Righto, the previously-promised design thoughts plus the DB so you can check it out if that's your thing. This is probably going to sprawl into a rather long post (ending update: yes, yes it has!)
TL;DR: spreadsheets were unsurprisingly used to optimize the design and I had to cheese the MSP calculations to make it fit in the 6,800km/s band; the DB is attached at the bottom.
Assuming some familiarity with the given ten design categories, let's first break the list down into groups.
Starting with the mandatory grouping:
- 6,000t or less
- 4,000km/s or more
- 1 layer of armour or more
- 6 months deployment time or more
- 2x max repair MSP or more
- 4 PPV or more, plus necessary crew, BFC, and power plant
- 96kkm BFC or more
- 9bkm endurance or more
- 192.5t of sensor dead mass across two sensors, plus necessary crew
Following up with the finite grouping: (we can get points here, but only a finite amount per category)
- up to 2 additional armour layers at +2 DP each
- up to 3 additional months deployment time at +1 DP each
- up to 2 additional max repair at +1 DP each
- up to 32kkm additional BFC range at +2 DP per 16kkm
- up to 1bkm additional endurance at +1 DP per 250mkm
Lastly the infinite grouping: (we can add as many as we can fit in 6kt)
- +1 DP per 200km/s above the minimum
- +0.5 DP per 1 PPV above the minimum
Next up, a couple of notes on the above groups. First, some of the negative DP categories have been flipped around to gain points starting from the low design value rather than lose points starting from the high design value; this is for simplicity of comparison but will not change the final DP value of the design when submitted. Second, the groupings omit yearly MSP usage (it's difficult to group but we'll extract points from it) and BFC tracking speed below hull speed (don't do this; adding BFC tracking mass is very cheap compared to the DP penalty).
With the categories grouped so they can be compared to one another we can start breaking down how much each is worth in DP (or, more specifically, how much tonnage it will cost to gain +1 DP from any category). As the mandatory and finite groupings can't fill the ship on their own (we could leave the ship small but the DP total is poor) we'll want to figure out which category in the infinite group will be used to fill the ship. This will also allow discarding of any finite group member that's worse than the preferred infinite group filler. For that, we look to speed and PPV and brute-force some calculations in a spreadsheet. I won't include the spreadsheet or the calculations here but I will include the final values.
For our two infinite grouping categories we can calculate their mass per DP efficiency:
- on a full-size 6kt hull, it costs roughly 90t in engine+fuel mass to add 200km/s (+1 DP) for the required fuel endurance; engine count, size, and %power optimization is even taken care of
- PPV is a fixed value per HS: 1 PPV per 1 HS, rounded down, for +0.5 DP; this means +1 DP is 100t of weapon mass (UNE-provided lasers are an even 200t for +2 DP)
Notably these values omit a few things. Crew mass is omitted for speed while crew, reactor, and fire control mass are omitted for PPV. Additionally, on a ship smaller than the full 6kt design limit, it takes roughly proportionately less mass to add 200km/s. However as engine+fuel mass per DP are already superior to PPV mass per DP we can safely ignore the extra mass sources of PPV and the chance of building a smaller ship for speed and choose to build solely for speed regardless. For verification purposes, testing designs that try to use PPV instead of speed as filler mass do end up with fewer overall DP but the analysis provides additional confidence; the same can be said about using a smaller ship with less available payload mass.
With our 90t per DP engine+fuel filler mass locked in we'll next want to to take a look at the categories from the finite grouping; any categories here that are cheaper to include than engine+fuel we'll want to make room for in our total payload mass while any categories that are more expensive than engine+fuel can be discarded from the ship and left at their minimum required values.
