compass rose revised

[pabrides]

Hello Shipmates,

I've been playing around trying to learn the old compass rose.  I found out a few things and developed some memory aids. Drawing my own compass helped tremendously. See attachment.  You will note the intersecting archs around the perimeter of the compass - these are drawn to divide the circle into points.  

Here are a few more memory aids.

The 4 large points contain a single letter, N, S, E, W (cardinal points)

The 4 secondary points contain two letters combining the cardinal points. NE, SE, SW, NW

The 8 smaller tertiary points have 3 letters combining the cardinal and secondary points. NNE, ENE, ESE, SSE, SSW, WSW, WNW, NNW.

The 16 smallest points all contain the word BY: North By East, NEBN, NEBE, EBN... etc.  These refer to the cardinal and secondary points only - the tertiary points are not used in reference to "by" points.  

A cardinal letter always follows the word BY - South West by West... etc.  There is no such heading as North by North West or South West by West South West.  Also I don't think there is such a heading as North by West and a quarter North... THAT point, rather, might be given as North and three quarters West.

Just playing with a quadrant at a time lessens the confusion.   For example,  just practice with the North East quadrant first and discover how it makes sense.  The others follow the same pattern. 

Draw your own rose with paper and a draftsman compass, you can't do that with a circle of 360 degress ... try drawing half of 45 and you'll get a headache; dividing a sector into 90 equal parts is no picknic. The old compass rose has a total of 32 points with the addition of quarter marks.  very easy to make.

  If the captain ordered North and a quarter East the helmsman would stear to the first tickmark to the right of North.   If North East and a half North was ordered the wheelman steared to the second mark to the left of NE... etc.  I was too lazy to draw every quarter mark.

Next time you're bored give the old compass points a try...  you'll soon realize it has some merit over the 360 degree system....  Who needs 360 degrees anyway.  You'll just wear yourself and the stearing gear out trying to keep that precise.  Might as well make the compass 720 degrees... lol.  

I own some pocket compasses that only show tick marks at 5 degree intervals - thats only 72 compass points.  Might as well have printed the old rose and made orienteering some fun.

The really interesting thing here is that after a while you won't need written point letters to tell you what point you're looking at.   As long as you know which large point is North you'll know the others, and North may be identified with color rather than a letter from the alphabet.  I bet that even before you begin studying the old compass points you could close your eyes and from the very start imagine 8 of them;  North,  North East,  East,  South East,  South,  South West,  West,  North West.  That's already a fourth of the points. Think a bit harder and imagine the points between these such as North North East... etc.  That's half the points.   

Admittedly,  the toughest points for me to learn were the BY points such as North by East, but adding a little relative bearing grease to my brain quickly put those points in order.  

The quarter marks were almost a no-brainer.  Just remember that the BY points have no quarter.

Have fun and keep at it - that's how tradition survives modernity.

Cheers

[pabrides]

I revised the post with additional comments for clarity

[PeterB]

Pabrides

In surveying and to a certain extent in advanced navigation bearings are often given with a reference direction, a number of degrees, and a direction to sweep.

For example: N 30° W spoken as “North thirty degrees west.”

This tells you to start at North and sweep thirty degrees to the westward. That would be the same as a true compass bearing of 330° because (360° – 30°) = 330°

The prefix is the reference direction and the suffix is the direction in which to sweep.

In southern latitudes where the south pole is elevated you very well may come to a solution for a bearing, course, or azimuth taken from the south pole. In that case you might see it expressed as something like S 50° E which tells you to start from true south and to sweep eastward 50 degrees. This is a true compass bearing of 130° since (180° – 50°) = 130°

In surveying I am led to believe, though I'm not a surveyor, that the reference direction can be any of the four cardinal points. Those are North, East, South, and West. So if you were to see a call out on a survey of E 10° N that would be a true compass direction of 80° because (90° – 10°) = 80°

In navigation we generally only use North and South as reference directions with one exception: That is when taking the bearing to a rising or setting body used to check our compasses. Usually this body is the sun, and the bearing is taken at sunrise or sunset. It is referenced to East at sunrise and West at sunset and in this special case it is no longer called a bearing but instead an amplitude. A sun amplitude of W 08° N tells you that the sun set (because W is the reference direction) 08° northward of true West. This is 270° + 8° = 278° true.

This method of prefixing with the reference direction and suffixing with the sweep direction is exactly like the “by” points on the old compass rose. The reference direction precedes the “by” while the sweep direction follows the “by.”

“West by south” starts at West and sweeps a little Southward.

“Northwest by north” starts at northwest and sweeps a little northward.

And “South by southwest” can't be a compass point at all, but rather a music and film festival held in Austin Texas!

I never could remember how those pesky "by" points went until I read your older post today and it all fell together for me. Now I don't know how I could have missed it!

Thanks!

PeterB