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Old 05-01-2009, 04:13 PM   #1
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I have read instances where a navigational reference has been given using something referred to as "points". Sometimes attached to a reference to a "quarter" whether that is port, starboard, stern and bow. Now, I am aware of the points of sail but I do not think this refers to that. For example, how would one interpret "1 point off the port quarter"? Are these cardinal points?

Kevin
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Old 05-01-2009, 08:09 PM   #2
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I have read instances where a navigational reference has been given using something referred to as "points". Sometimes attached to a reference to a "quarter" whether that is port, starboard, stern and bow. Now, I am aware of the points of sail but I do not think this refers to that. For example, how would one interpret "1 point off the port quarter"? Are these cardinal points?

Kevin
A point is 11.25 degrees.
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Old 05-02-2009, 07:35 AM   #3
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Allow me to explain:

The horizon and compass was of tradition and for practical reasons divided up into 32 points. Each point of the compass was given a name so, starting from North we have the 32 Points of the Compass:

Point ----- Direction ----- Azimuth

0 -------------- North -------------- 0 - 0'

1 -------------- N by E ------------ 11 - 15'

2 -------------- NNE --------------- 22 - 30'

3 -------------- NE by N ----------- 33 - 45'

4 -------------- NE ----------------- 45 - 0'

5 -------------- NE by E ----------- 56 - 15'

6 -------------- ENE ---------------- 67 - 30'

7 -------------- E by N ------------- 78 - 45'

8 -------------- East --------------- 90 - 0'

9 -------------- E by S ------------ 101 - 15'

10 ------------- ESE --------------- 112 - 30'

11 ------------- SE by E ---------- 123 - 45'

12 ------------- SE ---------------- 135 - 0'

13 ------------- SE by S ---------- 146 - 15'

14 ------------- SSE --------------- 157 - 30'

15 ------------- S by E ------------ 168 - 45'

16 ------------- South ------------- 180 - 0'

17 ------------- S by W ----------- 191 - 15'

18 ------------- SSW -------------- 202 - 30'

19 ------------- SW by S ---------- 213 - 45'

20 ------------- SW ---------------- 225 - 0'

21 ------------- SW by W --------- 236 - 15'

22 ------------- WSW ------------- 247 - 30'

23 ------------- W by S ----------- 258 - 45'

24 ------------- West -------------- 270 - 0'

25 ------------- W by N ----------- 281 - 15'

26 ------------- WNW ------------- 292 - 30'

27 ------------- NW by W --------- 303 - 45'

28 ------------- NW ---------------- 315 - 0'

29 ------------- NW by N ---------- 326 - 15'

30 ------------- NNW --------------- 337 - 30'

31 ------------- N by W ------------ 348 - 45'

Before the days of dampened compasses, i.e. liquid filled compass bowls, ships had only dry-card compasses. With no dampening preventing the swinging backwards and forwards of the compass card it was a very lively instrument. Mariners would have been unable to steer a course to the nearest degree or two but steered after points or half points.

The officer of the watch would instruct the helmsmen to steer, for example, "north east by east a half east". In other words a half point more than north east by east.

When I went to sea in the early 70's the points system was still used for reporting, e.g. "Flashing white light three points to port" although, with gyro compasses, courses were given more exactly in degrees. However, for my second mate's ticket I was still required to be able to box the compass, i.e. naming all the 32 points normaly in clockwise order. My "orals" examiner actualy asked me box the compass from west to east through south anti-clockwise.

That a compass point is 12.25 degrees is easily established by dividing the 360 degrees of the compass by its 32 points.

The history behind the points of the compass goes back to ancient Greece and originally, a device known as a wind rose was used to indicate the directions of the winds. The 32 points of the compass rose come from the directions of the eight major winds, the eight half-winds and the sixteen quarter-winds.

In the Middle Ages, the names of the winds were commonly known throughout the Mediterranean countries as tramontana (N), greco (NE), levante (E), siroco (SE), ostro (S), libeccio (SW), ponente (W) and maestro (NW).

As Christ was born in the east (The Levante) christians of the Middle Ages produced compasses where the east mark was represented by a cross. Nowadays, for convenience, we mark the north point.

The Chinese, inventors of the magnetic compass, also had their own version of the compass rose with 12 points.

Aye // Stephen
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Old 05-02-2009, 09:21 AM   #4
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Old 05-02-2009, 07:30 PM   #5
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thanks! for the compass lesson for all
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Old 05-02-2009, 10:27 PM   #6
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thanks! for the compass lesson for all d magnetic compass
Sorry, I don't intend to lecture but my fundamental training was that of a navigator of the more classical sort, i.e. back to basics. It is out-dated, out-moded and about as basic as you can get but I love it.

In today's society with GPS and digital charts there seems to be little room for the traditionalist but I am proud of the training I got. I am against electronic aids to navigation - in fact exactly the opposite. I think they are great but we should use them with caution.

In this respect, the magnetic compass is still the most basic navigational instrument but it is still a requirement for all ships to carry a calibrate. No matter how many gyro compasses a merchant ship carries it is still required to carry at least one magnetic compass.

This brings me to another issue. How often do we check the compass error? The variation is known but what about the deviation? The navies and merchant navies of the world should check their compass error once per watch. I know they don't but that was the guideline. How often do we yachtsmen take an amplitude, a transit or any other method of establishing compass error?

Hands on heart - when did YOU last check your compass error?

