Since I was to play Star Trek: 25th anniversery, I played EGA Trek instead, which is my the 2nd best classic trek game for the PC, IMO.

Anyway, EGA Trek is basically a spiced up version of the many "trek" games available. You have your a grid of 8x8 quadrants. Each quadrant contains 8x8 sectors. Each sector contains either a ship, a star base or a star.
The goal is to kill all Klingons and survive.

The game features three types of energy:
1) Main Energy (used for phasers and warp)
2) Impulse Energy - used to move inside a quadrant
3) Shields - used to deflect energy blasts

And while playing the game, I started to think about the correlation between shields, hits and damage.

In the series, the enterprise could be hit by some blasts, which wouldn't do much besides draining some energy from the shields.
Stronger blasts did damage and drained more energy from the shields.

So, I was wondering how one could simulate this. My best idea was to say that a shield will block all attacks up to a certain percent of the current shield energy.
To make the discussion simple, let's say it'll block all attack with less energy than 50% of the current energy.

If we have 500 units of energy in the shields, a hit with up to 250 units of energy will not cause damage to the ship, but simply drain this energy from the shields.

If something stronger hits the shields, the shields will at first block a part of the attack. The remaining energy will be split upon damage and shields, but the energy drain from the shields is increased.

Example:

 Shield Energy: 500
 Attack: 300
 Shield overload modifier: 1.25.

 Amount of energy the shield can block totally: 50% of 500 = 250
 Remaining energy: 50
 Energy split between shields and damage: 25/25
 Energy drained from shields: 250 + 25*1.25 = 287.5
 Damage: 25

 New shield level: 500 - 287 = 212.5

Then I thought that this looks strange, since the shield drain to hit ratio never felt like 1:1 in the series. As long as the shields were holding, everything was fine, and they could take quite some hits.

So, I added a shield drain modifier.

 Shield Energy: 500
 Attack: 300
 shield drain modifier: 0.5
 Shield overload modifier: 1.25.

 Amount of energy the shield can block totally: 50% of 500 = 250
 Energy blocked: 250
 Energy drained: 250 * 0.5 = 125
 Remaining attack energy: 50 
 Energy split between shields and damage: 25/25
 Energy drained from shields: 125 + 25*1.25 = 137.5
 Damage: 25

 New shield level: 500 - 137.5 = 362.5

This feels better. Esp. if one also plays with the "efficiency factor", also the amount of energy the shields can block totally or if the main reactor can provide some energy each round to refill the shields.

Let's say the main reactor can provide 5% of the maximum energy each round to the 3 energy systems, we can a behavior that seems more or less ok.
Several hits in a small time frame will cause more damage than the same number of hits, with the same power distributed over a larer time period - which seems to be the way it works in the series.

That way one can also transfer "more power to the shields" without giving the energy a "battery feel".

Ok, why am I posting this?
Mainly because I never thought about possible ways to implement shields, and I'd like to hear other ideas on how one could handle it, comments on my ideas, etc.

Justt wondering. While writing the above, it occured to me, that it would allow you to some nice things with regards to equipment.
Let's say that the shield efficiency (how much energy it can block) is also variable.

So, you can give smaller, but newer ships an advantage by increasing the efficiency (how much of the current shield energy can be blocked) and the drain modifiers.
It would also allow one to add a "building" aspect into the game. More max energy? Better efficiency? Better main reactor, so ethe shield reload is higher?

Give each of these options a price - not only with regards to actual costs, but also size or weight and the player has something to tinker with when he upgrades his ship (star base, or ship "level up").

Not sure it needs a remake. The original EGA Trek is still fun
I was basically wondering how one could implement trek like shields so that sentences the "Shields are down to 50%" and "Emergency power to shields" actually would make sense in game

For my ideas (which I haven't tried to implement yet but seem sweet to me), I'll first briefly explain quantum tunneling.

Say we have a particle moving to the right with a kinetic energy E. It encounters a potential barrier of height V. Classically, it will cross the barrier if E>V, with its kinetic energy reduced to E-V. If E<V, it will hit the barrier and (probably) rebound. If you absorb the kinetic energy into the potential barrier to reduce it, then this will already work very nicely for shields.

I like the quantum idea better though: in this case, there is a finite probability that even for E<V, the particle tunnels through the barrier and for E>V it can still bounce back. There are two possibilities I can think of for shields here: either you calculate the probability of the particle penetrating the barrier and roll for that. If it penetrates, it penetrates and otherwise you absorb the energy into the barrier and lower it. My preferred method would be to do this in proportion though: if the probability amplitude for penetration is 10% and for reflection is 90%, then you absorb 90% of the energy in the shields and 10% goes to the ship (likely the hull).

