Plotting Questions; Radar ranges; magnetic compass bearings; positions on Open CPN...

[Raymond Pincott]

What I suggest would be of great help if maybe OpenCPN developers add a facility to be able to apply Radar ranges and visual bearings to the electronic chart to verify the vessels automatic positioning system.
Prudent navigation requires the vessels position to be verified by two independent systems

[Wotname]

Originally Posted by Raymond Pincott

A. Seaworthy Lass I assumed was a name allocated to me by your computer system. I am happy to change the name!
B. I will post the question where ever you suggest is the most relevant forum, how do the change over?.........

We can move the thread to the OpenCPN seamlessly and will do so as soon as you suggest a suitable Thread Title. What would you like the title to be?

Maybe something like - "Plotting Questions and how to use ranges and bearings plot a fix from GPS"

[Alan Mighty]

Originally Posted by Adelie

C. Does the Nav Act of 2012 apply to all mariners sailing on what I assume is Ausy flagged vessels or just commercial vessels?

Your question is not answerable in that form, including because the Nav Act 2012 is in parts, some of which apply to all vessels and some only to Australian regulated vessels.

The Nav Act is open to perusal: https://www.legislation.gov.au/Details/C2019C00268

For Aus flagged vessels, the Nav Act 2012 applies wherever they are, in Aus waters, in the waters of Aus external territories, and elsewhere (Sections 6 and 7).

Section 9 is relevant for non-Aus flagged vessels and vessels not on the Australian Shipping Register:

"Despite sections 6 and 8, the master or owner of a foreign vessel,
or a recreational vessel that does not have Australian nationality,
does not:
(a) commit an offence against this Act that relates to the vessel;
or
(b) contravene a civil penalty provision of this Act that relates to
the vessel;
unless, at the time when the conduct constituting the alleged
offence or contravention occurs, the vessel is:
(c) in an Australian port; or
(d) entering or leaving an Australian port; or
(e) in the internal waters of Australia; or
(f) in the territorial sea of Australia, other than in the course of
innocent passage. "

Certain Sections only apply to Australian regulated vessels. Except that other vessels can OPT to be covered by those Sections.

.

[Dockhead]

Originally Posted by Raymond Pincott

What I suggest would be of great help if maybe OpenCPN developers add a facility to be able to apply Radar ranges and visual bearings to the electronic chart to verify the vessels automatic positioning system.
Prudent navigation requires the vessels position to be verified by two independent systems

The cursor in OpenCPN has a range and bearing indicator which appears at the bottom of the screen. Just put the cursor on the landmark and see if that corresponds to what your radar is telling you.

Even easier - use the radar overlay. OpenCPN has an excellent radar plug-in which is compatible with most radars. With radar overlay, so see at a glance if anything is wrong with your positioning. I run mine all the time.

[Raymond Pincott]

Thank you Watname. We can move the thread to the OpenCPN seamlessly and will do so as soon as you suggest a suitable Thread Title. What would you like the title to be?
Maybe something like - "Plotting Questions and how to use ranges and bearings plot a fix from GPS"

I suggest "Plotting Questions and how to use Radar ranges and magnetic compass bearings to put a fix on an electronic chart in OpenCPN"

[Raymond Pincott]

What I am after is when the vessels positioning system has failed, or a massive error has been put in by the satellite operators, the vessels position and Radar overlay may be ten miles out. Then how to still navigate using the electronic chart as a paper chart by use Radar ranges and magnetic compass bearings put positions on the chart to continue the voyage using OpenCPN.

[ChrisJHC]

Hi, Raymond,

Before you go too far down this rabbit hole, remember the limitations of the tools you’re trying to use:
Compass bearings will give you a reasonably accurate direction (+- 2 degrees on a boat in swell?) but no measure of range.
Radar will give you a pretty accurate range, however the direction can be inaccurate.

When plotting backbearings, you need to ensure that you extend the line past where you think you are. This is not a “nominal range”, it is just ensuring that your multiple backbearings extend far enough that they intersect somewhere close to where you are.

