Question

what is the sandy hour glass referred by salarino ? what would the hour glass make him remind of ?

Answer 1

In ancient days a glass full of sand was to indicate the passing of time.
The sight of the sandy hour glass would remind him of danger of hidden sand banks and shallow water. The danger of the ship getting stuck in the sand where the water is not sufficiently deep for a ship to sail over it smoothly.
Hope it helps you. . . . .

Answer 2

Sand running from one half of of time glass into the other reminded him of the sand banks and shallow water-- that place his ship can be wrecked, damaged or stuck.