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River Flow Problem Calculator (Boat in Stream)

Find downstream and upstream speeds from a boat speed in still water and the current speed, or work backward from downstream and upstream speeds, and get travel time for a given distance.

Input

Enter the boat speed in still water and the current speed to get the downstream and upstream speeds. You can also work backward from the downstream and upstream speeds.

km/h
km/h

Enter a distance to also get the downstream and upstream travel times (optional).

km

Result

Downstream and upstream speeds

Downstream

15km/h

Upstream

9km/h

Current 3Downstream15Upstream9

Boat speed in still water

12 km/h

Current speed

3 km/h

Travel time (distance 30 km)

Down 2 h / Up 3.333 h

Calculation steps

1

The boat speed in still water is 12 km/h and the current speed is 3 km/h.

2

Going downstream you add the current, so 12 + 3 = 15 km/h.

3

Going upstream you subtract the current, so 12 - 3 = 9 km/h.

4

Downstream travel time is 30 divided by 15 = 2 h.

5

Upstream travel time is 30 divided by 9 = 3.333 h.

How it works

  • Downstream speed equals boat speed plus current speed, and upstream speed equals boat speed minus current speed.
  • When downstream and upstream speeds are known, boat speed is their average and current speed is half their difference.
  • Enter a distance to get the travel time for each direction, computed as distance divided by speed.
  • If the current is as fast as or faster than the boat, the boat cannot move upstream, so no solution is shown.

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