The path in between the icebergs was wide. However, since the part of the iceberg submerged underwater was much larger than above, and under the flow of the current, the area of impact became much larger.
The large pieces of broken ice fell into the seawater. As they were more lightweight, they moved along the sea faster than the main body of the iceberg. Under the impetus of the current and the wind, the chunks of ice quickly and continuously rushed forward.
Most parts of the glacier did not strike the pirate ship. However, there were so many broken pieces of ice that it was inevitable some of them would collide with the ship.
The pirate ship was not a small boat but those ice floes were not small either. In addition, because the density was high and the mass was large, the impact generated on hitting the pirate ship would be huge.