Drop Tanks... Back From the Dead?
- Thread starter Ol'Weedy
- Start date
I didn't do the math, but the claim is that making a 160dton ship with 40dtons of drop tanks is cheaper than making a 200dton ship. Didn't interest me enough to double check the assertion, just saying if its true, it's stupid.
This assumes you fly around and never actually drop the tanks, I gather.
This assumes you fly around and never actually drop the tanks, I gather.
MasterGwydion
Emperor Mongoose
That is why they work best on commercial ships and not combat ships...
There's also a 0.4% of tank tonnage as an overhead from the ship using them. A 2000 ton ship with 1000 ton drop tanks loses 4 tons compared to a 3000 ton ship with 1000 tons of tank. Swings and roundabouts.
But yeah. I can see a role for them in safe areas as just being external fuel tanks that don't usually get dropped - almost always going to be cheaper overall.
And even in frontier areas, as long as the ship isn't *relying* on them, they could be useful. Most smaller ships would only need to allocate a ton for the fittings as a retrofit and could mount or demount for the extra fuel if they need to stage through a system they don't want to stop at. Although it should be noted that adding tanks DOES increase the fuel required overall if they're not discarded.
As an example, a Far Trader uses 20 tons per Jn and carries enough for a total of 2 parsecs.
If you add a 20 ton drop tank and keep it attached, your tonnage is 220 and you use 22 tons of fuel per parsec plus your jump is limited to J-1. To get a third parsec the drop tank has to be larger; a 30 ton one would work.
But yeah. I can see a role for them in safe areas as just being external fuel tanks that don't usually get dropped - almost always going to be cheaper overall.
And even in frontier areas, as long as the ship isn't *relying* on them, they could be useful. Most smaller ships would only need to allocate a ton for the fittings as a retrofit and could mount or demount for the extra fuel if they need to stage through a system they don't want to stop at. Although it should be noted that adding tanks DOES increase the fuel required overall if they're not discarded.
As an example, a Far Trader uses 20 tons per Jn and carries enough for a total of 2 parsecs.
If you add a 20 ton drop tank and keep it attached, your tonnage is 220 and you use 22 tons of fuel per parsec plus your jump is limited to J-1. To get a third parsec the drop tank has to be larger; a 30 ton one would work.
It may technically be cheaper but it has some definite downsides, starting with the vulnerability I mentioned above.
But also... it's built as a 160 ton ship. It can have one hardpoint and it has to allocate drives sufficient for a 200 ton ship, but may not benefit from them with the tanks dropped; if it was J-1 with tanks it will be... J-1 with them gone, and unless it's allocated 16 tons of internal jump fuel it's not going anywhere (a 20 ton allocation would be sensible, since that allows an extra J-1 with the tanks on or off). Same for M-Drive, although a generous Referee might allow them to travel at 1.25G. For combat purposes it's still only going to count as Thrust 1.
The cost saving is pretty minor too. Hull costs Cr 50,000 per ton, drop tanks cost Cr 25,000 per ton plus the cost of the fittings. Those are 0.4% of the tank tonnage at MCr0.5 per ton, so a 40 ton drop tank needs a 0.16 ton fitting, costing Cr 80,000.
So the 200 ton ship with 40 tons internal fuel is a base MCr10 hull. A 160 ton hull with 0.16 ton of tank fittings is MCr8.08. The tank costs MCr1, for a total of MCr9.08. You save MCr0.92 but can lose your ability to jump very easily.
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MasterGwydion
Emperor Mongoose
Would make more sense to have a 200-ton ship with 0 tons of internal jump fuel. You carry like an extra 39 tons of cargo per jump. Attach the drop tanks at the jump point. Suck the fuel, drop the tanks, and jump. A tug takes the drop tanks back to the starport, if they survived.
Condottiere
Emperor Mongoose
I'm pretty sure I've covered all possible legal applicable variants of drop tanking, at one point or another, and considered the illegal ones.
For starwarships, it tends to come down to (lack of) hardpoints and ten percent hull point destruction.
Leveraging it to cheapen hull cost gets minimal returns, for commercial shipping.
If you do have reactionary rockets as principal propulsion, it does allow carrying extra fuel to the jump point; or for a smallcraft, to the dogfight.
For starwarships, it tends to come down to (lack of) hardpoints and ten percent hull point destruction.
