If you foul your propeller on a rope when going ahead and you can reach the offending line, it’s worth trying to unravel it as follows:
Grab the rope and pull steadily. Activate the engine ‘stop’ toggle so that it can’t start (decompress it if it has this facility). Engage astern gear and turn the motor over with the starter. This will revolve the shaft back against the way the rope came on, if it’s possible to turn it at all. Keep pulling the rope and with luck it will clear. If you’re luck’s out, you’ll have to find the ship’s useful diving mask and hop over the side with the bread knife.