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Old 31-08-2015, 07:26   #46
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Re: AIS benefits

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Originally Posted by Kenomac View Post
Jon,

Here's a picture of the boats ahead of me that are equipped with radar deflectors.
They all seem to be missing a hull.

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Old 31-08-2015, 07:28   #47
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Re: AIS benefits

Picture of the two catamarans behind me without the deflectors. The catamarans have a much bigger footprint on the water than the Oyster monohulls have, but as you can clearly see on the radar image, the Oysters that are equipped with the deflector, show a much larger reflection than the catamarans.
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Old 31-08-2015, 07:29   #48
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Re: AIS benefits

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Originally Posted by Kenomac View Post
Picture of the two catamarans behind me without the deflectors. The catamarans have a much bigger footprint on the water than the Oyster monohull so, but as you can clearly see on the radar image, the Oysters that are equipped with the deflector, show a much larger reflection.
Stealth Cats........

Shhhhh..!

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Old 31-08-2015, 07:30   #49
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Re: AIS benefits

Ken..
when you take the tender to shore, do you have to pay to leave it somewhere?
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Old 31-08-2015, 07:33   #50
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Re: AIS benefits

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Ken..
when you take the tender to shore, do you have to pay to leave it somewhere?
No, they pay me. :-)

I go right into Portisco from this location, 5 minute dinghy ride past the super yachts, right up to the supermarket and restaurants. Remarkably nice marina staff in Portisco.
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Old 31-08-2015, 07:44   #51
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Re: AIS benefits

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Originally Posted by thomm225 View Post
AIS Benefits .
If I had an AIS I would have "seen" him easily an hour before I was close. If I was cruising a lot or doing lots of night sailing, I'd get an AIS (at least a receiver) now.
Great story. But don't waste your money on a receive only. The full Class B is not much more expensive and it lets them see you when you need them to.

Mark
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Old 31-08-2015, 07:45   #52
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Re: AIS benefits

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Good Lord!!
Now I remember you!!

You must have me mixed up with some one else, you wouldn't recognise me now from then, I'm about 40 lbs pudgier, three shades greyer and much much nicer.

Not only that, but I've traded in my 350 HP blacked out RIB for a family cruising boat and a desk job

Joking aside, I do really like my receive only AIS, for my cruising grounds I can't see much benefit to having a transmitter.

A big benefit I would see is helping SAR people find you if you got into trouble.

On another thread I think it was A64 posted an AIS based MOB product that looked really cool.

For collision avoidance- I wouldn't trust AIS alone, however, for detection prior to collision avoidance I think they are handy.



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Old 31-08-2015, 07:50   #53
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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.

Ken
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.
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Old 31-08-2015, 08:29   #54
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Re: AIS benefits

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Originally Posted by Kenomac View Post
Picture of the two catamarans behind me without the deflectors. The catamarans have a much bigger footprint on the water than the Oyster monohulls have, but as you can clearly see on the radar image, the Oysters that are equipped with the deflector, show a much larger reflection than the catamarans.
I note that your radar is mounted at the front of your mast. Could it be that the boats behind you are not showing on radar as clearly because of the interference caused by your mast? Go and ask one of the cats to swap places with the mono's and do it again!
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Old 31-08-2015, 08:40   #55
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Re: AIS benefits

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Originally Posted by Privilege View Post
I note that your radar is mounted at the front of your mast. Could it be that the boats behind you are not showing on radar as clearly because of the interference caused by your mast? Go and ask one of the cats to swap places with the mono's and do it again!
Ha Ha.

Jon and Privilege,

Please also note, that the pontoon shown between 9 and 10 o'clock has nearly 40 catamarans and monohulls presently moored on it, all between 40-50ft. You can see that the 62ft Oyster with the radar reflector at 11 o'clock is echoing a reflection nearly 1/3 the size of the pontoon containing nearly forty boats.
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Old 31-08-2015, 08:45   #56
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Re: AIS benefits

The pontoon pictured is the one on the radar screen between 9-10 o'clock.

I hope this demonstration finally puts this radar reflector argument to rest.

Ken
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Old 31-08-2015, 08:53   #57
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Re: AIS benefits

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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.
Are you saying that a 50ft Lagoon catamaran that's not equipped with AIS traveling at 8-9 knots at night or daytime hurrying to wards their next bareboat charter location is not something I should be worried about hitting? .. Because a boat of this size is not enough to sink or kill me? The picture in the post above shows many large catamarans in my immediate area, most of which do not have AIS.

I shouldn't be worried about them? Really?

Ken
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Old 31-08-2015, 09:08   #58
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Re: AIS benefits

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Originally Posted by Kenomac View Post
Quote:
Originally Posted by Jon Eisberg
While he may have seen you on radar, I doubt your reflector was much of a contributing factor...

You may as well toss that thing in a dumpster, every test I've ever seen has shown those Mobri-style reflectors to be next to worthless, almost right up there with the "Radar Flag"...

;-)
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
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...

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One of the most comprehensive tests of radar reflector performance was carried out in 1995 by West Marine www.ussailing.org. The conclusions were that the poor performance of the Firdell Blipper 210/5 and 210/7 were surprising given their popularity and reputation, and although a well packaged and clever device, the models tested (i.e. 210-5 and 210-7) were not large enough to have much value aboard a vessel. Furthermore, they were also unable to obtain results consistant with those supplied by Firdell, stating that their claims were consistant with a larger reflector. The Echomax range is included in the 2003 West Marine catalogue, replacing the Firdell Blipper.

Competing Products and Comparisons with EchoMax Radar Reflectors
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Old 31-08-2015, 09:23   #59
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Re: AIS benefits

RCS or Radar cross section is not intuitive, that is what you look at and think that would have a large Radar return, often may not, and in particular the orientation to a target can change it's RCS quite dramatically.
I believe that the very old fashioned corner reflector or a variation of that is pretty much the standard, now transponders that actively transmit, could make for a very large return, but how many different frequencies are used for Marine Radar?

Radar reflector is something I have been wanting for quite some time, as I want to be seen, so I can be avoided, yet it seems that many are snake oil?
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Old 31-08-2015, 10:42   #60
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Re: AIS benefits

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[...] Radar reflector is something I have been wanting for quite some time, as I want to be seen, so I can be avoided, yet it seems that many are snake oil?
The snake oil reflectors include the tubular Mobri/Plastimo, and the "Radar Flag".

The reasonably-sized corner reflectors (Davis, Firdell) work pretty well, but not spectacularly so.

The "Luenberg Lens"-based reflectors such as Tri-Lens are probably the best passive reflectors. Expensive and a bit heavy though.

The active transponders (See-Me) are quite effective, but may not respond to all radar frequencies (some do).

Here is a good site with reflector test data: The Radar Reflector Site
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