I'm going to assume you're using the basic rules (if you're using some other set like BFG:R, FAQ 2010, BFG:FR, or -shameless plug - BFG:XR), let me know.
In terms of general positioning, which is true for most ships with the traditional "1 front gun, 1 gun on each side" setup and no overlapping fields of fire (such as dorsal weapons), you'll want to use squadrons of ships combining their fire, and placed so that there's at least one enemy in each firing arc.
A single Kill Kroozer with only S4 heavy gunz and SD6 gunz on each side won't be able to hurt much other than escort ships by itself, but with even 2 in a squadron together, S8 and S2D6 is substantially more effective, due to the way the Gunnery Chart works. If the Ork player can position their ships in such a way that you've got one enemy close up on the broadside, and one out in front, you can unload both your front and side firepower (at two different targets). You can then try to stack up the damage with each of your squadrons so that you can at least try to put damage on at least a couple of ships per turn.
...That being said, my understanding is that Orks suffer from some balance issues in the classic rules. I'm not fully versed in how bad this actually is, but if you're both skilled players, you may be running into some overall mechanical problems as opposed to just tactical issues.
Also, I am not an expert on this game... so try things out. Maybe I'm totally off base