The narrow, crooked sea between Tåsinge and Fyn is called Svendborgsund (Svendborg Strait). Although “Sund” originally meant “to swim”, the strait has always been one of Denmark’s most navigated seas. It stretches 13 kilometres from Grasten in the east to Lehnskov in the west and takes its name from the market town of Svendborg, which grew around one of the best natural harbours in the Archipelago.
Svendborgsund is long and full of dynamic currents. The current is highly irregular, as it is much affected by the wind. Strong winds from the northwest usually results in westerly currents with speeds of up to six knots, and the same applies when the strong winds come from the east. In extreme cases, the current may follow the same direction for several days. If the wind conditions are calm, however, the current changes direction every six hours with speeds of 2-3 knots.
Although the strait has always been difficult to navigate, it was the route to the rest of Archipelago – and to the rest of the world. The numerous reefs and flats, sudden changes in depth and the ever-changing currents have combined to make the passage a hazardous – but at the same time beautiful – voyage. The fairway is steeply lined by wide, almost dry shoals on both sides, and winds its way around flats and islets. Except for a steep forested cliff between Øksnebjerg and Christiansminde, the Fyn part of the shoreline lies low with gentle green slopes.
In the 1960s, a chain of bridges were built, which connected Langeland and Fyn, and in the process connected Tåsinge, Langeland and Siø by land. Svendborgsundbroen (The Svendborg Strait Bridge) was completed in 1966, thus ending the ferry services in the strait. From the 1930s up until 1966, the crossing from Svendborg to Vindeby on Tåsinge was the second most busy ferry service in Denmark behind the Great Belt crossing. As long ago as the early 1960s, a million cars crossed the strait on the ferries each year!
The important strait has always been of vital importance for those in power. Several castle mounds dating back to the Middle Ages line it. On Tåsinge, the centre of power was Kærstrup. Further to the west, at the bend of the strait near Svendborg, the two Middle Age castles of Horseslot and Saksenborg were located very close to the shore. Saksenborg had a good location on a little spit reaching out into Svendborgsund south of the islet of Iholm, and from here, controlling the navigation of the strait was easy. The same can be said of Horseslot, which was located in Horseskov one kilometre along the coast further to the east. At different periods throughout time, these castles were able to collect duty or practice pirating. On Fyn, Skattertårnet in the fortified town of Svendborg as well as the royal castle of Ørkild have kept an eye on the strait.
The castles all originate in a period of time when The South Fyn Archipelago was very vulnerable. In the 12th century, Wendish pirates ravaged the area, and later, the Archipelago was a borderland between Denmark and the duchies of Sleswig and Holstein.
The strait used to be navigated by packet boats and ferries. The ferry called “Helge” from 1924 is still in service. “Helge” calls at five ports: Grasten, Troense, Valdemar’s Castle, Vindeby Øre and Christiansminde.