Stationary fishing gear includes lobster and hagfish traps, as well as gillnets and longlines. Because the hatches of the propeller clearing ports are typically placed above a vessel's waterline, some vessel operators may underestimate the risk of flooding associated with them. The assumption is that sea water will not rise up through a hatch opening that is above the waterline. However, because propeller clearing ports are placed in the same plane as the propeller in order that a fouled propeller can be easily cleared, any side wash from the vessel's propeller when it is operating will act like a pump and place considerable water pressure on the clearing port hatch opening. The pumping action of the propeller can, in some cases, be in excess of 1000 gallons per minute.
Photo demonstrates what happens when a vessel is maneuvered with a loose clearing port hatch cover.
This vessel's clearing port hatch is located on the weather deck, which makes flooding easy to detect. The Coast Guard advises fishermen considering the installation of propeller clearing ports to design the ports with the access hatch on the vessel's main deck. The Coast Guard strongly advises against the installation of clearing ports below the main deck in hulls that are not fitted with watertight bulkheads.