[FT] Hull strength and Stress

> Jared E Noble wrote:
...Snip...JTL
> That's it for now - Comments?

     Suspend logic.   Trying to understand why a weak hull ship
can have a very high thrust will hurt the brain.

:-)

Bye for now

Just to throw a new thread into the mix...

The Fleet book has freed up many aspects of the ship design system, allowing
easy creation of a more varied array of ships. This, IMHO, is a good thing.
One aspect of the design system that bugs me, though, is the hull strength
issue. Basically, for any given Mass, there are 5 hull strengths you can have
(10-50% at 10% increments.  For extremely small ships, some of these
levels may actually be the same due to rounding concerns.) So a mass 100 ship
can have 10,20,30,40 or 50 hull points. Why not 35? Is there some magic in the
breakpoints where they are.

What I propose (I don't know if anyone does this) is to allow a ship to be
designed with any hull value, with a minimum of 10% or 1 (whichever is more)
The hull rating (fragile, weak average, strong, super) is determined by
comparing against the standard% values. So the above mass 100 with hull 35 is
Average (because it does not yet reach 40%.)

** Hull Stress Ratings ** So now, what good are the named hull strengths?
Obviously 2 ships of equal mass and different hull values are not constructed
equal, and the difference is not in internal armor (because, ummm, that's what
armor is for). So it seems the increased hull is an indication of structural
strength,
'over-designing', etc.
I would think this could have additional, hopefully interesting, effects on
play (though it may invalidate a few designs as currently envisioned). Thus
the concept of Stress Ratings. This is more difficult to explain than it is to
use, so bear with me.

Stress Rating is simply defined as the maximum thrust your ship may
_safely_
withstand.  It is initiall equal to (Hull Integrity / 5% mass).  So
Fragile=2, Weak=4, Average=6, Strong=8, Super=10. Damage will reduce the Safe
Stress rating of your ship. Take your initial Stress, and mark ratings in the
DP track, just like crew points (see FTFB page 8). The first mark equals your
initial rating-1 (example time!)

FSE Jerez CA (Mass 88, Hull 26 (average) Stress=6)
26/6=4 1/3 round up to 5 to 1 mark every 5 boxes
The last box will always be the S.R. 1 box.

Original     With Stress
OOOOO*O      OOOO5*O
OOOO*OO      OO4O*OO
OOO*OO 3OO*O2 OOO*O* OOO*1*

So When the Jerez has taken 5 hits it may safety thrust only 5 pts. This
reduction does not it any way represent a loss of drive capability, but a
reduction in the integrity of the ship's hull.

** Overstress ** Note that in the above discussion it is noted that the Stress
rating is the
thrust your ship can _safely_ withstand. You are more that welcome to
expend more than this rating (assuming your drive is currently capable of it).

On any turn in which you apply more thrust than your current Stress rating,
Roll 1d6 for each point in which your thrust exceeded the Stress rating. Score
these
dice as beam dice with no re-roll, unless you are feeling particularly
mean. (no shields, of course, unless you wish to use ST 'Hull Integrity
Fields') and apply this damage directly to the hull.

Note that these dice are rolled when you move the ship, and damage is scored
immediately. You still make your complete move, regardless of the outcome of
the damage (unless, of course, your ship is destroyed by the damage.) Since
the damage is immediate, if a resulting threshold check cause the loss of
weaponry, you are out of luck when the time for combat comes around.

That's it for now - Comments?

I always assume that a weak hull ship is one that doesn't have a lot of
spare, a lot of access for damage-control, etc., as well as internal
partitioning. That means that thrust wouldn't necessarily be a problem.

> John Leary wrote:

> Jared E Noble wrote:

It is easy for me to understand....recently a highschool girl, in my
area, built a bridge out of toothpics that held up some 1000+ POUNDS.
If something so flimsey could hold up so much, a weak hulled high speed ship
is easy.

The more we think we know, the less we really do...

> Jared E Noble wrote:
<snip>
> What I propose (I don't know if anyone does this) is to allow a ship

I have been thinking the same thing, you just beat me to the list. When
designing ships, there are times that I would willingly trade some hull boxes
for a weapon or when strong hulls don't allow enough space for systems
but as a racial/empire trait, the ship should have more hull than
average.

Your proposal of the minimum of 10% is good and then setting the rating based
on where the percentage does fall. In the end, each mass for hull is counted
separately so swapping some hull mass for systems will work for current mass
and cost calculations. I don't think this will open a hole for munchkinism
since there are trade offs and cost changes while each mass is still accounted
for.

I have started doing this on a few ships. For example, B5 Nova conversion to
FB rules worked out too big with an average hull but to small with a weak hull
so a picked a hull mass and worked from there.

I would like to know what Jon (GZG) thinks about this since it would be a good
optional rule for the 3rd edition.

