What are limpet mines that were used to hit tanker carrying Indians in Strait of Hormuz?

A Panama-flagged tanker carrying 27 Indian crew members was hit by two limpet mines in Strait of Hormuz on Friday. Limpets are small, cone-shaped sea snails that hold onto rocks tightly. They are not supposed to cause large scale damage like sinking an entire ship. Rather, they immobilise the ship concerned and take it out of the action plan.