Reasons for knowing TVMDCAW - SailNet Community

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Go Back   SailNet Community > Skills and Seamanship > Seamanship & Navigation
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Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.


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Old 05-02-2012
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Reasons for knowing TVMDCAW

I've been volunteered to give a short instructional presentation on a nautical topic. The topic selected is titled "Variation, deviation and compasses"

The subject is easy enough but can you think of any answer to the inevitable question of why.

If you hop on a boat today with 4 people you probably have at least 6 GPS's on board.
Yes the satellites could fall out of the sky half way through our 3 hour cruise or the military could block the signal but can you think of any more likely ways, knowledge of the subject could come in handy.
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Old 05-02-2012
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Re: Reasons for knowing TVMDCAW

Assuming no handhelds on board
  • Dead battery
  • Bad ground causes a loss of electronics
  • Lightning strike takes out chartplotter
  • Chartplotter screen craps out (it's a Raymarine C-series)
  • Space aliens (hey it could happen!)

Or if you have a handheld as a backup:
  • You have no AA batteries
  • The handheld uses up it's batteries
  • Batteries in the handheld are a crusty mess because it's been laying in the nav desk forever
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Old 05-02-2012
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Re: Reasons for knowing TVMDCAW

GPS satellites do not have to fall out of the sky. They are occasionally shut down or down for maintenance. The system is supposed to keep enough up and running that you never know. Not always the case. In aircraft, there is integrity monitoring to determine whether there are sufficient signals to complete a course, not just receive your current position. They are also principally designed for military use and you can be certain they will jam them as they see fit for security purposes.
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Old 05-02-2012
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Re: Reasons for knowing TVMDCAW

Quote:
Originally Posted by davidpm View Post
I've been volunteered to give a short instructional presentation on a nautical topic. The topic selected is titled "Variation, deviation and compasses"

The subject is easy enough but can you think of any answer to the inevitable question of why.

If you hop on a boat today with 4 people you probably have at least 6 GPS's on board.
Yes the satellites could fall out of the sky half way through our 3 hour cruise or the military could block the signal but can you think of any more likely ways, knowledge of the subject could come in handy.
Yep the answer is if you do any navigation exercise that requires an examination you have to know it,
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Old 05-02-2012
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Re: Reasons for knowing TVMDCAW

Isn't it at least interesting when you're telling them why you add Whiskey to True Virgins?
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Old 05-02-2012
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Re: Reasons for knowing TVMDCAW

Drawing out two compass bearings to provide a pilot fix is about as visceral as Cartesian geometry gets. Cartesian geometry is the practical wedge of the entire enlightenment. Being able to perform the required technical steps connects one with the renaissance thinkers who enabled the modern era.

That's a long way from buying an app.
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Old 05-02-2012
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Re: Reasons for knowing TVMDCAW

Know the basics before you get all technical.

Life and death - danger bearings.

There is a reason we still teach arithmatic in the digital age.

If there is a problem, you should be able to recognize it and fix it.
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Last edited by jackdale; 05-02-2012 at 11:50 PM.
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Old 05-03-2012
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Re: Reasons for knowing TVMDCAW

btw - when I teach that portion it is a whole evening. If you want the notes PM me with your email and I will send them.
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Re: Reasons for knowing TVMDCAW

Quote:
Originally Posted by jackdale View Post
Know the basics before you get all technical.

Life and death - danger bearings.

There is a reason we still teach arithmatic in the digital age.

If there is a problem, you should be able to recognize it and fix it.
Jack makes a critical point that applies to all electronic navigating. Like it or not, most electronic navigation systems can do better than a human. The humans job is to supervise very diligently and have the skills to take over if the electrons aren't flowing properly.
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Re: Reasons for knowing TVMDCAW

Danger bearing is a great example of how this old school stuff can still be useful.

Thanks
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