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Old 26-10-2013, 20:35   #76
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Quote:
Originally Posted by rebel heart View Post
I was pretty surprised that I saw AIS contacts from > 95 miles away the other day. I was in Puerto Escondido and saw three ships (class A) in San Carlos pop up. My masthead is ~55' off the ground, and they're probably ~80' off the ground, but still, I was surprised to say the least.
First time I reported 100nm contacts I was ridiculed but now there should be enough that have reported this to make it believable. It also means that those who only get 10nm contacts should redo their coax/connectors/antenna install.

RF tech is magic. You can study and calculate all day but in reality is will surprise you every time. This is why I focused on RF transmitter design for more than 10 years. Only the pressing need to actually make some money pushed me away from it.
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Old 26-10-2013, 20:40   #77
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Re: New Inexpensive Ais Transponder

How about 2000 nautical mile range for Class-A AIS reception? I've seen that plenty of times. Of course my antenna for that was at 1000 feet elevation (at my old home), but that only puts my line of sight at around 50 miles.

On my boat, with a spreader-mounted AIS antenna I often receive signals from 100-200 miles. This is via tropospheric ducting propagation, which is certainly not reliable. Under more normal conditions I receive Class-A ships at 15-25 miles.
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Old 26-10-2013, 20:40   #78
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Re: New Inexpensive Ais Transponder

Quote:
Originally Posted by s/v Jedi View Post
First time I reported 100nm contacts I was ridiculed but now there should be enough that have reported this to make it believable. It also means that those who only get 10nm contacts should redo their coax/connectors/antenna install.

RF tech is magic. You can study and calculate all day but in reality is will surprise you every time. This is why I focused on RF transmitter design for more than 10 years. Only the pressing need to actually make some money pushed me away from it.
Yeah I worked a bit in RF and it's funny because you can do all this stuff to noodle it right and then if you you tilt the antenna three degrees and bark like a dog it will double or half it's ERP. Weird stuff. There are just so many variables.

I was the main engineer for my college radio station so the VHF spectrum is fairly up my alley in terms of propagation, cables, coupling, ERP/SWR, antennas, etc. I know guys who work on the 800mhz and other funky bands in the data world. A whole different ball of wax.
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Old 27-10-2013, 04:15   #79
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Re: New Inexpensive Ais Transponder

The IMO, current stand on AIS says it is not a collision avoidance tool.
http://www.navcen.uscg.gov/pdf/AIS/I...Guidelines.pdf
That might have some conflict with the col reg that says as does the USCG that you use all tool available and yes they must be on.
Dont forget that the AIS gives speed over the ground/heading and the col reg are based on speed in the water therefore the AIS will give you the wrong vessel aspect ( are we passing or the stand on vessel?)when you are going slow in current so ARPA and AIS will disagree, now which one will the company lawyer tell you to ignore??
I did work for a very large vessel operator and that question was asked by several crew the office came back with the IMO doc. I guess we will have to wait till that one is tested in court?
A box in the corner is not something to be concentrating on when you have arpa and look out the window obligations,the MAIB has AIS accidents listed because of this.
The IMO made us all install AIS but they didnt make us display it on the Radar as that is a significant cost on older radars or was it because it isnt a collision avoidance tool?
http://www.imo.org/blast/mainframe.asp?topic_id=754
Re radar reflectors, plenty of times i have been on watch in areas with yachts, I can see whatever radar reflector they have up the mast yet cannot see them on radar.
I notice this in Singapore I can see the bum boats as the larger engine is the reflector no doubt and yachts generally nothing...
Just an observation not a radar reflector test

PS yes I have also seen the VHF work longer range than line of site, not sure how to explain that
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Old 27-10-2013, 04:48   #80
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Re: New Inexpensive Ais Transponder

AIS

Automatic Identification Systems (AIS)
http://www.navcen.uscg.gov/pdf/AIS/I...Guidelines.pdf
and it contains;

USE OF AIS IN COLLISION AVOIDANCE SITUATIONS

39 The potential of AIS as an anti -collision device is recognized and AIS may be
recommended as such a device in due time.
As all IMO docs on rules you need a lawyer to interpret them. Written by lawyers to ensure you always have a get out
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Old 27-10-2013, 05:43   #81
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Re: New Inexpensive Ais Transponder

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Originally Posted by Tim R. View Post
Your first statement here is a very dangerous one. Many commercial ships will filter out Class B signals and they will not see you.
As noted above this is persistent statement. There are lots of second and third hand "a commercial captain told me" stories. What is missing is a screen shot of any commercial radar or chart plotter or MKD that shows a menu filtering Class B AIS.

