Otherwise you could just keep some nearby piece blinking so that the turn doesn't end before you've milked the cheat for all it's worth. Irrigating swamp takes 10 or 11 turns so this cheat is real handy. Repeat this process until you get where you want to go. I've also noticed what appears to be a glitch after doing this for a while in one turn. It seems the computer knows you're doing something not quite right, or the programming is straining with the large number of moves.
ALL ships can have unlimited movement.
This is really based on the original ship movement cheat, but is so much more powerful, and in a way so much simpler to implement, that I'm surprised it has not been written up before. In use, it is very similar to the movement cheat of sentrying units in towns. The simplest form of this will allow you to map the whole ocean with only two sails. Starting on the same square, move one until it has only one MP left, then sentry it. Move the other to the same square and unload it.