AIS Update

[Dunkers]

Bill's point about being mesmerised with another screen to watch is valid but, I feel, only until the novelty wears off. Its like any new "toy" on the boat, the first few days you are facinated by it but after that it becomes one of the rest of the pieces of equipment which are useful.

We have to pick and choose our gadgets to fit due to availability of space and, probably more importantly, our budget. I only heard about AIS a couple of months ago but when I go to the Southampton Boat Show this Saturday its on my list to check out and probably buy.

Thanks for the link to the Easysplitter, I'm investigating that. As has been pointed out I want to avoid my boat looking like the Russian spy trawlers who used to shadow our every exercise when I was in the Royal Navy.

[Talbot]

One of the real benefits of Shipplotter software for the AIS is the lack of need to watch the screen. There is a guard zone based on closest point of approach, and time to that CPA. If a ship triggers the guard zone, an alert is sounded and an alert message appears on the laptop, even if another programme is being used at the time.

Works really well.

[swagman]

I'd support Talbot and Jef - and I don't even have one. Yet.

But I think most people already know that not all vessels have it or use it and provided all users are reminded of that fact - its surely never going to be 'dangerous'.

I also guess our forefathers had similar discussions when they invented electric nav lamps.

I mean - who could trust such corrosive devices over the trusty oil lamp? Over time, more electric systems were installed, the costs came down, the quality and value increased, the sceptical were convinced, and today few would question what form of lamp to install on any kind of vessel.

Indeed - and oil lamp with limited brightness could today be seen as dangerous!

I'd suggest we are all better off to encourage sailing innovations like AIS. If a larger number install and use the system, the costs will fall even more, the quality of info is sure to increase, and we'll all find it more beneficial...........

Cheers
JOHN

[phiggins]

I installed a SR-161 AIS receiver and a VHF splitter to my mast top antenna. I got to test it out a few weeks ago when I crossed Lake Ontario from Toronto to Niagara on the Lake. I was pleased that I received a few, maybe 5 ,ships tracks while crossing.

After I got back to my marina in Scarborough I turned on the AIS and splitter and didn't receive anything. I wasn't too concerned because I thought perhaps there weren't many ships using AIS but after trying for a few hours everyday for a week I thought there must be something wrong. Finally I bypassed the splitter and immediately received one ship passing about 15nm out. I put the VHF cable back to the splitter and received nothing. Then I bypassed it again and received the ship right away.

The VHF radio works OK with the splitter.

So either the splitter is attenuating the VHF sgnal enough that it does not work or VHF splitter has become defective.

Has anyone else experienced this with a VHF splitter?

[jstevens]

A quick update on the posts reqarding a lack of targets in their home port. After 6 months of continuous AIS reception while underway and in many ports in the Western Med, two weeks ago I put into my winter berth at Lagos, PT. I am now in a radio black hole. I haven't received a single AIS target in that time nor have I received any NAVTEX messages. I don't understand what it is about this location (mountains, interference, etc.), but radio reception appears to be impossible.
So my previous posts where I thought others' lack of reception could be an installation or equipment problem may have been overstated. I was receiving AIS and NAVTEX traffic just before I entered this harbor.

John

[btrayfors]

phiggins,

Splitters come in several varieties. To my knowledge, all splitters have some attenuation (signal loss), averaging about 4 to 4.5db per split. This is a fair amount of loss (3db = double or half the power).

Why anyone would knowingly choose to put a splitter into a VHF circuit which carries CRITICAL VHF COMMUNICATIONS, and which almost certainly already has a significant signal loss due to the long coax run to the top of the mast, is quite beyond me.

No, I'm not an AIS hater. But I am a communications lover, and believe all communications modes aboard should be optimized, not compromised.

Bill
WA6CCA
S/V Born Free

[phiggins]

Well Bill I would be feeling really foolish but I put in the splitter unknowingly. Think it just fell out of the sky.

Most splitters including mine are suppose to have an insertion loss of less than one db.

Glad you weren't around when Columbus was setting off. You would have had him burned at the stake for having that evil astrolabe on board.

[btrayfors]

phiggins,

Right you are! I'm sorry for the bum info...was working from old knowlege. Indeed there are splitters with less than 1db insertion loss these days.

I did notice in the specs on one of these that you have to be sure that...

- there is always 12V to the splitter; and
- the AIS port must always be connected

....otherwise you risk permanent damage to the splitter.

Hope you find the problem with your splitter.

Re: Columbus...hey, as the owner of 4 sextants and with a history of teaching celestial navigation I'm certainly all for astrolabes :-))

Bill

[Sandero]

I agree with Bill.

I installed a NASA AIS using a separate antenna which is mounted 10' above the water line on the stern rail. Works fine enough as it has revealed targets beyond 10 NM which would give me more than enough time to take evasive action.

The cost of the antenna was hardly a factor and much less than a splitter.

