Estimating navigation correctly is very important for sailors, as much as plotting a course. Indeed, it is a matter of being in control of the space and time of navigation, and thus knowing how to plan one’s trip in a pleasure craft, whether short or long.
The tools for estimating navigation
You will be able to estimate navigation by the use of some tools. First of all, the squares and parallels, which can plot the course directly on the nautical chart.
Then you have the compass, which keeps the orientation of the boat’s heading on the course you have set.
It is also important to know the time of departure and arrival for estimated navigation.
The Estimated Position of Ship
The Estimated Position of Ship is the calculation of the space traveled at a given speed for a given time interval, thus:
S = v * t
Knowing the Estimated Position is not enough to conduct safe navigation because it does not take into account weather effects and thus current or wind action. The actual position could deviate from the estimated position.
In addition, you must consider the deviation error generated by metal and magnetic objects on board (on the compass needle).
Therefore, it is very important to keep your eyes open to the landmarks that indicate any deviation from the predetermined course. This skill is achieved mostly with experience.
Speed Log
The speed log (also: just log) measures miles traveled. It also measures the proper speed (VP), that is, the speed without wind and without current and the actual speed, with wind but without current.
In other words, the log indicates the boat’s speed in knots per hour, and in the presence of wind it indicates the actual speed (EV).
Types of log
1) Boat log: in ancient times, the log consisted of a reel on which a line was rolled with a wooden skid at the end that was ballasted enough to counteract the friction of the water. Knots were tied on the line at a distance of 15.43 m from each other. To measure the speed of the unit, the small boat was immersed in the water. Spinning the line, as soon as the first knot passed through the hand a 30-second hourglass was turned and counted how many knots flowed in that space of time.
With this instrument it was possible to calculate how many knots the boat was “spinning” at, a term still in use today. This log is no longer in use today;
2) Propeller log: by means of a tachometer it measures the revolutions of a small propeller fixed under the hull with the function of a sensor. Depending on how fast this small propeller turns, knots and miles traveled are calculated;
3) Towed propeller log: based on the number of revolutions counted in the propeller, speed and miles traveled are derived. The pitch of the propeller is known;
4) Pressure log: measures water pressure on the Pitot tube, an element attached under the hull;
5) Digital log: it measures the time it takes for a pulse to reach the receiving unit. The result is calculated in knots. The Doppler effect log under certain conditions is also capable of indicating the actual speed as well.