floating-guard

They had built around the sides of the ship, and little above the surface of the water, a stage, or flooring, on which the sentries walked during the whole night, singing out, every half hour, "all's well." Beside these sentries marching around the ship, they had a floating-guard in boats, rowing around all the ships, during the live long night.

Benjamin Waterhouse - A Journal of a Young Man of Massachusetts, 2nd ed.: Late A Surgeon On Board An American Privateer, Who Was: Captured At Sea By The British, In May, Eighteen Hundred: And Thirteen, And Was Confined First, At Melville Island,: Halifax, Then At Chatham, In England ... And Last, At: Dartmoor Prison. Interspersed With Observations, Anecdotes: And Remarks, Tending To Illustrate The Moral And Political: Characters Of Three Nations. To Which Is Added, A Correct: Engraving Of Dartmoor Prison, Representing The Massacre: Of American Prisoners, Written By Himself.