AIS/VHF two antennae's or one?

[Tally Ho]

I had a tug and barge “sneak” up in me on day…scared the crap out of me…realized I had turned off my AIS alarm when leaving the marina because a Laker boat in the other side of the steel mill was broadcasting. And even though he wasn’t moving, there was a steel mill between us and I was heading away from him, my Gamin GPS740 was chirping away.

I typically use my AIS receiver and display targets on my CP map. I have some settings to eliminate most of the false positives.

Greg

 

[Hello Below]

Len, I read your report about the BC and Washington Ferries. They are the very reason I bought my AIS. Both times that I have sailed the same waters they were traveling, they have called me. They saw my AIS signal, and we discussed our intentions and how we would avoid each other's path. The BC ferry was coming up Captain Passage on the West side of Prevost, heading for Long Harbor. We were making our way down Trincomall Channel on the East side of Salt Springs, turning West heading for anchorage in Annette Inlet on Prevost.

The BC Captain called our boat by name. We agreed to pass Starboard to Starboard. The fog and snowfall were so dense all we observed was a large dark shadow passing.

AIS is a powerful safety tool. I often check it. Sitting in a marina, I see multiple targets. When out on the water, it has not been an issue. I am usually set on a 10nm radius unless I am crossing waters where I know the ship traffic will be at high speed, like the Juan D'Fuca or Haro Strait.

John as critical as I am with Raymarine’s target limit, I swear by the benefit of AIS. I find it to be a primary navigation tool in the areas that you and I sail in.

 

[jssailem]

Len

 

[colemj]

AIS targets around us today. 200 isn't going to do it here.

 

[Hello Below]

When I purchased my AIS transponder, I bought a 6db VHF antenna (like the ones power boats use) for less than $100. I mounted the antenna for it on the stern pulpit.

From my Em-Trak 2 Watt transponder manual:

"The system has a Maximum Permissible Exposure (MPE) radius of 1.5m. This has been determined assuming the maximum power of the AIS transceiver and using antennas with a maximum gain of 3dBi. The antenna should be mounted 3.5m above the deck in order to meet RF exposure requirements. Higher gain antennas will require a greater MPE radius. Do not operate the unit when anyone is within the MPE radius of the antenna (unless they are shielded from the antenna field by a grounded metallic barrier). The antenna should not be co-located or operated in conjunction with any other transmitting antenna."

Not trying to be judgemental just passing on information.

 

[Hello Below]

AIS targets around us today. 200 isn't going to do it here.

Raymarine has some fixin' to do.

 

[stephen_i_w]

From my Em-Trak 2 Watt transponder manual:

"The system has a Maximum Permissible Exposure (MPE) radius of 1.5m. This has been determined assuming the maximum power of the AIS transceiver and using antennas with a maximum gain of 3dBi. The antenna should be mounted 3.5m above the deck in order to meet RF exposure requirements. Higher gain antennas will require a greater MPE radius. Do not operate the unit when anyone is within the MPE radius of the antenna (unless they are shielded from the antenna field by a grounded metallic barrier). The antenna should not be co-located or operated in conjunction with any other transmitting antenna."

Not trying to be judgemental just passing on information.

So, does this mean that using a 5-watt handheld VHF that operates on similar frequencies to AIS is dangerous?
Not trying to be judgemental just passing on information.

 

[Hello Below]

So, does this mean that using a 5-watt handheld VHF that operates on similar frequencies to AIS is dangerous?
Not trying to be judgemental just passing on information.

Nothing that proper head wear won't fix.

 

[Captain Larry-DH]

Maybe I’m being thick headed but please help me to understand why a limit of 100 (or 200) closest targets is impractical or dangerous. I‘ve never seen a situation where I’d need to worry about that many collisions at the same time.
Edit: 100+ boats all with a CPA less than 1/4 nm within minutes if each other? I know I’d have a hard time processing that with my eyes-on view, and think it would be near-impossible onscreen with the screen quality of my 9” chartplotter.

 

[Hello Below]

Maybe I’m being thick headed but please help me to understand why a limit of 100 (or 200) closest targets is impractical or dangerous. I‘ve never seen a situation where I’d need to worry about that many collisions at the same time.
Edit: 100+ boats all with a CPA less than 1/4 nm within minutes if each other? I know I’d have a hard time processing that with my eyes-on view, and think it would be near-impossible onscreen with the screen quality of my 9” chartplotter.

Until I became aware there was a limit on the number of vessels in the target list there were several moments of "Where the heck did that high speed navigationally restricted ferry come from?". That was just before some immediate evasive action was taken. Given that most other manufacturers do not have this limitation, I do believe it is unnecessary and inconvenient. Let's just say a Raymarine MFD is not on my Christmas list this year.

 

[jssailem]

Let's just say a Raymarine MFD is not on my Christmas list this year.

Is that a way of saying?
You know you have earned a spot on the Naughty list, and it is better to wish for things you can have than things you cannot.

 

[Hello Below]

John, in comparison to other years, this year I have been a complete angel.