GHA
Well-Known Member
Have a look at sporadic E propagation.
http://www.uksmg.org/content/sporade.htm
I've listened to Swiss Vhf hams in London before.
Class B AIS pros and cons
- Thread starter oldvarnish
- Start date
Have a look at sporadic E propagation.
http://www.uksmg.org/content/sporade.htm
I've listened to Swiss Vhf hams in London before.
neilf39
Well-Known Member
Picked up Guernsey CG on my handheld in the Solent the weekend before last, Was most surprised. I wondered why I had been hearing other transmissions in French beforehand. Must have been the atmospheric conditions.
MountainGoat
Well-Known Member
That's certainly true! I don't think the owners know where the "silent" switch is.
God, yes! Woe betide anyone who doesn't turn off AIS collision warnings when coming into a marina, especially if it's unfamiliar. Dealing with trying to get in and to a berth can be challenging enough without the AIS screaming at you constantly.
maby
Well-Known Member
for a safety system you really need to distinguish between what is reliably possible and what is occasionally possible. All radio is fundamentally line of sight in that radio waves (other than extremely low frequency) do not pass well through water or solid ground. If, standing next to your AIS antenna, you can't see the AIS antenna of the other boat, then you are dependent on something to bend the radio signal if you are going to receive it.
There are a variety of things that will do that ranging from atmospheric effects like sporadic E and temperature inversions resulting in ducting, aircraft passing over and even the moon - yes, radio amateurs regularly talk from one side of the world to the other by bouncing signals off the moon or meteor trails. Some of these modes are very predictable and reliable - we can hear long wave transmitters on the other side of Europe almost all the time - some are very unpredictable. They can be very effective - I had a long conversation with a radio ham on St. Kilda some years ago while I was standing on a beach near Bordeaux using a walkie-talkie at 50MHz and the signal was fine - that was with 5W into a little "rubber duck" antenna at a height of about five feet above sea level.
So, AIS at a range of more than about 20 miles should be considered unreliable - it may work, but for every boat you see, you will miss several others. Does it matter? Of course not - it's intended for collision avoidance - a range of five miles is plenty unless you are a very fast power boat and nobody needs more than about ten miles warning to avoid a collision.
RichardS
N/A
I can't really understand why people have alarms set on anything, apart from when they are stationary and trying to get some sleep. All mine are permanently off on everything.
If you need an alarm to tell you that you are in a possible collision situation with another ship or the seabed then surely you aren't using your eyes properly? You might miss something that doesn't have an alarm ...... like a boat that doesn't have AIS fitted.
Richard
Skylark
Well-Known Member
Thanks, GHA but if you take a look at my post #9 you'll read that I've already made reference to Sporadic E.
I think that Maby sums it up well in his post #24. As an aside, now that I've retired another of my "projects" is to fire-up my Trio hf transceiver. I haven't used it in years but I always renewed my A license (before it became free).
maby
Well-Known Member
I can't really understand why people have alarms set on anything, apart from when they are stationary and trying to get some sleep. All mine are permanently off on everything.
If you need an alarm to tell you that you are in a possible collision situation with another ship or the seabed then surely you aren't using your eyes properly? You might miss something that doesn't have an alarm ...... like a boat that doesn't have AIS fitted.
Richard
In daylight and with good visibility, you are right of course, but how about night time, fog or heavy rain? Sailing round the Solent in the dark, I'm very pleased to have AIS alarms turned on. OK, it does go off pretty frequently, but it only takes a moment to press the cancel button and it prompts me to check the screen and confirm that it is referring to a target that I was already aware of.
RichardS
N/A
But how often would any of us be coming into an "unfamiliar marina" in the dark as per post #23?
Richard
maby
Well-Known Member
Relatively infrequently, I agree, but your post seemed to be questioning the value of alarms under all circumstances - sorry if I misunderstood you!
RichardS
N/A
I'm sorry as well ..... you're right that I was indeed making a more general comment but it was the "alarms in marinas" comment which specifically piqued my interest because it is such a frequent complaint on the forum that it makes me wonder why people just don't turn off the alarms all the time as continually turning them on an off on regular occasions like entering and then leaving a marina would drive me to distraction.
Richard
MountainGoat
Well-Known Member
I can't really understand why people have alarms set on anything, apart from when they are stationary and trying to get some sleep. All mine are permanently off on everything.
If you need an alarm to tell you that you are in a possible collision situation with another ship or the seabed then surely you aren't using your eyes properly? You might miss something that doesn't have an alarm ...... like a boat that doesn't have AIS fitted.
We were crossing the Thames Estuary from Burnham to Ramsgate a week ago. The AIS alarm indicated a collision with a vessel coming out of the Medway before we could even see it. We made a tiny course alteration and about 15 minutes later missed it by more than a mile.
I found that extremely useful.
More useful was when we got to Dover, crossing the eastern entrance to get in the western when the P&O Pride of Canterbury was departing the eastern entrance. We only receive AIS, we don't transmit, so we knew what to do to alter course to avoid a collision and it made the work of everyone else, including the pilot on the ferry and the busy and hassled harbourmaster considerably easier.
RichardS
N/A
But don't you get all that information from the AIS screen anyway ..... or perhaps your display is not visible from the helm in which case I understand your need for the alarm?
Richard
MountainGoat
Well-Known Member
Chart plotter is below. No room for it on the binnacle, although I'm very tempted by a Raymarine i70s which has an AIS display.
maby
Well-Known Member
Our plotter is at the helm, but I still keep the alarm on - the screen can be very busy and I would not be confident of seeing a flashing icon immediately.
Bru
Well-Known Member
We're back to my long standing complaint about rubbish software
Turning alarms on and off invariably means digging down several layers of long winded menus
If I was specifying plotter software, a "Disable / Enable Alarms" button (or virtual button on a touch screen) would be readily available. Preferably one touch, at most two
Having to dig down into the menus to turn them on and off means I have them off most of the time (only enabling them in poor viz or at night) but this is far from ideal IMO
Turning alarms on and off invariably means digging down several layers of long winded menus
If I was specifying plotter software, a "Disable / Enable Alarms" button (or virtual button on a touch screen) would be readily available. Preferably one touch, at most two
Having to dig down into the menus to turn them on and off means I have them off most of the time (only enabling them in poor viz or at night) but this is far from ideal IMO
GHA
Well-Known Member
In a situation like that I always wonder what it's like for the guy on the big boat and usually try to do a biggish course change for a minute or so hoping that it will be more obvious that I'm doing something on purpose to keep out of the way.
Wonder if they notice..
johnalison
Well-Known Member
I've no use for alarms either. From time to time my plotter gives me a shallow anchor alarm, which is very kind of it, but completely un-called-for. I set a circle of 1 mile around my boat on the screen, but only to make a quick glance easier.
Uricanejack
Well-Known Member
In a situation like that I always wonder what it's like for the guy on the big boat and usually try to do a biggish course change for a minute or so hoping that it will be more obvious that I'm doing something on purpose to keep out of the way.
Wonder if they notice..
Most likely do and are pleasantly surprised