the waters of Winterfell can be very dangerous. Expecially in the south, the water around the Amaranthine castle rock can be very very tricky. The stream is strong and so many boats have been crashed on the rocks in the past.
Here is me, at the helm of the Star of Winterfell, in a particularly bad day when I barely escaped losing the boat and maybe worse.
As you can see other ships have been less lucky
Be careful if you sail in the area