That is the quick math. To get your totally correct hull speed, you would have to know your exact amount of wetted surface. Combined with the pitch of your bow (Bruce Number ) . This speed would only be good in slack water with no waves, as any wave action would change the speed. So unless the quick hull speed is drastically lower then the real speed though the water, I would just assume that the 1.34 multiplier is a little Conservative for your boat
!! WARNING !! The above information is to be used by intelligent people only. If you are Stupid, could be considered a moron, or otherwise. You are instructed to disregard this information and seek the help of a licensed and bonded professional.