the curve is the easy bit.
the sharp turn isn't. basically it's been partially cut and bent then left for the tree to heal itself before growth returns to normal.
80km from the cost, but next to a canal so ship building is unlikely but not impossible.
pine trees, so not unusual for either boats or walking sticks.
80-100 years old, not many wooden hulled large vessels being made then but plenty of smaller boats still with a wooden keel or risers.
both seem a likely but not ideal reason for it, the idea that it's from a felled tree left to rot seems unlikely though, they aren't in a nice straight line like the article suggests. the usage could easily be for building construction or such like.
which I guess is why nobody really knows why they are that way.