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Old 24-09-2013, 10:42   #61
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pirate Re: Big Ship Little Boat, who Gives way

I maintain my refusal to buy one... I don't need one...
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Old 24-09-2013, 10:48   #62
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Re: Big Ship Little Boat, who Gives way

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Originally Posted by Dockhead View Post
To give the ship your posit, get a transponder! He needs it before you see him, not after there's already a problem! The cost difference is now so trivial that I can think of no reason to have a receive-only AIS.
So along this line, any specific recommendations as far as brand or model AIS transceiver? I see the Sitex online for about $550.

From initial research it appears that a basic unit will send output via NMEA to any MFD display that accepts NMEA input? Am I correct?
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Old 24-09-2013, 10:50   #63
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Re: Big Ship Little Boat, who Gives way

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Yes, a good point, and I used to do this sometimes.
However, this maneuver has few disadvantages:

1. It's not as obvious to the other vessel
Generally by the time you are making evasive manoeuvres in regard to a large vessel when you are the stand on vessel, they are not in a position to be making a course correction significant enough to avoid you (they usually can't do much within a 2-3 nm of collision, depending on your closing speeds), so apart from unnerving their crew, this makes little difference .

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2. It is not very effective if the angle of your courses is more than 90 degrees;
I wouldn't say not effective, just progressively less effective. The closer the two headings, the less effective heading on a reciprocal course to the other vessel is as well (90 degree course change is best then).

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3. On the same heading and with way taken off you are unprepared to take further action if you are not achieving enough separation.
True. I try never to be in such a situation though .

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None of which matters much if distance is still great enough and angles are right, but the recip course is a more powerful and flexible maneuver for other cases.
I think the safest correction is so dependent on the relative heading and speed of the two vessels, that it is very unsafe making any generalisations about the best strategy for evasive manoeuvres.
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Old 24-09-2013, 11:15   #64
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Re: Big Ship Little Boat, who Gives way

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I maintain my refusal to buy one... I don't need one...
If you don't care probably doesn't matter to the other guy either since running over you in one of your little toy boats would not even scratch the paint on a real, manly sized yacht.

On the other hand, we could set up a Cruiser's Forum, save Boatman61 from himself fund. Then if all the members donated just ten cents you would have enough for an AIS or you could just buy a week's supply of rum.
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Old 24-09-2013, 11:17   #65
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Re: Big Ship Little Boat, who Gives way

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Originally Posted by Dockhead View Post
You just call the ship by name. Very effective! I'm a big fan of non-emergency DSC functions, but I wouldn't faff around with it in a potential collision situation.

To give the ship your posit, get a transponder! He needs it before you see him, not after there's already a problem! The cost difference is now so trivial that I can think of no reason to have a receive-only AIS.
I was thinking that one of the problems in relatively high traffic situations is one vessel knowing that that the vessel they are talking to is the vessel they are looking at. Rather than having to give the vessel your position verbally, having them take the time to plot the position you just gave them and then make sure that they are looking in the right place takes a bit longer than simply hitting a position send button and having your current position pop up in their ECDIS display. With Class B AIS the position they have on their display may be quite old in a close quarters situation. The protocol for class B is much less dependable than class A when it comes to making sure you're being seen . With the position send option you could simply push that button and then follow it up with a verbal call.

You use the term transponder, rather than tranceiver. I'm getting a bit technical here, but a transponder is a device that responds to an interogation from a transmitter and sends a signal in return. A transceiver is simply a radio that is capable of both send and receive. I am a pilot and am quite familiar with tansponders. I am not aware of any transponder capability in the AIS protocol. My understanding is that all transmissions are in the blind and the receive simply reports on those transmissions. From your boat's point of view it receives and displays transmissions from other AIS transmitting vessels in range. It does not interogate those transmitters and get a fresh update. In turn your transmitter simply sends out your AIS information in the blind on a regular schedule, which in class B is not all that often and there is no collision detect in class b so you can't even be sure your transmission was not walked on and therfore not received by any vessels. Consequently your AIS position mght be quite old. If I am mistaken on my understanding of how AIS works please correct me. I have looked at Internet AIS tracking sites and have noted that many times class B positions are 20 minutes or more old in relatively crowded areas and when theypop up again they can be quite far from their last AIS position.

Lastly I need to replace my secondary radio and with installation a full transceiver would cost me more than a $1000 more than buying the integrated receiver and plugging it into an existing antenna system. $1000 may not mean much to you but it does to some of us.
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Old 24-09-2013, 11:23   #66
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pirate Re: Big Ship Little Boat, who Gives way

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Originally Posted by skipmac View Post
If you don't care probably doesn't matter to the other guy either since running over you in one of your little toy boats would not even scratch the paint on a real, manly sized yacht.