Leveraging it to cheapen hull cost gets minimal returns, for commercial shipping.
If you do have reactionary rockets as principal propulsion, it does allow carrying extra fuel to the jump point; or for a smallcraft, to the dogfight.
Fluffy Bunny Feet
Cosmic Mongoose
Your basic power also drops from 40 to 32. Smaller power plant. At TL 12 that is 1 MCr/ton. So call it a total cost saving of 1.5 MCr, of ~52 MCr = ~2.9% savings. That actually understates it as you are most likely making a non streamlined hull so the hull price drops not from 10 MCr to 8 MCr (close hull) as you are not streamlined any more increasing the savings over all to 2.5 MCr or ~4.8%. You of course would only use this in areas where you didn't need to land or pay price premiums for service as a non landing ship, so old well established areas with lots of patrols and little or no pirates.
Your maintenance costs drop that same percentage. You use less power plant fuel. Your mortgage drops by ~10000 Cr/month.
Losing the ability to jump to a pirate attack ALSO keeps the pirates from jumping out with the ship. Saves you MCr even if you have to refit compared to buying new. If you drop the tank yourself you run away from the pirate at 1.25 g giving more time for help to arrive and if it does you can recover the tank. If pirates are a big issue I'd want a 2 or 3 g drive anyhow and this would up those to 2.5 and 3.75 g respectively giving a greater chance at escape by dropping the tank.
Now apply this to large ships of 1000 tons and more and as the shipping line executive give yourself a big bonus for up front and operating cost savings over the life of the ship.
Condottiere
Emperor Mongoose
You can always reconfigure the hull to dispersed, which drops the cost by fifty percent, and then lighten it.
Fluffy Bunny Feet
Cosmic Mongoose
That would be cheaper than the drop tanks. Wouldn't let you run away faster from pirates. Make it non gravity and run at a constant 1 g and it is not only cheaper but consumes less power and fuel. Doesn't help with g in jump though. You would need rotation for that.
Condottiere
Emperor Mongoose
If you non gravitate that, and switch off the inertial compensation field, redesign the deckplans for a tailsitter.
Though, I wouldn't actually try landing with that, tailsitting or otherwise.
Though, I wouldn't actually try landing with that, tailsitting or otherwise.
For a guaranteed safe run with drop tanks provided at every port, sure. Although there's expenses involved in running or paying for a tug and you should note that any jump where the tanks are dropped by a ship under TL15 gets an extra penalty to the jump task. Also, 59% of the time the tanks are not reusable, so that's a running cost that needs to be accounted for as well if you're using them in this manner.
But assuming TL15 ships and jumping between systems which have replacement tanks on hand, yes. The extra cargo side of things makes it worth looking at, most likely for big haulers.
Incidentally, the TL rule that Mongoose put in goes some way to explaining why the JTAS articles talk about them being a recent development for civilian use. A TL12 ship has a -3 to their jump task while dropping tanks.
Of course, they can always be used the way aircraft drop tanks are used - drop them when empty, then jump using internal tankage. I'd imagine Gazelles would do that now and then, though as a J-4 ship they really don't need to drop tanks very often.
Specifically regarding streamlining, if you are going to compare an all in one hull to a hull that operates without dropping its drop tanks, you should be comparing an unstreamlined or partially streamlined all-in-one hull, not a streamlined one, since the latter has paid for significant capabilites. The all in one ship should also be a close hull. Unsure from your post if you included that. As was already mentioned an open structure hull internal tankage is the same base cost as drop tanks, so they're actually more expensive to install there before you look at other factors like powerplant.
So going with a close structure for both options the all in one is MCr8 while the 160ton hull with fitting is MCr6.48 plus the MCr1 drop tank (which does not benefit from the close hull discount, unlike the internal storage), or MCr7.48, a cost difference of Cr 520,000.
Good point about the base hull power requirement. But a TL12 Powerplant provides 15 power per ton, so you only save 0.53 tons, which is a saving of MCr 0.53. I make the difference MCr1.05, which is admittedly not nothing.
The partially streamlined all-in one hull still retains advantages - it can skim and is able to land on planets that an overall unstreamlined hull cannot, although the drop tank version could always sacrifice the tanks to do so, and if they just detach them (and maybe stow them in cargo, or leave them in orbit) instead of using the drop tank procedure I don't have a problem with recovering and reattaching them, especially if empty.
