Untangling course and track

[clearsea]

There is so much inconsistency and imprecision in the recreational boating world regarding the use of the terms "course", "track", "speed" and "heading". The advent of GPS has brought all this into sharp focus. Cruisers need to know both paper-chart and electronic-chart navigation procedures. Standard terminology would help, methinks.

After years of debate, thought, teaching cruisers and re-reading the old authorities, here are my suggestions:

Track refers to path over the ground. There are 3 tenses:
1. Future: Intended Track (IT)
2. Present: Track Being Made Good (TBMG).
3. Past: Track Made Good (TMG). A GPS breadcrumb trail is a series of GPS fixes.

Course refers to path through the water. There are 3 tenses:
1. Future: Course to Steer (CTS).
2. Present: Course Being Steered (CBS).
3. Past: Course Steered (CS).

Abandon the confusing terms “Course Made Good” and “Course Over the Ground”. They describe track (path over the ground), not course (path through the water). “Course Made Good” is a misnomer for the correct term “Track Made Good”.

A Course line is not a Track line.

GPS displays Speed Over the Ground (SOG), not Speed Through the Water (STW).

GPS cannot display Heading (direction the bow is pointing), rather it estimates Heading using Track Being Made Good (TBMG).

[GordMay]

Greetings and welcom aboar.
That's pretty cear, clearsea.
You aim at (steer to) a course, and actually hit a track.

[Lodesman]

Intended track or Planned Track is the pencil-line on the chart - its purpose is obvious. Track Made Good is useful to determine set and drift (the somewhat misnamed "tidal triangle"), so it is also useful. What you call TBMG is what I would simply call Track and is irrelevant in a navigational planning context - see below in the GPS comment.

The Course corresponds to the Planned Track (true, compass or magnetic) and is what you steer when you lack set and drift info. Course to Steer is the Course corrected for set and drift - it's the course you steer in order to make good your Planned Track.

What you call CBS is Heading; what you call Course Steered(CS) is what I would simply call Course - it corresponds to Course, CTS or Heading and like TMG is used only to calculate the tidal triangle. (And to fill your log book.)

GPS does not give you an estimate of heading - it gives you Track; I hesitate to call it Track Made Good, as the GPS is giving near-instantaneous updates that equate closer to the current path over ground, whereas TMG is an average between two points on the actual path you travelled (past-tense) over the ground. Track is useful in a pilotage situation where there is sufficient set to make a significant difference between Track and Heading (ie. the bow is pointed at safe water, but you're tracking towards shoals).

My 2 cents.

Kevin

[Tempest245]

Interesting, though, I think the present termonology holds up pretty well even in the GPS age. GPS simply gives us instant feedback, and allows us to steer better courses from A to B. It doesn't replace the need to read and understand tide and current tables.

Without a good understanding the effects that wind, tide, current and human error have on a vessel traveling through the water from A to B any termonology could be lost on a student.

While, with instant GPS feedback...many today may not plot a current triangle in order to establish a course to steer, without that basic understanding ones GPS might report one day that they are going backwards.

[Sandero]

This is an interesting issue all because of leeway and current I suppose.

I am OK with the term COG because I understand stand it to mean a "projection" of where my boat is, and has been onto the sea floor as if there was no water or wind.

In terms of "futre" the GPS doesn't know current or leeway and just knows the cumulative speed and direction and based on that reading at the present time computes what would be course to steer to a waypoint.

So let's say I have a very strong cross current and leeway. If I plot a line to a way point it might read say 90°. But if I sail a 90° compass couse I will arrive north or south of the waypoint depending on which direction the cross current is. My course would be 90° but not the course to steer to get there.

One would think that you had steer somewhat into cross current somewhat so that you are crabbing, ie not pointing the bow at the direction you are traveling. Likewise when trying to make a mark upwind you head above the mark (of you can) and with leeway properly taken into consideration you will make the mark. The track in that case is actually straight at the mark. The bow is not point there (you are not steering to your destination but up current and up windward of it so to speak.

If a straight line to the destination is the shortest path, it should be the shortest time as well in constant conditions. But regardless if you establish an electronic line from the start point and keep to it you should make the fastest passage. This is rarely the case. Over time current angle and wind angle will shift. It may make more sense to sail off the rhumb line where there is a more favorable current or wind or sea condition.

Then there are the complex calculations which probably come into play when sailing off the wind. when dead down wind is not the fastest point of sail but may be the shortest path over the bottom.

This can get get very complex especially as conditions change.

