Beadnell Bay and High Newton-by-the-sea (Northumberland) are about 86 miles and less than 2 hours drive from Edinburgh. Beadnell has an enormous sandy beach, backed with dunes. The beach is open to the North Sea, and can get some serious wave conditions. It is an interesting place to sail. I usually sail at the Newton end of the bay in a Southerly or South Easterly wind. There are low rocks at the end of the bay which give some much needed shelter from waves at the launch point.
This area also gets good Northerly winds, in which case, you would go to the Northern end of Beadnell Bay, which is sheltered by the harbour. There are some rocks in the bay, with clear water channels between them. You may have to carry your kit some distance along the beach to get clear of the rocks.
Windsurfing around Edinburgh