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post #894 of Old 11-24-2012
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Re: HMS Bounty in trouble...

Originally Posted by PCP View Post
I guess the problem of following blindingly a plotter has some similarities with people following blindly car GPS information. People believe in that even when obviously the information doesn't make any make sense and that is about what you are talking about. That blind trust that in a car is funny is dangerous on a boat. I will not tell you the many car GPS anecdotes I have saw or new about, I will tell you one with a plotter:

My wife, on the cabin, stars to scream at me saying I am almost hitting a rock. I am outside at the wheel, it is a clear day I am navigating having a look from time to time to the plotter, seeing the marks and dangers and then navigating by eye and compass.

I was a bit frightening with the panic that I could hear in is voice but mostly amazed. I know I am careful. So, because I was navigating with the outside plotter out (to save energy) after looking around and seeing that all the things and marks were where they were supposed to be, including a signalized small isolated rock (100m to port) and because my wife was becoming almost hysterical I went below to see what the hell she was talking about and to calm her.

To my surprise the rock that was 100m to port was almost hitting the boat and I found out it was very difficult to convince my wife that I knew more than the machine. I had to take her to the cockpit to show her where was the rock.

No it is the opposite, she looks at the information on the plotter with a lot of skepticism and is always cheeking to see if everything is right ..
You seem to use this as an example of how a chartplotter makes you less safe. But the real irony here is your own example demonstrates that the chartplotter made you MORE safe, not LESS. You had a false alarm because the chartplotter had a 100 meter error. So as a result, you double-checked to make sure your ded reckoning position was correct. You had two sources of information that weren't agreeing, so you gave it some additional attention to resolve the discrepancy. This made you safer, not less safe.

Traditional navigational techniques using DR are not perfect either. In many cases, the chartplotter is far more precise than DR, especially if the landmarks that you are using are miles away. It's pretty simple trigonometry to show that an error of 5 degrees on your pelorus gives a 193 meter error on a landmark that's 1 nautical mile away. So you might just want to keep that chartplotter on!

I suspect that anybody who has ever graded the ASA 105 exam can tell you that there is an allowed range of correct answers to all the plotting test questions, because of the fact that parallel rules and dividers have some slop in their tolerances. On some charts, the width of your pencil is more than 100 meters!

Blind trust in any one method can lead to catastrophic results. More information is better, especially information that is accurate over 99% of the time (like GPS).

Rick S., Swarthmore, PA
USCG Certified Captain, 50 Ton Master and OUPV
ASA Certified 101/103/104/105/106

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2001 Catalina 34MkII Tall Rig Breakin' Away, Universal Diesel M35B, Mantus 35 lb. anchor, sailing out of Rock Hall Landing Marina

Last edited by TakeFive; 11-24-2012 at 06:40 PM.
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