One concept that many seem to misunderstand (I think) is that regardless of the original plotted line to a waypoint, the shortest and usually the quickest is the PRESENT rhumbline. And if you have been asleep for a few hours and drift miles off your previous rhumb line it makes not sense to sterr toward it but rather set a NEW course line / rhumb line to the destination.

[David M]

I think we need to be especially careful when we start changing or adding new navigation terms. There are already an adequate number of precise terms and clear definitions for navigation. Changing terms or changing the definitions of terms would only create confusion. We do not need more navigation terms because what we have now is quite sufficient. Uniformity of terms can relate to safety.

Its fine to have three or four letter NMEA sentences that describe whatever, but lets not confuse those with standard navigation terms that describe what you are putting down on a chart.

Electronic navigation should adapt to traditional charts...not the other way around. Additionally, traditional charts do not have software crashes or run out of battery power.

Bowditch clearly defines all the navigation terms. Their definitions are not flexible. Navigation terms not found in Bowditch are techno-gibberish. They mean whatever the person who invented the term wants the term to mean.

http://www.irbs.com/bowditch/

[clearsea]

Originally Posted by David M

I think we need to be especially careful when we start changing or adding new navigation terms. There are already an adequate number of precise terms and clear definitions for navigation. Changing terms or changing the definitions of terms would only create confusion. ... Bowditch clearly defines all the navigation terms. Their definitions are not flexible. Navigation terms not found in Bowditch are techno-gibberish. They mean whatever the person who invented the term wants the term to mean. Bowditch Online

I can't agree more. That's what got me thinking about rationalizing all the new terms and drift of old terms. Bowditch points out, for example, that "Course Over the Ground" is a misnomer (see Glossary), since it refers to the past sense of Track, and course = path through the water, track = path over the ground.

[clearsea]

Originally Posted by defjef

This is an interesting issue all because of leeway and current I suppose ...

Defjef, the questions in your post are on the money. Here's how I approach that fundamental navigation issue with the terminology framework:

The line one plots from the present position (if known) to a Waypoint is an Intended Track -- the path the navigator wants the boat to follow over the ground. The navigator validates safe water along the entire path. Sticking to that Intended Track in a boat is challenging because of all the factors that comprise "navigational current": water current, wind leeway, steering biases, condition of the hull, alignment of the keel, etc. These cause the boat to follow a path through the water (Course) that usually does not follow the Intended Track. To compensate, the navigator chooses a Course To Steer (CTS) that crabs the boat along the Intended Track. The boat's Heading usually is not the same as the Bearing to the waypoint.

This thinking underpins standard navigation procedures that are equally valid using either a paper chart or an electronic chartplotter. In fact, GPS-type charlplotting has made these old concepts even more important. My belief is that boaters using an electronic chartplotter should be well grounded in the old paper chart procedures, taught using terminologhy that works consistently in both worlds, and is consistent with long-established marine navigation traditions.

Although the term "waypoint" was not used much prior to GPS (or Loran), when all our plotting was on paper charts, a waypoint is merely a point at either end of a line on a paper chart from one desired position (fix or planned departure point) to another (arrival point). Nowadays, thanks to GPS, we have become more used to thinking of those points as Waypoints on Route Legs. A Passage is a series of Routes, and a Voyage is a series of Passages -- another consistent merging of old and new.

Originally Posted by defjef

One concept that many seem to misunderstand (I think) is that regardless of the original plotted line to a waypoint, the shortest and usually the quickest is the PRESENT rhumbline. And if you have been asleep for a few hours and drift miles off your previous rhumb line it makes not sense to sterr toward it but rather set a NEW course line / rhumb line to the destination.

A sound approach to following a Route Leg (Intended Track between two waypoints) is to set an acceptable Cross Track Error -- the lateral distance the boat can drift from the Intended Track during the leg. The navigator has to ensure that the water on either side of the Intended Track is safe. If for some reason the boat gets too far off the Intended Track, out of that safe corridor, then one of the safest procedures (depending on the situation), is to plot a Course To Steer to achieve a new Intended Track directly back to the original Intended Track, and then resume a Course To Steer along the original Intended Track.

[MarkJ]

Goodness! I can't disagree more! <-- in the nicest possible way, of course, as I respect David and don't know Clearsea but like his essay.

I think navigation is an evolving thing and I am happy to ditch the old and go with the new as it slowly evolves.

