In Creating a Route on Charts, Do You Use True or Magnetic ?

[George64]

Compass
+
Deviation
=
Magnetic
+
Variation
=
True
+
Drift
=
BWK
+
Tide
=
Ground course (the one you plot on your chart. If you don't have the tidal direction available one can also plot the BWK (don't have the English word) on the chart.)

This is what I was taught.

[sneuman]

Originally Posted by George64

Compass
+
Deviation
=
Magnetic
+
Variation
=
True
+
Drift
=
BWK
+
Tide
=
Ground course (the one you plot on your chart. If you don't have the tidal direction available one can also plot the BWK (don't have the English word) on the chart.)

This is what I was taught.

Yes, but the question is what to record on a paper chart.

[George64]

I would say the ground course or the course made good, assuming that you are not planning to cross the atlantic or so... Have to say, did not read the entire discussion

[wolfenzee]

Considering you are steering with a magnetic compass it is best to plot magnetic and ALSO set your GPS to magnetic.
Keep everything agreeing with each other and the simplest the less chance for error

[CaptainBW]

When I took classes for my captains license they taught us to always plot in TRUE. Convert everything to true so you don't have to follow your magnetic variance on the plot chart.

[Night_Sailor]

Real Navigators plot in True. You can also annotate the Magnetic or Compass course on the chart as well, but work in TRUE.

The primary reason to use True--for me at least, is that I prefer the USPS type plotters. They work great and can reference from the many lines of Latitude or Longitude found on a chart. This is a huge help when plotting. A compass rose is a PITA, IMHO. I use a compass rose primarily to check local Variation.

I tried using/plotting all in Magnetic was I was young and stupid and found I made many careless errors when I plotted in Magnetic. It seems to make sense to do everything in Magnetic which most people on plastic boats equate to Compass courses. But do not fall into that trap.

You are increasing your chances of making mistakes if you work always in Magnetic. It is less rigorous, there are fewer references point to plot from. It is IMHO less accurate working/walking from a compass rose. I see people working with crappy navigation tools of a compass rose and when I plot using my methods, in True, using Lat/Long lines--my plots are more accurate and my cocked hats are smaller.

When I switched to True, I found the extra steps (TVMDC) were no extra bother, extremely fast if you do them routinely, and my mistakes and careless errors virtually stopped.

BTW, I teach navigation professionally. Ask any professional navigator and most will tell you they plot in True--always. Pass your compass course to your helmsmen in Compass or Magnetic if you assume zero Deviation. Log your courses in True and log Variation and Deviation as well.

[lordgeoff]

Originally Posted by Night_Sailor

Real Navigators plot in True. You can also annotate the Magnetic or Compass course on the chart as well, but work in TRUE.

The primary reason to use True--for me at least, is that I prefer the USPS type plotters. They work great and can reference from the many lines of Latitude or Longitude found on a chart. This is a huge help when plotting. A compass rose is a PITA, IMHO. I use a compass rose primarily to check local Variation.

I tried using/plotting all in Magnetic was I was young and stupid and found I made many careless errors when I plotted in Magnetic. It seems to make sense to do everything in Magnetic which most people on plastic boats equate to Compass courses. But do not fall into that trap.

You are increasing your chances of making mistakes if you work always in Magnetic. It is less rigorous, there are fewer references point to plot from. It is IMHO less accurate working/walking from a compass rose. I see people working with crappy navigation tools of a compass rose and when I plot using my methods, in True, using Lat/Long lines--my plots are more accurate and my cocked hats are smaller.

When I switched to True, I found the extra steps (TVMDC) were no extra bother, extremely fast if you do them routinely, and my mistakes and careless errors virtually stopped.

BTW, I teach navigation professionally. Ask any professional navigator and most will tell you they plot in True--always. Pass your compass course to your helmsmen in Compass or Magnetic if you assume zero Deviation. Log your courses in True and log Variation and Deviation as well.

Thanks for that Night Sailor. I haven't any navigation qualifications but have done a fair bit of reading and now have a few miles under my belt. I have been using a laptop and nav program called Software On Board. I multiplexed the Raymarine navigation data into the program. I use CMAP electronic charts which interface with the SOB navigation program. Most of the sailing I've done is passage/cruising. I use the laptop to get a heading to where I'm going and tweak the autohelm until my actual Heading is the same as the Heading I need. I don't use the compass at all really as the combination of GPS, Autohelm, CMAP Charts and software steers me acurately. I double check my position with a separate hand held GPS and put my position on the paper chart every few hours and tweak the Autohelm to correct any drift that may be occuring. I use the CMAP and paper charts to check for the sharp and hard bits that I don't want to run into. I check headings to land features as a double check. The combination has been extremely accurate so far. I know everyone will say ... but what happens if the GPS network fails or my GPS fails. If the network fails then I will know where I am because of the position on the paper chart and DR from there. If my GPS fails I have a draw full of spare GPSs and boxes of batteries. I just find the compass/hand steer is no where near the accurracy of a GPS/Autohelm combination. Am I wrong?