[Pizzazz]

Not sure if I follow. Using a radar overlay is the optimal way to check the accuracy of your GPS input (overlaying the radar image on chart is equivalent to taking many bearings at once). If you see a large discrepancy, most likely it is a problem with true/magnetic, radar alignment, etc. If you are 100% certain your radar and compass are accurate and aligned, then disconnect the GPS input and use DR in OpenCPN to adjust the (guessed) position so that the radar image overlays the chart you are using. Repeat every 5 minutes.

Use extreme caution though, because 99.9% of the time the problem will be in your equipment and not in the GPS signal.

MV Ithaka

[requiem]

Originally Posted by ChrisJHC

Before you go too far down this rabbit hole, remember the limitations of the tools you’re trying to use

I'm not sure I'd consider basic position verification functions a "rabbit hole" just because consumer plotters omit them. Yes, radar overlays work very well so long as everything is indeed working as expected, but not all boats have radar and I've recently experienced one where it randomly decided it didn't want to talk to the plotter anymore.

I too would very much like to see basic plotting features; the ability to place and relocate (i.e. without altering bearing) multiple EBLs and VRMs would provide sufficient flexibility. For example, below is a sample running fix I did some time ago on SEAiq.

[Raymond Pincott]

Thank you "requem". That is the point I am trying to get across re being able to put a fix on a electronic chart in OpenCPN.
I do not know how wide the general marine world know about GPS jammers. They are cheap and available on the internet, just google GPS Jammers.

[skipperpete]

The jammers for sale online need to be in fairly close proximity to the receiver so not really a problem for a yacht at sea and according to the Australian government website (ACMA) it’s illegal to own or operate one. It’s also illegal to own or operate phone jammers but they seem to be fairly ubiquitous, an employer here in OZ installed a jammer in his aircraft manufacturing hangars to stop the employees from being distracted from their work........ possibly not a bad thing since the release of the findings into the “Everforward” grounding in Chesapeake bay.... the pilot was on the phone for most of the outbound journey, 5 calls totaling 60 minutes and was doing an email at the moment the draft exceeded the depth.

[StuM]

Are you familiar with the OCPN Draw plugin?


https://opencpn.org/OpenCPN/plugins/draw.html

[wholybee]

Originally Posted by Raymond Pincott

What I am after is when the vessels positioning system has failed, or a massive error has been put in by the satellite operators, the vessels position and Radar overlay may be ten miles out. Then how to still navigate using the electronic chart as a paper chart by use Radar ranges and magnetic compass bearings put positions on the chart to continue the voyage using OpenCPN.

Just use the "create route" function to draw lines on the chart exactly as you would on a paper chart.

In the case of a range and bearing from a radar, start the route at the landmark, and draw it in the inverse direction from the bearing, at the correct range. If you have bearings of several landmarks, then do the same, but from the multiple landmarks. Using similar techniques you can also do running fixes as well.

It is worth noting, "paper charts" are not being discontinued. "Raster" charts are being discontinued. You can still print paper charts from vector charts, and as long as people want to buy paper charts, the chart printer on demand companies will print them from vectors. Or, you can print them yourself.

[requiem]

Originally Posted by StuM

Are you familiar with the OCPN Draw plugin?


https://opencpn.org/OpenCPN/plugins/draw.html

Thanks for mentioning that! It does indeed provide a good chunk of this functionality, if a bit awkward to start with.

Playing with it a bit more, I found some of what I'd been doing wrong (e.g. opening the draw manager instead of the tool) and found ways to make it more effective. Enabling the left-click drag allows translation (a critical feature) and changing the start and end icons will minimise reading errors.

[Raymond Pincott]

Thank you StuM, I am not familiar with OCPN Draw plugin? I will investigate. Can you use ranges in OCPN Draw plugin? The issue is in restricted visibility when you cannot get a visual bearing and the radar can only give ranges, how can you apply the ranges in OpenCPN.