> ** Hull Stress Ratings **
I can see the reasoning behind this but I'm not sure I would use itin the
'keep it simple' world of FT. Other questions are in a vector environment,
would thrust used for pushes and rotation be added or effect this at all? (a
damage track for a thrust 8 ship would need 12 levels if they are added and
would be cluttered) In a cinematic world many of the inertial forces are
already ignored so why pay attention to this one? This would be a nice house
rule though.

> Jared wrote:

> One aspect of the design system that bugs me, though, is the hull

It can, but those 5 extra points are usually called "armour" <g> And yes, I
know it isn't identical. Allowing any ship to have between 10% (FRU) and 50%
(FRD) of its TMF for hull boxes works just as well as the current system.

> ** Hull Stress Ratings **

[Entire section snipped; I don't agree at all with the premises]

The hull integrity doesn't have very much to do with withstanding
acceleration stresses IMO. Even a Fragile-hulled ship is designed to
survive its own engines without falling apart. (Count the necessary
reinforcements into the Mass used for engines if you like!)

Instead, the hull integrity measures how much of the hull structure you
can *remove* - how many bulkheads can be breached, how many struts torn
off etc - before the ship no longer is able to survive the stresses
caused by its own engines, etc. Indeed, some of the "engine damage"
results may well be structural results instead - the hull takes such a
bad hit that the captain doesn't dare to use his engines for fear that the
ship be torn apart until the DCPs have assessed the damage.

My solid mechanics professor did a rather fascinating demonstration of
this in the first course I read for him. He is a rather big man - 90+
kilos judging from his looks - and he put an empty soft drink can on
its end and stepped on it. Stepped *up onto* it and stood there for almost a
minute, because the can didn't buckle or get crushed. He then stepped down,
made a very minor dent in the (cylindric) side of the
can, put it back down and stepped on it again - and the can was
immediately flattened. The small dent was enough to reduce the can's "hull
integrity" to less than it needed to survive the stresses put on it.

I imagine spaceships to work in a rather similar way. As long as the stresses
*and the hull structure* are within the design parameters all is well, but
when you remove enough of the hull structure that it drops
outside the parameters... things tend to go pear-shaped.

Regards,

> Jared wrote:

> ** Hull Stress Ratings **

OK, It is _designed_ to withstand it's own engines. That's what I tried
to model on the fly (the particulars for the design I submitted yesterday were
generated
at the time - trying to flesh out the rough concept - see below)

> Instead, the hull integrity measures how much of the hull structure you

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 affair. Why take
the leap from full strength (can take th8) to destroyed (when the ship is
destroyed) It seems a middle ground is reasonable (assuming it doesn't disrupt
game play too much).

Engine hits as structural damage: Ok that is a potential abstraction to
explain
it - but why? We havea damage track to show hull damage - we have
engines to show damage to them. Engines are already relatively small (at 5%
per rating) to reflect hull damage as well. 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.

> My solid mechanics professor did a rather fascinating demonstration of

great example, and actually to the point of the original idea I had-
that 'damaged' ships started to lose their integrity. The idea of tying
initial strength to the hull strength came yesterday as I was typing my
mini-rant about
set 10% increments in hull integrity. The 'integrity' concepts sounded like a
potential link, so I went exploring the concept - hope you all didn't
mind the brief trip.

> I imagine spaceships to work in a rather similar way. As long as the

Sure, I can buy that, but that still comes back to the basic idea of my
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, since that was the
max any ship could go. What this meant is that big ships, with their typically
meager thrust were never effected, but the smaller ships could be slowed down
(unless they
popped first - a common enough occurance.  So it pricipally would affect
cruisers - perhaps slowing them down for a couple of turns, and allowing
a decision phase where the ship captain must weigh risks vs. potential
benefits. The attempt to model dramatic moments from various SF sources was
also a factor, I admit.

Another quick note about what you said -
"As long as the stresses *and the hull structure* are within the design
parameters all is well"

Which is very well put. Since we have a system for modeling the source of the
stresses (the drive) as well as one readily available for hull structure (all
it needs is to have breakpoints determined) it seems that 90% of the support
is there to consider them as 2 easily used pieces of the equation, rather than
abstracting them into 1.

So I am more than happy to retract the concept of tying initial Stress Rating
from the proposal, but would like your opinion -
Does the concept (not necessarily implementation) of reducing the 'structural
integrity' due to damage make sense? Is it any more or less logical than a
ship which has lost 90% of it's hull points still thrusting around at th8? (I
know
that question sounds horribly biased, and that was not my intent - I
just can't figure out how to word it to not reflect bias one way or the
other.) 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 actually
further damage the hull?

> Regards,

Jared, I think your ideas about hull stress ratings and damage are good
strarting points. I like the idea of creating ships with any amount of hull
integrity as long as it is above 10%. I also like the idea of being able to
model the damage to the ship as it relates to maximum safe thrust. Here are a
few ideas I have on the subject.

