There may be many reasons.
When the boat is dead in the water, the sharks may start to wonder whether thatīs food at some point. With ramming and test bites they try to find out whether the vessel is food and still alive enough to hurt the shark. The boat has about the right size for a whale carcass.
Some species are territorial and keep other potential predators out of their territory.
Last but not least bait fish may seek shelter under the boat. Sharks may collide with the boat when hunting for the bait fish.
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If it isnīt broken, it doesnīt have enough features yet.