We will start by breaking down the boat into components, and deal with each in turn. In this way we can simplify the process of understanding.

The Hull is not considered as a hull when selecting a propeller, merely as an object that has to be pushed through the water against the resistance of the water, so we do not care if the hull is a trawler or cruising yacht, we only care how it reacts when being pushed through the water.

Similarly, the Engine is no more than our power source, all we need to know are some specifications, it doesn’t matter what make or model of engine you use, as long as you know the specifications.

The same is true for the rest of the components.

The sole factor that is of prime importance is that you enter the correct data, there is no point whatsoever in proceeding further unless you have accurate data. If you enter a guess with the assumption that it is “good enough” you are mistaken, as that error will be compounded and compounded again as the calculations progress and the final answer will be wrong enough to be completely useless. The danger is that you do not realise this and treat such an answer as gospel truth, so please take great care with your base data.