[wolfenzee]

It may just be that I am old fashion...but I think there is more to it really, I learned to steer by a compass and I find it more comforting to look at than computer display.

[goboatingnow]

always plot in true,
dave

[wolfenzee]

There is a proper way that has been used for hundreds of years...it is proper because it is right. Alls of the gadgets and gizmos and other high tech stuff has has taken all the work out of navigating and as long your computer or batteries or any number of things doesn't fail you can get away with out knowing how to navigate....electronics have made people lazy. For the same r4eason I prefer steering by a magnetic compass I prefer looking at a paper chart...though I like all the tech stuff too.

[Captain Bill]

This thread has been an interesting read, because I learned to navigate in formally in aircraft before boats. In aircraft, and keep in mind this was before GPS, all nav aids were laid out in magnetic, not true direction (they still are by the way). So a VOR would indicate magnetic north at its position, not true north. These were adjusted regularly for changing variation. One instructor put it bluntly, if you plot a leg of your course so long that you can actually fly it accurately enough for variation to make a difference your leg is too long, and that was at aircraft speeds. If changes in variation along a route are causing you a problem, you should plot more intermediate points. If you're crossing an ocean and drawing a straight line on a chart that goes for thousands of miles you are not following a great circle route and you are going much further than you need to. An approximation of a great circle will result in much smaller line segments on which variation won't be an issue.

In aircraft navigation we use a bit different nomencature than is being used here. In aircraft parlence a course is a set of lines drawn on a chart that get you from point a to point b without hitting anything sticking up from the ground or going over some place your not allowed to go. That is not too different in concept from a route. The heading is the direction the nose of the aircraft is pointed that accounts for all of the external forces trying to push the aircraft off of that course line as indicated by a magnetic compass or instruments calibrated to the magnetic compass. The reason the magnetic compass was stressed was that it was passive. All of the other systems required some sort of power or external support, but if all else failed the magnetic compass could still get you home. If you plot your course segments in magnetic on a current chart (in aviation you are required to use current charts) variation is already accounted for and you don't need to worry about it.

Now my informal navigation training started when I was 10 and that was in true, in the Boy Scouts. We were taught to use the north star as a compass and determine true direction to within a couple of degrees without a compass. We were eventually able to complete a 2 mile compass course at night without a compass. True or magnetic doesn't really matter as long as you don't mix them together.

[wolfenzee]

That would explain why my father (the man who taught me how to navigate, sail, appreciate fine boats and passed on his dream to sail about the world) taught me to plot magnetic, he was a pilot.
USN Capt. L.E.Ewoldt class of 1937

[phantomracer]

great thread.. my original question was what you use.. not really what is right or wrong.. still very interesting.

My significant issue is the inconsistancy with my plotter. I can set it to mag or true for everything other than the course plotting page, where it is true only. My preference is plotting is magnetic, which I didn't realize I couldn't do. One would think everything on the plotter would be the same. No idea why I can choose mag for everything, but can't plot in it. Just strange, IMO.

Whether it is true, mag (only choices on the plotter), it should be consistant. It is not, which, IMO, is a significant issue

[Captain Bill]

Originally Posted by phantomracer

My significant issue is the inconsistancy with my plotter. I can set it to mag or true for everything other than the course plotting page, where it is true only. My preference is plotting is magnetic, which I didn't realize I couldn't do. One would think everything on the plotter would be the same. No idea why I can choose mag for everything, but can't plot in it. Just strange, IMO.

There are almost always exceptions to the rules so lets just say that if I was anyone but you I would use magnetic on paper charts per your original question. In your case it would seem that plotting in magnetic would make transferring your route to the chart plotter a major PITA. So in your particular case and any one else who happens to own your brand of chart plotter, you would probably find it easier to plot in true. You will still need to convert to magnetic to determine your heading, because if your chartplotter goes belly up the only thing you'll have is magnetic. You'll need to have both calculated on your paper charts to make them useful backups to the chartplotter. Do you mind sharing the type of chartplotter with us? Maybe someone knows a way around your problem.

[phantomracer]

I mentioned (post 11) it is a lowrance HDS8. Great plotter.. but very strange that the course plotting tool is only in true. I called Lowrance to see how to change it.. Never got a call back. Posted on their facebook page the same question. Ignored as well. whether or not it is 'normal' or 'right' , it would be nice to have the option.

I rarely pre-plot courses in the plotter.. I just noticed the difference when I was doublechecking my paper plotting on the gps plotter.. was kinda blown away all my course legs were 17 degrees off..I couldn't be THAT far off..could I???? then it hit me.. I now know what I am up against.. so I can compensate.. That was the gist of my original question..

Actually the gps I use 99.8% of the time is my handheld. The lowrance is below deck and is rarely used..sometimes I use it to control the autopilot..or for the anchor drag alarm.. or for looking at AIS targets.. My lil garmin colorado is more than enough to get me through buzzards bay...when im not looking at the paper chart