I would like to geta few answers ton the question and then I will relate for those who do not know how it is done.

Aye // Stephen
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Old 05-03-2009, 01:17 AM   #7
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Not a lecture--an enjoyable post!

We actually have two magnetic compasses for use onboard. One in the binnacle and one which mounts below the cockpit in the most "magnetically neutral" location we can find on the boat. The second compass is used for an autopilot. We recently sent it to the manufacturer for them to check it out, re-calibrate, change anything needed. It will be back at the boat sometime later this week and we'll begin the process of making sure its location is "neutral" which, according to the mfr that means not within 3 ft of anything large and ferrous--especially shrouds, prop shafts or other "line" type items.

Besides us, I don't anyone with a small boat who makes a compass correction card for use at the helm. Most folks just use what they've got and assume it's right.

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Old 05-03-2009, 04:41 AM   #8
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It can be very important to check your deviation. Obviously this rings truer in a steel hulled vessel than a GRP or wooden hull.

A vessel's magnetism is continuously changing, not only due to the things brought aboard, taken ashore or moved to a different location on board but even the craft's own magnetic field changes. If the vessel lies with one heading for a long time, such as at the dock or laid up ashore, then the magnetic field of the vessel tends to align with the earth's magnetic field.

Compass error changes from heading to heading too. A perfectly adjusted compass will have a deviation table which looks like a sine wave. Often, however, there are bulges on the curve.

The most important issue with establishing the compass error is the fact that a compass can be influenced without you noticing it. It could simply be someone putting a spanner in the wrong place (the old classic with beer tins no longer applies since they switched to aluminium cans) or you could be in an area of magnetic abnormality. Where known, these are marked on the chart but the degree of abnormality is not shown. Of course, your compass could also be faulty. Always have a second good quality compass along with you! The second compass should either be able to sit in the housing of the main steering compass or arrangements should be made for the compass to be able to be mounted where it can easily be seen by the helmsman. However, do not have both compasses close to each other.

With the advent of GPS, the magnetic compass has lost some of its status, especially the need to verify the compass error. As I have previously stated, I am very much in favour of electronic AIDS to navigation but electronics do sometimes stop working! I would not attempt an ocean passage without two good magnetic compasses on board and a sextant. It is a bit like your liferaft - hopefully you will never need it but if you do you will be glad you brought it along.

Aye // Stephen
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Old 05-04-2009, 03:38 PM   #9
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Hands on heart - when did YOU last check your compass error?
Thank you sir! That was more than I would have reasonably expected. I have printed it off for discussion down at the harbour. I may even post it, if I can get permission. As a former Artillery officer (working in mils), I am habitual about calibrating. Most make sport with me over it, but then, I have never missed the mark I sought. I learned the hard way, early on, to recalibrate regularly if you are on the move. More sagely words were never spoken.

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Old 05-04-2009, 04:02 PM   #10
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Thank you for your kind response to my post.

By all means feel free to copy what I wrote and use it elsewhere. If you do, please include a reference to the posts origin and, if possible, a hyperlink to CruiserLog.

I am off to Italy first thing tomorrow and do not have time to do more now but, if there is a demand for it I will, when I get back, explain how to resolve the compass error using transits and amplitudes of the sun.

Aye // Stephen
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Old 05-04-2009, 07:39 PM   #11
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"Compass error changes from heading to heading too. A perfectly adjusted compass will have a deviation table which looks like a sine wave. Often, however, there are bulges on the curve."

at one point, our compass chart by the helm (um...I guess the proper term is deviation table) looked like an egg-head crossed with a cauliflower.
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Old 05-05-2009, 03:55 PM   #12
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This brings me to another issue. How often do we check the compass error? The variation is known but what about the deviation? The navies and merchant navies of the world should check their compass error once per watch. I know they don't but that was the guideline. How often do we yachtsmen take an amplitude, a transit or any other method of establishing compass error?

Hands on heart - when did YOU last check your compass error?

I would like to geta few answers ton the question and then I will relate for those who do not know how it is done.

Aye // Stephen
I have two steering compasses on both sides of the companion way and have never really checked the compass error - turning the whole ship around a deviation pole and checking the readings every 10(?) with a reference compass ... I know it is more complicated but I had the chance about 20 years ago to participate in a professionally done checking and compensation on a Swan. It took hours, but the result was a very nice curve!

Well I have a fibreglass boat and the checking I do is to once in a wile check, if both compasses show the same direction. I did that once being tied up to a steel piling and both compasses showed the exact opposite direction. Then I started to look for this huge source of deviaton and did not find it, including taking out the whole compass ... until an our later I looked at this old steel piling, being tied up to ... .

So, never check in the harbour...

Uwe

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Old 05-05-2009, 04:58 PM   #13
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By all means feel free to copy what I wrote and use it elsewhere. If you do, please include a reference to the posts origin and, if possible, a hyperlink to CruiserLog.

Aye // Stephen
I am just going to print directly from the forum - so the references and other comments will be included. You never know, you might start seeing other Britannia Yacht Club folks in here before too long!

If you know of a text that walks you through doing a compass check, I would be grateful for the citation. I want to compile an aide memoire and that is definitely something that needs to go in.

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Old 05-06-2009, 05:08 PM   #14
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At the moment I am sitting in a hotel room in Genoa and am a little pushed for time but I will get on to this from home at the weekend.

Believe me -the method is pretty simple.

Aye // Stephen
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