The length of a trip halfway around the world by boat depends on the weather conditions, size and type of the boat and the starting and ending points. Some cruise lines offer 106-day around-the-world packages, so one can estimate that a cruise halfway around the world takes about 53 days.
The Clipper Round the World Yacht Race is 11 months long. Dividing that trip in half would place a trip halfway around the world on a boat at about 5 1/2 months.
Sailing around the world is a different situation entirely. Since a sailboat's maximum speed is determined by the length of the boat and the waterline length, the amount of time required to sail halfway around the world, assuming perfect conditions, depend on the individual boat specifications. An around-the-world trip is 21,600 nautical miles; therefore, the total journey calculation could be determined by taking half that number and dividing it by the maximum knot speed of the vessel.