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Old 31-08-2015, 11:05   #61
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Re: AIS benefits

Quote:
Originally Posted by Jon Eisberg View Post
Seems you're confused about the type of radar "deflector" that I'm referring to... thomm225 describes his as "tubular... attached to an upper shroud", which I'm presuming - given the size of his boat - to be this type, originally known as a Mobri, now marketed by Plastimo:




These are a far cry from what you appear to have on your boat. The USSailing test declared them to be essentially "invisible", and the more recent report done in 2007 for MAIB in the wake of the OUZO sinking had this to say:

" A 4" tube reflector is not considered suitable due to its poor performance. It is also recommended that the 2" tube reflector is unsuitable as the performance of this target will be even lower."

From the pic you posted awhile ago, it looks like yours is a Firdell Blipper... It's impossible to tell from your pic what brand those other Oysters have, but they might be an Echomax, which are quite similar in appearance to your Firdell from a distance... In addition, they may even be running an active "Sea-Me" type reflector, who knows?

certainly, your reflector is better than nothing... But in the tests I've cited previously, the results for the Blipper were somewhat disappointing. It appears the Echomax, among others, is the better performer...
Point of clarification.

Here's a picture of the radar reflectors fitted on our Oyster and the other two Oysters pictured in previous posts. Two weeks ago, Jon made the same statements disparaging the reflector pictured when I stated on another thread that a large ferry skipper stated over the radio when contacted during a very windy night from five miles out, "no problem, we see you just fine... Don't worry about anything." We first saw him on radar, then contacted him via the AIS information on our receive only system, just to be sure he saw us.

Apparently, not all radar reflectors are created equal. Not trying to pick a fight with Jon, but I think we're each talking about two different types of reflectors, but each time the subject of radar reflectors comes up.... Out come the remarks condemning all reflectors. I just want to clear this up for some folks who might be thinking of purchasing a reflector.

Ken
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Old 31-08-2015, 11:14   #62
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Re: AIS benefits

Rustic Charm,
No worries!

I've been in a bad mood all weekend....got bit by a spider on my hand, swelled up, and couldn't finish my projects 'til this morning..
All better now.

Fair winds my friend.

John
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Old 31-08-2015, 11:24   #63
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Re: AIS benefits

I'm with Ken on this!
I agree 100%!
Quote:
Originally Posted by Kenomac View Post
The only downside I can see is what I pointed out in an earlier post, it's when people install only the AIS and forgo radar and sustaining a vigilant watch... thinking that AIS is somehow a new and superior technology which renders the other two unnecessary. They depend almost totally on the AIS alarm warning them of others.... but AIS is far from foolproof. Many of the boats they will cross paths with, don't even have AIS.
Ken
I have AIS transponder (and a Vesper Watchmate display), and love 'em...but it isn't a replacement for standing a watch, nor for radar...

Fair winds to all...

John
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Old 31-08-2015, 11:27   #64
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Re: AIS benefits

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Originally Posted by Banshe View Post
While radar still has it's uses, very few watch-keepers aboard big ships monitor it continuously. They may glance at it now and again...

I like AIS and agree with many of your points about its merits, but how do you know this (above) to be true?

-Chris
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Old 31-08-2015, 11:33   #65
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Re: AIS benefits

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Originally Posted by Kenomac View Post
The only downside I can see is what I pointed out in an earlier post, it's when people install only the AIS and forgo radar and sustaining a vigilant watch... thinking that AIS is somehow a new and superior technology which renders the other two unnecessary. They depend almost totally on the AIS alarm warning them of others.... but AIS is far from foolproof. Many of the boats they will cross paths with, don't even have AIS.
Quote:
Originally Posted by MarkJ View Post
I disagree.

Every vessel big enough to kill you has AIS.
I just did the coastal trip from NYC around Caper Hatteras to Beaufort and EVERY floating object had AIS except for a few sport fishing boats and they have a guy at the wheel sans autopilot.

So its really time to understand the reality that any boat of size enough to sunk you in a collision will have AIS.
The percentage chance of an errant duffer that you neither see with your own eyes nor see on AIS hitting u is so remote.
Its time to let RADAR do the job its best at, fog.

Doesn't seem like it would take much of a boat to sink us if a collision occurred. Especially at any kind of speed...

Around here, I can usually see somewhere between 10 and 100 boats underway with my Mark I Eyeball to every one that is transmitting an AIS signal. Most of those are capable of seriously holing our boat in a collision...

