Practical advice for all sailors. Tom Cunliffe has sailed tens of thousands of miles all over the world and has been a Yachtmaster Examiner since 1978
This photo is a rather exaggerated case of wind-against-tide. The water’s easy to read because you’d expect things to be rough and they were. In lesser situations you can still tell when the tide turns, or spot a useful eddy, if you educate yourself about sea shape.
When the breeze blows against any sort of stream, even one running at a knot or less, the front of each small wave (the downwind side) is steeper, while small but recognisable streaks of foam run actively down its back towards the wind. It works in deep water too, as anyone can testify who has crossed the Gulf Stream or hit the equatorial counter-current when they should have been enjoying a favouring two-knot shove.