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In further as it stands one can build a 'mothball hangar' that would normally have an insane maintenance cost but can considerably cut down on the maintenance cost of other ships sitting in port, using one designed for the ship above we have:
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In your example, you build a hangar that costs ~4k bp in order to save ~1.5k MSP per year, while requiring an additional 4,123 tons of maintenance capacity.
Assuming you need to build two maintenance facilities (60BP each) to provide the extra capacity, and with MSP costing 0.25 BP each, your annual savings represents a rate of return on your investment of ~9.1% while occupying 100k workers.
You also have an up-front cost of the shipyard needed to build that carrier (~11k bp, depending on your tech level), and the ongoing workforce that yard requires (almost 10m workers).
You are going to have to make (and use) a lot of these carriers and/or wait a very long time to recoup the cost of that yard.
There are simpler ways to get far better returns in the game.
For example, suppose instead of building that shipyard you build financial centers of equivalent cost.
Let's say 90 fincens. Costs 10.8k bp, and 10.8k corbomite.
Uses only 4.5m workers. Less than half what the yard needs.
Returns annual income equal to 27 times your "wealth per million workers" tech level.
Even if you are still at the starting tech level (100 per million workers per year), and have no wealth creation bonus from your governor or sector, that's 2.7kbp per year.
So a bare minimum rate of return of 25%, using half as many workers.
With a couple tech levels and a modest governor bonus, it's not hard to be making your investment back in two years or less.