When the pitot tube that provides water pressure information to run your boat's speedometer clogs, it's an annoyance. While the Mercury SmartCraft display is able to extract speed data from a GPS receiver on boats so equipped, if your boat is not equipped with a GPS unit, it will have no source of speed information. You can avoid the fines you might incur from exceeding boat speed limits, where imposed, and keep your speedometer working properly with a compressor and a small piece of wire.
Items you will need
Compressor
Thin piece of wire
Inspect the pitot tube opening, located at the leading edge of the lower unit. To clean debris from the pitot, press in on the speedometer hose junction and pull the hose out. This opens both ends of the tube, and allows you to blow compressed air through the pitot with low-pressure compressed air from a compressor.
Run a thin piece of wire through the pitot tube to ensure it's open, and to ensure it drains completely if wet debris was trapped inside.
Reconnect the pitot tube before storage.