drive performance with external cargo, drop tanks or clamped ships

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h1ro
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drive performance with external cargo, drop tanks or clamped ships

Postby h1ro » Tue Apr 11, 2017 6:18 am

Should drive performance for ships with drop tanks, external cargo or clamped ships be calculated from the base volume of the drive as it would be for a non tweaked drive or from the volume of the adjusted drive? I think the former as the base volume is what the drive performance is figured on before you tweak it to make it smaller and spend all that money in the primitive/advanced tech section.

I've searched and not turned up an answer to this but have seen reference to an earlier discussion, if there is a thread can someone kindly point me towards it rather than rehashing it further? Thanks!
AndrewW
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Re: drive performance with external cargo, drop tanks or clamped ships

Postby AndrewW » Tue Apr 11, 2017 9:56 am

h1ro wrote:
Tue Apr 11, 2017 6:18 am
Should drive performance for ships with drop tanks, external cargo or clamped ships be calculated from the base volume of the drive as it would be for a non tweaked drive or from the volume of the adjusted drive? I think the former as the base volume is what the drive performance is figured on before you tweak it to make it smaller and spend all that money in the primitive/advanced tech section.
Drive performance should be calculated as normal for the total tons needed, this would include external cargo or attached ships. Drop tanks would not be included in jump drive calculations unless they where to remain attached during jump. After this modifications can be applied.
Condottiere
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Re: drive performance with external cargo, drop tanks or clamped ships

Postby Condottiere » Tue Apr 11, 2017 10:51 am

It depends.

If it was designed to carry that volume as standard, then you mention that performance first, with an asterisk.

If your external load varies, list the performance for a range of the most common volumes, starting from bareback to full.

Applies as well as you switch to engines with differing performance; you only want to know what you can squeeze out of the current motors, anything before that is a historical note.
h1ro
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Re: drive performance with external cargo, drop tanks or clamped ships

Postby h1ro » Tue Apr 11, 2017 4:44 pm

AndrewW wrote:
Tue Apr 11, 2017 9:56 am
Drive performance should be calculated as normal for the total tons needed, this would include external cargo or attached ships. Drop tanks would not be included in jump drive calculations unless they where to remain attached during jump. After this modifications can be applied.
Thanks!
PsiTraveller
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Re: drive performance with external cargo, drop tanks or clamped ships

Postby PsiTraveller » Tue Apr 11, 2017 7:53 pm

What Condottiere said. You need to calculate based on what you are currently carrying.

Also keep in mind Tech level when calculating Jump engine performance. You may have a ship that can do Jump 2 at 600 tons (400 tons of ship and 200 tons carried in a Jump Net or external cargo mounts), when only moving 400 tons and no extra cargo the ship could jump further, but it will depend on if the software and Tech level of the drives is high enough.
h1ro
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Re: drive performance with external cargo, drop tanks or clamped ships

Postby h1ro » Tue Apr 11, 2017 11:56 pm

Thanks for the TL reminder.

And, when reverse calculating the jump drive performance of a ship with external cargo or clamped ships, take 5 off the base volume then look up the percentage and drive rating.
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Re: drive performance with external cargo, drop tanks or clamped ships

Postby AndrewW » Wed Apr 12, 2017 12:28 am

h1ro wrote:
Tue Apr 11, 2017 11:56 pm
And, when reverse calculating the jump drive performance of a ship with external cargo or clamped ships, take 5 off the base volume then look up the percentage and drive rating.
Use the original drive volume for any calculations.
h1ro
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Re: drive performance with external cargo, drop tanks or clamped ships

Postby h1ro » Wed Apr 12, 2017 12:35 am

AndrewW wrote:
Wed Apr 12, 2017 12:28 am
Use the original drive volume for any calculations.
To clarify:

100 ton ship, jump 2 needs 5% which is 5 tons to which you add 5 so the final drive is 10 tons and it costs MCr15.0

Reversing the calculation to get the jump drive rating with 100 tons of external cargo (or clamped ship) I use the 5 tons which is 2.5% of 200 tons and so jump is 1.

Right?

