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Ship Maintenance Details
(note that this is from 2008. There may have been changes I'm unaware of.)
Engineering Spaces are 1 HS and 15 BP. There are smaller versions at 0.5 HS, 0.25 HS and 0.1 HS that can be researched.
Base Percentage Failure Chance per annum is Tonnage / 100 (or Class Size / 2) per year since overhaul. For example, an 8000 ton ship has a base failure rate of 80% per annum for every year since overhaul. So with 2.5 years on the maintenance clock, the annual failure rate would be 200%.
This is modified by the amount of engineering spaces within the ship, with 4% of hull space having no effect. So a ship with 2% of its hull space dedicated to engineering would have double the chance of failure compared to a ship with 4%. A ship with 6% would have only two-thirds of the normal failure chance.
So a 7000 ton ship would normally have a 70% annual failure rate for every year since overhaul. If total engineering spaces were only 2.5% of the total size the failure rate would be 70 x 4/2.5 = 112%. If the ship had 1.5 years on its maintenance clock, the annual failure chance would be 112% x 1.5 = 168%. This figure is shown on the Class Summary, showing the annual rate per year since overhaul and also the chance during a single 5-day increment. The Ship Summary has the same information but based on the actual time since overhaul for that ship.
A ship with no engineering spaces at all suffers a severe penalty and will have base failure rate equal to Size x 10, or Tonnage/5. So a 5000 ton ship with no engineering spaces will a 1000% annual failure rate. This is actually acceptable in some cases for tiny ships such as fighters. For example, a 225 ton fighter with no engineering spaces would have an annual failure rate of 45%, which is probably OK give the amount of flight time. Adding a 0.1 HS engineering spaces would drop that to an annual failure rate of 4%.
Here is the top section from the class summary of a destroyer with three engineering spaces (2.1% of its hull space). IFR is the incremental failure rate, which is the chance of a failure during a standard 5-day increment. This should give much more of an immediate feel for the impact on maintenance of your design decisions that under the previous rules
Scharnhorst III class Missile Destroyer 7200 tons 388 Crew 1272 BP TCS 144 TH 720 EM 0 5000 km/s Armour 5-33 Shields 0-0 Sensors 8/0/0/0 Damage Control Rating 23 PPV 54 Annual Failure Rate: 138% IFR: 1.9% Maintenance Capacity 331 MSP Magazine 360
If this destroyer adds two more engineering spaces (total 3.4% of hull space), it changes to the following
Scharnhorst III class Missile Destroyer 7300 tons 408 Crew 1304 BP TCS 146 TH 720 EM 0 4931 km/s Armour 5-33 Shields 0-0 Sensors 8/0/0/0 Damage Control Rating 25 PPV 54 Annual Failure Rate: 85% IFR: 1.2% Maintenance Capacity 558 MSP Magazine 360
When a failure occurs, it is applied to a ship as if it were a strength-2 internal hit, except that internal armour has no effect and a maximum of one system can be affected. Systems with HTK of 3 or greater will therefore have a greater resistance to failure. This is to balance the effects of failure between ships that have a few large, expensive systems compared to many small, inexpensive systems.
If a system fails, the ship's maintenance supplies are checked to see if sufficient supplies are available to fix the problem. The cost in maintenance supplies to make the repair is equal to the build cost of the system. I was originally going to make this the cost but in the end decided to produce 4x as many maintenance supplies for the same cost, which makes no difference in economic terms compared to the original idea but makes it a lot easier to see how far your current maintenance supplies are likely to go. If insufficient supplies are available, the system fails as if it was damaged by hostile fire. Note that secondary explosions are possible due to maintenance failure.
There is no valid reason for assuming that more expensive systems would require larger spare parts as opposed to simply more expensive ones. Many expensive spares parts in today's military are actually small in size. Therefore there is no reason to relate engineering capacity to the maximum amount of maintenance supplies that could be carried. Instead, a ship with 4% of its hull space dedicated to engineering will carry enough maintenance supplies to fix half the systems on the ship, based on cost. So if a ship costs 900 BP and has 4% engineering spaces, it will carry 450 maintenance supply points, enough to fix 450 BP worth of systems. A ship with 2% dedicated to engineering spaces will carry enough to fix a quarter of the systems while a ship with 8% will carry enough supplies to fix every system on the ship.
