TIP- Turn or burn!

[PoorOldSpike]

In case players haven't noticed, ships in CMANO/Inferno/Chains will only fire their point-defence weapons if the target is in their firing arc. For example if you've got a CIWS gatling or cannon whose arc is partially blocked by the ships superstructure, it won't fire if sea-skimmers are coming in from that blind spot.
Ships in the game on plotted courses don't automatically turn to open their arcs, so you have to manually order your vessels to turn by dragging the end of their waypoint to turn the ship broadside (or near-broadside) on to the skimmers.

PS- If you hear the rat-a-tat of a point-def gun firing and can see it's tracer, that doesn't mean ALL the ships p-def guns are firing.
For example if skimmers are coming in on your bows, only the gun on your forward decking will engage them; the gun on the rear decking will remain silent because its forward arc is blocked by the superstructure, so turn manually to allow the rear gun to fire too.
As regards enemy computer-controlled vessels, they never turn to open their arcs which places them at a disadvantage because you can cunningly manoeuvre to hit them in their blind spots..