The speed of an inflatable fishing boat depends on the design of the inflatable and the size of the outboard motor used to propel the craft. A soft-bottom or RU-style inflatable, because it cannot plane, can only navigate at a top speed of less than five miles per hour. A six-passenger RIB with a deep V-hull can achieve speeds of 70 knots or up to 80 miles an hour, depending on weight and size.