In terms of speed, USA MARC-V known one of the fastest boat(120+km/h) in military. Turkish MRTP is also competing with it and reaching similar levels. That's why MRTP family sells like appetizer around the World.
No vessel (Boat,Aircraft,Tank,APC,Car) ever operates at highest stated speed. If maximum stated speed is 120 Km/hr, optimum speed would be below 100Km/hr.
Is it even possible 203kmh on water(Sea)?
Of course not.
At this speed there is 90% chance that said boat would dissociate before leaving port.
Even in controlled setting like speedboat races, accidents are common (there is always one or more in every race) for 200+ Km/hr speed boats.