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Old 12-08-2017, 09:39 AM   #11
Tomsdad
 
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Default Re: A new magical airship scheme

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Originally Posted by Fred Brackin View Post
You need something (cables I guess) to transfer lift from the balloonets in a conventional airship so you're probably not losing anything that way.

I don't think there are any huge structural requirements for the deck from the spell. You might make the deck strong enough that a caster could stand at the center of the spell area just to be safe.
If nothing else if some of the deck is not completely enveloped by the domes you want it to be strong enough to stay together against the wear and tear it might experience floating around the sky. Do the domes fail if the deck gets damaged enough to no longer act as an anchor*?

One thing, while for example string winds might not be able damage a vacuum dome directly, they might push against the dome strongly enough to put pressure on the whole deck that the dome shares with others.

*I.e. is catastrophic deck failure here suddenly losing buoyancy?
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Old 12-08-2017, 09:50 AM   #12
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Default Re: A new magical airship scheme

The deck has to bear the weight of itself and anything it carries, just as if it were a bridge, or suspended by cables from a conventional balloon. The sphere(s) will exert an upward force from their center (presumably; I suppose you could argue for the interior of the lift sphere or its boundary), so there are the bending moments and shear forces you'd have just as it were a platform centered on a pole.

The airship mage-ineers might prefer several smaller spheres to one large one for such reasons. Since the cost of an AE spell is linear with radius, but the buoyancy is a cube, as it's a function of volume, fewer spheres will be preferred for cost reasons. Then there's possibly a desire for redundancy for military reasons, if enemy mages can dispel or suppress your spheres. So that at least gives you a design question designers can argue about in-game.

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Do the domes fail if the deck gets damaged enough to no longer act as an anchor?
Even if the magic survives, the (mundane) deck itself could fail, allowing the sphere to tear itself loose, taking its anchor point up into the sky. That's bad news for the airship.

Buoyancy drops as altitude increases (assuming air density on the magical planet behaves as on real-world Earth). So there's some altitude at which the spheres will stop rising, possibly the edge of space if there's vacuum inside. Perhaps the space above a battle is littered with drifting bubbles, or there are enterprising scavengers braving the extreme conditions to salvage those spheres (say, if there are valuable material components needed in the enchantment construct).

Last edited by Anaraxes; 12-08-2017 at 09:56 AM.
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Old 12-08-2017, 11:18 AM   #13
sir_pudding
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Default Re: A new magical airship scheme

Why would a magical sphere of vacuum be buoyant rather than just sit there? Usually in FRPGs vacuum effects are aphysical in this way, otherwise they would be pretty useless as attacks.
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Old 12-08-2017, 11:46 AM   #14
Fred Brackin
 
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Default Re: A new magical airship scheme

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Why would a magical sphere of vacuum be buoyant rather than just sit there? Usually in FRPGs vacuum effects are aphysical in this way, otherwise they would be pretty useless as attacks.
A magical sphere of vacuum would just sit there if it were anchored to an immobile object. If the object is mobile the sphere goes with it.

There is only one vacuum attack in Gurps Magic and that is the usually short-lived vacuum produced by Destroy Air. There is no great body of vacuum attacks to cite as precedent.
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Old 12-08-2017, 11:51 AM   #15
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Default Re: A new magical airship scheme

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Why would a magical sphere of vacuum be buoyant rather than just sit there? Usually in FRPGs vacuum effects are aphysical in this way, otherwise they would be pretty useless as attacks.
I think they're just ignored for convenience sake, whereas here it's the basis of a design principle, so it's fair to focus on the "scientific" effects. But I'm not sure what kind of magical vacuum attacks you're thinking of that should otherwise be anchored.
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Old 12-08-2017, 02:53 PM   #16
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Default Re: A new magical airship scheme

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I think they're just ignored for convenience sake, whereas here it's the basis of a design principle, so it's fair to focus on the "scientific" effects. But I'm not sure what kind of magical vacuum attacks you're thinking of that should otherwise be anchored.
This: http://www.dandwiki.com/wiki/Vacuum_(3.5e_Spell), for example is similar in concept to Atmospheric Dome and if it just floated away would be pretty useless.
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Old 12-08-2017, 02:56 PM   #17
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Default Re: A new magical airship scheme

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Perhaps the space above a battle is littered with drifting bubbles, or there are enterprising scavengers braving the extreme conditions to salvage those spheres (say, if there are valuable material components needed in the enchantment construct).
If you get up there by buoyancy with bubbles of your own . . . How are you going to get the ones you've caught down again?

There seems to be a need for a bubble whose Maxwell's Demon can have its settings changed. That's the equivalent for these things of valving off gas in a conventional airship.
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Old 12-08-2017, 03:31 PM   #18
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If you get up there by buoyancy with bubbles of your own . . . How are you going to get the ones you've caught down again?
I wasn't thinking you'd bring down the whole sphere. Just the orichalcum latticework holding the gems and dragonwing scales in the proper positions -- or whatever the valuable material components for the setting might be. If there aren't any, just the Will and the Word to create the enchantment, then of course there's nothing to salvage. (GURPS Magic doesn't have an Item: section for Atmosphere Dome, so it's up to GMs and houserules to have permanently enchanted airships, if desired, and set the cost of that enchantment.) Just a whimsical detail, should anyone find that appealing.

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There seems to be a need for a bubble whose Maxwell's Demon can have its settings changed. That's the equivalent for these things of valving off gas in a conventional airship.
I knew there was a good reason to take Abyssal as my bonus language.
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Old 12-08-2017, 08:58 PM   #19
Fred Brackin
 
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Default Re: A new magical airship scheme

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This: http://www.dandwiki.com/wiki/Vacuum_(3.5e_Spell), for example is similar in concept to Atmospheric Dome and if it just floated away would be pretty useless.
That's blank page in somebody's D&D 3.5 homebrew. Only of interest to see if somebody can come up with something else of even less relevance to a concept in Gurps Magic.
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Old 12-08-2017, 09:06 PM   #20
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Default Re: A new magical airship scheme

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That's blank page in somebody's D&D 3.5 homebrew. Only of interest to see if somebody can come up with something else of even less relevance to a concept in Gurps Magic.
Well it was supposed to be a link to, I thought, an SRD spell
.
My point is that bubbles of magical vacuum can't be assumed to follow physics, although I suppose Aristotlean mechanics would have outer space as the natural place of rest for the void.
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