Getting Your Bearings
Navigation skills to keep you on track to your destination.
Getting Your BearingsNavigation skills to keep you on track to your destination. |
|
One of boating's truisms is, "Keep the boat where the land isn't." It's a silly statement, but obviously fundamental to safe passage making. Successfully avoiding land begins with knowing where you and your boat are in relation to it, and never is this more important than when you're approaching an unfamiliar harbour or anchorage.
The nautical chart is our first line of defense against running into trouble. It shows us hazards both above and below the waterline: things like shoals, rocks and even the submerged wrecks of those who perhaps weren't as safety conscious. Unfortunately, charts don't show us where we are: that's something we have to figure out for ourselves, and that requires a little bit of navigation know-how.
Electronic aids like GPS, Loran and radar are a real help when it comes to finding, or fixing, our position. With GPS for example, compact receivers continuously display the unit's latitude and longitude co-ordinates, give or take a few metres. These coordinates can then be plotted on a nautical chart. There are even GPS units with built-in digital charts!
Unfortunately, there's another truism of boating which states that the chance of a piece of equipment failing is directly related to how much it's needed. There comes a time when just about every boater is called upon to determine their position without high-tech aids.
A safe approach to a harbour or anchorage begins with finding your position relative to your destination and then determining a course that will get you where you want to go while avoiding hazards.
Determining your position is called getting a fix. If you happen to be within a few metres of a charted fairway buoy or other object, plotting your fix on the chart is as easy as finding an intersection on a road map: find the buoy and there you are.
When you're not near a charted object, but there are at least two in sight, it's still possible to get an accurate fix. You do this by determining the direction of the objects and then doing some simple plotting on your chart. These objects can be any number of things -- a church steeple, a distant buoy or lighthouse, the end of a jetty, a water tower; but they must appear on the chart and, of course, they must be visible. You must also know the chart symbol for the object. (The guides for chart symbols in Canada and the United States are for sale in most chandleries and are both called Chart #1.)
 |
BearingsChecking the direction an object is called taking a bearing and it's done with a compass. Most types of compasses can be used, but some are easier than others. A hand-bearing compass is designed specifically for taking bearings. To use it, you simply point it in the direction of the object you're sighting, and read off the compass bearing in degrees. |
Armed with a couple of bearings taken at roughly the same time, you can now plot these on your chart. Find the object you took a bearing of and draw a line from it in the same direction as your bearing. To do this, you'll have to determine the angle of the line you want to plot. Most charts include a compass rose from which you can transfer the angle of the bearing using parallel rulers. A compass rose will usually have both a magnetic and true scale: Use the magnetic scale as it's a magnetic bearing you got with the compass (a bearing relative to the magnetic north pole). [More on Magnetic vs True]
These lines you've plotted on the chart are called lines of position (LOP), because your position is somewhere along each line. Where the two LOP's intersect is where you are, or at least, where you were when you took the bearings. The faster you're moving, the more important it is to take and plot bearings quickly.
Once you have an accurate fix of your location, you can determine a course to steer to your destination and steer clear of trouble. And you'll be able to check your progress with more bearings and fixes. You'll be able to avoid underwater hazards, keep clear of commercial traffic schemes, and make sure your boat doesn't you become a symbol on some future chart!
|
See an illustrated step-by-step guide to taking bearings, and plotting lines of position and a fix. |
The Ottawa Sailing & Powerboating School offers three courses in navigation. The 4-hour "Navigation for Beginners" seminar provides a quick look at some navigation fundamentals. This is a good introduction to navigation with enough detail for the boater who spends their time in small bodies of water and well-marked rivers.
The 25-hour Coastal Navigation course covers the Canadian Yachting Coastal Navigation standard. This is the course for those cruising larger inland and coastal waters.
The school's 25-hour Celestial Navigation course also covers the CYA standard and prepares boaters for offshore cruising. To find out more and find out when courses are being offered, contact the school at www.boattraining.com .
Copyright 2000, Eric Calvert