Calculating mass per DP efficiency for the five finite grouping categories: (no spreadsheets were needed for these thankfully, just tinkering in the Class Design window)
- armour layers on a 6kt ship are 370-375t for+2 DP, or 185t for +1 DP, nearly twice that of engine+fuel; instead of +4 DP for +2 armour, we can swap to +8 DP for engine+fuel
- one month of deploy time for a fully crewed 6kt vessel that's likely to be all engines and one gun is 15-20t; we absolutely want to include a full 9 months of deployment for +3 DP
- our max repair will be about 200 MSP, which fits in 20t of maintenance storage (with no crew) for +1 DP; it's a no-brainer to include a full 4x max repair in the design for +2 DP
- using a 6,800km/s (3.4x) single-weapon fire control, 16kkm range steps change the mass by 21.25t for +2 DP or 10.625t for +1 DP; also a no-brainer to run max 4x range for +4 DP
- using those same 6,800km/s 175% engines, 250mkm of fuel for +1 DP is a little less than 20t of fuel, so we'll add the 80t of fuel to hit the full 10bkm range for the full +4 DP
The above analysis does allude to the engines that will power the final ship design but before we walk through the different engine design options let's go back to the design categories and list off the complete features list that those engines will need to move:
- still 6,000t or less
- as much speed as possible
- only 1 layer of armour
- full 9 months of deployment time
- full 4x max repair of MSP
- only 4 PPV from a single UNE-provided laser, plus a 2.04 power reactor because I'm not sure the 0.5t-lighter 2.00 power reactor is legally enough (it's technically 1.99588 power!)
- max 128kkm BFC, tuned to track at the ship's speed (6,800km/s in the final design)
- full 10bkm endurance
- still 192.5t of sensor dead mass
Notably the yearly MSP is still absent from the above list; there are only nine bullet points here while the initial design categories listed ten. Due to the discrete nature of engine size we're going to have "spare" tonnage for each ship design that leverages a given engine design; engineering space goes into that tonnage and is used to both bring the MSP capacity up to 4x max repair but also to bring the yearly MSP down. Largely, we'll trade engineering space out for maintenance storage in to hit our 4x max repair capacity while keeping yearly MSP use as low as possible.
Starting up with engine designs by returning to the spreadsheets, mass-optimized engine+fuel tonnage for each 200km/s speed band (4,000km/s, 4,200km/s, etc) almost exclusively prefers the max 175% power. The exceptions to this lie on the very low end of the spectrum: 4,000km/s engine+fuel is lightest at 165% power, while 4,200km/s and 4,400km/s prefer 170% power. Any discrete speed bands starting at 4,600km/s (or higher) use the least mass possible while running the maximum 175% power tech with the extra fuel necessary to feed them to obtain the chosen 10bkm endurance.
With engine %power determined we can start prototyping engine designs and building the rest of the ship around them. Due to the engine size tech we'll exclusively be using twin engines; a single max-size 40HS engine can't even push a 6kt ship at the required 4,000km/s, while exceeding twin 40HS and rolling over to triple 27HS engine is so large that we can't fit the features list into 6kt of ship any more. A note on unit size, we'll stick with fewer, larger engine units to save fuel rather than many smaller engine units to save on max repair as fuel greatly out-masses MSP.
Iterating with engine prototypes, we'll find that twin engines smaller than the "ideal" leave too much ship size on the table (and therefore move slower and deliver fewer DP than simply adding a larger engine), while twin engines larger than the "ideal" eat up too much ship size and actually cost us DP in the design because we can't get enough engineering space on board any longer. I've found the sweet spot is twin 34-36 HS 175% power engines; smaller engines run slower while larger engines burn more MSP.
Discussing those three engine options then:
- twin 34HS engines leave us with a significant amount of "spare" tonnage and allow engineering space to lower yearly MSP to 50 and move at 6,400km/s for a total of 24 DP
- twin 35HS engines leave us with less "spare" tonnage and require backing off the engineering space; this design runs faster at 6,600km/s but loses yearly MSP to 75 for the same 24 DP
- twin 36HS engines typically use too much of the "spare" tonnage and back off yearly MSP to 125 at 6,800km/s for a lower total of 23 DP. However, it's very close to working
Due to the discrete nature of designed DP it's not out of the question that other entrants find one of the 24 DP designs and it becomes a race for optimizing that design, in order of the tie-breaking criteria. The first criteria, and the only one we'll care about, is speed. This is where that not-quite-there 6,800km/s twin 36HS designs comes back: squeezing this design to work and get it up to 24 DP by saving mass and getting the yearly MSP back down to 100 was the goal. For this we'll turn to a better understanding of failure rate mechanics that I've been unable to find but that I could iterate on in the Class Design window.
