Originally Posted by davidpm
I found this from Wikipedia:
.....Since waves rarely break onto a shore at right angles, the upward movement of water onto the beach (swash) occurs at an oblique angle.
Some of that article is correct but some is erroneous, like the foregoing. Wikipedia can be a research tool but it is open source and much of what is written is simply opinion.
But, for the sake of the exercise, if you have it open Google Earth and zoom in on any shoreline. What you will observe is that the surf break is always parallel with the shore line. While waves at sea (or on a river for that matter) may approach the shore at an angle, they always curve into the shore to hit it in parallel lines. This is so, in part, because the (energy) flow that hits the more shallow water first is slowed and deflected upward, and the wave height increased, while the flow beyond continues at speed until it too hits the shallows. Surfers take advantage of this phenomena to surf at angles to the beach as the "shore break" will begin on the side nearest the shore and progress along its length but the break itself always parallels the beach.
N'any case, get yourself a hockey puck, a plastic board, and a grease pencil and you may find it's easier to lay a mark than without.