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Old 28-05-2018, 09:13   #16
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Re: Collision Avoidance

Experience indicates that fog can come down after you have been "out there" on an otherwise clear day. You didn't go out into the fog. The fog caught up to you.

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Old 28-05-2018, 14:16   #17
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Re: Collision Avoidance

Originally Posted by glmeadows View Post
I am considering to use an AIS transponder (Vesper XB8000) and passive radar reflectors in my small cruising sail boat.

Radar AND AIS would be the ultimate solution but with the radar reflectors and an AIS transponder, my thinking goes like this.

If I have AIS, anyone who has AIS will be able to see me and I will see them. With the reflectors anyone with radar should be able to see me and take defensive action. If they ONLY have radar, I won't be able to see them and will need to depend on their defensive measures. Given all this, if they don't have either radar or AIS, they shouldn't be out at night or in the fog.

For the moment, this covers a lot of bases using both AIS and radar reflectors and it also fits my budget. Question...

Would anyone insist upon having both (I.e. Radar and AIS) ? If so, why since being on the water in adverse weather or at night is always a risk even given all the equipment and operational watch and awareness. Again, the only thing I won't see are targets who ONLY have radar. Also, if they've got radar they most likely have AIS.

I think some of your assumptions are incorrect. Around here, most boats do NOT have AIS, and many boats do NOT have radar. Most boats with radar will likely NOT have AIS (just from a numbers perspective).

Operators with radar and/or AIS may or may not be looking at the data, or may not be skilled with their systems (especially radars).

Many boats without either radar or AIS are out at night, and in fog (although the latter case often isn't planned).

IOW, depending on AIS wouldn't buy you much, around here. Maybe 1 in every 1000 boats might have it... And depending on somebody else a) having radar, b) using it at all, and c) using it skillfully puts you at their mercy.

Contrast that with taking active measures (like installing radar) yourself.

Of course I think radar and AIS are useful tools, but just because they exist doesn't mean they solve everything.


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Old 30-05-2018, 12:06   #18
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Re: Collision Avoidance

Not every ship have their AIS on. This one didn't. And the weather was not all the time as clear as in this picture.

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Old 30-05-2018, 16:00   #19
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Re: Collision Avoidance

Originally Posted by TeddyDiver View Post
Not every ship have their AIS on. This one didn't. And the weather was not all the time as clear as in this picture.


You're not alone, Teddy. Coastally, here in Australia, only two ships that I personally know of, one's AIS had quit working, they were planning to get it repaired in their next port of call. (They're required to have them on and be working here.) The other one was one where no one answered the radio call, nor the DSCC call, and the skipper was later disciplined, for a watchperson's error.

There is uncertainty in life, it's intrinsic, and we all have to cope with it. As to the OP, there are aspects of his plan he just didn't have the experience to know about, and now, he's been warned.

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Old 07-07-2018, 08:26   #20
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radar range

posted this question on wrong forum,here we go again.

AiniA has a posting with theoretical distances for line of sight that I was familiar and prompted my question regarding effective range of a sailboat installed radar.

Understand the height on the dome unit will determine the possible max range and yet even half way a mast height numbers do not seem to match the advertised range.
I just purchased a new radar and of course debating between transom vs mast,I know the higher the better but worth it?
In summary
A 20 miles range radar factory specs? true?

Originally Posted by AiniA View Post
Much, much less than this. It obviously depends on the height of your eye and the height of the freighter. A couple of formulas help

For Imperial
SquareRoot(Height above surface in feet / 0.5736) = distance to horizon in miles (not nautical)

For metric
SquareRoot(height above surface in centimetres / 6.752) = distance to horizon in kilometres

So if your eye is 7 feet about the sea you can only see about 3.2 miles. If a ship is 25 high, keep in mind the bulk of the ship will be below this height, although lights could be higher. In any case, 25 feet means the horizon is about 6.6 miles. Add these two together and you can see the 25 foot above part of the ship at a little less than 10 miles or about 8.5 nautical miles.

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