When sailing you cant just rely on Ray Marine instruments to help you navigate to a point of interest. Why cant you rely on these instruments: In this article we will explain the main reasons why you cant rely on these instruments to set a true or magnetic bearing to reach your point of interest.
All sailors rely on Software application sonar radar to help them navigate through local water, coastal waters an inland waters to help them find a point of interest.
True an magnetic bearing points. Finding Distance an time from bearing to bearing
These electronic devices can be confused due to magnets that the earth encounters along the way. They can display false readings an lead you into a pool of danger an isolated waters.
This is why when you do the bearing degree manually you can rely on your markers to get your point of interest safely.
The instruments can be used safely an according to inland coastal waters you should not have any problems with interference from satellites or magnetic instruments on the boat that will change the course of steer.
Explained:
In nautical navigation the absolute bearing is the clockwise angle between north and an object observed from the vessel. If the north used as reference is the true geographical north then the bearing is a true bearing whereas if the reference used is magnetic north then the bearing is a magnetic bearing.
True an magnetic bearing points. Finding Distance an time from bearing to bearing
Once you have marked your path to the first bearing point you have measured the the distance of the point a to point b. You will need to use a divider ruler to extract the true bearing point degree.
To measure the distance an time required to reach the bearing degree you want to go. You must select a speed you think you will be traveling at.
1 nautical mile takes 10 minutes to reach there when you know the speed your going at.
for example 1 nautical mile takes roughly 10 minutes to travel.
If the boat is traveling between 5-6 knots -
Use your Single Handed Divider to measure the distance between your starting bearing point an the end of the bearing point. Take the divider the tool below, an go to the longitude at the edge of your chart. Here you can measure the time that is required by extracting the number for which the nm are. Then use the method 1 nautical mile equals 10minutes. You then have the time required to reach your start to end bearing point.
Dividers and compasses are drawing instruments that have been used since antiquity to measure distances, transfer lengths from one drawing to another, and draw circles.
The portland ruler will allow you to extract the bearing degree by pointing the the north circle inline with the maps vertical lines on the map.
once you have your true bearing you must always minus 12 degrees off the true bearing because the earth north centre is always off 12 degrees from the
7" Single Handed Divider - Hand held bearing point compass.
A hand bearing compass is a small, portable compass that is not meant to replace a boat's primarily steering compass. It is used to take a bearing easier than with the steering compass. Bearings are taken by holding the compass in the hand close to the eye and by looking over the compass card to the bearing object. The construction of the hand bearing compass should allow simultaneous viewing of the bearing object and the compass card reading. Despite the simple construction, the measurement results, when used from a deviation-free location are remarkably good.
Hand bearing compasses usually have photoluminescent compass cards. Exposing the compass card to the cabin light or a torchlight ensures enough luminescence for taking night bearings. During daytime usage, exposure to intense sunlight should be avoided.
Bearing of prominent charted objects can be plotted in a nautical chart to obtain a Line-of-Position. The intersection of two or more such lines yields a position fix. The Line-of-Position is a straight line in the chart starting from the sighted object - because this is normally the only known point of the bearing line - drawn in the OPPOSITE direction of the bearing measured in the location of the observer.
Notice, that two kind of bearings are involved:
the bearing from the sighted object to the observer and
the bearing from the observer to the sighted object
These bearings differ by 180°. The bearings read from the hand bearing compass normally are the bearings from the observer to the sighted object. When using an unknown bearing compass, it should be checked what kind of bearing the reading of the compass shows. The process of drawing bearing lines into the chart to obtain a Line-of-Position and finding a position fix is called plotting.
The Portland Course Plotter is one of the most popular chart work instruments and is widely used by RYA practical & shore based instructors. It provides a quick method of plotting course and bearings and gives a direct reading of corrections for magnetic variation.
Example 1
Example 2
Author Alternative Sailing
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