FWIW, I like guard zones on both AIS and RADAR, fog or no fog.

-Chris
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Old 31-08-2015, 11:33   #66
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Re: AIS benefits

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Originally Posted by ranger42c View Post
I like AIS and agree with many of your points about its merits, but how do you know this (above) to be true?

-Chris
Its true, one watch officer on a bridge. Bridge is 75 feet across, chart table is usually in the back, bridge computer is usually in the back, you need to spend a certain amount of time looking out the window. However, in restricted visibility that would require a RADAR for collision avoidance, the interval that a RADAR will be checked is very frequently. More frequently than AIS- at least it is for me.

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Old 31-08-2015, 11:33   #67
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Re: AIS benefits

Quote:
Originally Posted by ranger42c View Post
Quote:
Originally Posted by Banshe
While radar still has it's uses, very few watch-keepers aboard big ships monitor it continuously. They may glance at it now and again...
I like AIS and agree with many of your points about its merits, but how do you know this (above) to be true?

-Chris
Anecdotal evidence? Several years ago while halfway between Hawaii and California I was talking with a big ship (via VHF). I asked them how my radar return looked and the answer was "Just a minute while I turn on the radar." A minute passed, then: "Yes, I see you just fine."

I'm not going to depend on humans being infallible.
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Old 31-08-2015, 11:36   #68
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Re: AIS benefits

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Originally Posted by Kenomac View Post
Jon,

You keep writing this, I don't know where you heard it, but it's simply NOT TRUE.

I just took a picture of the radar image in my anchorage a minute ago. Those two big dots at 11 and 1 o'clock are two Oyster yachts 56 and 62ft, each equipped with one of the radar defectors you disparage. The two smaller images near the bottom of the screen and close to my boat at 5 o'clock, are two catamarans which are not equipped with the radar deflecting device. All four yachts are roughly the same size. The two ahead of me with the deflector.... The two behind without.

Ken
All things being equal the same 'target' will look 'fatter' on your PPI at a distance than when the same target is closer to you...its all to do with horizontal beam width and the way it is displayed.... nothing to do with target strength.....

That looks like a Firdell that you have .... Mobris are a different and far inferior animal all together.
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Old 31-08-2015, 11:50   #69
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Re: AIS benefits

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Originally Posted by FamilyVan View Post
Its true, one watch officer on a bridge. Bridge is 75 feet across, chart table is usually in the back, bridge computer is usually in the back, you need to spend a certain amount of time looking out the window. However, in restricted visibility that would require a RADAR for collision avoidance, the interval that a RADAR will be checked is very frequently. More frequently than AIS- at least it is for me.

Only one human on watch? That's normal?


Quote:
Originally Posted by Paul Elliott View Post
Anecdotal evidence? Several years ago while halfway between Hawaii and California I was talking with a big ship (via VHF). I asked them how my radar return looked and the answer was "Just a minute while I turn on the radar." A minute passed, then: "Yes, I see you just fine."
Is it appropriate that be logically extended to apply to all (or most? or many?) ships?



Quote:
Originally Posted by Paul Elliott View Post
I'm not going to depend on humans being infallible.
And maybe only one of those on watch at any given time, at that.

But I suspect a fallible human can screw up with AIS as easily as with RADAR...

-Chris
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Old 31-08-2015, 11:50   #70
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Re: AIS benefits

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Originally Posted by ranger42c View Post
I like AIS and agree with many of your points about its merits, but how do you know this (above) to be true?

-Chris
The statement that I don't agree with is that AIS is monitored 24/7, that's non sense, an AIS can't be monitored 24/7 for the same reasons a RADAR can't be monitored 24/7. This theoretical bridge the op created would have to have a watch officer dedicated to AIS watch, which would be a waste of money.

As a veteran watch keeping officer (up until last year) I can say, my AIS received less, not more attention than my RADAR. And in good visibility, they both received less attention than looking out the window while drinking coffee and trying to chat up the female cadet and/or talking about cars/trucks/hunting/fishing/partying/girls etc.

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Old 31-08-2015, 11:51   #71
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Re: AIS benefits

Quote:
Originally Posted by El Pinguino View Post
All things being equal the same 'target' will look 'fatter' on your PPI at a distance than when the same target is closer to you...its all to do with horizontal beam width and the way it is displayed.... nothing to do with target strength.....

That looks like a Firdell that you have .... Mobris are a different and far inferior animal all together.
Then how do you explain the pontoon reflection in comparison to the 62ft Oyster at 11 o'clock which are a similar distance away from my boat where the Oyster appears 1/3 the size of the pontoon containing 30 or more boats? I'm not trying to be a wise guy... I'd like to know?

