Heading vs Course vs Bearing
How many times have you heard someone discuss where they’re going in a boat and drop the words heading or bearing or course or track? We’re on track to the marina. We’re on a heading due south. On a course to meet a friend. Bearing north at 12 knots. Whatever it might be, they’re generally all used the same way by many boaters. But is this accurate? Well, not exactly.
Heading or Actual Direction Explained
Heading is confusing for some people and is often misused. Typically, when someone is asked what their heading is, they’ll say where they are headed. But those are two different words. If you’re going back to the marina, that isn’t necessarily your heading at all.
Instead, the heading is the direction the boat is pointed at any given moment. In other words, your true heading is your actual direction. Which means your heading can change frequently and unintentionally. If a gust of wind pushes you off course, you’re on a new heading. Your course isn’t different but your heading is.
A good way to remember this is that heading is not where you intend to go. Heading is just whatever you’re pointed at. Your nose picks the heading of your face at any given moment. You can turn your head and your course has not changed but your heading did.
Course is what many people mean when they say heading. Your desired course is the intended direction you planned on going. So your course may have been due east but you had to navigate around an island so your heading changed to accommodate that. Your course and intended path remains the same, however. Most boaters want their course and their heading to be the same. But, as with our island example, things come up that make you change heading all the time.
Course is typically a straight line between two points. This is not always navigable for the reasons we’ve mentioned, and potentially many more. Your course heading needs to adjust and often is based around a reference point.
Bearing may overlap with course and heading but it doesn’t have to. Instead, bearing is the angle in degrees between north and the direction of your destination. This is also called a navigation bearing or magnetic bearing. But that’s not the only bearing you need to know about. There’s also relative bearing.
Relative Bearing Explained
Relative bearing is similar to navigational bearing. In this case, however, we’re not calculating degrees between north and the destination. It’s between the heading of the vessel and the destination. So your relative bearing could be 0 degrees if your heading and course are all aligned. But it could also be off if, as in our example, you need to navigate around an island. This is all based on the relative position to your boat at the time you calculate it. Where you are pointing relative to a given waypoint or destination helps you determine relative bearing.
When we refer to a relative bearing course it’s worth knowing where we start exactly. In this case you’re measuring in a straight line from the observation station of the vessel. You can measure to whatever object or point of interest you’re interested in from that point to get the correct figures.
When a lookout on a boat raises a warning about something, this is always done in a relative way. The lookout would never know the course of the boat and it would be irrelevant to their duties. Anyone serving as a lookout understands that the bow of his boat will always be 0 degrees and can work in a 360 degree circle, relative to the vessel, from there.
Relative bearing is always most relevant to you and the crew on your boat. True bearing is relevant for navigation and also for others looking to find you.
What About Tack or Track?
You’ll also run across the words tack and track in nautical use sometimes. They are not the same term and refer to different things.
Track in nautical terms typically means what you think it means. It’s the same as how you might use it on land, as in you left a track behind you from walking in the mud. Your track over water is the actual path you took from the start of your voyage to your current position. Since track is always what you did do and not what you’re going to do, it’s not all that helpful in present tense navigation.
Tack, on the other hand, is not a reference to navigation but it is a boating term. This is a maneuver that allows you to sail through the wind. Sometimes people will mistakenly use this term as well when they’re referencing either course or heading. You may hear someone say “we’re on the right tack” or something similar. It’s obviously just a colloquial expression. Still, it can get confusing for people who aren’t fully familiar with nautical terminology.
If you’re researching navigation and come across terms like desired track and intended track, be aware that these are not standard nautical navigation terms. You’ll most likely run across these when researching things like flying. Pilots are much more concerned with how their planes are tracking over land than anyone in a boat needs to be.
In these cases, the word track is essentially a substitute for course.
How to Calculate Bearing
Understanding magnetic or true bearing vs relative bearing vs true course can seem daunting. However, it’s not that difficult once you get the hang of it. Basically there are three important numbers involved here and if you know two you can determine the third. This is standard for many equations and makes it easier to move back and forth between them. At any given moment you should always be able to determine your ship’s heading. So that means you just need to figure out true bearing or relative bearing. Let’s take a look.
True Bearing – Ship’s Heading = Relative Bearing
Relative Bearing + Ships Heading = True Bearing
Let’s try some practical examples to make it clearer.
