Toward the end of a hike along the coast, I came across this turtle feeding in a shallow tidal area. There was good grazing to be had, but the problem was that the ledge was continually swept by incoming waves.
The turtle would swim in and access the ledge from the shore side (on the right in the top photo). Then he lumped forward to where the good grazing was and buried his head in it.
Waves would surge in and sluice over him (below). Sometimes, the receding wave had enough oomph that it would wash the turtle over the front edge of the ledge. Then he’d swim around and start over again.