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Old 09-03-2015, 06:07   #16
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Re: True or Compas

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Originally Posted by Reefmagnet View Post

The usual method is to plot true bearing and then use the variation (from the chart) and deviation (from a deviation - error - card for the actual compass) and use these values to calculate the compass bearing required. Also, don't forget that the effects of drift will also need to be factored as well at times.

Of course, in this day and age of push button navigation, this is all almost as irrelevant as using a sextant to most navigators.

This is what I was taught to do and will continue to do
But I am surprised that their is no "Standard Way"
As a follow up question
I was on a boat recently where I was told that the magnetic compass had been
Compensated for deviation. I am aware of how this can be done for one direction
But can't see how it can be done for all 360 degrees. As the boat swings through 360 degrees, won't the metal on the boat effect the compass differently.?

As to being irrelevant, that might indeed be true, but it gives me something to do on board, I like to compete with the electronics,and if they blow up
I'll have some idea where we are and how to get to where we want to go.
Plus they are great memory boxes.
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Old 09-03-2015, 06:14   #17
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Re: True or Compas

OK
I will just put in a touch of (my) reality here..
I sail coastal. Visual checks of position, chartplotter etc. Tend to err on the side of careful.
I am very happy to steer within 5 degrees of intended course, and update as required (at least hourly, when putting the "x" on the paper chart).


Given that local magnetic variation is ~8 degrees, and don't change much, why fuss? Sort of head off on the compass, or visual, or a good point of sail on the breeze and have a nice trip.


Others will have different needs, but that's cool.


Ian
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Old 09-03-2015, 06:25   #18
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Re: True or Compas

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Originally Posted by Time2Go View Post
This is what I was taught to do and will continue to do
But I am surprised that their is no "Standard Way"
As a follow up question
I was on a boat recently where I was told that the magnetic compass had been
Compensated for deviation. I am aware of how this can be done for one direction
But can't see how it can be done for all 360 degrees. As the boat swings through 360 degrees, won't the metal on the boat effect the compass differently.?

As to being irrelevant, that might indeed be true, but it gives me something to do on board, I like to compete with the electronics,and if they blow up
I'll have some idea where we are and how to get to where we want to go.
Plus they are great memory boxes.
There is a "standard" way. It's True. Navigational calculations are done in True and converted to compas for steering if you're using a magnetic compas.

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Old 09-03-2015, 06:30   #19
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Re: True or Compas

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Originally Posted by Kindred Spirits View Post
I am very happy to steer within 5 degrees of intended course, and update as required (at least hourly, when putting the "x" on the paper chart).


Given that local magnetic variation is ~8 degrees, and don't change much, why fuss? Sort of head off on the compass, or visual, or a good point of sail on the breeze and have a nice trip.


Others will have different needs, but that's cool.


Ian
If one "can" steer within 5 degrees then hat's off to them! I think my compass is graduated in 5 degree increments - LOL

Then consider my compass was swung when I bought the boat - on cardinal headings only. The compass card is long washed away.

I have been on a lot of boats in the last 10 years. Not one had a compass card on it.

If someone is updating all their charts to reflect the yearly change in variation and then using that in the calcs and then trying to steer that course, well... Never mind.

DOn't get me wrong Everyone should know how to do this and everyone should be tested on it. It's the fundamentals of navigation.
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Old 09-03-2015, 06:30   #20
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Re: True or Compas

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Originally Posted by Kindred Spirits View Post
OK
I will just put in a touch of (my) reality here..
I sail coastal. Visual checks of position, chartplotter etc. Tend to err on the side of careful.
I am very happy to steer within 5 degrees of intended course, and update as required (at least hourly, when putting the "x" on the paper chart).


Given that local magnetic variation is ~8 degrees, and don't change much, why fuss? Sort of head off on the compass, or visual, or a good point of sail on the breeze and have a nice trip.


Others will have different needs, but that's cool.


Ian
Pilotage may work for you in a local context, but the OP clearly has some where he would like to go and would like to know the correct way to use a chart. Why would we tell him anything but the right way.

If you're averaging 2.5 degrees on either side of your course line, you are still more or less averaging your course line. Why would you intentionally introduce errors and average 5 degrees off the wrong course line. In many cases accurate navigation does matter.

