After a long but rewarding life in an office cubicle, Sally the office worker became Sally the retiree. Feeling unfulfilled, and with ancestors who had served admirably in the Navy, Sally the retiree decided to take to the sea; Sally the retiree found a new hobby and became Sally the sailor. Sally the sailor wanted to test her mettle and decided to sail the outline of Bermuda Triangle leaving from the third mooring from the end of the dock of the Miami Marina.
Sally the sailor's first leg took her, with a favorable wind, to Bermuda in just 120 hours.
After resupplying, Sally the sailor prepared for the most challenging leg of the trip. The constant, southern trade winds forced Sally the sailor to change tack again and again. Battling the head winds added 2 days to a journey that Sally the sailor planned to only take another 120 hours.
The final leg back featured many near-windless days and nights. sally the sailor planned ahead when resupplying in Puerto Rico and went ahead under engine power in order to complete the final leg of her journey in only 10 days.
Once Sally the sailor arrived back at the third mooring from the end of the dock of the Miami Marina, she recounted her trip with Ed the marina head. Sally the sailor then proudly showed Ed the marina head her calculation of her average velocity for the triangle trip. Upon seeing this, Ed the marina head laughed and said her calculation is wrong and that the answer is a much lower number. Sally the sailor was quite sure she accounted for boat speed, wind speed and direction, ocean currents, and even the coriolis force. Ed the marina head assured her that her answer was still too high. What is the actual answer? And what mistake did Sally the mistake maker make?