When I got this chart, there was no explanation. I found another source that says the ship hit the rocks and then drifted full circle back to the island. The speed at impact is about 10-12 knots. It slows to 6.5 knots very quickly, heads out to sea, spins full circle and then seems to drift back to the island. It's speed at that point is 0.5 knots of thereabout.
What I don't understand is why it lost power.