South Australia maybe doesn't have much change in variation, but try sailing up here close to the magnetic north pole. You may not have an engine or electronics in your boat causing deviation, but most boats do.

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Old 09-03-2015, 06:31   #21
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Re: True or Compas

Quote:
Originally Posted by Time2Go View Post
This is what I was taught to do and will continue to do
But I am surprised that their is no "Standard Way"
As a follow up question
I was on a boat recently where I was told that the magnetic compass had been
Compensated for deviation. I am aware of how this can be done for one direction
But can't see how it can be done for all 360 degrees. As the boat swings through 360 degrees, won't the metal on the boat effect the compass differently.?
Correct. A deviation card has deviation values listed for different headings of the compass it has been drawn up for.
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Old 09-03-2015, 06:36   #22
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Re: True or Compas

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I'm starting to suspect that maybe the OP is talking ECS plotting. In this case you do whatever takes your fancy because the numbers on the steering compass are all but meaningless, as one just follows the highway on the plotter.
Not referring to ECS but traditional paper and pencil charts
I have always plotted in true as having been taught this way
This is to say that all drawn lines on my charts have T65 or T230 etc
Who can forget
"West is best East is least, True virgins make dull company"
I always plan plot and draw in true and then calculate
Compass course to steer.
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Old 09-03-2015, 06:40   #23
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Re: True or Compas

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"True virgins make dull company"
Tsk Tsk Tsk.... In this politically correct day and age we say "True Virgins Make Delightful Company"
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Old 09-03-2015, 06:44   #24
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Re: True or Compas

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Originally Posted by FamilyVan View Post

South Australia maybe doesn't have much change in variation, but try sailing up here close to the magnetic north pole. You may not have an engine or electronics in your boat causing deviation, but most boats do.
Ooooh!

Let's talk declination and the impact on turning error!
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Old 09-03-2015, 07:01   #25
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Re: True or Compas

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Ooooh!

Let's talk declination and the impact on turning error!
I get the impression the OP is interested in basic coastal navigation, as might be taught by the RYA or Power and Sail Squadron or Boy Scouts. Not advanced navigation, so I was trying to stick to basic principles familiar to average cruising sailors. Advanced and celestial navigation I think would belong on a different thread.



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Old 09-03-2015, 10:43   #26
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Re: True or Compas

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Tsk Tsk Tsk.... In this politically correct day and age we say "True Virgins Make Delightful Company"
An extended version I've come up with for teaching Coastal Nav:

"True Virgins Make Dull Company Add Whiskey Subtract Ethics"

" Delightful" just doesn't work as well for this ditty. ;-)

Use the above if "corrupting", ie, going from T to M or M to C.

Reverse (Add Ethics Subtract Whiskey) if "purifying", ie. going from C to M or M to T.

Makes it easier to remember how to treat E & W.
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Old 09-03-2015, 10:49   #27
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Re: True or Compas

Whatever works for you and is accurate is best.
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Old 09-03-2015, 10:51   #28
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Re: True or Compas

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Originally Posted by belizesailor View Post
An extended version I've come up with for teaching Coastal Nav:

"True Virgins Make Dull Company Add Whiskey Subtract Ethics"

" Delightful" just doesn't work as well for this ditty. ;-)

Use the above if "corrupting", ie, going from T to M or M to C.

Reverse (Add Ethics Subtract Whiskey) if "purifying", ie. going from C to M or M to T.

Makes it easier to remember how to treat E & W.
Or Can Dead Men Vote Twice At Easter (compas to true add east) or True Virgins Make Dull Companions All Winter (true to compas add west)

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Old 09-03-2015, 10:57   #29
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Re: True or Compas

I like "West is Best and East is Least" for TVMDC.
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Old 09-03-2015, 11:26   #30
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Re: True or Compas

I prefer to plot everything true. However the United States Power Squadrons are now just confusing everyone by making students plot magnetic. To me it is a bit confusing and I will continue to mark my charts as they are plotted ... True. My deck log has the steering course in it. Of course, they have dummied up all their courses from when I took them years ago. I guess like anything else teach to least common denominator with a very heavy reliance Electronic Navigation. Don't get me wrong, I like EN, but am reticent to rely on like it's infallible. (My soap box)
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