And hey... if my masthead VHF antenna goes south, I could, in a pinch, use the AIS antenna for VHF! Redundacy

Jef
sv Shiva
Contest 36s

[btrayfors]

Jef and phiggins,

Well, I've slept on it (almost always a good thing) and I still don't like the idea of putting anything in the antenna circuit of a VHF transmitter. Here's my reasoning:

1. this is a CRITICAL circuit in which you cannot afford any breakdowns;
2. AIS splitter devices often (mostly? always?) include ACTIVE devices...switches; these can and will break at some point;
3. I believe there's no good way to put any kind of splitter in a single VHF antenna circuit which will work well for both DSC and AIS; many boats are now installing DSC VHF and HF radios, and in the future nearly all will be doing so;
4. the "insertion loss" claims are only part of the story, witness the following tech specs from the "Easy Splitter":
Quote
Technical Data
• Active Antenna Splitter "EASY Split", Part No. 5-A-014
• Topology:
Frequency selective, passive Power Divider with 4 Ports and active Saftey switches
• Ports :
1) VHF Antenna IN/OUT, 50 Ohm, SO239
2) VHF Radio IN/OUT, 50 Ohm, SO239
3) AIS Receiver OUT, 50 Ohm, BNC
4) FM Radio OUT, 50 Ohm, Chinch
• Port Coupling : Factors:
1 - 2 (VHF-Antenna - VHF-Radio): 145 - 165 MHz, VHF Radio receiving: < 3.8dB, VHF Radio ON AIR: < 0.8dB
1 - 3 (VHF-Antenna - AIS-Receiver): 145 - 165 MHz, VHF Radio receiving: < 3.8dB, VHF Radio ON AIR: > 30dB (channel switched off)
1 - 4 (VHF-Antenna - FM Radio): 80 - 108 MHz, VHF Radio receiving: < 3dB, VHF Radio ON AIR: > 40dB (channel switched off)
2 - 3 (VHF-Radio - AIS-Receiver): 145 - 165 MHz, VHF Radio receiving: > 20dB, VHF Radio ON AIR: > 30dB (channel switched off)
• Power Handling :
Maximum Transmit Power of VHF Radio: 30W
Minimum Transmit Power of VHF Radio: 400mW
• Attack Time : (Saftey Switches): < 10msec, after Ramp up of Transmitter Power (lower limit: 400mW)

Unquote

Look particularly at the "Port Coupling" factors for ports 1 (the VHF antenna) and 2 (the VHF radio). Looks like when the radio is in receive mode, there's a 3.8db "factor" (read attenuation) which drops to 0.8db when the radio is transmitting.

However, quite aside from the signal attenuation question, I just don't think it's a good idea. And, it's expensive. And, there are better ways to get good performance without compromising your VHF lifeline (as Jeff has pointed out in his installation).

Bill

[Dunkers]

Well Bill, you have certainly given me something to think about!! I was going to breeze along to an electronics stand, have a look at AIS in action and buy it along with a splitter. However, having read your and others' arguments I see the sense in having a dedicated aerial for the AIS and as has been pointed out it can double as a spare VHF aerial as well. Its not worth taking the chance of the attenuation blocking out a weak signal and having the equipment not working to its optimum. As I have a ketch mounting an extra aerial on the mizzen is easy but I suppose I was just trying to be lazy and not have to go up the "stick". Time to dust off the bosun's chair!

Thanks to all who have contributed to this thread, its helped me and I'm sure others who are on the threshold of buying an AIS

David

[CSY Man]

Nah, masthead mounting of an AIS antenna is not good for the reasons cited above.

I have seen a 26 NM range with this antenna mounted about 7 to 8 feet above the water..

[CSY Man]

Well, the problems I had with not reading Ship's name and call sign seems to be solved:

Got a software up date from Standard Horizon yesterday.

Now all is OK.

[CSY Man]

A note from a guy that think splitters are just fine.

Re the splitter, yes you will see some loss of signal with the splitter. For example on my boat it drops from ~24 miles to ~18 miles coverage. I have a standard small VHF radio antenna on the top of my sailboat mast. I think it is worth looking at the trade offs for and against a splitter. For example, 18 miles is still plenty of distance to take appropriate action and the convenience of not having to install another antenna on the boat for me outweighs the disadvantage of the signal loss. For others, they want max distance at any cost and for them a separate high gain antenna as high as possible is the right choice.

He has valid points, but I am still happy with my rail mounted VHF antenna for the SR 161. You milage may vary..

[russa]

I have been using the NASA AIS plugged into my laptop and also into the Raymarine C120.

It works very well and in the traffic seperation zones crossing the English Channel I am very grateful for the extra information over and above radar.

Obviously all data whether from radar, ais or naked eyes and ears needs to be cross checked - but in most circumstances there are lots of cross checks that can be done from each of these sources. I love it - I wish it was on every boat.

Crossing the Channel recently in the company of a friends yacht we were both completely unable to "see" each other on the radar - I use a passive Echomax radar reflector - he uses the SeaMe active radar reflector luckily we have eyes and visibility was good.

I have put wiring info and some screen shots on my blog site if you are interested http://altendorff.co.uk/category/sailing-hardware/ais/

I also cant speak highly enough about the Brookhouse multiplexer. I have used it to connect Seatalk, NMEA0183, NMEA200 and USB. Its the magic ingredient to getting all the Raymarine equipment, DSC radio, AIS, and laptop to speak to each other.