West Pier Lighthouse

 Jess was off to Pilates so I piloted down to the town and went for a stroll around the harbour.
More snaps of waves trying to get something interesting (failed) and so headed out onto the western arm. Got a shot of the northern lighthouse the other day so thought I'd even up the score with the western. 
Rain had left puddles which means reflections, I wandered up and down the harbour arm trying to get the puddle distance correct for the height of the lighthouse. I'm pretty sure school geometry would have calculated it but that was a long time ago so I went for the trial and error method, ie wandering about and crouching down regularly as far as I dared. (must have looked odd from afar)  Having calculated all that I had to wait for the wind to drop a bit for less ripples in the puddles.
What is the equation for how much the wind needs to drop for the ripples to stop in puddles I wonder ?