(Just to be sure what "original drive volume" means).
AndrewW
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Re: drive performance with external cargo, drop tanks or clamped ships

Postby AndrewW » Wed Apr 12, 2017 2:17 am

h1ro wrote:
Wed Apr 12, 2017 12:35 am

100 ton ship, jump 2 needs 5% which is 5 tons to which you add 5 so the final drive is 10 tons and it costs MCr15.0

Reversing the calculation to get the jump drive rating with 100 tons of external cargo (or clamped ship) I use the 5 tons which is 2.5% of 200 tons and so jump is 1.
An effective 200 tons in that case. So would need 10 tons of drive for jump-1, or 15 tons of drive for jump-2. You will also need to calculate the jump fuel based on the full size (with any 'extras').

Original size, just means based on the size (and TL) of the jump drive before any modifications such as reduced size.
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Re: drive performance with external cargo, drop tanks or clamped ships

Postby h1ro » Wed Apr 12, 2017 3:16 am

AndrewW wrote:
Wed Apr 12, 2017 2:17 am
An effective 200 tons in that case. So would need 10 tons of drive for jump-1, or 15 tons of drive for jump-2. You will also need to calculate the jump fuel based on the full size (with any 'extras').

Original size, just means based on the size (and TL) of the jump drive before any modifications such as reduced size.
OK, that's not how I've been doing it but I get what you mean. What I've been doing is using external cargo and clamped ships exclusive of the hull of the ship they're attached to so that when the ship is "clean" it has an uber drive and smaller hull. Smaller hull means cheaper hull as the cargo and externally clamped ships have their own "hull".

Will revisit the spreadsheet... :|
h1ro
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Re: drive performance with external cargo, drop tanks or clamped ships

Postby h1ro » Wed Apr 12, 2017 3:52 am

But!

That still leaves the question of how are you calculating the drive performance for the ship in it's other configurations?

I get that it makes sense to calculate the highest displacement first, tho I have been doing the lowest first with the ship in it's "clean" state.

All I was doing was going backwards!

In my Traveller group we've often used ships with external cargo, hauling 300 tons at J1 and then being able to much higher jump numbers when clean.

That's the bonus of external cargo, or are you saying we've misinterpreted the rules and that the ship is limited to it's jump performance when fully loaded? (Obviously, you need to have the jump software for the highest jump).
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Re: drive performance with external cargo, drop tanks or clamped ships

Postby AndrewW » Wed Apr 12, 2017 4:43 am

h1ro wrote:
Wed Apr 12, 2017 3:52 am
That's the bonus of external cargo, or are you saying we've misinterpreted the rules and that the ship is limited to it's jump performance when fully loaded? (Obviously, you need to have the jump software for the highest jump).
The jump performance is calculated at current displacement, if there's nothing connected to docking clamps for example it may have a higher jump capability. Besides jump software the jump drive also needs to be of at least the required TL to perform that jump number.
h1ro
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Re: drive performance with external cargo, drop tanks or clamped ships

Postby h1ro » Wed Apr 12, 2017 4:51 am

Ok, thanks. I'm pretty sure that's what I'm doing but I'll head back to the sheet and check it.
PsiTraveller
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Re: drive performance with external cargo, drop tanks or clamped ships

Postby PsiTraveller » Wed Apr 12, 2017 1:09 pm

Doing the 300 Ton J1 is a good way to make money. The higher jump range when jumping clean is the proper way to calculate. You calculate capacity of what is about to jump. You were also right about deducting the 5 tons of Jump drive from the calculation.

I wrote an adventure for TAS based on this very math. (Seed of Doubt), and a trading system (Jump Station Echo) (blatant plugs!)
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Re: drive performance with external cargo, drop tanks or clamped ships

Postby steve98052 » Thu Apr 20, 2017 6:52 am

The jump drive needs to be built for the desired jump, not just of sufficient tech level. It's possible to build a TL15 Jump-1 drive, and if one is installed in (for example) a 200 dton ship designed to haul another 200 dtons of external cargo, it's still a Jump-1 ship when it's not carrying the external cargo. On the other hand, if it's built as a Jump-2 drive, it would be able to do Jump-2 without the load and Jump-1 with an external load.

Of course, if there's no extra cost for a ship that can do Jump-2 unloaded and Jump-1 loaded (compared to the cost of one that's Jump-1 in any case), one might as well build it for Jump-2.
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Re: drive performance with external cargo, drop tanks or clamped ships

Postby Condottiere » Thu Apr 20, 2017 5:54 pm

Unless you plan to tweak it, a factor one jump drive is unlikely to be built on technological level fifteen blueprints.

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