Also I am teaching someone and its much safer for me to teach her the terms as used by the plotters on our boat that we use for navigation. I don't use paper charts for nav on oour boat.
If I say I want a COG of 250 thats what I want and I want her to acheive that. She can because the GPS has COG. For her to have to translate is just unnecessary, slow, error prone and consequently perhaps unsafe

Defjef mentions crabbing... coming into this last port, Bundaberg, there was about 3 miles of leading markers and a cross current so strong it was amazing. It was 5 am and I didnt want to get to the end of the leads till daylight so I had to go at 3.5kts. Fair Dinkum we were at 45 degrees to the course! Pointed that way, going this way! Nic was a little worried I was trying to kill her so I showed her my COG. She cared about where the bow was facing as she hadnt been on the wheel. I was on the wheel (auto pilot) so I couldn’t give a rats bum where the bow was pointed as long and the boat was going down the leads.

OK thats a slight mis-truth. I had intended to have a bit of sail up but the apparent wind made it imposable Oh woe. We had to motor in.

Point being I never referred to a paper chart at all. I used my plotter and its terminology

Go with the modern and let the old go the way of the museum

Mark

[clearsea]

Originally Posted by Lodesman

Intended track or Planned Track is the pencil-line on the chart - its purpose is obvious. Track Made Good is useful to determine set and drift (the somewhat misnamed "tidal triangle"), so it is also useful. What you call TBMG is what I would simply call Track and is irrelevant in a navigational planning context - see below in the GPS comment.

Kevin, Thanks for food for thought and giving me an opportunity to reflect carefully on what I proposed. I am not convinced that I am off base here. As you say, TBMG is not useful for the Planning phase of navigation, but it is very useful in the Under Way phase of navigation. TBMG is what some GPS manufacturers call "heading", a misnomer in marine navigation.

Originally Posted by Lodesman

The Course corresponds to the Planned Track (true, compass or magnetic) and is what you steer when you lack set and drift info. Course to Steer is the Course corrected for set and drift - it's the course you steer in order to make good your Planned Track.

Learning from Bowditch, I make a clear distinction between Course and Track. I suspect there may be have been a drift to confuse the terms perhaps because Course has a different sense in aviation navigation (?). CTS is the Course chosen to attempt to follow the Intended Track, as you say, but I would not describe CTS as being the Course corrected for set and drift -- CTS is one of the three tenses of Course.

Originally Posted by Lodesman

What you call CBS is Heading; what you call Course Steered(CS) is what I would simply call Course - it corresponds to Course, CTS or Heading and like TMG is used only to calculate the tidal triangle. (And to fill your log book.)

Course Being Steered is not the Heading, but the helmsman does attempt to maintain a Heading equal to CBS. It is simply the presents sense of the Course, as told to the helmsman. As you say, it should be logged.

Originally Posted by Lodesman

GPS does not give you an estimate of heading - it gives you Track; I hesitate to call it Track Made Good, as the GPS is giving near-instantaneous updates that equate closer to the current path over ground, whereas TMG is an average between two points on the actual path you travelled (past-tense) over the ground.

Strictly speaking, GPS doesn't give near-instantaneous updates, it provides GPS Fixes in a fixed time frame: every one second, for example. TMG is the line between two consecutive fixes. I agree in the utility of the old paper-chart navigation procedure of working out TMG between two fixes spaced minutes or hours apart, but I think it is important for students to understand that it is equally correct to view the line between two GPS fixes as TMG. The breadcrumb trail is simply a string of dozens or hundreds or thousands of TMGs between frequent GPS fixes. These two equally valid uses of TMG have different uses. One shows the boater how they are steering or where that fishing hole was (breadcrumb trail), while the other is used to work out the effect current and leeway have had on the boat over the past few minutes or hours.

Originally Posted by Lodesman

Track is useful in a pilotage situation where there is sufficient set to make a significant difference between Track and Heading (ie. the bow is pointed at safe water, but you're tracking towards shoals).

I have given up on "conning" and "piloting". They have value on big ships with formal bridge staff, and may have been useful on small boats in their day, but to my thinking they are no longer useful terms on recreational boats. Today, with GPS, the same procedures used in blue water or along the coast apply in the harbour. I think it is more valuable to think about "steering" and "navigating", terms both more familiar to modern boaters, and consistent with old navigation procedures.

[clearsea]

Originally Posted by MarkJ

I think navigation is an evolving thing and I am happy to ditch the old and go with the new as it slowly evolves. Also I am teaching someone and its much safer for me to teach her the terms as used by the plotters on our boat that we use for navigation. I don't use paper charts for nav on our boat.