Thanks

Ken
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Old 31-08-2015, 12:00   #72
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Re: AIS benefits

Quote:
Originally Posted by ranger42c View Post
Quote:
Originally Posted by Paul Elliott
Anecdotal evidence? Several years ago while halfway between Hawaii and California I was talking with a big ship (via VHF). I asked them how my radar return looked and the answer was "Just a minute while I turn on the radar." A minute passed, then: "Yes, I see you just fine."
Is it appropriate that be logically extended to apply to all (or most? or many?) ships?
Of course not, and I never intended to imply such. My point is merely that it happens sometimes.

Quote:
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Quote:
Originally Posted by Paul Elliott
I'm not going to depend on humans being infallible.
And maybe only one of those on watch at any given time, at that.

But I suspect a fallible human can screw up with AIS as easily as with RADAR...

-Chris
We can all screw up. I include myself among the fallible. I have anecdotal evidence of that as well. Radar reflectors don't change that, AIS transponders don't change that, nothing changes that. But I have both a reflector and a transponder, just to improve my odds.

Kind of a silly argument, but I don't think we're really arguing...
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Old 31-08-2015, 12:24   #73
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Re: AIS benefits

Quote:
Originally Posted by Kenomac View Post
The only downside I can see is what I pointed out in an earlier post, it's when people install only the AIS and forgo radar and sustaining a vigilant watch... thinking that AIS is somehow a new and superior technology which renders the other two unnecessary. They depend almost totally on the AIS alarm warning them of others.... but AIS is far from foolproof. Many of the boats they will cross paths with, don't even have AIS.

Ken

My reference was to a helmsman calling confirmation via vhf in the fog not being a nuisance.


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Old 31-08-2015, 12:32   #74
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Re: AIS benefits

Jon, et al,
I'd like to briefly add some hard facts to this discussion...
Primarily about Radar Reflectors / RCS, and AIS transponder "filtering"...

1) First off, Jon Eisberg is correct about the "tubular" Morbi-type reflectors being practically useless....(but as long as they are oriented perfectly vertical, they do provide some improvement in RCS of most fiberglass boats....just not very much...and once they move from perfectly vertical, they are totally useless!!)
{Although, in full disclosure, while I have the ubiquitous Davis Echomaster, in the catch-rain position, at my top spreader.....the original owner of my boat did strap two of those Morbi reflectors on the shrouds, and one is still there, 11 years on!! }

If anyone would like to see THE definitive study on marine radar reflectors, it is available on-line for free!!!
The UK gov't (UK MAIB) commissioned this study in 2006, and it was published in 2007....(this is what Jon was referring to as the "us sailing study")

Anyone other than military surveillance radar and targeting radar personnel, wishing to understand marine radar and the Radar Cross Section (RCS) of various "reflectors" should read this document, front-to-back!! (I've not only read it all, and understand it all, I keep a copy of it in my doc folder to show others when questioned about radar reflectors)

Please have a look:

http://www.ussailing.org/wp-content/...tor%20Test.pdf

Understand that this was for the standard X-band (9Ghz) marine radar...(not S-band, 3Ghz, marine radar)
Quote:
Originally Posted by a64pilot View Post
but how many different frequencies are used for Marine Radar?
A64, there are only two freqs for marine radar....the standard X-band (9Ghz) is ubiquitous on both pleasure boat and commercial vessel....and S-band (3Ghz) is really only see on LARGE ships, cause the antennas are big (12' across or so) and they are expensive!!!

Ships along coasts, near harbors, maneuvering, etc. WILL be using the standard X-band (9ghz) marine radar....and many will also run this radar when offshore...
But, some shut down the X-band radar when offshore...and they use their S-band radar, which has the advantage of "seeing thru rain"....so they can see targets obscured by rain!!!
(I do not have a definitive answer as to what % of ships turn off their X-band radar at sea....but, do know that some do...)




2) I realize this is a thread about AIS, not radar reflectors...
But, for those non-tech types, who might not get all the data in the UK MAIB report, the gist is this...

--- Most radar reflectors work okay when oriented at the correct angle to the radar beam...BUT...
But, our boats move about quite a bit, and especially monohulls being heeled-over, this makes most radar reflectors poor, in many situations...

--- None of the consumer marine passive reflectors met the "standard" (ISO 8729)....but some came close, and some are cheap enough (Davis Echomaster) that every boat should have 'em...

