Strong waves pounded the outer sea wall (breakwater) until a large section collapsed.

Thereafter the sea simply ran over and into the port and the now unprotected yachts didn't stand a chance.

A thread in another forum contains multiple links and videos for anyone that is interested:

http://www.cruisersforum.com/forums/f106/storm-in-italy-marina-rapallo-devestated-209552.html

The storm Adrian hit Ligurian coast on October 29 and the Low crossed northern Italy and then Switzerland.
In the Ligurian Sea winds were forecast up to 40 knots and more (mean wind/10 minutes which corresponds to « Wind » layer on Windy.).

Gusts at more than 80 knots were forecast on Corsica, same in some parts of Nothern Italy as shown by Gusts layer.

In southern Corsica a gust was measured at 102 knots for a mean wind at 48 knots. Such a gap is very unusual.
It is probable that the damage to the boats on the Ligurian coast was more due to the sea than to the wind itself.
The damage on the trees are due to the gusts. But it is very difficult to predict them especially in the mountains.

https://community.windy.com/topic/7052/arctic-outbreak-across-the-western-europe