You should take note of the specifics: The formula is for a displacement hull. You almost certainly do not have a displacement hull. A modified displacement hull, or semi-displacement, or semi-planing hull, but NOT a full displacement hull.
The calculations for a "fixed definition type" are fairly easy to do, thus you have the online calculator for a displacement type. But more complex types need far more detail and work to give an exact answer. Or rather, a more nearly exact answer. All of the calcs will be approximations. Very good approximations, perhaps, but still, not an exact answer.
Having said all of that, I cannot conceive of a situation where you wold need better than three significant digits of precision ( slide rule accuracy ). The actions of seas other than dead calm ( plus the water temp and salinity ) will cause even the very best o calculations to get thrown out of the window...
But here are a few things to keep in mind: The hull speed of your boat will be between the square root of the waterline length and 1.34 x that figure. It is easier to get in the boat and make a couple of opposing speed runs at the maximum speed your boat will go without any noticeable bow rise. then average those speeds together for a usable figure, and call it "hull speed".
Riding "on the hump" is always a mistake. You will encounter maximum stress, as well a minimum handling and fuel economy while "on the hump". Usually, you will also have minimum operator visibility.
Planing is a "feature" of hulls than can plane. It allows a boat to exceed "maximum true displacement hull maximum speed", while achieving a reasonable fuel burn. Only a full planing hull, on a full plane, can exceed the fuel economy of a displacement hull at below hull speed. All others ( read this as "every boat you might see at your marina" ) have a hull form that is somewhere between full displacement and full planing. Any calc you do ( other than a full blown engineering run ) will only yield an approximation.
As for those questions, to which you did not know the answer, my response is: for that particular calculation, yes, those numbers are important.
Or you could do like the rest of us, and use the approximation formula, as well as empirical test data to derive a useful, real world answer.
And "stay off the hump".
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Note: I am not flaming, but it is difficult to "speak in detail" without sounding like Sr. M. Attila on a rant.
The general question is answered simply, without all of the calculations: In any boat, operating the vessel without bow rise will offer best economy, as well as least strain on equipment.
A true displacement hull simply cannot exceed "hull speed" without truly tremendous amounts of energy. In practical terms, a displacement hull will never plane, but only dig deeper into a hole of it's own making as you increase the power.
Deep V, and "modified Vee" hulls are semi- displacement or planing hulls. They can exceed hull speed with "judicious application of power" to achieve a higher than hull speed velocity. The different types do this with varying degrees of economy, but all will first encounter "the hump" as speed increases, and most will get past the "water mountain ( what used to be the bow wave when the hull was acting like a displacement type ). Operating in this range is generally not desirable for many reasons, so it is best to simply exit that portion of your speed range promptly.
