Both Free and locked.
Hello Aubrey,I assume you have a fixed bladed propeller.?. Your question goes much deeper and is very technical for both the vessel speed and for the transmissions health and well being. First the boat speed. The answer is both locked and freewheeling. If the propeller is completely exposed to the water flow, such as a strut hung prop and shaft, allow it to free wheel. If the propeller is located in an aperture or located behind a massive deadwood lock it down. Second and most important!!! Check with the transmission manufacturer to determine if the transmission is capable of free wheeling. Most lubrication cycles for most modern transmissions do not pump when the engine is not rotating the transmission. This could cause excessive wear and massive heat over long high speed free wheeling times. You may be required to run the engine with the transmission engaged every 8 eight hours for 1 hour to lubricate the transmission parts. Third. Almost all mechanical transmissions lock up in reverse only. Forward gear does not lock the transmission. If the transmission is hydraulic it will free wheel in both directions and not lock down. Hope this helps. Kevin