Originally posted by Shaken_Widow:

you don't want tail wind, that's slower than full wind to the sides.

No, it's not. Or rather, it is, but only by about 3%. Since sailing speeds are never higher than 10 m/s, that's a difference of less than 0.3 m/s. For comparison, it's less than 10% of the speed difference between walking and running.

"All wind directions from crosswind to tailwind end up being roughly the same (with the optimal wind angle being only ~3% faster)."
https://valheim.fandom.com/wiki/Boats#Sailing_with_the_wind

It's only recently that humanity has discovered how to sail faster with a crosswind than a tailwind; unfortunately, Viking longships predate that design evolution.

TL;DR: Anything other than a headwind generates forward motion at roughly the same rate.