> Jared E Noble wrote:

> If integrity measures how much you can remove before before it can no

I agree. There is nothing wrong with an optional rule that allows you to model
a slowly (or quickly!) deteriorating hull integrity. The problem I have with
the system you proposed, and then quickly retracted, is that it seems to be an
additional burden to smaller ships, as they are less likely to have enough
hull points to soak up any stress damage and they are exactly the kind of
ships that would be designed with high thrust factors. We should assume that
all ships are designed to withstand the thrust factor with which they have
been built. So why not just reduce the "safe thrust factor" proportional to
the amount of damage the ship has taken? At the first threshold check, have
the ship's maximum safe thrust be 75% of the original thrust, rounded up to
the nearest whole number. At the second and third checks, the ship would be at
50% and 25%, respectively.

> So I am more than happy to retract the concept of tying initial Stress
(I know
> that question sounds horribly biased, and that was not my intent - I

I like your idea, and that's why I proposed the system mentioned above. The
way I propose to handle damage from stress is a bit different from what you
proposed. I like the idea you had about having to roll a die for each level of
thrust above the maximum safe rating. I feel we should keep that. On a roll of
a 4 or 5, the ship takes one point of structural damage. On a roll of a 6, the
ship takes two points
of structural damage, if you're using the optional re-roll rules (and
who doesn't?)
re-roll all sixes.
Structural damage, though, should be handle differently from normal weapons
damage. First, it never effects armor. It's unlikely that a ship will have
armor left after the first threshold check, but it is certainly possible,
however, in
sci-fi, I've never seen hull plating break off in chunks when a ship
makes a crazy move or accelerates, so I'd like to keep the armor out of the
mix. Second, in a turn, the first point of damage is removed from the highest
available row, the second point of damage from the next available row, and so
on. If you've already taken stress damage on the last available row this turn,
start taking it from the top again. This means that the ship doesn't take the
full effect of the damage unless the ship is further damaged. I feel this is
in keeping with the dramatic elements of fiction which we are trying to model
by this rule. The choice of which box to check on a row lower than the top
row, is up to the player. In other words, you don't have to check all the
boxes on the lower rows in any particular order. You'll probably want to keep
all the damage to the "far" side of the hull track and skip over all of the
boxes with DCPs for as long as possible. The combination of only taking damage
half the time (only on fours, fives, and sixes) along with the delayed effect
of damage makes this systema real crap shoot, which is EXACTLY what we're
trying to model.

Engineer: Sir, we've lost a lot of hull integrity. Recommended safe limit is
thrust factor two. Captain: What happens if I exceed the recommended safe
limit? Engineer: There's nothing in the tech manuals about this. Executive
Officer: I guess no one has ever been this desperate.

Let me know what you think.

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

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"

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
<g>

> Engine hits as structural damage: Ok that is a potential abstraction

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

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

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

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.

[snip]

> >I imagine spaceships to work in a rather similar way. As long as the

> taken, reduce maximum safe acc by 2, starting at 8 for all ships,

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.

[snip]

> Does the concept (not necessarily implementation) of reducing the

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 undamaged.

> Is it any more or less logical than a ship which has lost 90% of it's

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

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 wrote:

Ahhh, memories of MODS (Mechanics of Deformable Solids - 2nd yr course)

"Fluid Dynamicist turned Ballistician?" One of theses days, we gotta find
out what you do for a living.  (8-)

J.

Jerry Han asked:

> "Fluid Dynamicist turned Ballistician?" One of theses days, we gotta

Fluid dynamics has a little something to do with how missiles behave
in-flight, as well as how their engines perform <g>

Later,

> Fluid dynamics has a little something to do with how missiles behave

First time I read that, I saw "...how their >engineers< perform."

(visualizing:
Oerjan to his boss--
"We are studying the viscosity of akvavit relative to beer--ah, I mean,
various alcohol fuels...."

> On Sun, 28 Mar 1999, Oerjan Ohlson wrote:

> Jerry Han asked:

translation: "i could tell you, but then i'd have to kill you." :-).

Tom

> Thomas Anderson wrote:

You know, you're the first fluid dynamicist person I've met who actually

admits fluid dynamics is useful. Most of the people I ran into in University
called themselves 'Aerospace Engineers' or something, even if they did nothing
but fluid dynamics. (Well, except for the person who taught my undergrad fluid
dynamics, but he was just one of those damn
mathies, like me.  (8-) )

> translation: "i could tell you, but then i'd have to kill you." :-).

Hmmm. I knew there was something fishy going on there.... no, not the light,
NOT THE LIGHT!!!!

)!@$*()!@*$)(!@*#)(@*!)($&!@)($&)(!@#)(!@*#)(*!@@(#1