This is for something I’m writing and all of the Googling has left me lost with nautical terms. If I’m taking an old Norse Longboat and I’m sailing on the sea and there is a current going south, and the wind is also going south, do I go faster than the current? Does it depend on the speed of the wind? I guess I just don’t understand if the current takes control of the boat or if you can use it to boost your speed.
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Sailing into the current will slow the boat down a bit, but not by the same speed as the current. Its only slowing the boat down because of drag on the hull, its not like a plane flying into a headwind.
If the boat is sailing with the current it’ll get a slight speed boost because there is less drag on the hull. If the current is faster than the wind it’ll be like sailing into the wind which won’t work so well so you’d drop the sails and float in that scenario
> If I’m taking an old Norse Longboat and I’m sailing on the sea and there is a current going south, and the wind is also going south, do I go faster than the current?
Yes, you can go faster than the current. The current is water pushing in a certain direction. If you’re sailing on a boat in the water and you are traveling in the same direction as the current you’ll go faster. If you were sailing in the opposite direction you’d go slower.
If there’s a two-knot current to the south, and a ten-knot wind to the south, then the boat sees that as an eight-knot wind to the south. It will sail exactly as it would if there were no current and an eight-knot wind. Of course, whatever speed the boat sails at on the water in those conditions, you’d have to add back the two-knot current to work out speed and position on a map.
Putting it another way, the boat doesn’t care what the wind speed is relative to the ground, it only cares about the wind speed relative to the water. So for sailing boats in a current, convert the wind speed over land to wind speed over the water, use your knowledge of the boat’s sailing characteristics to predict its speed in the water, then add back the speed of the current to find the boat’s speed over land.
This is relatively simple if the wind and current are in the same or opposite directions, because you can just add and subtract numbers (scalars). When you have things like an easterly current and a southerly wind you have to do two-dimensional [vector additions and subtractions](http://mathworld.wolfram.com/VectorAddition.html), either graphically or with mathematics. Aircraft use a [wind triangle](https://en.wikipedia.org/wiki/Wind_triangle) to navigate in winds, and have a [special slide rule](https://en.wikipedia.org/wiki/E6B) to do this kind of calculation.
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