A Simplified Guide to Small Marine Craft Navigation.

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Chapter 20 (v.1) - DR Computer, an aid to Navigation.

Submitted: May 12, 2017

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Submitted: May 12, 2017



DR Computer, an aid to Navigation.



There are available on the marine market a variety of DR Computers or Navigation Systems that feed information from several of the separate instruments such as the log and wind measuring devices into a central processing unit, which then outputs an indication, the dead reckoning position, DR, or a fix if linked to a hyperbolic navigation system.

However, like so many electronic instruments computers present their information in a precise form, possibly to several decimal places, and this can give a false impression of the accuracy of the DR or estimated position derived from it.

Note, a DR is only an educated guess based on speed, distance, and time, whereas a fix is by far more reliable.

This can only ever be as accurate as the information that has been fed into the computer. As previously stated in this guide a log can be inaccurate, and even the course which is steered can have a bias to one side or the other.

Estimation of the set and drift of the tidal stream and the amount of leeway, drift due to wind, are at best intelligent guesswork. By plotting this information on a chart in the traditional way, a navigator is made more aware of these inaccuracies, and in consequence, makes them more cautious. On the other hand, computers are much quicker and more accurate than mental processes provided the American computer adage “garbage in, garbage out” is remembered.

The true value of a computer lies in enabling the navigator to assess future action quickly and simply so that he can decide the best course to his destination, and this can be an advantage in bad weather when it becomes difficult to use a chart table.


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