[Ragnarok-X]

Good hints, Atrocities, but a problem comes up. If his ships have impressive ship defense, then most probably torpedos at long range wont even hit, due to the -10 combat modifier per square.
Then again if you have one level more combat sensors than he has ECM and you properly train your ships and fleets you can make up that.

My suggestion would be to increase attack % and use long range weapons. I wouldnt use defense % since my strategy would be stay without his weapons range, while being able to score hits myself.
Keep in mind to always have a few repairships with you, so you engines will be repaired each turn. A few turns later you may be able to mass more ships then he can disable and can finally overcome him. You could try launching fighters and manully moving them into the sector where his ships are, i think repulsors cant target fighters and so you may be able to defeat him without losses at all ?