All the above means that larger ships will have higher failure rates, given the same proportion of engineering spaces, but that as they are more expensive they will generally carry more maintenance supplies. As a comparison, assume a 5000 ton ship and a 10,000 ship, both of which have 4% of their hull spaces dedicated to Engineering. They will have 50% and 100% failure rates respectively so the larger ship will have twice as many failures (on average). However, assuming the larger ship is twice as expensive too and therefore has twice the number of maintenance supplies, it will be able to handle twice as many failures. In effect, one 10,000 ship will cost approximately the same to maintain as two 5000 ton ships. The cost of individual failures on the larger ships will not be any higher if they are using similar systems to smaller ships. If they are using larger (and more expensive) systems then the HTK rules will come into effect as larger systems are more resistant to failure.
If a ship design requires additional maintenance supplies, or is perhaps a support ship carrying maintenance for others, there is a Maintenance Storage Bay system that is 5 HS, 15 BP, and can hold 1000 maintenance supply points. This has no engineering capability but it costs far less on a per-HS basis and holds more than double the usual amount held by an equivalent amount of engineering spaces on an early or mid-game warship. I may add a couple more generations of this system with increased capacity as regular engineering spaces will tend to hold a greater value of maintenance supplies at higher tech levels.
Maintenance Supplies are produced by maintenance facilities at a base rate of 200 per year per facility. 1 point of wealth, 0.5 tons of Duranium, 0.25 tons of Uridium and 0.25 tons of Gallicite are required for every 4 Maintenance Supply Points. The rate of supply point production can be increased through research. Production of maintenance supplies can be started and stopped in the same way as fuel production.
In terms of fleet orders, Maintenance Supplies are now treated in a very similar way to fuel. You can designate a ship class as a Supply Ship in the same way you can designate a tanker. There are five new orders as follows:
Resupply from Colony Resupply Target Fleet Resupply from Target Fleet Resupply from own Supply Ships Unload 90% Maint Supplies to Colony
'Equalise Maintenance Supplies': All available maintenance supplies will be distributed between all ships in the fleet, regardless of class, so that all ships have the same percentage of their maximum capacity.
An Equalise Maintenance button has also been added to the Task Group window. On the Ship window, manual maintenance transfer sections have been added to the Miscellaneous tab for colonies and other ships. On the Population window, the projected mineral use has been updated to include production of maintenance supplies for those populations with maintenance production switched on.
A ship has a damage control rating, which is equal to the aggregate ratings of all damage control systems plus the total hull spaces devoted to engineering. The three damage control systems (Damage Control, Improved Damage Control and Advanced Damage Control) are 3 HS and have ratings of 10, 20 and 30 respectively. So a ship with 4 HS of engineering spaces plus a Damage Control system would have a damage control rating of 14. This means that all ships will have a limited inherent damage control capability, even without a dedicated damage control system.
As before, you select which system you wish to try and repair on the Damage Control tab of the ship window. In any increment, the percentage chance of fixing the system is equal to:
((Seconds in increment / System Cost) x Damage Control Rating) / 10
So a ship with a damage control rating of 14 trying to fix a 30 BP engine in a 5 second increment would have a change equal to ((5/30) x 14) / 10 = 0.23%. In a 5 minute increment, the chance would be ((300/30) x 14) / 10 = 14%. In a one hour increment the chance would be 168% so success would be automatic. From a realism perspective this is probably optimistic, but allowing the chance of repairs within a tactical timescale makes for much better fiction :)
For damage control purposes, each system costs twice the number of maintenance supply points to repair as it does to fix a maintenance failure. So a 40 BP engine requires 40 MSP to fix due to a system failure as it occurs but 80 MSP to repair due to combat damage or a maintenance failure where insufficient MSP were available at the time.