In the market for a new chartplotter with virtual AIS display

superheat6k said:
One would assume a 'Virtual AIS' marker does not actually exist. Bramble post and the Nab certainly do.
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I think Bob interpreted your request as for either a "virtual point" or an "AIS AtoN". The Bramble post is not the former, but it is the latter.

I believe there used to be a couple of virtual aids for testing purposes off Calshot, but I'm not sure if they're still there since I tend to have my AIS display turned off in the Solent.

The Cherbourg fairway buoy has been virtual for a number of years now, but I think you'd be doing well to see it from the Hamble :)

Pete
 
prv said:
I think Bob interpreted your request as for either a "virtual point" or an "AIS AtoN".
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Yes, I was being very literal but on my understanding that both former and latter would use message 21 and therefore be displayed as such (diamond with '+' in the centre). [If the eventual virtual sources display omits the 'v' under the '+' inside the diamond, that would be OK for my purposes].

The premise I am working on is that displaying Message 21 will become increasingly important over my remaining sailing years. Hence my comment in #1. "..... down west and across southern Ireland 'fixed' station AIS such as lighthouses are proliferating........ when totally virtual buoys start appearing, I don't want to spend further!"

Thanks everyone
Bob
 
RIBW said:
Yes, I was being very literal but on my understanding that both former and latter would use message 21 and therefore be displayed as such ...
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That's right but message 21 includes a flag that defines whether an Aid to Navigation is real or virtual. I would expect AIS display software to clearly differentiate between real AtoNs and Virtual AtoNs. Sadly, not all do
 
Called by the boat today. I could not see anything AIS lighting up other than vessel in motion, but possibly the AtoN is a very weak VHF signal, as I could only see the Red Funnel ferry off Cowes from the top of the Hamble, and i reckon there would be loads of class B transponders bleeping away at ~ 5.30 during Cowes week.

So for now I have reserve an opinion / answer on my set displaying AtoN as an AIS target. Matsutec do not offer any separate explanation of AIS AtoN, nor what the mark on the screen would look like. The only described mark is a boat as a triangle with a 2 minute stick in front.

They have emailed me again today explaining the same thing that all AIS targets are displayed. But possibly a translation issue here.
 
AIS offer some useful new options.
Virtual AToN can easily be set up to mark new or temporary dangers as the don't need to be physically on the location,
AIS transmitters placed on floating marks can detect when is moving off station and alert the owner or automatically change it's state .
 
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AMCD300 said:
Very useful article. Thank you.
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Yes, very good.

On a slightly different tack, I note in the Raymarine link:
"AIS allows calculation of Closest Point of Approach (CPA) but does not give an indication of whether you will pass ahead or astern of another vessel. Its down to you to use the information to work this out and make the right decision in accordance with the regulations (COLREGS). "

They go on to explain how their new kit addresses this shortcoming. Being able to predict if a vessel is passing ahead or behind is extremely useful at sea.
This year I fitted a Vesper Watchmate and found this feature (which is output in a slightly different manner to Raymarine) excellent. Do consider it esp if you sail single/shorthanded.
 
doug748 said:
Yes, very good.

On a slightly different tack, I note in the Raymarine link:
"AIS allows calculation of Closest Point of Approach (CPA) but does not give an indication of whether you will pass ahead or astern of another vessel. Its down to you to use the information to work this out and make the right decision in accordance with the regulations (COLREGS). "

They go on to explain how their new kit addresses this shortcoming. Being able to predict if a vessel is passing ahead or behind is extremely useful at sea.
This year I fitted a Vesper Watchmate and found this feature (which is output in a slightly different manner to Raymarine) excellent. Do consider it esp if you sail single/shorthanded.
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It is in fact impossible to determine exactly if the other ship pass ahead or astern since you don't know where on the ship the GPS position is measured. If you take into account the length of one of the larger cruise ships with LOA > 300 meters the CPA could easily be 300 meters off that's why they draw these dangerous zone boxes on Ryamarine MFD.
 
knuterikt said:
It is in fact impossible to determine exactly if the other ship pass ahead or astern since you don't know where on the ship the GPS position is measured. If you take into account the length of one of the larger cruise ships with LOA > 300 meters the CPA could easily be 300 meters off that's why they draw these dangerous zone boxes on Ryamarine MFD.
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It is possible, the ships GPS position should be part of the AIS message. Opencpn can draw the ship actual size,

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Then the OpenCPN AIS CPA display must be as good as there is, though with update times it might not be the best idea to cut it fine across the bow just based on AIS data.....


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knuterikt said:
It is in fact impossible to determine exactly if the other ship pass ahead or astern since you don't know where on the ship the GPS position is measured. .
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As already pointed out but to expand on it, as part of the initial installation process of both Class A and Class B transceivers the installer should specify the length and beam of the vessel and where within that "box" the GPS receiver for the AIS (be it internal or external) is located. Of course, the possibility for human error and/or incompetence renders this info less than 100% reliable
 
Sorry for a thread drift...

I've never given much thought to AIS and towing... can it warn if you are going to try and cross between a tug and tow?

The screenshot above made my brain think...
 
Dear All,
"Events, Dear Boy, Events" have conspired to cause me to move from Cornwall to Bembridge for the next year.

Using Marine traffic, I can see the Bembridge harbour entrance buoys are showing up (as AIS). Does anyone know anything about these signals (Message Type etc)?

I would normally email the harbour staff for this type of question but, for some reason, my emails to them disappear into the ether and I have resorted to snailmail between us!

Has the the use of virtual/synthetic AIS signal started to proliferate ?

Cheers
Bob
PS I still need to buy that new chartplotter.
 
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