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Re: [FT] Hull strength and Stress

From: "Oerjan Ohlson" <oerjan.ohlson@t...>
Date: Sat, 27 Mar 1999 18:34:33 +0100
Subject: Re: [FT] Hull strength and Stress

I've been meaning to reply to this earlier, but other things got in the
way :-(

> >> ** Hull Stress Ratings **

> >Instead, the hull integrity measures how much of the hull structure
> >can *remove* - how many bulkheads can be breached, how many 
> > struts torn off etc - before the ship no longer is able to survive
> > stresses caused by its own engines, etc. 

I should've been a bit clearer here. The "etc" includes all those other
- and rather important - things like better shielding, redundancy etc
which delay the breakdown of systems represented by the normal treshold
checks. The same applies to the "destroyed" status - it isn't
specifically structural breakdown, or fusion reactor
shutdown/explosion, or whatever other specific demise of a ship you
care to think of, but it can be any of them. Well, OK, the reactor is
covered by FB Core Systems nowadays <g>

> >Indeed, some of the "engine damage"
> >results may well be structural results instead - the hull takes such
> >bad hit that the captain doesn't dare to use his engines for fear
> >the ship be torn apart until the DCPs have assessed the damage.
> 2 points, so I'll respond separately
> If integrity measures how much you can remove before before it can no
> longer withstand its own engines, then is it an all-or-nothing
> Why take the leap from full strength (can take th8) to destroyed
> the ship is destroyed)

But do you? If you include effects - real or imagined - of structural
damage into the engine treshold hits as I outlined above, it isn't all
or nothing. Far from it - you have four steps: full power, half power,
no power and destroyed... that's two steps more than any other system
in the game has.

Having said that, the difference between a beam not being dangerously
deformed and the same beam being plasticised all through (and thus
bending badly or breaking) can come very fast. It depends quite a bit
on what materials you have, of course; being a fluid dynamicist turned
ballistician I'm not too up to date on the solid mechanic properties of
modern materials :-( Even less on those of future materials, of course

> Engine hits as structural damage: Ok that is a potential abstraction
> explain it - but why? We havea damage track to show hull damage - we
> have engines to show damage to them.

We have a damage track to regulate how fast *everything* on the ship
breaks down, not just the hull itself. As for why, you answered it
yourself below: the dramatic feel :-)

>  Engines are already relatively small (at 5% per rating) to
> reflect hull damage as well.

The engine systems can reflect this particular effect of hull damage,
since there aren't any hull symbols vulnerable to treshold checks.

> Also if the captain "doesn't dare to use his
> engines for fear..." there are certainly times when it could become a

> necessity - high mission motivation type stuff...That dramiatic feel,
you > know.

This is one of the things you can (and I do) read into the DCP every FB
ship has marked on its very last hull box. As long as the ship isn't
destroyed, there's *always* a chance of getting some or all of your
engines back - but you have to use your own fantasy to decide if this
is because the	engine was broken but now repaired, or because the
captain initially feared that the ship's hull integrity was too
weakened but now has decided to take the risk in spite of all those red
lights <g> One way to represent a high crew motivation would be to give
the crew a bonus to its DCP rolls.


> >I imagine spaceships to work in a rather similar way. As long as the
> >stresses *and the hull structure* are within the design parameters
> >is well, but when you remove enough of the hull structure that it
> >outside the parameters... things tend to go pear-shaped.
> Sure, I can buy that, but that still comes back to the basic idea of
> thought (and my original intent).  The first time I thought of the
idea was 
> for FT2, and basically what I considered was that for every threshold

> taken, reduce maximum safe acc by 2, starting at 8 for all ships,
> that was the max any ship could go. 

There's something called a "safety factor" in engineering; this is
ratio between the stress level a given component can actually survive
and the maximum stress level you expect it to suffer. For a starship,
I'd expect this safety factor to be at least 4 (in its undamaged
state); AFAIK not even today's highly-slimmed fighter aircraft go below
a stress safety factor of 2 for any component.


> Does the concept (not necessarily implementation) of reducing the 
> 'structural integrity' due to damage make sense? 

It makes sense, certainly. It's just that I consider "all hull boxes
gone" to be the point where the ship's stress safety factor falls below
1 (and it therefore risks starting to take damage from its own
engines), whereas you consider that point to be when the ship is

> Is it any more or less logical than a ship which has lost 90% of it's
> points still thrusting  around at th8?

As I see it, the ship which has lost 90% of its hull points has had its
stress safety factor lowered from (eg) 4+ to 1.3, but it is still above
1 - and 1.0 means that the ship (just) survives its own full thrust
without taking permanent damage.

> Is it illogical to assume that a ship, after taking damage, could
have it's 
> hull weakened to the point that full use of its own drives could
> further damage the hull?

Certainly not. This is one of the more likely things to happen when the
last hull box goes IMO. What I think is illogical is to assume that
this will happen when the ship has only suffered a little damage - the
soft drink can in my professor's demo being a 1-point hull (or, more
accurately, a hull suddenly accelerating at thrust-40 or something like
that after taking damage <g>).

Oerjan Ohlson

"Life is like a sewer.
  What you get out of it, depends on what you put into it."
- Hen3ry

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