The circumnavigation of Eastern North America by water is known as The Great Loop. Also improperly referred to as the Great Circle Route (see definition of a great circle), the trip varies from 5,000 miles to 7,500 miles depending on the options used. The boats used range from personal watercraft (jet-skis) to 60-foot yachts. Both sailboats and powerboats are used but the most common boats are 34 - 45 ft Recreational trawlers. The main factorsthat govern the size of the boat is the limited draft (5 feet) in some locations on the loop and the height of one bridge (19 feet) in Chicago, Illinois. People traveling The Great Loop are known as "loopers." The number of people attempting this voyage is growing with the Baby Boomers reaching retirement age. In 2007 more than 150 boat owners notified America's Great Loop Cruisers' Association that they are planning to attempt the loop in the coming season.