At 21.12 hours on 19 Aug 1942, U-217 tried to stop the unescorted and unarmed Sea Gull D. (Master Reginald Cozier) with a shot across the bow about 150 miles northeast of Curaçao, but the round actually hit the top of the sail. Because the schooner tried to escape the U-boat then opened fire, hitting the stern with a second round which destroyed the wheel-house, killed two passengers and wounded the master. A third hit amidships caused a panic among the survivors who now tried to abandon ship in the four lifeboats, capsizing two of them on launch. The passengers aboard were natives of St. Vincent hired by Lago Oil & Transport Co Ltd to work on Aruba and their khaki overalls were apparently mistaken by the Germans as uniforms of soldiers. About 10 minutes after opening fire, U-217 was forced to cease the attack when an aircraft approached from the south, strafed the crash diving U-boat and dropped four depth charges at 21.30 hours. Soon thereafter two more aircraft arrived and one of them attacked the U-boat when she surfaced after about two hours, dropping three depth charges at 23.45 hours. U-217 was damaged in the air attacks and forced to retreat to the north to carry out repairs.

In the meantime, the Sea Gull D. was kept from sinking by sailing close to the wind to keep the shell holes out of the water. After a half an hour the Greek steam merchant Kassos (Master Hartofilax) was spotted, which had been stopped by the same U-boat at 18.02 hours and released shortly thereafter because she was en route in Swiss charter. The schooner was tied to the starboard side of the steamer until the survivors and all valuable goods were transferred. The vessel proved to be too damaged to be towed, so she was cut loose and left behind to sink. Ten of the survivors went to the hospital on their arrival in Curaçao on 20 August and were joined by two of the 15 survivors that arrived at Curaçao in one of the lifeboats on 21 August. The master and 19 other survivors in a second lifeboat landed at Puerto Cabello on 24 August.