Israel’s legal weapons blockade is legal, and those ships are subject to search and seizure, as it clearly says in the laws of blockade, especially during a war that Hamas initiated.
A blockade, an act of war whereby one party blocks entry to or departure from a defined part of an enemy’s territory, most often its coasts. Blockades are regulated by international law and custom and require advance warning to neutral states and impartial application.
Hamas has declared itself an enemy of Israel since they were elected and before. They have been very honest about their objective to destroy Israel and to replace it with an Islamic State.