You want to determine the relative bearing of Snake Island. The true bearing of Snake Island is 225° T. That T in the equation stands for true because we’re using true and not magnetic in this case. Your current heading is 059° T. A simple calculation here will give you the relative bearing.
225 – 59 = 166°
Likewise, if you want to know the true bearing you can substitute other numbers. Let’s say you need to know the true bearing of Bruin Channel. The relative bearing is 325°. Your course is 135° T. According to the calculation relative bearing + heading = true bearing so 325 + 135 = 460. But is that right? Not exactly!
Compass heading works in a full circle, don’t forget. Compass direction is all measured clockwise and it goes from 0 to 360 degrees. That’s one full circle. So if our math says we’ve gone to 460 degrees, we need to subtract one full circle of 360 degrees. Because you’re not going to spin in an entire circle for no reason, right? Instead, you take the leftover of 460 – 360. That means your true bearing is 100°
Let’s try one more tricky one that can be confusing to people who are new to these calculations. The true bearing of Bear Island is 224° T. Your heading is 270° T. The calculation says that relative bearing is true bearing minus ship’s heading. So that means 224 – 270. But that equals Negative 46. Is that right? No.
Just as above when we went over 360 with our compass bearings and had to subtract, here we have gone below zero so we need to add. Everything has to exist on the circle so we need to add 360 in this case. Negative 46 plus 360 = 314°
Why Understanding Navigation is Important
Many modern boaters rely entirely on technology to help them navigate. And there’s no doubt GPS and other electronic tools are invaluable and have made boating safer and easier. But being able to calculate heading, course and bearing without technology could be extremely important. Remember that technology is only helpful when you have access to it. If your GPS becomes damaged or loses powers, it’s just a paperweight. Knowing how to make calculations with older tools like a compass and just a pen and paper is important for ensuring your safety and the safety of your crew.
We always recommend you have several navigation aids on board at any given time. GPS is vital, but have access to a compass. Make sure you have charts as well, and dividers. Learn the right terms and learn the calculations. When you have one or two backups, there’s nothing that you can’t overcome at sea.
True North or Magnetic North?
Another thing worth remembering with this calculation is what north we mean. Another confusing bit to be sure, but there is true north and magnetic north. True north is a fixed point on a map and it will never change. It’s what most of us might call the North Pole. But magnetic north is not necessarily true north. We know a compass points us north based on the earth’s magnetic field. But this field can and does fluctuate. Magnetic north can shift over time thanks to magnetic variation. Also, electrical and magnetic interference near a compass can drastically alter its readings. So when we do these bearing calculations, we’re referring to true north. That means you never have to worry about the point changing or shifting.
If your heading is based on magnetic north then that is your magnetic heading. Likewise if it’s true north than that works as your true heading.
So What Is Magnetic Bearing vs True Bearing?
This speaks to our last point. We mentioned magnetic bearing and true bearing earlier. The difference is how you calculated absolute bearing. Either can give you an accurate navigational reading, you just need to be consistent. If you use true geographical north as the absolute bearing, then you’re calculating true bearing. If you used magnetic north as the bearing, then you’re calculating magnetic bearing. So when you seek to find your relative bearings, keep this in mind.
It’s worth noting that compass bearing and magnetic bearing are slightly different things. For practical purposes a magnetic bearing and a compass bearing should be nearly identical. That said, the compass bearing can be slightly off for the reasons we’ve mentioned. If there’s a large iron deposit somewhere near you, or even just some magnets, your compass bearing will be very slightly off. It’s rare that this will cause significant enough trouble to alter anyone’s navigation. Especially in this day and age when so much navigation involves more precise tools like GPS.
The Bottom Line
The English language plays fast and loose with a lot of rules. We give multiple meanings to words all the time. If you call something cool are you referring to temperature or that you think it’s very nice or interesting? Likewise, many people, especially those not very well versed in sailing, will swap out terms like bearing, heading and course all the time. So you need to keep context in mind and who you’re talking to. But if you’re doing true navigation, you need to know the difference. Especially if you’re looking to get help at sea. If you need rescue and offer a relative bearing instead of a true bearing, that could be a costly error. Likewise if you mention your course but mistake it for heading.
Knowing what each term means, and how to calculate them, is just good sailing. As always, when you’re out on the water, stay safe and have fun.