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Author Topic: displacement to length  (Read 1068 times)

Hairbear541

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displacement to length
« on: 12 January 2020, 22:16:35 »
is there any formula to figure out displacement or weight  to length of warships..ie black fleet warships . can anyone help ????

Daryk

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Re: displacement to length
« Reply #1 on: 12 January 2020, 22:25:07 »
None that I know of... when I make deck plans, I try to work with the given dimensions and the art.  It doesn't always work out...

Hairbear541

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Re: displacement to length
« Reply #2 on: 13 January 2020, 00:19:14 »
evening there daryk , i've asked simular questions about other processes in building  js and ds , but never get even this much of an answer . so thanks a million for the comeback , at least your honest about things . i guess it all go's back to fasa having nobody even familiar with real naval construction rules . nor did they have any inklying of naval weapons...ie , main battery cannon ranges are always much longer than secondary batteries , much less the different aa batteries . i know i could probably be said to be preaching to the choir . jut had to vent a little about the sheer stupidity of some of the construction rules or lack there of .

Daryk

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Re: displacement to length
« Reply #3 on: 13 January 2020, 05:21:41 »
No worries, venting is what forums are for!  :thumbsup:

Hptm. Streiger

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Re: displacement to length
« Reply #4 on: 13 January 2020, 07:31:38 »
Have done a warship as commission once, was one of the early models (where I had plenty of time to complete it) so I also used GurpsVehicleBuilder for giving that vehicle some stats.
This and some others come around 100kg/m³ to 200kg/m³ - so a McKenna might end with a volume of 190,000,000m³ to 95,000,000m³ let's assume we take the "lore length" of 405m you have an average cross profile of 469,000m² to 234,000m²

The alternative we consider that its a "cylinder" with a radius 386m (for the low density) or better 273m.
Of course, the average "density" is just a rough estimation and i used the lore length.

Sharpnel

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Re: displacement to length
« Reply #5 on: 13 January 2020, 07:51:48 »
Jumpships and Warships, when I design them, is at least 1000 metric tons per meter of length.
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Hairbear541

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Re: displacement to length
« Reply #6 on: 13 January 2020, 12:50:17 »
thanks guys for the feedback , but you know even using what tn sharpnel uses the main hull plating would still be beer can thin and any armoring would only have the thickness of vinyl floor tiling . and don't get me talking about the ships structure , because even at 1g of thrust it would look like stomped on beer can . but i guess i'll have to go with what i can get . since the creators of this game were not dealing in reality , and if i were 40 yrs younger i would probally try find out just what in the hell they were smoking .

monbvol

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Re: displacement to length
« Reply #7 on: 13 January 2020, 14:27:27 »
Yeah many designs could have their dimensions cut in half or so and not have any problems.

worktroll

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Re: displacement to length
« Reply #8 on: 13 January 2020, 16:03:38 »
thanks guys for the feedback , but you know even using what tn sharpnel uses the main hull plating would still be beer can thin and any armoring would only have the thickness of vinyl floor tiling .

I did similar maths a long, long time ago - based on effectively cylindrical hulls at stated lengths and proportional diameters - and turns out mylar is more accurate than vinyl. :)
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monbvol

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Re: displacement to length
« Reply #9 on: 13 January 2020, 16:26:38 »
Some ships are bad enough I am convinced large parts actually have negative density or at least pure true vacuum.

Cannonshop

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Re: displacement to length
« Reply #10 on: 13 January 2020, 16:48:12 »
remembr that Battletech began as a reworking of Traveller.  If you presume the displacement is in "Hydrogen tons" (aka the volume of a sphere of hydrogen, weighing one ton)  some of it makes...

...even less sense. lol.
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Hairbear541

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Re: displacement to length
« Reply #11 on: 13 January 2020, 17:37:52 »
hey , guys i'm not trying to shoot bt down , i've played this game every since it came out back in the 80's . but as i said in a previous post , boy oh boy would i love to find out what they were lacing their j's with , some truly mind altering stuff . guess i'll have to go over to wolfshipyards and ask the question (was there ever a builders manual made for bsg , and if so what its name was , and where if possible i can get a copy) .
even js are way way under weight : case in point the monolith which canon says weighs in at 430,000mt should be more like 4,300,000mt just going by how huge this sucker is .

Hptm. Streiger

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Re: displacement to length
« Reply #12 on: 14 January 2020, 05:08:29 »
I must disagree, you should not do the mistake in comparing stuff from BT with stuff from today.

As some examples, you should consider new materials science that already made huge steps forward compared to the 80s, take that metal foam behind a ceramic plate... its more effective than armored steel and only weigh 75%. Carbon or other materials offer resilience and stability for a fraction of the weight of aluminum sheets.

