Tugboat, or Tug, a boat with a powerful engine used to tow or push ships and barges. Tugboats are usually small and are used mainly in harbors, rivers, and canals. They are generally about 100 feet (30 m) long and about 25 feet (8 m) wide. Most tugs use diesel or diesel-electric engines of up to about 2,000 horsepower. Larger, oceangoing tugs, up to about 300 feet (90 m) long, are used to aid disabled ships.