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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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  #11  
Old 05-03-2012
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Re: Reasons for knowing TVMDCAW

A GPS tells you where you are and where you have been, not where you are going. You need to know how to use a compass to figure out where you are going. I was on a 7 day passage a few years ago. We had 2 handhelds and a chart plotter. One handheld went over the side in a storm, the other had the batteries go dead and we didn't have enough extras, and the chart plotter shorted out during the storm. Without a paper chart and a compass we would mad landfall at the wrong destination.
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Old 05-03-2012
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Re: Reasons for knowing TVMDCAW

If we are on a long passage, we record our position every 30 to 60 minutes, confirm it visually if possible and also record compass heading and speed. This way, if we lose the electronics, we are able to estimate our position. I will also check that depth on the sounder is reasonable for where the gps says we are. If we are close enough to pass a nav aid or very notable land feature, we use removable post it notes to mark it and the time on a chart. Pretty simple back up.
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Old 05-03-2012
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Re: Reasons for knowing TVMDCAW

I have known CPR and the Heimlich for years. Never had to use them. I'm still glad I took the class.
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Re: Reasons for knowing TVMDCAW

Just because you own a calculator doesn't mean you shouldn't be able to perform basic arithmetic by hand (or better yet in your head). Knowing the basics allows you to not just place blind trust in your chart plotter/handheld but to use it as a tool.

Hardware fails, software has errors, people make mistakes. Although I am far likelier than my GPS to make a mistake when plotting my position, I have seen my handheld tell me I travelled 500 miles in a few minutes by bicycle.

Trust no one and keep your phaser handy ;-)
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Old 05-03-2012
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Re: Reasons for knowing TVMDCAW

Quote:
Originally Posted by ronspiker View Post
A GPS tells you where you are and where you have been, not where you are going. You need to know how to use a compass to figure out where you are going. I was on a 7 day passage a few years ago. We had 2 handhelds and a chart plotter. One handheld went over the side in a storm, the other had the batteries go dead and we didn't have enough extras, and the chart plotter shorted out during the storm. Without a paper chart and a compass we would mad landfall at the wrong destination.
I'll use your story if you don't mind. Real world is best.
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Old 05-03-2012
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Re: Reasons for knowing TVMDCAW

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Originally Posted by Minnewaska View Post
If we are on a long passage, we record our position every 30 to 60 minutes, confirm it visually if possible and also record compass heading and speed. This way, if we lose the electronics, we are able to estimate our position. I will also check that depth on the sounder is reasonable for where the gps says we are. If we are close enough to pass a nav aid or very notable land feature, we use removable post it notes to mark it and the time on a chart. Pretty simple back up.
So do we. The only thing I add is:

I draw a vector to the destination on a paper map. I then plot the dot (time, incl GPS coord for LAT and LON) every 30-60 minutes depending on the weather. Ii will actually go two hours or more for long runs in the daylight where the weather is good.

My log has:

Time (military), coord, wind (T), speed (I only use SOG), heading (Mag... that is just me), and sea state. I also put in under a log anything unusual or any changes made. I make my own logs and keep them in those lab looking books that are ral cheap and cannot have paper torn out.

Also, put in where you are going from and where to. Mark completion. It is not that you will forget on the trip, but when makin return trips it is a awesome tool (we used it a LOT) to plan your departure. Believe me, you will forget how long it takes to get from Tampa to FMB or Marathon to Tortugas, whatever... and this is real time. It is important in most of these areas where we go not to make arrival at night, and in some cases (like he Tortugas) I MUCH prefer arriving around noon when we can see Coral heads well.

Just some thoughts.

ALso David, to answer you question, it is good to know because 1) Electronics will fail. 2) THe pure aspect of seamanship.

Great job reaching that stuff. Now what is a compass again and which button on my chartplotter do I press to get it?? (snicker).

Brian
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Re: Reasons for knowing TVMDCAW

Quote:
Originally Posted by ronspiker View Post
A GPS tells you where you are and where you have been, not where you are going. You need to know how to use a compass to figure out where you are going. I was on a 7 day passage a few years ago. We had 2 handhelds and a chart plotter. One handheld went over the side in a storm, the other had the batteries go dead and we didn't have enough extras, and the chart plotter shorted out during the storm. Without a paper chart and a compass we would mad landfall at the wrong destination.
So you dead reckoned for 7 days at sea and hit the island you wanted? Crap, I couldn't do that. 7 days and I would be lucky to hit the continent of North America (snicker).

I have only dead reckoned once and not for very long on a trip from Tortugas. Crapping electronic cables on my ST6000 (E80 autpilot) came out and just a word of warning, when that happens, the whole system basically goes haywire. Oops. They didn't mention that in the manual.

I finally got the handheld up (which saved a mutiny) and tracked down our issue and got the GPS up, but I found it VERY hard to dead reckon and keep a course. Also requires constan steering. Had my butt puckered. incidentally, we were obviously well outside of sight of land.

Great job if you dead reckoned at sea for 7 days and hit your target. I assume you also used a sextant?

Brian
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Re: Reasons for knowing TVMDCAW

OK Fine... I got ther TVMDC part, but what's the AW...??
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Re: Reasons for knowing TVMDCAW

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Originally Posted by Squidd View Post
OK Fine... I got ther TVMDC part, but what's the AW...??

Add Westerly deviation and variation. Subtract east.
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Re: Reasons for knowing TVMDCAW

Add West

(shorter variation of East is Least, West is Best)
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