Sorry, there is a formula but it depends on many things. Primarily wetted hull length. A 20' v planing hull might have a displacement hull speed of 5.5mph, or less. It's easy to exceed the hull speed on a planing hull as you get into a partial planing condition with enough power. That's why your fuel mileage is atrocious at speeds like 12 mph and gets so much better when you are fully on plane. So if you have an inflatable powered by a 4hp you can often go faster than it's hull speed but it might take a 8hp to plane and could then run at half throttle. With a pure displacement hull you will eventually just suck the hull into the water with more and more force on it.
Look at the wave along the length of your hull One wave length is your displacement maximum speed from the bow wave starting to go up to the dip in the middle of your side to the wave finally going back to water level at the transom. You will also feel the sway side to side at the back of the hull close to your displacement speed as the transom creates vortex shedding that pulls the transom slightly from one side to the other.
Speed-length ratio (speed in knots divided by the square root of the waterline in feet) is the formula. A record level single scull might have a ratio of 2. A typical sailboat might have a ratio of just 1.3. Entry and exit angles matter as does displacement