On the other hand, we could set up a Cruiser's Forum, save Boatman61 from himself fund. Then if all the members donated just ten cents you would have enough for an AIS or you could just buy a week's supply of rum.
If you made it 25 cents/member... I could buy a boat to fit one on...
But sitting on a beach getting a tan... Naah... don't need one..
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Old 24-09-2013, 11:29   #67
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Re: Big Ship Little Boat, who Gives way

Well if you are on the beach as your location says, you don't need the AIS and big boats, small boats, any boat should logically try to stay out of your way.
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Old 24-09-2013, 11:31   #68
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Re: Big Ship Little Boat, who Gives way

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Nigel,
. At 6 miles I Was still seeing red and green and decided I was not comfortable as IMO the encounter was going to be very close. I changed course 90 degrees to his course and increased my speed to clear his bow by the maximum amount. Shortly after I changed course he changed course to port and re-established a close quarters situation. At about 4.5 miles I again changed course to 90 degrees from his new course. At 4 miles my plot showed he had changed course again and we were again in a close quarters situation. At that time I called him on VHF and asked him if he saw me and what his intentions were and if he saw me. I do not have AIS but I did have my radar reflector up. After a moment's hesitation he did say that he saw me and he was altering course to starboard. Interestingly he turned back to the same heading he was on when I first saw him on radar. .

Hi Bill

Given the hesitation when you asked if he saw you, my take is that he had not.
Your altering course at 6 miles apart is too early as you are stand on.
Even at 4 miles, out, I would not have been overly concerned.
Cruise ships run to a schedule so if he had of seen you, he might have decided to leave the alteration at 3 to 4 miles separation, in the incorrect assumption that altering course early would cost him miles and time.
You said this was about 2300, thats normally the 3rd Mates watch, the most junior of the watchkeepers.

It may have been that he had seen you on radar and decided to try and sneak across your bow by altering to port. If he was not looking for you visually, it would be easy to miss your alteration if he was using radar alone. Using radar plot, it takes a few minutes to properly detect a course change. He might have thought that at 6 miles apart, the COLREGS did not apply when approaching a small vessel. (wrong decision in my opinion)


At sea (while earning my living), my instructions to OOW are to (if conditions allow), alter course early if they are the give way vessel, and to make it big if possible, I'm not on a schedule to such a degree. If possible, I want the stand on vessel to see a change in our side lights.
This will be at about 5 to 6 miles apart in open ocean.
As the waters become busier and more confined, the distance at which alterations are made become smaller, as does the acceptable CPA, there just is not the room for everyone to maintain big CPA's and early and large alterations. On the other hand, I'm expecting everyone out there to be extra vigilant (or a Lert)

Crossing the shipping lanes in the North Sea, if the lanes are busy, we might leave it to about 2 miles apart before making a move, and aim for a CPA of between 0.5 to 1 mile.

Getting back to my own sail boat, if I was in open waters, I would be getting a bit twitchy if a ship had not appeared to alter by the time it was two miles away. At night, the big flash light would be shining on the sails.
Between 2 to 1 miles I would be planning a bail out stratagy, and if nothing had happened at a mile away, I would bail out.

In the confined waters, those distances might be halved depending on whether we were in shipping lanes or not.

There really is no hard and fast rule as to when ships should alter, I think some have put forward suggestions, but there are so many variables, it is not possible to apply fixed distances
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Old 24-09-2013, 11:38   #69
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pirate Re: Big Ship Little Boat, who Gives way

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Well if you are on the beach as your location says, you don't need the AIS and big boats, small boats, any boat should logically try to stay out of your way.
Egg Zachery.... Don't need one.. won't buy one..
But I'll likely be using some one else's in a couple of days... if one's fitted
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Old 24-09-2013, 12:02   #70
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Re: Big Ship Little Boat, who Gives way

Thanks Nigel, Next time I'll wait a little longer before taking evasive action.
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Old 24-09-2013, 12:19   #71
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Re: Big Ship Little Boat, who Gives way

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Hi Bill

Given the hesitation when you asked if he saw you, my take is that he had not.
Your altering course at 6 miles apart is too early as you are stand on.
Even at 4 miles, out, I would not have been overly concerned.
Cruise ships run to a schedule so if he had of seen you, he might have decided to leave the alteration at 3 to 4 miles separation, in the incorrect assumption that altering course early would cost him miles and time.
You said this was about 2300, thats normally the 3rd Mates watch, the most junior of the watchkeepers.