Also glass-fiber instead of copper saves weight en masse (wasn't it alone to reduce the mass of an M1A2 by 3tons)
I made a quick example with GVB. Let's assume we build a habitat with a common technique of the last decades. For 3 guys, purely battery-driven with environment control and life support and provisions for 7days. It ends near 30,000lbs. The same habitat with "fictional" tech - might only weigh 10,000lbs. Saving lots of mass for electronics ad structural material.

Oh.... just realized that my argument is based on the wrong number of the McKenna length (i used 405m instead of 1450m -> that's the "TRO2750" length not the "TRO3057" length aye?)


Hairbear541

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Re: displacement to length
« Reply #13 on: 14 January 2020, 10:47:10 »
i'm not ruling out advances in material sciences , since we now have transparent aluminum(a star trek staple) , that may in the near future be replacing all the glass windows of the iss , and quite likely all other space faring craft of all the space faring nations .

MechWarriorFox

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Re: displacement to length
« Reply #14 on: 19 January 2020, 04:02:39 »
I must disagree, you should not do the mistake in comparing stuff from BT with stuff from today.

As some examples, you should consider new materials science that already made huge steps forward compared to the 80s, take that metal foam behind a ceramic plate... its more effective than armored steel and only weigh 75%. Carbon or other materials offer resilience and stability for a fraction of the weight of aluminum sheets.

Also glass-fiber instead of copper saves weight en masse (wasn't it alone to reduce the mass of an M1A2 by 3tons)
I made a quick example with GVB. Let's assume we build a habitat with a common technique of the last decades. For 3 guys, purely battery-driven with environment control and life support and provisions for 7days. It ends near 30,000lbs. The same habitat with "fictional" tech - might only weigh 10,000lbs. Saving lots of mass for electronics ad structural material.

Oh.... just realized that my argument is based on the wrong number of the McKenna length (i used 405m instead of 1450m -> that's the "TRO2750" length not the "TRO3057" length aye?)
I would say that Battletech made predictions based on an '80s viewpoint and things make far more sense. Then again, we've got what is essentially EndoSteel these days. ;)

monbvol

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Re: displacement to length
« Reply #15 on: 19 January 2020, 12:51:41 »
And it isn't so much that materials can be strong but that it is more that as I stated some designs have such low density that they have to have areas where there isn't any air to breath.

Nicoli

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Re: displacement to length
« Reply #16 on: 19 January 2020, 20:40:21 »
We can't forget what potential uses of aerogel might have in future armor, especially in space where weight is more of an issue then size.

And it isn't so much that materials can be strong but that it is more that as I stated some designs have such low density that they have to have areas where there isn't any air to breath.
Why would that be a bad thing. Vacuum areas acting as spaced armor or just buffer areas would be just as expected in space as the void areas in Battleships from WWII and even modern armored vehicles.

Cannonshop

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Re: displacement to length
« Reply #17 on: 19 January 2020, 22:30:17 »
We can't forget what potential uses of aerogel might have in future armor, especially in space where weight is more of an issue then size.
Why would that be a bad thing. Vacuum areas acting as spaced armor or just buffer areas would be just as expected in space as the void areas in Battleships from WWII and even modern armored vehicles.

Weight is only a problem if you're building your space-ships on the ground. Mass is a more significant factor than weight in space.
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monbvol

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Re: displacement to length
« Reply #18 on: 19 January 2020, 23:02:16 »
Why would that be a bad thing. Vacuum areas acting as spaced armor or just buffer areas would be just as expected in space as the void areas in Battleships from WWII and even modern armored vehicles.

Now I do realize due to lack of exacting dimensions any numbers I can calculate are at best educated guesses but when I get numbers of around ~50kg/m3 I do have to wonder just how much void area there is and if there is some sort of negative density involved in some of these compartments.

Hptm. Streiger

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Re: displacement to length
« Reply #19 on: 20 January 2020, 04:09:42 »
Large parts of the BT space ships consist intentionaly of areas that are lighter than air.
Although my rough estimation of the McKenna - ends with 40kg/m³  8)

Maybe I should make a 3D model of a BT Warship - then we could add objects and density and stuff like that.
Although - when you consider the cargo bays.... 255,000 tons of air is quite some volume, same is true for 1,600 tons of hydrogen
« Last Edit: 20 January 2020, 06:06:20 by Hptm. Streiger »

Daryk

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Re: displacement to length
« Reply #20 on: 20 January 2020, 06:41:18 »
For the sake of your sanity, I don't recommend doing a 3D model...

