1. METHODS OF LOCATING SOUNDING
Group Members:
Sarath Poduval
Savalia Ashish
Savalia Hiren
Saavan Bhua
Assisted by : Megha Mam

2. Methods of locating Sounding:
By cross rope.
By range and time intervals.
By range and one angle from the shore.
By range and one angle from the boat.
By two angles from the shore.
By two angles from the boat.
By one angle from shore and one from boat.
By intersecting ranges.
By tacheometer.

3. Locating by cross rope:
This is the most accurate method of locating the soundings and may be used for narrow river, narrow lakes and for harbours.
A single wire or rope is stretched between two supports at the two points A and B on the opposite banks. The width is divided into a number of segments, and tags are attached at the division points. The distances are marked from a reference tag, also called zero tag. The zero mark is transferred to the ground by a plumb bob.
The boat is rowed to a point a1 below the tag no.1 and a sounding is taken. Similarly, other points are located.

4. Location by cross rope

5. 2. Locating by range and time interval:
The range lines are marked as shown. The sounding boat is rowed from the shore near point a on the range line and rowed along the range line. After some time the boat attains a constant speed.
A sounding is taken at point a1, and the time of observation is noted.Knowing the speed of boat and time interval, distance aa1 is calculated. Likewise, soundings are taken at points a2,a3 etc. and time of observations are noted. Thus, the distances of the various sounding points a2,a3 etc. are determined.

6. Location by range and time interval

7. 3. Location by range and one angle from the shore:
There are four range lines AA’,BB’,CC’, and DD’.The theodolite is set up at the station B’ for locating points on the range line AA’. The theodolite is oriented along B’A’. Let x1 be the perpendicular distances of the point B’ from the point A’.
The sounding boat is rowed along the line AA’. The first sounding is taken at a1 and the corresponding angle is measured as α1.
tan α1= A’a1/x1
A’a1 = x1.tan α1

8. Likewise, the other points a2,a3 etc. are located on the range line AA’.
Now, the instrument is shifted to the station C’. The boat is rowed from a3 to point b3. The horizontal angles of the points b3,b2,b1 from C’ are measured. Thus the points are located. This method is quite accurate and convenient. It is mostly used in practise.

9. Location by range and one angle from the shore

10. 4. Location by range and one angle from boat:
For locating sounding points on the range line AA’, a signal is fixed at point B on the range line BB’.
The sounding boat is rowed along the range line AA’ to the sounding point a1 and the angle Aa1B=α1 is measured with a nautical sextant mounted on the boat.
The distance Aa1 is given by,
tan α1= d/Aa1
Aa1= d/tan α1
Likewise the points a2,a3 etc. are located.
Now, the signal is fixed at point C, the boat is rowed along range line BB’ and the sounding points b1,b2,b3 are located.

11. Location by range and one angle from boat

12. 5. Location by two angles from shore:
This method is used when it is not possible to keep the sounding boat on a fixed range line. The method requires two theodolites. The instruments are set up at two known stations A and B on the shore line.
When the sounding boat is at P1, whose location is required, horizontal angles at both the instruments measured as α1 and α2.The time at which the sounding is taken should be noted. The distance d between A and B is also measured.
The co-ordinates of point P1 may be computed from the relations:
x=d tan α2/(tan α1+ tan α2)
y=d tan α1.tan α2/(tan α1+ tan α2)

13. Location by two angles from shore

14. 6. Location by two angles from boat:
In this method the location of sounding is made by measuring two angles α1 and α2 simultaneously with a sextant from the sounding boat at P to three prominent signals A,B and C. The location of P is determined by solving three point problem.
The precision is poor when the point P is near the circumference of the circle passing through A,B and C. If the stations A,B and C are on a straight line or if point B is nearer to the boat P than points A and C, the location of P is accurate.

15. Location by two angles from boat

16. 7. Location by one angle from shore and one from boat:
In this method, two points A and B are selected on the shore. The point A is the instrument station and point B is the shore signal point.
P is the sounding point which is to be located. When the boat is at P, the angle α is measured with the theodolite at A and angle β is measured at the boat with anautical sextant. Knowing the distance d between A and B the position of P can be determined from its coordinates xand y.
x=[d sin (α+ β)/sin β].cos α
y=[d sin (α+ β)/sin β].sin α

17. Location by one angle from shore and one from boat

18. 8. Location by intersecting ranges:
Two sets of intersecting ranges are shown one set perpendicular to the shore and the other set inclined to the shore.
To locate the sounding point a1, row the boat to the point where the ranges AA’ and CB’ intersect. The signals are fixed at points B,B’,C,C’ etc. so that the points of intersection can be located by sighting.

19. Location by intersecting ranges

20. 9. Location by tacheometer :
The method is very much useful in smooth waters. Three ranges lines AA’,BB’ and CC’ are shown. The tacheometer is set up at station A’ and oriented along AA’. A levelling staff is held vertically on the bottom of the sounding boat. The boatman rows the boat along the range line from shore to a1. When the boat reaches the oint a1, a stadia reading is taken on the staff and asounding is also taken.
The horizontal distance between the instrument station and the boat is calculated by,

21. D=f/I S+ (f + d)
S = staff intercept
I = stadia interval
f = focal lenth of objective
d = distance of vertical axis from optical centre of objective.

22. Location by tacheometer