Travel on water is generally measured in knots (nautical miles per hour). The fastest speedboats today are cruising briefly at speeds over 200 miles per hour. However, a lot will depend on the type of cargo and the size of the vessel. Most boats comfortably travel at around 18-20 knots and cruise ships (weighing in at around 80,000 tons) cruise at about 13 knots. It depends on the horsepower. A boats speed all depends on the pitch of the wheel or propeller. It has a LOT to do with the hull too. I'll give you a real-world example: Marty Stone is a professional bass angler who uses 200-horse Mercury engines on his boats. He can go 75mph, no problem at all. Bass boats are made so very little of them is in the water when they're on plane. I went to WorldCat's website and looked at prop test data for the smallest center console they make that runs over-200hp engines. Those boats come out of the factory with two outboards, and there's not a configuration and power setting available that will push that boat faster than about 58mph. Horsepower ain't everything, folks; if it was, the 77-foot Hatteras with twin 2400-horse MTU diesels could outrun an unlimited hydroplane. The 175,000 pounds the boat weighs might have something to do with its relative pokiness.