To that end, a few design options that allow movement within a metric's tonnage while changing values other than that specific metric:
- I prefer to using 50t Standard fuel tanks. They're the smallest fuel tank that retains HTK and have the highest HTK-to-mass ratio as a result; doubly useful given we have no armour
- v2.5.1 still has crew requirements for 50t and 250t maintenance storage while only the 250t version has HTK; as a result, I fill with 10t maintenance storage to lower crew tonnage
- yearly MSP usage has some manner of correlation with component size and unique component count; we'll want to bloat the vessel with many smaller components to lower yearly MSP
The final above bullet point is of particular interest for squeezing the twin 36HS design. While engineering spaces use more crew per unit mass when broken down into smaller components and are therefore disqualified from lowering yearly MSP by splitting them, neither fuel tanks nor maintenance storage have any crew requirements and are therefore ripe for abuse. Even better, maintenance storage modules have a fixed cost per ton so we can split them into smaller components for free; fuel tanks do not have this trait and are a large part of the somewhat extreme cost of the final ship design.
Starting with MSP: 175% power 36HS engines have a repair cost of 201.6 MSP and our target is 4x max repair; unsurprisingly the engines are the most costly component so we'll need at least 806.4 MSP on board. As the final design utilizes three engineering spaces and one small engineering space, we'll need another 550 MSP to hit 807 total, or 55t of maintenance storage. Discarding the idea of a 50t maintenance storage bay because of the crew requirement, we could aim for 5x 10t small storage and 2x 2.5t tiny storage; however, the ship gains a new unique component by splitting one of the two 2.5t tiny storage bays into 5x 0.5t fighter storage bays. Swapping any 10t small storage out for smaller components doesn't seem to change anything however.
And now for the real MSP abuse: fuel tanks. The final design leverages 699.9t of fuel to deliver 10bkm of range using twin 36HS 175% power engines pushing 5,930t of ship; this fuel tonnage is very specific. Any less reports 9.9bkm range and any more is wasted tonnage that lowers the final speed and removes an entire 200km/s band for a -1 DP result. We could do this using 14x 50t Standard fuel tanks and pick up 14 internal HTK while doing so; this is exactly what the suggested design does. However, due to yearly MSP usage dropping as components get smaller and more unique components are introduced, we won't be doing that.
Instead, using 6,999x 0.1t Minimal fuel tanks is almost the ideal despite the absolutely revolting BP, wealth, duranium, and boronide costs. We will, however, reintroduce a 1t Fighter fuel tank and a 5t Tiny fuel tank to increase unique component count and continue to drag the yearly MSP usage down, but trying to reintroduce a 10t Small fuel tank increases the yearly MSP usage so we won't be doing that; instead, 1 Tiny, 1 Fighter, and 6,939 Minimal tanks are left to store the fuel in some sort of cruel joke against the shipyard workers that would need to weld them all into the hull.
The final result is a twin 36HS 175% power engine design that hits 24 DP: the yearly MSP usage has been brought down to 100 while maintaining the remainder of the design criteria that were laid out when we went through design optimization. The final ship design, laid out in Class Design window order, is then as follows:
- 1x UNE-provided 55t Active Search Sensor
- 7.3x 50t Duranium Armour, automatically added for 1-29 layer-column configuration
- 1x 170t Single-Weapon Beam Fire Control, providing 128kkm range and 6,800km/s tracking
- 1x 50t Bridge, automatically added because we're heavier than 1,000t
- 385t of Crew Quarters, automatically added for 9 months deployment time
- 2x 1,800t (36HS) 175% power Engines
- 175t of Engineering, laid out in 3x 50t + 1x 25t configuration
- 699.9t of Fuel Storage, laid out in 1x 5t + 1x 1t + 6,939x 0.1t configuration
- 1x UNE-provided 200t H&C LL-12 Laser Gun
- 55t of Maintenance Storage, laid out in 5x 10t + 1x 2.5t + 5x 0.5t configuration
- 1x 37t (0.74HS) Power Plant, delivering ~2.04 power instead of 1.99588 power
- 1x UNE-provided 137.5t Thermal Sensor
For what it's worth, a twin 35HS 175% engined ship pushes well into the 6,600km/s band at 24 DP without the obnoxious MSP and fuel reworks, while backing off from those reworks leaves the twin 36HS 175% engined ship either slightly below 6,800km/s, slightly below 4x max repair, and/or slightly above 100 MSP per year. Those ship designs are probably the ones to deploy if there's need for a hull north of 6,500km/s in the Nuclear Thermal era!
Class Design screenshot and DB are attached below. This post became significantly longer than I expected but I enjoy teaching so hopefully at least one person has learned a new ship design trick rather than being all for naught!