A 200 ton hull ship can also mount two hardpoints. A 160 ton ship with 40 tons of drop tank can only mount one. But that's unlikely to be a major issue for a large commercial ship anyway.
For my money, I think a better design would have a 20 ton internal tank and a 20 ton external one on a 180 ton hull, or for the 160 ton hull to have some internal tankage, or some other configuration that makes sense for the jump capacity desired. That retains the ability to jump if something happens to the tanks as well as the ability to return to base to get them replaced eventually.
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The RAW is a lot of verbiage and mechanics to say "Drop tanks are ineffective, unsafe, and functionally unusable." Which is fine with me because I don't like them or the implications of them.
However, the rules making drop tanks so ineffective does directly contradict the old canon (JTAS #2: TNS reports) that they have been in commercial use in the Core for over a decade and are making long haul commercial service viable. The RAW mechanics absolutely do not allow for that.
They were trying to have a conversation about what if they actually did work. We all know that they don't, so obviously the discussion is going to have to be assuming a house rule that the "more likely destroyed than not" rule doesn't apply.
However, the rules making drop tanks so ineffective does directly contradict the old canon (JTAS #2: TNS reports) that they have been in commercial use in the Core for over a decade and are making long haul commercial service viable. The RAW mechanics absolutely do not allow for that.
They were trying to have a conversation about what if they actually did work. We all know that they don't, so obviously the discussion is going to have to be assuming a house rule that the "more likely destroyed than not" rule doesn't apply.
Well, the Mongoose rule that dropping tanks and jumping (which is what JTAS is talking about) imposes a penalty of -15 on the jump task plus the ship TL addresses that a bit. At TL12 that's a -3. So if reliable use has a risk until TL 15 it's not surprising that we see some military use* at TL14 and civilian use only starting up recently. But they do need to be replaced, so the ships using them are reliant on local production. That all makes sense. As does the point that being vulnerable in combat is not a major concern in the Core.
Cost wise, it's easy to calculate that they do allow larger cargos to be jumped, though you would need cargo worth more than Cr25,000 per ton to cover the consumption of the tanks. But the speculative trade tables support that not being a problem.
(*Our prime example being the Gazelle, which has the ABILITY to Jump 5 by dropping tanks... but retains a healthy J-4 by leaving them in place. Most Gazelles, most of the time do not drop tanks (and for that matter are often making two J-2's on a patrol to somewhere and back). If they do have to and wear that -1 to jump penalty on top of their -5 for jump distance... well, they're Navy and hopefully have a good Astrogator and Engineer who take their time setting that one up.)
Cost wise, it's easy to calculate that they do allow larger cargos to be jumped, though you would need cargo worth more than Cr25,000 per ton to cover the consumption of the tanks. But the speculative trade tables support that not being a problem.
(*Our prime example being the Gazelle, which has the ABILITY to Jump 5 by dropping tanks... but retains a healthy J-4 by leaving them in place. Most Gazelles, most of the time do not drop tanks (and for that matter are often making two J-2's on a patrol to somewhere and back). If they do have to and wear that -1 to jump penalty on top of their -5 for jump distance... well, they're Navy and hopefully have a good Astrogator and Engineer who take their time setting that one up.)
Condottiere
Emperor Mongoose
Militaries aren't really concerned with cost, if something gives them an edge.
Faced by wartime metal shortages and a need to extend the range of fighter craft, the British came up with drop tanks made of glue-impregnated kraft paper, which had excellent tolerance characteristics for extreme heat and cold necessary for operation on an aircraft as well as being waterproof.
Maybe we could substitute the twenty five kilostarbux per tonne hulls with stainless steel.
Faced by wartime metal shortages and a need to extend the range of fighter craft, the British came up with drop tanks made of glue-impregnated kraft paper, which had excellent tolerance characteristics for extreme heat and cold necessary for operation on an aircraft as well as being waterproof.
Maybe we could substitute the twenty five kilostarbux per tonne hulls with stainless steel.
Conceivably you could have an exploration ship with the capacity to fabricate its own drop tanks. It seems to be a TL12 technology; MGT High Guard doesn't assign a TL aside from severely discouraging any low tech ship from using them, but HG '79 did indeed require a TL12 component.
And if you're eating rocks to make stuff, the money cost sort of becomes moot. It's just the time cost.
And if you're eating rocks to make stuff, the money cost sort of becomes moot. It's just the time cost.
