G'day Gents,
A view from inside the cockpit.
Often when following a B747 on an overwater approach, for example to RW34L at YSSY across Botany Bay, in still conditions you could clearly see the where the wingtip vortices had descended and left their mark on the water surface of the bay. The southern shore of Botany Bay is about 3nm from the touchdown point and the approach altitude there would be around 1000ft and often the vortex tracks would extend all the way from the landing threshold to the southern shore of the bay spreading outwards as distance from the touchdown point increased.
Cheers,
BH.