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 Post subject: shipbuilding take 2
PostPosted: Sat Jul 14, 2012 4:34 pm 
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Joined: Thu Jul 03, 2008 2:09 am
Posts: 573
Location: Queensland
Rereading my older 'shipbuilding' post made me wince and be a bit embarrassed at how clunky and 'meh' it all was; lots of flailing about with very little useful outcome. So, I'm taking a second stab at things but without the anal-retentive fake detail... just estimates.

The hull is based on a sphere inside a bounding box, similar to before, but with the acceptance that it is an approximation. I won't even worry about configurations directly as much of that sort of thing can be looked sideways at with my use of hull proportions.
Given a hull displacement and the hull's proportions, the rest can be figured relatively easily. The hull proportions are ratios of length to width to height, such as l:w:h. A type 's', for example, would be 1350m^3 and l:w:h of ~5 : 3.2 : 1 (37.5:24:7.5).
I divide the actual volume by .5236 to be an approximation of the size of the hull's bounding box, and then divide that volume by the different ratios to get the size of the cubes that make up such a bounding box. Taking the cube root of that number gets the length of the cubes that compose the bounding box.
(1350/.5236)/(5*3.2*1) = 161.144 m^3
161.144^(1/3) = 5.44 m

If I multiply the result by the length, width and height proportions, I can have an approximation of the overall dimensions for the hull.
My example is a worst case scenario because a wedge, such as a type 's' uses takes up a much smaller volume inside its bounding box than a stretched out sphere takes. I can live with it as it would be an extreme case that is not overly common compared to most of the other ships/vehicles that can be made, and I would sacrifice that small bit of 'detail' in favor of ease in use. As the dimensions are approximations, I can fudge when drawing deckplans. The important thing is that performance stats will work out assuming I use the same procedure for all ships and vehicles.

length = ~27.2m
width = ~17.4m
height = ~5.44m

Having an idea of basic dimensions will be used to limit spinal mounts as hull length limits spinal mount tunnel length, and to limit agility through the longest dimension affecting the hull's moment of inertia.

the hull's surface area is proportional to the surface area of the hull's bounding box. As it is based on a sphere/ellipsoid within a bounding box, stretched as the box is stretched, That proportion is .5236, the same as the area of a sphere to the area of that sphere's bounding box.

(27.2*17.4)+(27.2*5.44)+(17.4*5.44)*2*.5236 = ~750m^2

frontal x-section can be approximated by width*height*.7854, for use in estimating atmospheric speeds
lifting area can be approximated by length*width*.7854, for use in estimating aero performance.
Surface area relates to the number of hardpoints available for mounting turrets, sensors, radiators, etc.
I have an idea that the level of streamlining ( drag_coeff.) is related to the number of hardpoints actually used vs. the number of hardpoints available. Fewer protrusions off the hull makes for better streamlining. Naturally, pop-up fixtures will not count against streamlining, but they will take up volume inside the hull and cost more.

For thrust and structure, I will base it on a 100dt ship with an MT armor of 40, massing 1000 tonnes, and is capable of 10g's structurally, or 10,000 tonnes thrust.
The base structure comes from the hull material itself and each 5% of the ship's volume adds another point of structure.
The amount of thrust the hull can handle is based on the square cube law.
A 600dton ship, without extra structure would be able to handle ...
6^(-2/3) *10g's* 1000tonnes* 1structure = 17,200 tonnes thrust for 2.86g's
if we add 60dtons of structure to this hull..
6^(-2/3) *10g's* 1000tonnes* 3structure = 51,620 tonnes thrust for 8.6 g's, assuming a ship's mass of 6000tonnes.
Naturally, reducing the ship's mass will allow for greater g's for a given amount of allowable thrust.

Big ships will wallow about unless large volumes of structure are added and small ships can handle huge amounts of thrust without crumpling.
Big ships will have fewer hardpoints than standard trav. Big ships will not do well in atmospheres compared to standard trav.
Big ships may have powerful spinal mounts.

I will guess that the amount of thrust the hull is capable of and the total surface area can be used to estimate crush depth when diving.
More structural capability lets a hull go deeper... and less surface area lets a hull go deeper.

my quest for a perfect game continues....

My SF-RPG Universe stuff

 Post subject: Re: shipbuilding take 2
PostPosted: Tue Jul 17, 2012 12:34 am 
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Joined: Thu Jul 03, 2008 2:09 am
Posts: 573
Location: Queensland
after some thought, I realise that I need to have a reasonable way to add a centrifuge section to a ship.
If it is in the shape of a torus, my previous idea wouldn't work unless the 'length' is the same as the centrifuge's circumference.
Then there is the actual attachment...
I need to decide how to allocate the hardpoint idea with module attachments for ships. Perhaps 1 hardpoint lost on both the ship and the module for every 100m^2 of contact between them?
Say I had a ship made of cubes stuck together.
4 cubes in a row with 18 hardpoints ( 4 on 4 sides and 1 on each end ), and I want to add 2 more cubes as engine pods ala a Gazell class escort, one on each side, then I'd lose 2 hardpoints on the main hull and one on each module. I'd have a ship with 26 hardpoints total... a good way to gain surface area for engine exhaust and radiators maybe.

The same might apply to adding ferris-wheel, centrifuge modules.

I'll have to think about this a bit more.

My SF-RPG Universe stuff

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