Quote:
Originally Posted by St. Elsewhere View Post
it is worth considering that none of the early AIS-A equipment was capable of receiving AIS-B signals.
Not true according to my understanding. I believe that what the very early Class A software did not manage was the Class B static information (boat name and configuration); the dynamic information (MMSI, course, speed, and position) was properly shown. No longer a person.
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Old 27-10-2013, 06:48   #82
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Re: New Inexpensive Ais Transponder

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As noted above this is persistent statement. There are lots of second and third hand "a commercial captain told me" stories. What is missing is a screen shot of any commercial radar or chart plotter or MKD that shows a menu filtering Class B AIS..
Yes they can!

Check the manual for the commercial Furuno FAR2157 50kW radar:

http://www.furunousa.com/ProductDocu...B%202-2011.pdf

Page 246 (menu tree), I highlighted the Class B filter funtions.

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Old 27-10-2013, 07:09   #83
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Re: New Inexpensive Ais Transponder

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Yes they can!
Cool! I really like data. That's the first I've seen. It looks like only the DISP menu is relevant but its the first indication I have seen of any reality.
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Old 27-10-2013, 07:20   #84
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Cool! I really like data. That's the first I've seen. It looks like only the DISP menu is relevant but its the first indication I have seen of any reality.
This has been demonstrated by Steve Dashew years ago. The archives are brimming with the posts of that...
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Old 27-10-2013, 10:16   #85
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Re: New Inexpensive Ais Transponder

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Originally Posted by s/v Jedi View Post
This has been demonstrated by Steve Dashew years ago. The archives are brimming with the posts of that...
I follow a lot of fora and mostly I just see statements. This is the first I've seen--and perhaps I've missed it before--that actually has some demonstration that filtering of Class B AIS transmissions is possible.
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Old 27-10-2013, 10:23   #86
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Re: New Inexpensive Ais Transponder

My point was dont worry about that, worry that many vessels are not looking at the AIS anyway especially when they dont have the overlay on the radar.
You want to be seen have an active radar reflector
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Old 27-10-2013, 11:08   #87
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Re: New Inexpensive Ais Transponder

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[...] when you are going slow in current so ARPA and AIS will disagree [...]
Would you care to explain this? Assume constant current or different currents, the relative distance and courses of the two vessels will work out the same whether you are using ARPA or AIS.
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Old 27-10-2013, 11:39   #88
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Re: New Inexpensive Ais Transponder

yes cpa will be the same
now look at the vessel that is underway and making way but at current speed so stationary to the seabed so AIS says stationary
another vessel drifting in the current and AIS says that is moving due to the GPS data
ARPA will give you the opposite situation
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Old 27-10-2013, 12:37   #89
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Re: New Inexpensive Ais Transponder

AIS only gives Heading and not CoG
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Old 27-10-2013, 13:15   #90
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Despite what Powerboat is saying , AIS under IMO guidelines plays a part in collision avoidance namely


"40 Nevertheless, AIS information may be used to assist in collision avoidance decision- making. When using the AIS in the ship-to-ship mode for anti-collision purposes, the following cautionary points should be borne in mind:
.1 AIS is an additional source of navigational information. It does not replace, but supports, navigational systems such as radar target-tracking and VTS; and
.2 the use of AIS does not negate the responsibility of the OOW to comply at all times with the Collision Regulations."

Furthermore the IMO clearly states that it is intended to become such a function in " due time" presumably when carriage is mandated on all vessel ( we're already getting close to yachts being required as all fishing vessels now in eu requird to have AIS )

Furthermore AIS is primarily designed to transmit your information to aid in vessel identification and play a role in collision avoidance , which brings in the nonsense that is receive only AIS, since its used as a collision avoidance tool only

Other that that I don't see the point of Powerboat comments, are you trying to denigrate AIS

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