BRASILIA - At least 13 people drowned when an overcrowded boat capsized early on Friday on a tributary near the mouth of the Amazon River, police said.Divers were searching the hold of the sunken vessel for about a dozen people who are still missing after rescuers picked up 46 survivors.Most of the passengers were asleep in the hold when the boat capsized in strong currents on a curve of a river snaking through Marajó Island en route to the port city of Belém, capital of the northern state of Para.