I read about an incident back in the 60's or 70's involving a similar situation,but with a freighter and a MUCH larger giant jelly fish. The ship was traveling through rough seas and the bow dipped down into a big oncoming wave which deposited an enormous jellyfish weighing tons onto the bow of the ship. One man was stung by the huge tentacles and died. It took the combined efforts of the ship's crew and another ship that had responded to wash the giant jellyfish over the side using firehoses. I'll try looking for a link to this story.
ok I found a link to the story here
http://theshadowlands.net/serpent2.htm
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In 1865 a giant lion's mane jellyfish was found in the Massachusetts Bay. The bell was 7 1/2 feet and it's tentacles measured 120 feet long and a width of 245 ft.. In 1973, the Kuranda, collided with a giant jellyfish that was estimated to have weighed 20 tons. The Captain of the Kuranda, Langley Smith, estimated the tentacles length to be over 200 ft long. With the aid of another ship, the giant jellyfish was forced off the front of the ship. A sample of the slime left behind was analyzed and found to be from a lion's mane jellyfish. One crew members died during this encounter after being stung by the creature. In 1969 2 divers encountered a jellyfish that they claimed was 150 to 200 ft in diameter. There also have been reports of giant jellyfish attacking small boats and pursuing divers.