Fuel consumption of tugs

[andrea69 (OP)]

I've used this tug to deliver two big OH to Mercury. The OH are 12.500.000 tons each, and I needed many months to deliver them at 12km/sec, still I've used only 4% of fuel. How is it possible? Bug, or something I'm not considering?

Code: [Select]

Sallustio class Tug    40,600 tons     849 Crew     1095 BP      TCS 812  TH 3100  EM 0
3817 km/s     Armour 1-105     Shields 0-0     Sensors 1/1/0/0     Damage Control Rating 1     PPV 0
MSP 17    Max Repair 100 MSP
Tractor Beam     

Nuclear Pulse Engine E0.9 (31)    Power 100    Fuel Use 9%    Signature 100    Armour 0    Exp 1%
Fuel Capacity 200,000 Litres    Range 98.5 billion km   (298 days at full power)

This design is classed as a Commercial Vessel for maintenance purposes


[metalax]

Fuel use is ultimately determined by distance covered rather than speed.

[Theokrat]

Fuel use is ultimately determined by distance covered rather than speed.

Which should not be the case for tugs. A tug that is tractoring another ship should be assumed to have all its engines on (unless the combination is set to travle at lower speeds than the combined maximum), and thus should use fuel at the full rate. This does not seem to be the case. Instead the reduction in speed seems to imply a fuel usage that would correspond to nearly idle engines. (i.e. the fuel seems to be used at a rate as if the tug traveled at the reduced speed alone.

[metalax]

True, sounds like it may be an oversight. I'd post it in the bug reports thread.

[clement]

My understanding of the way it works is that the engines use X amount of fuel to operate at full power.

The speed the vessel or vessels move at is related to the power generated by the engines vs. the total mass the engines are attempting to move.

In your case, a tug moving from point A to B will always use the same amount of fuel, whether it weighs 40,600 (just the tug) or 12,540,600 (tug + OH). It will just take a lot longer, as you experienced, since the Power produced by the engines will move the combined mass much slower than only the tug.

3100 Power pushing 40,600 tons = ~13.1 tons per unit of engine power
vs.
3100 Power pushing 12,540,600 tons = ~4,045.4 tons per unit of engine power

[andrea69 (OP)]

In your case, a tug moving from point A to B will always use the same amount of fuel, whether it weighs 40,600 (just the tug) or 12,540,600 (tug + OH). It will just take a lot longer, as you experienced, since the Power produced by the engines will move the combined mass much slower than only the tug.

Fuel usage should depend on time, not on distance covered. In fact, if on the class design screen I add the OH modules directly to the tug, speed and range decrease, while the time stay the same

[Person012345]

I think it's done for simplicity.

[andrea69 (OP)]

Well, if that is the reason I can live with that, anyway I posted it in the official bug thread, I'l see if Steve replies there.

[sloanjh]

My recollection is that I logged a bug with Steve about this a while back.  The problem is (IIRC) that the code confuses "full speed" with "full power", which is incorrect for tugs.  The way I remember it going, if you have a 20kkm/s ship (A) in a TG with a 10kkm/s ship (B), and the TG is going at 10kkm/s, then ship A's engines are only running at 50% power, so should use 50% fuel.  So fuel consumption is hit with a factor of (TG speed)/(max ship speed) for each ship.  During towing operations, the (max ship speed) that should be used is that of tug+tow, but it's not, hence a bug.

John

[Nathan_]

It works that way for thermal signatures as well.