More Compass Correction Techniques

[HenryC]

The intuitive, brute force method is simply to plot a fix on three charted aids to navigation (ATONs).  If the three lines of position (LOPs) cross at one spot, you have no systematic error.  If the LOPs form a triangle, the size of the triangle gives you an indication of your compass error. You can add or subtract a degree from each of your bearings and re-plot the LOPs to see if the triangle grows or shrinks, and and continue iterating until you derive the correction that makes it disappear. Of course, no correction method will eliminate plotting errors, ATON misidentifications, or random error.

An alternative, and certainly more elegant, method is the "Franklin Piloting Technique", developed by Master Chief Quartermaster Byron Franklin, USN (Ret.).  Please refer to the following link:

http://www.qmss.com/article/franklin_piloting.html

[Potcake boy]

Here's my homegrown technique - it is based on solid science.
Pick a day with no wind and no current.  Start from a fixed point and proceed on a steady heading (for simplicity I use a major compass point).  After approximately 1/4 mile turn sharply 180 degrees and head straight back to the original mark.  The error from 180 degrees is double your actual compass error, so correct your compass 1/2 of that error.
This method, although not suitable for naval vessels has always proved accurate enough for my navigational needs.

Ron

[HenryC]

You are obviously a better helmsman than I am...

Seriously, I hate to flog a dead horse on this issue, but this forum seems like a place that "gets it", and will profit from this message.

Don't get me wrong, there is nothing wrong with modern methods of electronic navigation. GPS and other systems like it are now so reliable, accurate and inexpensive that it would be irresponsible to go to sea without them. On the other hand, the idea that this technology makes navigational skills obsolete is not only dead wrong, it is downright dangerous.

GPS is the magic bullet. You press a button and you get a position. What navigator wouldn't want that? On the other hand, plotting a fix is only the beginning of the navigational process. Whether generated by electronics, triangulation from bearings, aids to navigation, or celestial observations, the fix is not the end of the process, it's where it begins. What follows is where the navigator earns his pay. First, the position is interpreted in relation to the existing dead reckoning track: how close, or how far off, is it? This immediately makes the mariner aware of the effect of conditions on the motion of his vessel, as well as the accuracy of his methods. As the new DR track is layed out, the immediate future of the ship is predicted; on the chart is a visual description even a non-navigator can understand of where and when hazards can be expected, or if new opportunities for verifying the position can be expected to materialize. What navigator has not felt the thrill of seeing a light pop up over the horizon, right on schedule, justifying the previous night's fix and dead reckoning. It's a terrific feeling, isn't it?

Then there's the feeling you get when the light or other ATON you expected is NOT there. Is your navigation off? Did an unexpected current affect your course, could the light be out of service? Until you determine why, you are aware that your ship is potentially standing into danger, and you know you have to get to the bottom of it, it is your job, your responsibility. A lifetime of situations like this builds up a deep intuition, a reservoir of memory and skill we can draw on and which defines the true mariner. How often have you not made an observation, or written down a result, and a little voice in the back of your head tells you "Wait a minute. That doesn't seem right, something's wrong." Psychologists tell us that a great deal of mental processing occurs subconsciously, without our being aware of it, but it is mental activity nonetheless. You can call it intuition, judgement, or experience, but you can only get it one way: on watch.

You don't get that feeling with electronics, and you don't develop that kind of subconscious skill.
You press a button and get a position. The machines are reliable and you can have confidence in their accuracy, but what happens when they don't work due to malfunction, operator error, or battle damage? Panic, disorientation, confusion; because the operator has no other skills and resources, no experience to draw on. Even when the equipment is working perfectly, operators sometimes lose confidence in its operation and make a panicky decision leading to disaster. Aviators are trained to "trust their instruments", but they can become disoriented too. GPS-assisted groundings are now as common as radar-assisted collisions. No one denies the usefulness of electronic aids to navigation, but the danger in their use arises from the fact that the skills of the navigator are neglected. Instead, the operator expends his time and effort and professional comittment on operating the equipment and mastering it's many bells and whistles, or in learning new versions and user interfaces, all of which seem to change almost on a daily basis.

It seems that the best feature of modern navigation technology, its ease of operation, has now been perverted so that navigating through the menus and typing in cryptic commands is harder than using a sextant and reducing a sight. And of course, after you learn it all, it becomes obsolete in about six months. The hardware and software is often highly customizable, so even expertise with a specific system can mean a steep learning curve when you are faced with identical gear somewhere else. You get so busy "managing" the technology that sometimes you forget to look out the bridge windows.

One of the skills a navigator develops is a healthy skepticism for his sources of information. Charts have errors, so do publications. You are attuned to math mistakes and observational errors, you are aware how easy it is to misunderstand a shipmate under stressful conditions. Over the centuries, navigators have developed procedures and methods to minimize these problems, and a critical attitude to help them evaluate and verify the accuracy of the information they use. This is not the case with electronics, and especially with software. What appears on the screen or comes out of the printer does so with an air of legitimacy that makes it easy to forget that if garbage goes in to a system, then only garbage will come out. The gear may be foolproof, but the data it operates on is the same data we use with traditional methods.

There are still charts in the inventory that were based on original surveys by Capt. Cook over two hundred years ago. They're actually pretty good charts, and certainly better than nothing, but if you're using one you are well aware of its history, its value and its limitations, and you rely on that unconscious judgement, your mariner's intuition, when you plot your fixes and take your bearings. Your whiz-bang graphical GPS electronic charting system may be drawing your course on that same chart, but its flawless appearance on the monitor screen does not alert the machine operator to the potential dangers of data compiled centuries ago. A true navigator would know that instinctively.