Give the number of 'bug' reports concerning the interaction of engineering and maintenance storage, I thought it would be worth explaining the mechanics in detail.

Ships have the following parameters

- Failure Modifier = (Hull Spaces * 0.04) / Number of Engineering Spaces
- Base Failure Chance = (Hull Spaces / 2) * Failure Modifier
- Maintenance Supplies = Round Down((1 / Failure Modifier) * (Cost / 2)) + MSP from Maintenance Storage

As can be seen above, the Failure modifier is based on a combination of size and engineering spaces. Two hulls of different sizes with the same percentage of space dedicated to engineering will have the same failure modifier. The base failure rate is based on hull size and failure modifier. If two ships have the same failure modifier, then the base failure rate will be linear with size. A ship of 10,000 tons will have double the failure rate of a ship of 5000 tons. The amount of maintenance supplies is based on cost, because a more expensive ship relative to its size will require additional MSP to fix failures. Two ships with the same failure modifier and the same ratio of size to cost will have the same amount of MSP per engineering space

Below is a table showing failure rates and MSP for different ship sizes, with the same ratios of cost, size and engineering percentages.

Here is the same table with only 1 ENG per ship. This creates a double problem, as the fail rate increases and the number of MSP decreases. Maintenance life falls exponetially.

So when you add maintenance storage and don't see the exact number of MSP added you expect, that is because you are changing the size, cost and engineering percentage of the hull, which affects base MSP and in turn the total MSP.