Occupying your mind with water
Long time ago I went to one of this slide shows about traveling in an alternative way. The guy talking about his travels and adventures was Waldthaler Tilmann. He explores the world riding his bicycle and even if it is not the same as sailing I learned something useful. Answering a question about how he masters boring and long distance riding on the bike, for example through the desert he explained the following:
Before he starts in the morning he picks a topic, for example water and during the day he thinks about everything connected to it, from the chemical formula to the liter he uses or how much liters he needs a day, to the daily moments where water is used and so on... this helps him to stay focus and avoids the mind wandering around without target making exhausting rides even more difficult.
Its an interesting approach maybe you want to try it once.