Fleet Tankers and the Tug Life
I use the “Fleet Tanker” hull designation for a tanker that supports forward military fleet operations by moving with the fleet–not at full military fleet speed, but at a high percentage of it (usually 60%).
(“Military fleet speed” is my doctrinal design requirement for the speed of large military warships. Not small response/patrol craft, and not slow missile boats–I’m talking about the big boys, with the big guns, that go to where the big bad-guy fleets are and fight them.)
At Ion engine tech, my military fleet speed is 10kkmps.
My requirement for an ion-tech fleet tanker is to move 6kkmps and to carry enough fuel to move 50bkm and have 25ML to spare.
The specs:
Scort class Fleet Tanker 53,332 tons 565 Crew 3,979.3 BP TCS 1,067 TH 6,400 EM 0
6000 km/s Armour 1-126 Shields 0-0 HTK 72 Sensors 1/0/0/0 DCR 28-5 PPV 0
Maint Life 1.13 Years MSP 3,305 AFR 813% IFR 11.3% 1YR 2,609 5YR 39,137 Max Repair 1,600 MSP
Lieutenant Commander Control Rating 1 BRG
Intended Deployment Time: 7.1 months CDE 50% Morale Check RequiredM-MP 5kt@200%0.5LEPH (2) Power 6400 Fuel Use 89.44% Signature 3200 Exp 20%
Fuel Capacity 38,500,000 Litres Range 145.3 billion km (280 days at full power)
Refuelling Capability: 30,000 litres per hour Complete Refuel 1,283 hoursTHS 11 5t (1) Sensitivity 1.1 Detect 1000: 8.3m km
That’s 10kt of 200% engine delivering 25ML of fuel 25bkm from base with enough fuel left to make the 25bkm return trip.
The thing is expensive. And big. Which means it needs a big yard. And operational MSP burn is significant.
Brief aside: Note that the reported 1YR cost of 2609 is incorrect. (See Bug details in the 2.7.1 bug thread.)
Without going into the details of the calculation, suffice it to say that I can actually expect a single 6-month sortie to consume ~1200 MSP on average.
With moderately below average luck, I can easily have two engine failures during a 6-month mission. I need to carry 3200+ MSP to withstand that.
So there’s the classic single-ship solution.
But how does this look if we want to live the Tug Life?
Take the extra fuel and the refueling system off of this thing, add a tractor beam, and use it to haul around a tanker station holding that extra fuel.
Like so:
Scort-tug class Fleet Tanker 18,966 tons 485 Crew 3,688.8 BP TCS 379 TH 6,400 EM 0
16872 km/s Armour 1-63 Shields 0-0 HTK 57 Sensors 1/0/0/0 DCR 14-7 PPV 0
Maint Life 1.55 Years MSP 3,701 AFR 206% IFR 2.9% 1YR 1,767 5YR 26,499 Max Repair 1,600 MSP
Tractor Beam
Lieutenant Commander Control Rating 1 BRG
Intended Deployment Time: 7.2 months CDE 50% Morale Check RequiredM-MP 5kt@200%0.5LEPH (2) Power 6400 Fuel Use 89.44% Signature 3200 Exp 20%
Fuel Capacity 6,724,000 Litres Range 71.3 billion km (48 days at full power)THS 11 5t (1) Sensitivity 1.1 Detect 1000: 8.3m km
And:
Scort-tank class Fleet Tanker 34,366 tons 30 Crew 222.8 BP TCS 687 TH 0 EM 0
1 km/s No Armour Shields 0-0 HTK 11 Sensors 1/0/0/0 DCR 1-0 PPV 0
MSP 4 Max Repair 25 MSP
Lieutenant Commander Control Rating 1 BRG
Intended Deployment Time: 3 months CDE 50%Fuel Capacity 32,000,000 Litres Range N/A
Refuelling Capability: 30,000 litres per hour Complete Refuel 1,066 hoursTHS 11 5t (1) Sensitivity 1.1 Detect 1000: 8.3m km
Total cost is 3902.9 (vs 3979.3). 2% cheaper. (But see below about cost of maintenance facilities.)
Total tonnage is 53,332. Same total size and same exact engines means same speed when tugging.
Total fuel 38.724ML (vs 38.5ML). Keeping the payload as 25ML, that gives ~1.66% more operational range.
So a smidge cheaper to build and a smidge more range.
Meh.
What else do I gain?
Instead of a 53.3kt mil yard, I need a 19kt mil yard. (I can build the station with construction factories, or co-build it in pretty much any yard for a commercial tug or tanker of roughly the same size.)
So I save ~8.5M workers. That’s big. I also save ~8k BP, ~4k DUR, and ~4k NEU (exact amount depends on Shipyard Operation Time/Cost Saving tech level).
I also get a big reduction in the time needed for initial yard size expansion.
I need 19kt of maintenance capacity instead of 53.3kt.
That’s enormous, even at mid to late tech.
At, say, 3200 tons supported per mfac, I need ~5.94 mfacs instead of ~16.66.
That’s a savings of ~644BP (and 322 DUR and NEU).
The total cost of ownership is ~4259BP instead of ~4979BP.
In other words, this approach is not 2% cheaper, it is ~14.5% cheaper.
And I save another half-million workers.
I also gain the ability to run the tug without the tanker attached.
Which means I can pre-deliver the tanks to a location, and then go sit at some nearby colony to reset deployment clock (and/or pause or reset maintenance clock) until the tanks need picking up.
Also, the tug is incredibly fast when unladen. I can use it to respond to any emergency that justifies the fuel cost.
Theoretically I use less crew (515 vs 565), but I’m going to use conscripts on these anyway.
I think 14.5% reduction in total cost of ownership plus freeing up ~9M workers are the big wins here.
TugLife powers on.