Mark, We sort of agree on some things. Yes, navigation is evolving, and we need to be able to adopt the new, but I disagree that we should sever tradition. While it might be safer for a crew on one boat with one system to learn the quirks of terminology on that boat's gear, I think that in general it is better for the industry to promote model-independent procedures that work in all situations and are grounded in older, relevant navigation practices. My thinking is that the lessons of past generations of navigations were learned in hard ways. But like you I want the crew to be able to safely navigate with the gear at hand, so practicalities rule.

I have convinced myself of the value of carrying and using paper charts, and knowing paper-chart procedures. I think (maybe I'm wrong) that knowledge of paper-chart procedures helps electronic charptlotter users considerably. Paper charts give position sense broader than the chartplotter screen, both during planning and navigating under way, so I think they have their moments. I also plot a GPS fix on paper charts every few hours during longer passages.

Reading original Bowditch from 200 years ago, I could imagine that he was foreshadowing the arrival of GPS, one of the most dramatic navigation turning points in history.

One thing about all this I know for sure: never bring up controversial navigation thoughts in the cockpit -- good way to ruin a nice breakfast, afternoon, or evening. Navigators are a pretty independent bunch of cats.

[Sandero]

Originally Posted by clearsea

A sound approach to following a Route Leg (Intended Track between two waypoints) is to set an acceptable Cross Track Error -- the lateral distance the boat can drift from the Intended Track during the leg. The navigator has to ensure that the water on either side of the Intended Track is safe. If for some reason the boat gets too far off the Intended Track, out of that safe corridor, then one of the safest procedures (depending on the situation), is to plot a Course To Steer to achieve a new Intended Track directly back to the original Intended Track, and then resume a Course To Steer along the original Intended Track.

That's incorrect I believe. The shortest distance and quickest passage, assuming no hazzards and other influences such as wind and current is ALWAYS the rhumb line from your current position to the desitination (waypoint) or if really long distance it would be a great circle. It makes no sense to chose a heading which is NOT to the destination but to an imaginary track which you have moved off of.

This is no different then, for example. going to sleep or being hove to... whatever and then plotting your present GPS fix, then lay a course line from your orignal starting point to your destination and heading directly at it as if it is a road you must be on. Doesn't matter a bit. What matter at that moment is the most direct path to the destination. Set a course to it and resume your journey.

Sure you can set a cross track error limit which is like how wide is the road you can weave around on your passage.

If it is too wide you S about and that makes the jouney longer in fact. The amount of yawing can be significant. Let's say your autopilot can't handle following seas and yaws from side to side, but doesn't even exceed the cross track limit so it appears that you are on the intended course line. If you could plot this track you would see something that lookes like a slolem and you know that this is MUCH longer than a straight path down the fall line. So depending on the period and the amplitude of the yaw you could almost travel 2x the distance of the straight path and remain within the cross track error parameter.

[MarkJ]

Originally Posted by clearsea

I have convinced myself of the value of carrying and using paper charts, and knowing paper-chart procedures.

Ahhh there be the difference

Wipe your mind of all and everything for a weekend. Take the boat out to some place you've never been and its tricky to navigate and turn on a plotter and look at it from the viewpoint of a babe in the woods (ok a little older).

Navigation becomes intuitive again No needing to look up some old duffers 200 year old book, in fact no need to even know things faked like flat pages and variations between true, grid and magnetic. All you do is sail, see, discover and enjoy.

With this extra time you will find other things to fill the void of not having to think about navigation. And that is where it will be interesting! I wonder what you will see?

Remember when Cook cleared off from the cloud lands for the second time he, too, chucked out all the past: he took a watch.

If Cooky was heading out today would he have Bowdich under his arm, his chronometer, a coupla paper charts and a Plane Table and leave the wife at home? No! Of course he wouldn't! He'd take the grizzly girl, a GPS and a laptop

History is pockmarked with the establishment hating the new discovers. The Vatican has just realised that Darwin was right and evolution doesn't conflict with the Bible- http://www.telegraph.co.uk/news/newstopics/religion/4588289/The-Vatican-claims-Darwins-theory-of-evolution-is-compatible-with-Christianity.html

We must make sure we welcome what is new, because the next generation will be using the new anyway, and couldn’t give two figs about what us old buggers say, think or read

Mark

[Sandero]

I learned the old style navigation and consider it valuable as it informs me about how to figure out marine navigation. I have the plotting instruments on board and all the paper charts where I sail.

