Aptitude (Boats And Streams Tutorials & Tricks)

Boats And Streams Tutorials & Tricks

Introduction

In area-velocity method generally the discharge measurements are made by keepingthe boat stationary at the point of observation or vertical. Depth and velocity aremeasured by sculling the boat to this point. The drifting of the boat, time consumes instationary boat method and necessity of instant value of discharge during floods fortaking anti-damaging action of flood on the bridge piers and other structuresnecessitated the adoption of moving boat method.

Formula for finding out Boats and Streams.

 1. Downstream/Upstream: In water, the direction along the stream is called downstream. And, the direction against the stream is called upstream.

2. If the speed of a boat in still water is u km/hr and the speed of the stream is vkm/hr, then: Speed downstream = (u + v) km/hr. Speed upstream = (u - v) km/hr.

3. If the speed downstream is a km/hr and the speed upstream is b km/hr, then: Speed in still water = 1/2 (a + b) km/hr. Rate of stream = 1/2 (a - b) km/hr.

4. Stream: Moving water of the river is called stream.

5. Still Water:If the water is not moving then it is called still water.

6. Upstream:Upstream: If a boat or a swimmer moves in the opposite direction of the stream then it is called upstream.

7. Downstream: If a boat or a swimmer moves in the same direction of the stream then it is called downstream.

8. Points to remember When speed of boat or a swimmer is given then it normally means speed in still water.

Some Basic Formulas
Rule 1: If speed of boat or swimmer is x km/h and the speed of stream is y km/h then, Speed of boat or swimmer upstream = (x − y) km/h Speed of boat or swimmer downstream = (x + y) km/h Rule 2:Speed of boat or swimmer in still water is given by Speed of stream is given by

Sample Example

Ex

A man can row a boat in upstream at 6 kmph and downstream at 12 kmph. Find the man's rate in still water and the rate of current ?

A

 Rate in still water = 1/2(6+12) = 9 km/hr Rate of current = 1/2(12-6) = 3 km/hr

Ex

A man can row 15 km /hr in still water. It takes him twice as long to row upstream as to row downstream. Find the rate of stream ?

A

 Let man's rate in upstream be x km/hr, then his rate in downstream is = 2x kmph Rate in still water = 1/2(2x+x) = 3x/2 km/hr 3x/2 = 15, x = 10 km/hr So rate in down stream= 2x= 20 km/hr Rate of stream = 1/2(20-1