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Old 15-07-2013, 12:09   #946
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Re: Freighters vs. Sailboats

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Originally Posted by goboatingnow View Post
I disagree , my experience is that most large freighters in the open do not expect to alter course for a sailboat. Hence well in advance , one should adjust course to ensure a widening CPA.
What do you base that on? I can see it where they haven't seen you or picked you up on radar, but most professional mariners know the colregs and abide by them.
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Old 15-07-2013, 13:17   #947
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Re: Freighters vs. Sailboats

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Originally Posted by Lodesman View Post
What do you base that on? I can see it where they haven't seen you or picked you up on radar, but most professional mariners know the colregs and abide by them.
It's really hard to say...all my acquaintances of Capts and pilots all concur that they will make a small correction as soon as they see a sailboat, or even what they perceive as a slow moving power vessel. This is because they would rather a little one early than a major one later and NONE of them want to hit something or even scare someone as the USCG or other agency is too much work after the fact. Now Capts from other parts of the world...who knows for sure...

Now I have had more than one tug Capt say that most recs are speed bumps if they chose to be...but I'm talking guys that have to get into and mix it up in tight quarters with pretty good sized barges and loads and relatively small tugs.
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Old 15-07-2013, 13:22   #948
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Re: Freighters vs. Sailboats

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Originally Posted by cappy208 View Post
Scituate fishing vessel sinks in harbor after collision at sea - Scituate - Your Town - Boston.com

They're closer than you think!!!! People don't pay attention no matter where they are, and what they are doing.

You don't need multiple targets, just one will do!

It never happens? Port fishing vessel sinks: Missing Lady Luck sparks memory of 1996 tragedy NewburyportNews.com, Newburyport, MA


Like you said, one on one! In your example Mr. Fishing boat either did not have proper lookout or he lost the challenge.

I cruise Buzzard's Bay frequently, our boat is docked in Fairhaven, MA which borders on Buzzard's Bay. One frequently will see couple of tugs with a tow or a push in the shipping channel. Note-- the CG now requires TWO tugs for oil barges since the oil spill a few years ago at Cleveland Ledge.
This of course is in addition to the traffic headed to or from the Cape Cod Canal.

Anytime anybody is in open waters where shipping is conducted, they better pay attention or become a statistic or pay attention and challenge then become a statistic.
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Old 15-07-2013, 14:43   #949
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Re: Freighters vs. Sailboats

Potential sources of errors in chart plotter displays:

1- incomplete representation of the chart you think it is displaying (bits left off to condense the pic to chart plotter size, or chart survey is from the 1800's.)

2-GPS error, which can vary up to 65' in any direction from the point you occupy at the moment it receives its position. Imaginary, but pretty darn good.

3-The actual size of the icon displayed: trust me, your boat isn't as large as the area displayed on the chart that is covered by your icon, ditto all the other targets displayed.

To me what it comes down to is that radar gives you real, almost in-the-moment data, while the AIS data has delays some of the time and that affects what your chart plotter shows you as well.

I think it is a problem of human perception that we tend to believe the representations on the screen as if they were some absolute truth; and all they are is fancy electronics, with some useful information. The Mark I Eyeball is a wonderful piloting tool.

FWIW

Ann
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Old 15-07-2013, 14:52   #950
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Re: Freighters vs. Sailboats

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Originally Posted by Ann T. Cate View Post
The Mark I Eyeball is a wonderful piloting tool.

FWIW

Ann
Especially if it is connected to a brain that has not had its' fear program overwritten by a "rules" program!

But this thread shows that there is some brain virus out there that has inflected a lot of people.
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Old 15-07-2013, 15:05   #951
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Re: Freighters vs. Sailboats

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Originally Posted by Lodesman View Post
I've attached an excerpt from the Admiralty Manual of Seamanship, to help you come to terms with this simple concept.
Helps if I actually attach it:
Attached Files
File Type: pdf ams - fine.pdf (37.5 KB, 19 views)
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Old 15-07-2013, 15:19   #952
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Re: Freighters vs. Sailboats

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Flag Uniform.
I gathered that from the dimensions you mentioned, but I don't think formation manoeuvres are that challenging from the guide's perspective.
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Old 15-07-2013, 16:44   #953
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Re: Freighters vs. Sailboats

I believe I'll just drive defensively.
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Old 15-07-2013, 16:51   #954
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Good to hear you have confidence in the data AIS is giving. I may well find I trust it enough, after I see it in action first-hand. Have you actually compared the AIS side-by-side with systematic radar plotting? Do you find the AIS plot is pretty accurate over time (assuming neither vessel needed to alter)?
Only having a basic radar onboard I've never tried a side by side comparison, but if the data is fresh then I've never seen anything to doubt the accuracy ais. Living onboard in London I'd sometimes use it to check the next river bus was running on time
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Old 15-07-2013, 19:55   #955
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Re: Freighters vs. Sailboats

Take this as an opportunity to learn about how the AIS function works. The next time a taxi comes up river, take not of its distance. then note when it stops. Not when it departs the dock. There will always be a lag in data. You will see it leaving, when the AIS has it still arriving. The course it was on, and the speeds were accurate, the new courses and speed are accurate...... when they were sent.
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Old 15-07-2013, 20:02   #956
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Re: Freighters vs. Sailboats

I learned early that keeping a constant eye on targets helps you keep track of specific targets. How many times have you been unable to monitor all the targets? Most operators only sporadically watch the radar, or electronic data. It is REALLY easy to lose track of and confuse targets.

Maybe this is part of the dilemma?
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Old 15-07-2013, 20:23   #957
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Re: Freighters vs. Sailboats

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Originally Posted by Ann T. Cate View Post
To me what it comes down to is that radar gives you real, almost in-the-moment data, while the AIS data has delays some of the time and that affects what your chart plotter shows you as well.
RADAR derived data (ARPA) is not very accurate, or (most importantly) delayed.

A most succinctly described incident was the collision between a CG vessel Cowslip and the containership Evergrade on the columbia river. The CG cutter Cowslip was relying solely on ARPA for navigation information.
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Old 15-07-2013, 20:41   #958
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Originally Posted by cappy208 View Post
Take this as an opportunity to learn about how the AIS function works. The next time a taxi comes up river, take not of its distance. then note when it stops. Not when it departs the dock. There will always be a lag in data. You will see it leaving, when the AIS has it still arriving. The course it was on, and the speeds were accurate, the new courses and speed are accurate...... when they were sent.
The fast clippers transmit every couple of seconds when going full speed, there is a slight lag when at a pontoon but not much. I have watched them, what's also interesting is the mile or more difference between live ais and marine traffic for fast vessels.
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Old 15-07-2013, 21:11   #959
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Re: Freighters vs. Sailboats

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Originally Posted by conachair View Post
The fast clippers transmit every couple of seconds when going full speed, there is a slight lag when at a pontoon but not much. I have watched them, what's also interesting is the mile or more difference between live ais and marine traffic for fast vessels.
They are going a mile in a couple of seconds?

OR, what is "marine traffic for fast vessels?
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Old 15-07-2013, 21:59   #960
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Re: Freighters vs. Sailboats

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Originally Posted by Therapy View Post
They are going a mile in a couple of seconds?

OR, what is "marine traffic for fast vessels?
I think the reference is to the Marine Traffic web site or app.

They have this disclaimer

Quote:
Vessel positions may be up to one hour old or incomplete. Data is provided for informational reasons only and is not related by any means to the safety of navigation. All rights reserved. No part of MarineTraffic may be copied, reproduced or retransmitted in any material and form or by any other means.
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