Question

which property of the pole star make it very useful for sailors

Answer 1

the property of the pole star that makes it useful for sailors is the stationary position of it in the direction of geographic north pole

Answer 2

property of a pole star is that it is always located in the north direction.
as the sailors got known that the pole star always located in the north direction they knew all the direction around them.
pole star help sailors in many unusual conditions such as when there is storm events and cyclones appearing in the seas or oceans in which the sailors are going along they got lost in that so the pole star help them to find their direction of their destination.