tugboat, small, strongly built vessel, used to guide large oceangoing ships into and out of port and to tow barges, dredging and salvage equipment, and disabled vessels. Tugboats range in overall length from 70 to 210 ft (21-64 m), and their engines generate from 750 to 3,000 horsepower. Steam power dominated tugboat design until diesel and diesel-electric drives were developed. Most tugs are built of wood or metal-sheathed wood; the resiliency of a wooden hull prevents damage to both tugboat and vessel in berthing operations.