AIS / SEAME

yoda

yoda

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Now I'm sure lots of us are considering fitting one or both of the above but the latest test in ST on AIS mentioned the version that transmitts data as well as receiving it. This got me to thinking abouts the merits of this against a SEAME set. Could somebody with more technical knowledge on both perhaps enlighten us on the relative merits of the two.

My first guess at the difference is that seame transmits only when hit by radar while the active AIS transmits all the time and therefor draws higher currents.

Yoda
 
Seame is an active radar reflector. It receives the signal sent out by a radar and sends it back at a higher level than just the normal reflection. Hence, it's just like a large radar reflector but is physically small.

AIS is a totally different beast all together. Don't be confused by a certain manufacturer calling its receiver an AIS Radar. AIS is not radar. AIS is an active system where each transponder sends out its vessels data for anyone with the right kit to receive.

The point being, you need an AIS receiver to receive AIS and only large vessels need to send out their signals at present. Small vessels will start to sent out data when transponders specifically designed for small vessels start to become more popoular.

With radar on the other hand you will see everything that reflects a signal which is just about everything from waves & rain if you don't use it right to other vessels, buoys and the coast.

So, radar is far more expensive but a Seame is just a very good radar reflector that will enable you to be seen better. AIS receivers for the yotty are far cheaper and allow you to see the big boys but at the moment nothing else.
 
I read the review and was surprised to find that some sets are now available which transmit on AIS B. Up to now I'd assumed AIS for yots was just a passive receive-only option, albeit a very useful and valuable one. I was about to lurch off and buy one but this has made me pause, see how soon others will follow with transmit capability.

The big danger of course is that every yottie on the planet ends up transmitting on AIS B and there's so much clutter the big ships just turn it off to avoid all the clutter. We should use it with discretion i.e. only when in or near active big ship lanes.
 
Both have drawbacks. SeaMe only operates on X-band and thus has no impact on ship's larger S-band radar, so it depends on which radar watch-keepers are looking at. SeaMe output also degrades considerably when the antenna heels with the vessel but is better than a passive radar reflector. AIS by maritime law is only required on vessels of over 300grt. Thus if you have an AIS receiver/plotter, you are unlikely to see fishing vessels and other smaller craft on it. If you have a class B (transmitting) AIS then all vessels over 300grt should see you at normal VHF range for the height of your AIS antenna but again, not all smaller vessels will be equiped to see your transmission. Having your own radar and knowing how to use it properly is still best.
 
Might I make a point here about AIS transmitters on yachts.
Although you might be transmitting all the necessary AIS info it all depends on the big boys being able to use it properly.
Some ships will only have a small receiver set such as the NASA "Radar" and therefore may not have a chart background. Therefore they will not have all the ships which are transmitting in geographical context. If its buried at the back of the bridge they won't be checking it very often as they have other duties at the front of the bridge. These duties will include such activities as reading mail/books, making tea, chatting to the lookout, etc.
If they don't keep an efficient eye-ball lookout and can still hit small boat without an AIS receiver, why should they avoid them when its fitted.
Please don't trust the big boys to avoid YOU just because they are fitted with hi-tech gear. Having spent 10 years on small, medium and BIG ships I wouldn't trust them. Most are only fitted because they have to and still don't set them up correctly. Also, I have just finished fitting AIS receivers up and down the Clyde River and have watched the AIS pictures, its an eye-opener.
Having said all that, I shall still be buying an AIS engine to add to my Laptop Nav Chart station but will still rely on my own eyes.
 
Radar a 1942 definition
R=Radio
A= aided
D=direction
A=and
R=Ranging

Does AIS passive radar fit the description Yes
Most service radars are passive anyway to prevent the enemy from detecting their whereabouts
 
I've found the nasa ais radar helpful on a few ocassions. I think that transmittting the cog and sog from a yacht is a lot less useful as we don't use autopilot so much and by the time a ship is worried about us we will be avoiding them.
I kind of take the view that I want to know what the ships are doing and I'll generally let them get on with it, so I want aids that bring info to me, not them.
I wonder if AIS B will just cause too much clutter unless we get some clever 'threat analysis' software?
 
Ships over 300grt must have a class A AIS system, not a NASA AIS radar! Decent systems will be programmed to sound collision alerts as do their radars, I think you find that audio alerts will catch watch-keepers attention. I really don't understand why you consider a chart background and "geographical context" of importance. I get the feeling you havn't used AIS nor spent any time on a ship's bridge and are inventing what you think...
 
[ QUOTE ]
I've found the nasa ais radar helpful on a few ocassions.

[/ QUOTE ]I haven't seen anyone post about their own experiences here before. Would you buy one again if you bought another boat, for example?
 
Thanks Oldhand, maybe 12 yrs with Brocklebanks and various other shipping companies wasn't enough. It was before AIS and as the Radio Electronics Officer I know how Deck Officers regard electronics. Alarms are something that interferes with their Chart correctiosn and other hobbies.
Lets not start a slanging match on this forum.
 
hi, for what its worth my opinion is that the AIS is well worth having, especially as it is not all that costly. I have ths NASA stand alone one, you can immediately see from the display when a vessel is on a possible collision course and read off its speed and course. As far as I'm concerned it has proved its worth on several occasions. For example, on returning from Cherbourg in August I was approaching the east bound shipping lane and saw two ships hull down in the west. On consulting the AIS to get their info I was suprised to see that there were actually nine ships in a tight group all on the same heading and travelling at much the same speeds. It was plain to see that unless some action was taken I was going to be in the middle of them! Given the circumstances I don't think any of them were going to alter course. As it was a clear day and I was under sail I didn't have the radar on but I doubt that it would have so clearly indicated the situation.
 
not sure that you've understood airborne1's post which itself indicate a better understanding of what is going on than you give credit for? Most AIS receivers on merchantmen are not much better than Nasa's is what he is saying, I think. They conform to the minimum IMO standard.
 
Exactly so. The other thing is, other vessels, fishing boats etc. may not have them and if we get to rely on it rather than Radar those that don't have it become invisible. I must say having an AIS transmitter would be something I would certainly derive comfort from when crossing traffic lanes, especially at night or in bad vis... Isn't it true that Seeme or whatever it's called is only useful to X band? Or have I got that wrong? The best though seems to be to have AIS integrated with your radar so that anything without an AIS signal is still seen on the screen. Big ship Radar can do this OK and compare ARPA with AIS signals to see if they coincide. Not sure if yachtie MARPA can be made to do this. Might be asking too much for the price? That would be good though wouldn't it....? Note to self... Question for Jan boat show!
 
Hi

Lets not get to carried away with X band S band thing - S band radar will have trouble "seeing" a block of flats let alone a yacht. That said AIS is a useful aid as is the seame, they both have limitations but when used in conjuction with a few sets of MKI eyeballs give the skipper and crew a sense of wellbeing and security. I would be be happy without either as long as the watchkeeping and lookout was up to scratch.
 
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