One of the strategic advantages of building a fleet in Erie was that the bay formed by Presque Isle was cut off from the Lake Erie by a sandbar, which prevented British warships from being able to enter the bay. The brigs "Niagara" and "Lawrence" both had a draft of , which was too deep to cross the sandbar. On 4 August, "Niagara" was pulled onto the sandbar using its anchor in a technique called and was lightened by removing its cannons and ballast. A pair of barges, called "camels", were placed on either side of the ship. The camels were sunk and secured to "Niagara". The water was pumped out of the camel, lifting the ship. By the following day, "Niagara" was safely over the sandbar and was rearmed; "Lawrence" was floated over the sandbar a couple of days before "Niagara". During the construction, the area was usually under daily surveillance by the British. On the day "Lawrence" crossed the sandbar, a pair of British warships, and , observed for an hour but failed to notice Perry's actions.