Two sites for Federal batteries were selected upriver from the fort to cut it off from Savannah, just as Lee had anticipated. The first was at Point Venus at the east end of Jones Island along the north bank of the Savannah River North Channel. Confederate Commodore Josiah Tattnall had sunk a stone schooner to obstruct the northward channel connecting the river to the Union-held Port Royal, and he patrolled the river with Confederate gunboats. The Federals had to clear the obstruction on their most direct supply line first; it required three weeks. A camp and supply depot was established on the next island north, Dawfuskie Island.