--- The Large Tri-Lens (although heavy and pricey) performs well, and both the ubiquitous (and cheap) Davis Echomaster (in the "catch-rain" position), and the Echomax 230, also do "okay" to "acceptable" (my opinion here, based on price vs. performance, etc.)....

--- Aside, from them....none of the others are worth much at all..

--- Active Radar Target Enhancers (called RTE's), are VERY VERY good!!!
They are pricey, and require mounting in the clear to be really effective (mast top is best), need wiring, etc...but they DO work VERY WELL!!!!

Please note that now, 8 years since this report was published, that both Glomax and SeeMe, now market dual-band RTE's....

Ships along coasts, near harbors, maneuvering, etc. WILL be using the standard X-band (9ghz) marine radar....and many will also run this radar when offshore...
But, some shut down the X-band radar when offshore...and they use their S-band radar, which has the advantage of "seeing thru rain"....so they can see targets obscured by rain!!!
(I do not have a definitive answer as to what % of ships turn off their X-band radar at sea....but, do know that some do...)


Edit:
In addition to the dry MAIB report http://www.ussailing.org/wp-content/...tor%20Test.pdf
some might like to read Panbo's take http://www.panbo.com/archives/2007/0...ally_work.html
or even a UK vendor's take http://www.safety-marine.co.uk/spage...-reflector.htm
My point is, the definitive info is out there....a short google search is all you need do...so, if you don't agree with my words here, have a look at the UK MAIB's report, etc...












3) Okay, enough about radar reflectors!!
How about we put to rest the oft-heard myth that commercial vessels "filter out" Class B targets! (sorry Jon!)
Quote:
Originally Posted by Jon Eisberg View Post
Hopefully, a more sophisticated means of filtering, than simply eliminating all Class B targets, which some commercial vessels, in certain situations, have been doing for some time...
Fact #1 :
The Class A AIS transponder does NOT filter anything out....it receives all AIS transponder data that is within range, Class A and Class B, all the time!!!
This cannot be disabled / filtered!!

Fact #2:
The Class A AIS transponders, are required to have a certain MKD (Minimal Keyboard Display), and alarms....and all AIS transponder data received is always available there (even if few bridge crews look at it!)

Fact #3:
Most ships crew do not watch the AIS transponder's MKD....but rather watch their main ECDIS and/or their main radar screen, when not looking out the bridge windows maintaining a visual watch....where they also display targets/data received from the AIS transponder...
(and this is where they "filter out" targets, based on "anchored"/"moored", "SOG" below a certain number, etc., and also where they would filter out Class B targets, should they desire to do so...)

Fact #4:
The Class A transponder (and MKD) will alarm, if any AIS transponder data received is calculated to cause a CPA at or below the minimum set by the vessel's captain (or shipping company's rules), no matter if that target is "filtered-out" by the ECDIS / Radar Display, or not!!!


Fact #5:
Not all commercial crews are watching what they are supposed to be watching, when on watch....some might be "on-line", some might be in the head, some drinking coffee and reading, some playing cards or chit-chatting, etc. etc...
We are all human, and none of us are perfect after all!





I'm not working on a commercial ship's bridge, so don't have first hand info to pass on....but according to some commercial mariners here on CF (and some posting on Panbo), they don't "filter-out" Class B targets, but rather do "filter-out" targets in crowded harbors that are "anchored/moored" and many also filter-out vessels making < 0.5ktz SOG....
But, when at sea, they don't have any "filters" on their ECDIS systems / Radar displays...
(now, as for those fast ferries that some of you run across??? I have no info for you...sorry!)




Whew, I thought I was going to be brief!
But, I do hope some of you find the above info helpful...

Fair winds..

John
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Old 31-08-2015, 13:42   #75
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Re: AIS benefits

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Of course not, and I never intended to imply such. My point is merely that it happens sometimes.


We can all screw up. I include myself among the fallible. I have anecdotal evidence of that as well. Radar reflectors don't change that, AIS transponders don't change that, nothing changes that. But I have both a reflector and a transponder, just to improve my odds.

Kind of a silly argument, but I don't think we're really arguing...

To be sure, I was merely musing...

And yep, I too can find anecdotal evidence (at best) of my... er... occasional (very occasional, mind you) screw-ups. Worse, so too can wifey find same (or even more) evidence from time to time.

Anyway, I like more tools in the toolbox, too.


Especially in case one of those watch officers is looking at she screen I might not be showing up on!

-Chris
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