When Rick and two of his buddies were about 20, with just enough college to make them dangerous, they decided to do a similar thing -- they were going to paddle from Cincinnati to New Orleans. They turned a canoe into a trimaran, using gutter downspouts for amas (crimping the ends).
They had it all figured out: They would rotate on paddling, with the guys in the front and the back working while the one in the middle rested. Calculating the currents of the Ohio River and the Mississippi River, they figured they would be in New Orleans in 30 days.
After the first day of paddling all day, they thought they had gone a long way. They pulled out that evening on the riverbank and went to a local beverage establishment to get a beer. They asked where they were and found out they were still in Cincinnati. At the end of a week of paddling, they only made it to Louisville, Kentucky -- that's where they gave up their mission, pulled out, and left their "trimaran" at a local marina.
Their mistake had been in calculating the current going with them but in neglecting to calculate the wind going against them -- the prevailing wind in that area is out of the southwest. (This was before Rick had ever gotten involved with sailing, or he obviously would have considered that factor.)