So in other words there's no max speed since we're not talking about fixed power.
Power isn’t what’s important. It’s power per volume/weight. If you have an infinitely dense power source then you can send matter at the speed of light through any medium. Is this really an important point to make?
Edit: Oh I see what’s going on above in this thread. It’s nuanced but I believe the original point was that in the Real World with Real Power Sources you have a Real Top Speed. You can’t just always dump more power into your ship to increase it and the right way to increase the max speed is to control hull dimensions.
Hull speed is a pretty simplistic approximation of the actual physics behind it, but generally the rule holds: A displacement hull cannot exceed its hull speed. What will rather happen is that the bow wave will pile up and eat your energy. It’s actually a problem if a very powerful boat pulls a smaller one, the bow wave on the smaller boat piles up, making the smaller boats bow rise up until the stern slips under the water and it sinks. (Or something else gives in under increasing strain before that happens)
Now, other hull forms can be built: glider hulls for example that glide on the water surface (think fast sports boats etc.), but scaling those up will certainly be problematic if you’re trying to aim for high carrying capacity. Cats/Multi hull designs sort of cheat the physics: the determining factor is roughly the length of the water line and multi hull designs obviously have more waterline for a given total length.
You mentioned even with unlimited amount of energy and power the speed is still capped and limited by Hull Length and Shape.
This reads to me if I could get a Nuclear Fusion reactor in my ship that has 10 times the power my Max Speed would still be the same. This doesn't sound right to me.