It may have been that he had seen you on radar and decided to try and sneak across your bow by altering to port. If he was not looking for you visually, it would be easy to miss your alteration if he was using radar alone. Using radar plot, it takes a few minutes to properly detect a course change. He might have thought that at 6 miles apart, the COLREGS did not apply when approaching a small vessel. (wrong decision in my opinion)


At sea (while earning my living), my instructions to OOW are to (if conditions allow), alter course early if they are the give way vessel, and to make it big if possible, I'm not on a schedule to such a degree. If possible, I want the stand on vessel to see a change in our side lights.
This will be at about 5 to 6 miles apart in open ocean.
As the waters become busier and more confined, the distance at which alterations are made become smaller, as does the acceptable CPA, there just is not the room for everyone to maintain big CPA's and early and large alterations. On the other hand, I'm expecting everyone out there to be extra vigilant (or a Lert)

Crossing the shipping lanes in the North Sea, if the lanes are busy, we might leave it to about 2 miles apart before making a move, and aim for a CPA of between 0.5 to 1 mile.

Getting back to my own sail boat, if I was in open waters, I would be getting a bit twitchy if a ship had not appeared to alter by the time it was two miles away. At night, the big flash light would be shining on the sails.
Between 2 to 1 miles I would be planning a bail out stratagy, and if nothing had happened at a mile away, I would bail out.

In the confined waters, those distances might be halved depending on whether we were in shipping lanes or not.

There really is no hard and fast rule as to when ships should alter, I think some have put forward suggestions, but there are so many variables, it is not possible to apply fixed distances
Nigel, thanks for all this feedback.
I think, however, when you should alter course depends not just on distance, but closing speeds. It is the time to impact that is the vital consideration.

Other factors such as your ease of manoeuvrability (eg, close hauled or on a broach reach or on a spinnaker run) and your own boat speed also significantly affect when you need to make a correction.
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Old 24-09-2013, 12:39   #72
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Re: Big Ship Little Boat, who Gives way

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Nigel, thanks for all this feedback.
I think, however, when you should alter course depends not just on distance, but closing speeds. It is the time to impact that is the vital consideration.

Other factors such as your ease of manoeuvrability (eg, close hauled or on a broach reach or on a spinnaker run) and your own boat speed also significantly affect when you need to make a correction.
So many alternatives and so little time to type them all out
Of course you are correct, it's all down to circumstances and conditions (as mentioned a few times in the Colregs), and a main reason why arbitrary distances for taking action are not suggested.

Right now we're getting ready to leave Aberdeen and heading over to the Dutch side of the North Sea for a rigmove. I've advised our cadet he'll be going solo on the 8 to 12 watch, should be interesting, see how well theory is put into practise.
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Old 24-09-2013, 12:44   #73
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Re: Big Ship Little Boat, who Gives way

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So many alternatives and so little time to type them all out
Of course you are correct, it's all down to circumstances and conditions (as mentioned a few times in the Colregs), and a main reason why arbitrary distances for taking action are not suggested.

Right now we're getting ready to leave Aberdeen and heading over to the Dutch side of the North Sea for a rigmove. I've advised our cadet he'll be going solo on the 8 to 12 watch, should be interesting, see how well theory is put into practise.
Have a great run.
I didn't stress quite enough how much all the info you posted has been appreciated, and so obviously not just by me. Again, thank you .
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Old 24-09-2013, 13:12   #74
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Re: Big Ship Little Boat, who Gives way

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... With Class B AIS the position they have on their display may be quite old in a close quarters situation. The protocol for class B is much less dependable than class A when it comes to making sure you're being seen . With the position send option you could simply push that button and then follow it up with a verbal call.
Class B is actually pretty good for "normal-speed" sailboats. If your speed is greater than 2 kts the position report update rate is 30 seconds. At normal sailing or motoring speeds you don't move all that far in 30 seconds. Unless you are in a very high AIS-traffic area it is unlikely that your reports will be delayed by more than one minute, which is still pretty good. Now if you're on a speedboat, or one of the America's Cup 72-ft cats, the 30-second update rate could be a problem.

Quote:
You use the term transponder, rather than tranceiver. I'm getting a bit technical here, but a transponder is a device that responds to an interogation from a transmitter and sends a signal in return. A transceiver is simply a radio that is capable of both send and receive. I am a pilot and am quite familiar with tansponders. I am not aware of any transponder capability in the AIS protocol. [...]
You are technically correct, but this is common usage and I believe the AIS specs also call it a transponder. I know the difference, but I'm still going to call it a transponder.

Quote:
I have looked at Internet AIS tracking sites and have noted that many times class B positions are 20 minutes or more old in relatively crowded areas and when they pop up again they can be quite far from their last AIS position. ...
A 20-minute delay is due to something other than congestion (except in the most extreme cases). The AIS tracking websites rely on receivers located in an ad-hoc manner, and they often have dead spots. I've not noticed this type of delay on San Francisco bay, which is moderately busy.
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Old 24-09-2013, 14:07   #75
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Re: Big Ship Little Boat, who Gives way

Just so you can see what's out there here's a couple of screen prints of the English Channel from marinetraffic.com

The vertical black line in the left picture I added for scale, is about 5 nm.
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