Either way, hits will reduce the shield strength and chance of blocking and at the same time there is always a moderate chance of taking damage, so shields provide mostly statistical rather than absolute protection. Powerful hits instantly overload the shields and do damage to the ship. I think all of this is also reasonably consistent with the Star Trek way of shield operation.

Of course, the only way I ever implemented shields at all is by having them take the damage instead of the hull. This is easy, but I think the method I outlined above (distribute damage between the shields and the ship in proportion with the fractions depending on the strength of the shields and the energy of the projectile) will be both quasi-realistic and fun. The statistical distribution of full damage has the same result on average but has the disadvantage that even at full shields, your hull can take the full impact of a photon torpedo.

Actually, I think they do. Think of phrases like `shields are holding, minor damage only' or the combat sequence at the end of Star Trek VI, where the Enterprise takes quite a beating before Scotty's `Shields collapsing!'
The ships don't take full damage, but I get the impression that the shields become much less efficient at blocking fire as they take damage.

Nope, shields block physical objects as well as particle beams. See for instance the TNG episode Relics, in which Geordi and Scotty use an old ship to jam open the portal of a Dyson sphere, or indeed the episode you mentioned (Preemptive Strike), in which Lieutenant Ro takes a Maquis figher craft through the Enterprise shields at a weak spot, but only because Picard order Worf to let them pass (ie, weaken the shields enough for the shuttle to pass through).
I'm sure there are more examples. More interesting, earlier episodes of the original Star Trek suggested that you cannot fire weapons from within the shields either: they had to drop shields to fire torpedoes and phasers or use the transporter (as they also need to do in TNG). The point about phasers and photon torpedoes not being able to get out while inside the shields was later forgotten or abandoned though...

A photon torpedo is very much a physical object. I'm not sure if you get to see one in Next Generation, but you get to see them in Star Trek III and Star Trek VI at least (Spock was buried in one). It's a warhead with a detonation payload of anti-matter. And they don't go through shields (see Star Trek Generations, for instance) although the energy released by a torpedo blast can overload the shields if it detonates too close (eg, The Nth Degree).

And no I'm going to do something else, because being able to quote those episodes from memory scares the hell out of me.

Well, they beam with raised shields as well if they need. But I don't think we should expand this to a discussion of logical flaws in a Scifi series.

back to my original topic: how would you handle such a protection? You don't have to look at it from the Star Trek or even scifi side, consider it to be a protective spell in a fantasy setting if you like.
Or an armor in a modern setting, it doesn't really matter

I just want to discuss the basic idea of it, and how one could implement such thing.

What about this:
Ship has two stats:
-Hull integrity (or hitpoints if you wish)
-Shields
Shields have also stat called "damage resistance". So when some blast hits the shields it does damege to the shields equal to its dmg statistic plus does damage to hull if dmg statistic is greater than "damage resistance"

Shileds -= weapon_dmg;
Hull -= weapon_dmg - dmg_resistance;

Shields block whatever objects the plot requires them to block, and the screenplay writer(s) will always find an excuse for something to penetrate the shield / damage the hull / wiggle around persons on the bridge, provided the plot and / or dramatic curve of the movie demands so.

Anyway, as far as damage goes, I prefer to have a minimum blow strength that is required for a single blow to cause any damage at all. Otherwise, my itsy-bitsy 0.5 mW laser gun can destroy a giant asteroid, provided I keep firing at it long enough.
Other than that, all I do is linear damage to the shields, and once they're down, linear damage to hull. Shields recharge, hull doesn't unless you repair it. Works for me.

Shields don't recharge, but their energy source does, energy can also be temporarily rerouted from other systems not as aparantly vital...

Seperate Thought: One thing I wondered about in startrek was that they were out gunned all the time, with a shuttle bay full of shuttles, why didn't they ever use the shuttles to battle? (or even try supe up the shuttles to battle?) (1 big ship) < (1 big ship + 15 tiny ships) ...

They need to drop shields to launch the shuttle, which implies a scenario along the lines of

launch shuttle
drop shields
enemy photon torpedo
BOOM

Besides, I think the amount of shuttles isn't that large. I think the Enterprise is supposed to carry ten; Voyager is supposed to carry two (so that they managed to loose about twenty over the run of the series can in my opinion only be explained by assuming that they reserved replicator power so they could build a big one right into the shuttlebay so all they had to do was say `Computer, one shuttlecraft!').

Small note: whether or not the shields need to be lowered depends on the plot and speed of the shuttle

As does the conversion between warp factor/lightyear per day or even full impulse/lightyear per day (sic!).
In fact, that can even change in the course of an episode (Star Trek Generations, Enterprise: Broken Bow).

I still don't think shields should ever "recharge" but the shield's power source can... of course to simply things, most implimentations (in games) have the power source as an unknown embedded in the actual shield technology, and the shields do appear to just "recharge" -- ex: protoss in starcraft...

edit: I want a dylithium crystal!