How you will drive the boat?

Question

You want to pilot your boat across a river with a fast moving current. You want to reach the port directly across from you. Describe how you will drive the boat.

 

Frames of Reference question.

 

Explain in detail please.

Answer 1

Not knowing the speed of the current, the speed of the craft, or the distance across the river, you will have to wing it. From a point on the shoreline where you plan to launch, look for two distant points of reference that line up visually. Pointing upstream, maneuver the boat crossstream while maintaining the alignment of those two distant points.

If only the speed of the craft is known, standing at the point of launch on the water line, you will need to estimate the distance across the river (r), and the speed of the current (c). Estimate (r) by multilying the height (s) of you eyes by the tangent of the angle, downward from your eyes, along the line to the opposite shoreline. Estimate (c) by tossing a floating object to a point believed to be where the average currents speed is located, measure its angle (a), from the same launch point, in reference to a line perpendicular to the near shoreline after it has travesed 10 seconds. Divide this angle(a) by 10, to get a better estimate for one second of travel. Calculate the total distance of travel. Your total length of travel will be the square root of r squared + c squared (Dorothy would be proud of me). Take that value and divide it by the speed of your craft. This will give you an estimated time(t) of travel. Heading upstream at the original angle (a), derived using the floatation, proceed in that direction for the estimated time of (t).

If all distances are known in advance, substitute them properly, using the same process.

Answer 2

You drive it at an angle across the river yet also upstream so that your speed upstream equals the speed of the current downstream, giving only a net motion straight across the river.

 

The faster the river is running, the more you have to point upstream to cancel its motion, so the slower you get across the river.