What are the most dangerous icebergs?
All icebergs are dangerous to shipping but depending on size, shape, and location some icebergs can be more troublesome than others. Obviously, icebergs nearest the Atlantic shipping lanes are of greatest concern to mariners. Large icebergs, because of their great mass, can inflict the most damage on a ship. However, they are usually easy to detect on a ship's radar and therefore can be avoided.
On the other hand, the smaller an iceberg, the harder it is for ships to detect and avoid. For example, many growlers or bergy bits are mostly submerged and are about the size a small vessel. These "hidden" icebergs can cause a significant amount of damage.
Lastly, an iceberg's shape is a factor. A smoothed iceberg can be more difficult to detect.