There is such expression "fish looks for where is deeper, and the person – where it is better", this very exact reflection of fishing process. Therefore fans of fishing for the greatest success need to learn to determine depth of a reservoir and the nature of a relief of a bottom.

## It is required to you

- - manual lot;
- - mechanical lot;
- - sonic depth finder;
- - heavy load;
- - two strong ropes of various length.

## Instruction

1. The most effective modern device for measurement of depth of a bottom — the device under the name "lot". It allows to determine **reservoir** depth with a margin error less than 1%. As a rule, fishermen use one of its versions — the sonic depth finder, however is also other types of lots intended for manual and mechanical measurement.

2. Manual lot is the 5-kilogram cargo attached on the end of a thin cable which is called lotlin. On all length lotlinya marks with the indication of intervals of depth are put. Measurement by manual lot happens at a small speed of the water transport, about 5-9 km/h. For big depths use so-called dirafts which cargo can reach 30 kg.

3. Mechanical lot in comparison with manual – more optimal solution since the speed of transport can be quite high, up to 28 km/h. It is connected with the fact that the vertical position of use of the device is not of particular importance. Measurement by mechanical lot happens by lowering in water of the tube soldered since other end. On walls of a tube marks by which determine reservoir depth are put.

4. The sonic depth finder – the electronic device answering modern requirements of science and technology. The largest depth which the device can determine is 12 km, and measurements can be taken at a high speed, up to 50 km/h. There is a set of the firms releasing sonic depth finders, but all of them consist of the sensor, the transmitter, the screen and the receiver.

5. At inclusion the transmitter of the sonic depth finder sends an electric impulse to the sensor which, in turn, forms of it a sound wave and sends it to water. The wave is reflected and comes back, and the sensor will transform it back to an electric signal. The receiver distinguishes a signal and sends it to the screen. Measurement of the sonic depth finder not single, it works constantly with a certain frequency that allows to make measurements with the maximum accuracy.

6. It is worth noticing that there is one more way which does not demand costs of purchase of the special device. This method was thought up in the Soviet Union in the mid-sixties and is a combination of mathematical calculations and uses of a simple make-shift.

7. So, tie two strong ropes of unequal length for which ends attach floats to heavy load. Cargo is lowered on a bottom of a reservoir and measure distance between the emerged floats.

8. On a special formula calculate reservoir depth: H = (1/2*a) * √ (4*a^2*L_1^2 – (L_2^2 – L_1^2 + a^2)), where: a – distance between floats; L_1 and L_2 – lengths of ropes, and L_2> L_1; H – reservoir depth.