An article contributed by Space Junkie
No problem. Considerable math follows, but it’s simple algebra. Still, sit back, grab something to drink, and here we go.
There are two ways to go about ensuring your ship has the speed you want. One way is easier but requires that you set the final tonnage of the ship ahead of time. The other lets you free form the tonnage but requires a more annoying engine calculation.
• The easy way means you set the tonnage ahead of time and it is set in stone, with the engine tonnage figured out first
• The hard way lets you pick the tonnage of the various other items first, like weapons and armor, except for engines, and figures out the engine tonnage last
Set the tonnage in your mind for the ship you want to design. For example, you want to make a 250,000 ton warship. No matter what you put into it, including engines, it must be 250,000 tons when everything is said and done. In this case, the engine calculation is easy. Suppose you want that ship to have 3 action points. Just add enough engines to result in 750,000 total thrust output (250,000 * 3). Let’s say you have Mk II Antimatter Engine technology completed. Those have a thrust rating of 750 each. To reach your goal of 750,000 total thrust output, you’d need 1000 of those. Of the 250,000 tons you have already determined your ship will be when it’s all done, you just used up 1000 engines * 100 tons each = 100,000 tons. You have 150,000 tons left to put whatever you want on that ship. That would be weapons, armor, defensive systems, fuel tankage, a Nuclear Transwarp Drive and whatever else other than engines.
100,000 tons of just engines was a lot out of 250,000 tons total, so suppose you decide that you don’t need it to have 3 action points, and that 2 is enough. After all, you need more remaining tonnage for weapons and armor if you are to successfully fight off your countless enemies. In this case you’d only need 500,000 total thrust output (250,000 ton ship * 2). 500,000 divided by 750 thrust per engine = 666.66, which you must round up to 667. If you put just 666 of those engines on that ship, you’d only have 666 * 750 = 499,500 total thrust on the ship, which is not quite enough. You need 500,000 and therefore you must put on 667 of them. This gives it 667 * 750 = 500,250 total thrust. Yes, 250 thrust at the end is wasted, but it has the necessary 500,000 and therefore the ship has the desired 2 action points. 667 * 100 tons per engine = 66,700 total tons used up for engines. That leaves 250,000 – 66,700 = 183,300 tons for other things (weapons, armor, fuel tankage, defensive systems, one Nuclear Transwarp Drive, whatever). Your ship is now speed 2 instead of speed 3 as in the first example, but it has 183,300 tons left over for the non-engine items instead of only 150,000. Your call.
You don’t know what the tonnage of your ship will be, but you still want it to be speed 2 at the end. You want it to be something around 250,000 tons but the exact final tonnage is up in the air. You decide that it must absolutely have 50,000 tons of weapons, another 50,000 tons of armor, 25,000 tons of fuel tankage, one Nuclear Transwarp Drive which is 25,000 tons, engines and nothing else. Okay, that’s 150,000 tons you’ve used up for weapons, armor, fuel tankage and a Nuclear Transwarp Drive. You want it to be speed 2 and all you have left is to figure out how many engines to put on the thing to get there.
Here are the formulas you will need for this:
150,000 + 100 X = the final total tonnage of the ship, whatever that turns out to be. X is the number of engines you put on the ship, but you don’t know what that is yet
Final tonnage of the ship * 2 = the total thrust output you must have to get it to speed 2. Let’s stick with the Mk II Antimatter Engine thrust output of 750
Let’s simplify those formulas to make them easier to read.
150,000 + 100 X = T
T * 2 = X * 750
By dividing both sides of the second one by two, it becomes:
T = (X * 750) / 2
Therefore,
150,000 + 100 X = (X * 750) / 2
Multiply both sides by 2 to get rid of that pesky divide by 2 on the right side:
300,000 + 200 X = X * 750
Subtract 200 X from both sides to get to;
300,000 = X * 550
Divide both sides by 550:
300,000 / 550 = X
Thus,
X = 545.45, which we must round up to 546
And that’s what you wanted all along: how many engines, Mk II Antimatter Engines specifically, that this ship will need. Ok, let’s finalize the design:
50,000 tons of weapons +
50,000 tons of armor +
25,000 tons of fuel tankage +
25,000 tons for one Nuclear Transwarp Drive +
54,600 tons of Mk II Antimatter Engines =
204,600 ton ship
Let’s check the math for the action point part. 546 Mk II Antimatter Engines * 750 = 409,500 total thrust output. You needed 204,600 (what the tonnage of the ship turned out to be) times 2 to get it to speed 2, which is 204,600 * 2 = 409,200 total thrust. You ended up with 409,500 total thrust, just enough to do the job with only 300 wasted. If you put one less engine on, at 545, you wouldn’t have quite enough, so always round up when you have a fractional amount of engines that you need.
Easy way got you precisely the 250,000 ton ship you wanted. Hard way worked out fine, with some more necessary calculations, but ended up with only a 204,600 ton ship. Maybe you wanted it to be bigger than that? Could you just add another 45,400 tons of weapons to get it to 250,000 tons? No, no, you can’t do that, because that extra tonnage would need more engines, specifically 2 times 45,400 more thrust to keep up, and that means some of that tonnage had to be engines, which complicates everything. You’d either pick the easy way, or the hard way, but you can’t just add more tonnage in willy-nilly or it fouls things up.
The nice thing about the easy way is that it’s easy. The nice thing about the hard way is that you ended up with 50,000 tons of weapons and 50,000 tons of armor on what turned out to be only a 204,600 speed 2 warship. That’s roughly 25 per cent of its final tonnage in weapons and another 25 per cent in armor. That’s more efficient than the easy way ship, which had exactly 20% weapons and 20% armor (50,000 divided by 250,000 for each of those). The smaller hard way ship has the same armor and weapons but is smaller. The bigger easy way ship has the same number of weapons and armor but is larger. To catch up to that 25% number on the easy way ship, you should have put 62,500 tons of weapons and 62,500 tons of armor on it. That’s simple enough – after all, in the speed 2 easy way calculation, you ended up with 183,300 free tons that you could do whatever you wanted with. Weapons, armor, fuel tankage, one Nuclear Transwarp Drive and whatever else. As long as it ends up at exactly 250,000 tons including the engines, it would be speed 2 – because you made absolutely sure to have at least 500,000 total thrust on the thing, and you figured out the # of engines first before adding anything else.
Personally, I would just make the thing 250,000 ahead of time, save all of the annoying calculations, and there you go. The easy way, and all your ships will end up with nice, round numbers of total tonnage, like 250,000 of 1,000,000 or whatever you choose, instead of oddball amounts that result from the hard way. Me, I like the easy way 😊 but both methods work out in the end.