GErock.jpg

I've found the Bluecharts generally very accurate around the coast of
Maine but on stunning error in a very well traveled channel right in
Portland Harbor came to light recently when the brand new fireboat
tore a shaft off and damaged most of its centerline.

Here is how Bluecharts shows a section of Whitehead Passage:

http://www.rogerlongboats.com/images...eadGarmin1.jpg

and here is how NOAA shows it on their most detailed chart:

http://www.rogerlongboats.com/images/Whitehead.jpg


Did they try to cut too close to G'3' ? That's one reason I'm wary of
vector charts. At least the NOAA raster charts have withstood the
test of time, and the rocks in Maine don't move around all that much.

Welcome back, BTW.

On Nov 27, 6:52*pm, Wayne.B wrote:

Did they try to cut too close to G'3' ?

There has been a remarkable lack of information about this event aside
from newspaper references to "uncharted rocks". However, a friend who
grew up on Peaks Island (across the channel) told me that his friends
heard the impact and it was so loud that they ran down to the beach to
see what it was. According to them, the boat was inside G "3".
According to the Bluecharts, you should be able to do that but it
would be foolish. Damage was on the port side and the boat was headed
west.

Not shown on either chart is the ledge around the beacon that is
nearly dry at low tide. Much of it would be inside the symbol though
due to the scale.

--
Roger Long

Roger Long wrote:

On Nov 27, 6:52*pm, Wayne.B wrote:

Did they try to cut too close to G'3' ?

There has been a remarkable lack of information about this event aside
from newspaper references to "uncharted rocks". However, a friend who
grew up on Peaks Island (across the channel) told me that his friends
heard the impact and it was so loud that they ran down to the beach to
see what it was. According to them, the boat was inside G "3".
According to the Bluecharts, you should be able to do that but it
would be foolish. Damage was on the port side and the boat was headed
west.

Not shown on either chart is the ledge around the beacon that is
nearly dry at low tide. Much of it would be inside the symbol though
due to the scale.

Greeteings, Roger,

It's not nice to laugh at others' troubles, but i had to, just a
little, when I read about it in the P-H.

I recently did some work based on the "Digital Chart of the World"
(ONC aeronautical charts digitized by ESRI) and found the digitizing
hopelessly wrong in some places -- relevant because I am sure the NOAA
vector charts are in large part made by contractors' digitizing of
paper charts, probably mylar originals).

We are off for Bermuda tomorrow, now that this low is out of the way.

Best,

Michael Porter Marine Design
mporter at mp-marine dot com
www.mp-marine.com

On Nov 28, 9:27*am, Michael Porter
I am sure the NOAA
vector charts are in large part made by contractors' digitizing of
paper charts, probably mylar originals).


I've seen or heard several references to the basis for all vector
charts being work done by the Russians during the cold war in case
they ever needed to invade. It's a good story and I suspect that
it's true since the timing and investment make it more plausible that
Garmin et. al. purchased and updated work done over a period of
several years than that they came up with it from scratch. I'd like
to know for sure though.

Have a great passage to Bermuda.

--
Roger Long

Wayne.B wrote:
"Armond Perretta" wrote:

Has anyone tried this in a similar situation (i.e., specifically
where the GPS does not correspond to the latest charts)? Is this a
good idea in the first place?

... The corrections typically apply only to a limited area since they are
the
result of charting error, not GPS lat/lon error. In my experience it
is all too easy to forget that you have applied an offset ...

I did this quite a bit the first time I visited Nova Scotia. At that time
the GPS system did not exist for recreational yachts. Earlier, also
pre-GPS, I had used this method in Bermuda and, later, the Bahama Islands.
As you note the range for these corrections is quite limited, but it was
essentially "the only game in town" if one wanted to have some sort of
electronic piloting information available.

However according to several "experts" (including ALL the available cruising
guides and several correspondents who have make passages to the area), the
south and southwest shore of Newfoundland is covered by charts that do not
match up to GPS data. I am referring to the latest CHS paper charts and the
latest NDI electronic charts, all corrected to the latest updates available.
So it seems that using the old LORAN offset trick would at the very least
provide useful additional piloting information. That's the idea I'm toying
with.

--
Good luck and good sailing.
s/v Kerry Deare of Barnegat
http://home.comcast.net/~kerrydeare