Hptm. Streiger

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Re: displacement to length
« Reply #21 on: 20 January 2020, 07:10:43 »
For the sake of your sanity, I don't recommend doing a 3D model...
Considering that I was driven nuts by the Pike, Shreck AC and AC2 carrier, already... It can't be that hard its just that I need to consider the weapon pods first.... how large is a Naval PPC, how does the ammunition feed for a 4,000ton automatic cannon looks like - ok it only fires 1ton of ammunition per minute (that is less ammunition compared to a UAC20)

Oh, noes the gear in my brain start spinning.....

Daryk

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Re: displacement to length
« Reply #22 on: 20 January 2020, 07:52:02 »
And do the slide into insanity begins...  ::)

Hptm. Streiger

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Re: displacement to length
« Reply #23 on: 20 January 2020, 11:04:46 »
And do the slide into insanity begins...  ::)
the problem is the engine, do I use the BT stats that defy Newton, or do I use "Epstein drives"

Daryk

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Re: displacement to length
« Reply #24 on: 20 January 2020, 11:08:49 »
If you're doing BT ships, you should use BT engines.

Hptm. Streiger

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Re: displacement to length
« Reply #25 on: 20 January 2020, 12:30:08 »
If you're doing BT ships, you should use BT engines.

So 2000tons of fuel providing 50 burn days of 1g thrust....omg - even assuming the exhaust velocity of the BT sub-light drive emits particles with 300,000km/s the Congress Frigatte still might need 109,000tons of fuel. Not to mention that the 111 PetaWatt engine would provide enough energy to boil all oceans on Terra......
I really hope I've made some rounding and comma errors here....

Doesn't seem so - travel time from the Nadir to Earth (10 AU) would be 9 days - and consume 19kt of fuel.
« Last Edit: 20 January 2020, 12:33:21 by Hptm. Streiger »

Daryk

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Re: displacement to length
« Reply #26 on: 20 January 2020, 12:37:09 »
Strategic thrust is a whole other ball of snakes.  The efficiency of strategic drives has always exceeded that possible with pure matter/anti-matter annihilation.  Someone once theorized that since Kearny and Fuchida first developed their theories based on something going on in a fusion reactor that maybe the same thing that permits FTL travel provides the extra energy.

Hptm. Streiger

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Re: displacement to length
« Reply #27 on: 20 January 2020, 13:10:46 »
Strategic thrust is a whole other ball of snakes.  The efficiency of strategic drives has always exceeded that possible with pure matter/anti-matter annihilation.  Someone once theorized that since Kearny and Fuchida first developed their theories based on something going on in a fusion reactor that maybe the same thing that permits FTL travel provides the extra energy.
...ok tactical fuel makes more sense - the 2000 tons of fuel for the Congress would provide ~2 days of 1g thrust. (far from possible, however, but better than strategic fuel) So lets cut the acceleration by factor 10 (you don't need a grav-deck when you can accel with 1g)

the exhaust velocity of 10% c. Now let's assume that our Frigate is 10% accelerating 80% coasting and 10% decelerating when we put more mass - read water in the exhaust flow we get more acceleration, so 0.4g instead of 0.1g. This might result in a travel time of 19 days for 10AU, and leave whooping 70% mass for the other stuff but fuel.  (And when I remember the Congress has 20% cargo).
** I hope I made the calculation right, based on formulas to be found at Atomic Rockets.

Daryk

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Re: displacement to length
« Reply #28 on: 20 January 2020, 13:43:44 »
Atomic Rockets is a great source for making your science fiction harder.  I'll also say I have long advocated for cutting Strategic Thrust by a factor of 10 to get it in the realm of reality.  Taking the fusion reaction beyond H-H can almost get you there.

Nicoli

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Re: displacement to length
« Reply #29 on: 20 January 2020, 17:00:59 »
Weight is only a problem if you're building your space-ships on the ground. Mass is a more significant factor than weight in space.
Lol, phone deleted my post first time I wrote it and screwed it up on the second time.
Now I do realize due to lack of exacting dimensions any numbers I can calculate are at best educated guesses but when I get numbers of around ~50kg/m3 I do have to wonder just how much void area there is and if there is some sort of negative density involved in some of these compartments.
50kg/m3 is low but that all comes from the assumption that we are using modern common structural building techniques along with ideas of needing to compress a ship into the limits of something that needs to move through water. Aerogels are extremely light and we are just scratching the surface of their uses for example. Their electrical insulating and heat shielding properties would be extremely useful in a composite armor. While this would most likely make the armor very bulky, it would have a significantly reduced mass. I'm the same way structural metal components can be made using metallic foam filled beams and panels that also trade bulk for significantly reduced mass. Combine that with likely a double hull system with significant void 2-5m between the inner and outer hulls to dissipate any explosive force from explosive munitions.

 

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