The forces that acted on the outstretched centreboard were too great: the centreboard box tore out of the hull. The fact that the boat did not sink immediately is thanks to the inner wall of the centreboard box, which became the second side of the boat.
In general, the centreboards of the Iroquois catamarans built by Macalpine-Downie in the 1960s were retracted in heavy weather to take the weight off the centreboard box. The owner of the German yacht "Mona" had obviously forgotten to do this in the rush of the inclement weather - and lost the entire centreboard off the Dutch coast near Walcheren.
The 9.50 metre long catamaran was on its way back from Harwich to its home port of Brouwershaven with two people on board when the side of the ship tore away at the centreboard box flanged directly to the hull.
At half past six in the evening, the rescue cruiser "Koopmansdank" was alerted by the rescue station "Neeltje Jans" to come to the aid of a sinking boat. When it reached the "Mona", it was taking on water, but was able to continue its journey to the outer harbour of the Roompot lock at the mouth of the Oosterschelde under its own power, accompanied by the rescue cruiser. Given the extensive damage to the starboard hull, it is almost a miracle that the boat was able to reach the harbour without outside assistance.
Iroquois catamarans were among the pioneers of ocean-going double hulls in the late 1960s. The German Rudolf Wagner crossed the Atlantic single-handed in 1967 with his "Hobby", an Iroquois of the first design. Just over a year later, YACHT (issue 14/68) sailed an identical boat and capsized during test runs on the IJsselmeer in 6 to 7 force winds. After the test, experience gained from the sea emergency led designer Macalpine-Downie to make extensive changes to his design in order to offer an even safer and more stable touring catamaran in the MK II version. This improved model was also the one that lost the centreboard box, but this was probably due to the fact that the aged ship had now had to withstand the rough conditions on the North Sea for almost 40 years. Despite the safety changes in the second version of the Iroquois, it is surely a coincidence that the inner wall of the torn-off centreboard box also formed a second side of the ship and that the emergency ended so lightly.
