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

[John A]

It's a shame that the purist and selt righteous of this forum ask for personnal opinions or experiences from people who have developed a system for their own use, and then spend the next week picking those experiences apart for their own egotistical purpose.

[boatman61]

Originally Posted by John A

It's a shame that the purist and selt righteous of this forum ask for personnal opinions or experiences from people who have developed a system for their own use, and then spend the next week picking those experiences apart for their own egotistical purpose.

Could it be.... thats why they do.....

[GordMay]

It’s a shame that some of us choose to assign mean or hostile motives to those that dare to critique the ideas that others have expressed.

[witchcraft]

We always use true when plotting and planning. When sailing we convert our magnetic (compass course) to true. Our chartplotter will do either,however we have it set for true.
BTW we always do our paper chartwork when cruising in case something goes wrong with the electronic stuff.
Fair winds
Witchcraft

[John A]

Originally Posted by GordMay

It’s a shame that some of us choose to assign mean or hostile motives to those that dare to critique the ideas that others have expressed.

If you assume that my motive was mean spirted or hostaile then you have misinterpreted my response. That was not my intent. But then you have once again made a judgement without considering other facts.

We have all taken to the sailing adventure to persue an independence found it few other sports. That independences has allowed us to find ways to do things, that we enjoy sharing with others on this forem. If we continue to hold those who are actually sailing the world in judgement then they are going to stop posting on this forem amd we are going to continue to slide to the opinions of those whose experiences are the same as ours.

Have you ever wondered why this forem has tens of thousands of members by only about 20 active posters?

Sure, someones way of doing something may not work given differenent conditions. But I'll bet that when the conditions change, then the way to do something will be changed too.

Who cares if the SSS wants to call a compass by another term?

[beetle]

Originally Posted by GordMay

Unfortunately, that wouldn't work when crossing isogonic lines at high latitudes, or near magnetic anomalies, where the variation/declination can change at a rate of over 1.5 degrees per mile.

I didn't believe that the TransPac folks used such an imprecise (& technicaly inaccurate) term as "mechanical compass"; but apparently they have:
➥ 2004 Transpac Inspection

Well, how might one best differentiate between a 'normal' compass and a fluxgate compass? The term we came up with is 'mechanical'. Perhaps there's a better term to use, in that the regular compass has moving parts, pivot points, and a rotating card - those seemed fairly mechanical in nature - and fluxgates don't have those things (though some do have pivot points to allow the internal components to remain as level as possible).

The most recent minimum equipment requirements are here, rule 4.27 has the compass call-out.

For hi-latitude sailing the best compasses out there are the spun gyros, but that's outside my budget My understanding is that near the poles it becomes difficult for a compass to notice changes in direction, and as a result the singlehanders comment on sluggish autopilot response - that's why some are using spun gyros.

I'm not sure how an isogonic line plays into the equation, other than that at high latitudes the lines are spaced quite closely together and therefore the variation is changing a lot over a short distance travelled east or west. I thought that the reason compasses become sluggish at high latitudes is that the magnetic lines are traveling more vertically than horizontally at the poles; something to go investigate!

And now back to engine installation - today the Yanmar shall start. I've got one more bit of 2/0 battery cable to make up and we're good to go.

- rob/beetle

[wolfenzee]

This thread wasn't about steering by hand using a magnetic compass vs steering with autopilot using electronic GPS bearing, it was about plotting a course, all compass roses have both true and magnetic deviation.....this is simply the whether the bearing of the course I plan to steer is true or magnetic.
The method a course is plotted should be in sync with the primary way the boat is steered, call me old fashion but an auto pilot is not even secondary on my boat. primary human, secondary wind-vane (under sail), tertiary auto pilot (under power and with human supervision)

[boatman61]

Basically this thread is about whats best for you... if it works for you thats all that matters... anything else is down to personal preference... each to their own and lets forget the I'm smarter than you crap.
whoever makes it into Port is smarter than the guy who don't... full stop

[wolfenzee]

Thanks....I am tired of trying to defend my lack of gadgets and gizmos.

[capn_billl]

That only works if you sailing in a small area. Where I am at the magnetic deviation changes from -15degs, to + 15 degs within a few hundred miles. Setting up the compass to work on true wouldn't work.

[beetle]

Originally Posted by capn_billl

That only works if you sailing in a small area. Where I am at the magnetic deviation changes from -15degs, to + 15 degs within a few hundred miles. Setting up the compass to work on true wouldn't work.

Wow! - where is that? And you're right, setting a compass to true there would not be helpful.

[mrohr]

The std. compass reads magnetic, so I just stay with magnetic in all calculations and log all courses PSC (per steering compass) ; works a charm.

[Lodesman]

Originally Posted by capn_billl

That only works if you sailing in a small area. Where I am at the magnetic deviation changes from -15degs, to + 15 degs within a few hundred miles. Setting up the compass to work on true wouldn't work.

You mean 'variation'. 'Deviation' is caused by the magnetic influences in your boat - I should hope that doesn't change that much.

[wolfenzee]

Originally Posted by Lodesman

You mean 'variation'. 'Deviation' is caused by the magnetic influences in your boat - I should hope that doesn't change that much.

Actually the term is declination:The angular difference between magnetic north and true north (defined in reference to the Geographic North Pole), at any particular location on the Earth's surface,
Deviation would be what you get if you plot the course in true and hand it to the helmsman who steers by magnetic.

[Lodesman]

The terms are synonymous. The helmsman steers by compass.

Neat reference (not for navigation): http://upload.wikimedia.org/wikipedi...8/Mv-world.jpg