Hi,
I'm new to this so bear with me please. I am trying to design an attack ship to win in combat and I have finished researching all tech trees/branches. The computer opponents are many levels behind and yet even with the base ship size crammed full of shields and the best weapons, tracking, ecm and everything else, the best weapon I have can do 140 points of damage where as my enemy uses a dreadnaught, ie 1 size smaller at has an acid weapon that does 300 points of damage. I get destroyed every time. how come on a lower tech the computer gets much better attack capabilities?

I've found that the key to constantly win battles is range. If you have a range advantage you can cripple the enemy and when they get close you finish them with medium range weapons. Of course defense against long range missiles and some shields/armor is needed too.
So keep out of range of the enemy until you have done enough damage with your longer range weapons and then swoop in for the kill.
Alternatively make "wall ships". These are ships you put in front with just a tiny weapon that can target most things, not only ships and fill them up with defenses. Have the rest of your fleet stand behind them and fire away.

If your enemy have acid weapons they have a special technology used by their race. These are more powerful than the standard weapons that all can research and use.
Personally I tend to not use special technology when creating a race. Usually I have more use putting race points in faster research and other similar things.

Oh and what mounts are you using for your weapons? A few weapons on bigger mounts is much more powerful than more weapons on smaller mounts.

Thanks very much Tarm, for your wisdom, I'll have to check my mounts and see.