Do you mean something like a calculator, where the input is your engine size/boost, desired tonnage, speed and range, and the output is basically how many engines you need to achieve that speed, how much fuel you need to achieve that range?
I was thinking something like what you have now, but tweaked a little. Right now you input Desired Tonnage/Speed/Range, plus Max Engine+Fuel. But there's no way to specify your engine design or to calculate the max speed/range as an output instead of an input.
Make it so you can input four out of these five:
Tonnage
Speed
Range
Max Engine+Fuel%
Engine Component Stats
And it then solves for the thing you didn't put in, using the same Max Space/Matching Tonnage slider that you have currently. So you can see "What percentage space would I have to devote to get to this speed at this tonnage with these engines," or "What speed could I get from X% of space using these engines on a design targeting this tonnage," or what tonnage would I have to be to get X speed out of these engines," and so on.
Make sense? I haven't gotten much sleep in the past few days, so I'm not sure how coherent I am, but hopefully this gives you an idea of what I'm talking about.
hmm, knowing the engine specs, the examples you have are as what I said, a calculator is needed if one of the other 4 listed there is unknown.
"What percentage space would I have to devote to get to this speed at this tonnage with these engines," -> known the tonnage and the speed, then the total engine power needed to achieve that speed is known. then the number of engines to achieve that total engine power is known. Then the total engine space is known, thus the percentage of engine space is known (and cannot be changed to optimize anything). Add or subtract fuel freely to achieve the range, since the engine and the speed is fixed, then its range is only based on how much fuel is added.
"What speed could I get from X% of space using these engines on a design targeting this tonnage," -> the goal is somewhat ambiguous here. if no range limit is given in this case, then the obvious optimal speed you are going to get is devoting the X% all to engines. Thus you can calculate the hull size one engine can push (engine size / X%), then you can get the speed in this case.
"What tonnage would I have to be to get X speed out of these engines," -> known speed and engine specs, then the hull size of one engine can push to that speed is known. Then multiply by the number of engines to be used, you get the full size of the ship.
I did plan for a calculator using the same UI on the ship optimizer page, and possibly other optimization goals. However, so far I haven't think of anything interesting. I will keep your ideas in mind.