And I have 3 GPS plotters which I love since they are very good at math and don't waste paper and pencils! My favorite one is the tiny Garmin PDA IQue 3600 which has only charts and a heading line and leaves a bread crumb trail. The heading line I assume is a line connect the last two fixes it did since it assumed that you travel from on to the other and that's where you are "headed" hahaha. This is basically "true". And I use this heading line to turn the boat so that it points at where I want to go. And this may be crabbing and do forth because it doesn't know from current or that it's on a boat with a pointy end.

I don't dial in a direction from a GPS which tells me the course to steer, I simply turn the boat so that the heading line is crossing my destination (not going over thin water, rocks, obstructions or land) and VOILA. Depending on the motion of the boat between it fixes and the so forth the heading line can love about line someone aiming a search light looking for a target. But in that case, I use my judgment and average it out. In calmer conditions it is very constant.

If I refer to the COG during a journing were I was always pointing to the destination using the heading line it may vary and show the influence of current and leeway (crabbing) and as MarkJ noted the heading line is not the CL of the boat extended but the line of motion of the boat. And it can be unnerving to be going in a direction and the bow not pointing there. Usually the difference is quite subtle and unnoticable, but in reality in sailing it's always there.

As a safety precaution I have the charts opened to my sailing area and can resort to them and traditional plotting if I have a failure of all three GPS. But one has a self contained battery and that's not likely.

I don't think I am confused by the terms because I understand the concepts and what's happening. I suppose others may not be as clear about this. Just don't hit me please.

[Lodesman]

Originally Posted by clearsea

Learning from Bowditch, I make a clear distinction between Course and Track. I suspect there may be have been a drift to confuse the terms perhaps because Course has a different sense in aviation navigation (?). CTS is the Course chosen to attempt to follow the Intended Track, as you say, but I would not describe CTS as being the Course corrected for set and drift -- CTS is one of the three tenses of Course.

I think it's necessary to point out that Bowditch got his definitions from Moore, who essentially took the terms from the Admiralty, and then 200 yeas worth of editors have put their marks on them. That said, I think you will find that very little, if any, of what I've described differs from Bowditch. Bowditch does not make the distinctions in terms of tense, but rather uses that which is practical to the realities of marine navigation. AFAIK, CTS is not described in Bowditch, other than where it is used in the section on DR and EP - which is exactly what I described.

Course Being Steered is not the Heading, but the helmsman does attempt to maintain a Heading equal to CBS. It is simply the presents sense of the Course, as told to the helmsman. As you say, it should be logged.

The helmsman tries to maintain a Course - nothing more. As no helmsman can maintain a course precisely the boat will yaw back and forth - a snapshot in time (of the bow or the compass) will show Heading.

Strictly speaking, GPS doesn't give near-instantaneous updates, it provides GPS Fixes in a fixed time frame: every one second, for example. TMG is the line between two consecutive fixes. I agree in the utility of the old paper-chart navigation procedure of working out TMG between two fixes spaced minutes or hours apart, but I think it is important for students to understand that it is equally correct to view the line between two GPS fixes as TMG.

Fix updates every second is "near instantaneous" and does not represent a usable TMG. TMG only has one function and that is to determine set and drift.

The breadcrumb trail is simply a string of dozens or hundreds or thousands of TMGs between frequent GPS fixes. These two equally valid uses of TMG have different uses. One shows the boater how they are steering or where that fishing hole was (breadcrumb trail), while the other is used to work out the effect current and leeway have had on the boat over the past few minutes or hours.

Try as I might, I can't think of the breadcrumb trail as having any utility, but am open to persuasion. If I want to find a fishing hole, a saved position, waypoint, plot (whatever you want to call it) is just as useful.

I have given up on "conning" and "piloting". They have value on big ships with formal bridge staff, and may have been useful on small boats in their day, but to my thinking they are no longer useful terms on recreational boats. Today, with GPS, the same procedures used in blue water or along the coast apply in the harbour. I think it is more valuable to think about "steering" and "navigating", terms both more familiar to modern boaters, and consistent with old navigation procedures.

I agree - I wouldn't use conning or piloting in a recreational sense. I think you may have misunderstood my use of the term "pilotage" - used in context with "offshore", "coastal" and "inshore", pilotage denotes very close proximity to navigational hazards.

Despite having been trained in classical navigation, I tend to agree with Mark, that modern electronic navigation equipment demands an approach that is optimized to that equipment, not one that is a modification of paper methods. I still think there is some usefulness in knowing the tried and true methods, as a backup if nothing else.

Kevin