The Navigation Acts supported the system of mercantilism because they further limited the way that the colonies could trade, which meant that the colonists could not afford to compete with the British manufacturing companies and were essentially forced to produce specific goods. Mercantilism was a policy that the British instituted with the colonies in order to ensure that everything the colonies did from an economic standpoint, would benefit the British.
In Mercantilism, laws are passed that dictate where a colony can ship its goods as well as add tariffs and duty tax on items imported from other countries so that the colony must buy goods from the mother country. The American colonies were forced to buy British goods because those were the goods that they could afford. By using Mercantilism, the British were able to obtain most of their raw goods from the American colonies, create their products and then ship those products to countries around the world in addition to selling them to the colonies.
The Navigation Acts specifically passed four new rules that restricted the colonies ability to trade even further than the initial mercantilism laws had done. However, the colonists began smuggling goods around the restrictions. This would eventually be one of the reasons why the colonists wanted to rebel and start the American Revolutionary War.