Extruding from a domed surface

Hello all.

I’ve hit another stumbling block that I need some help with please. how do I go about cutting a hole the same diameter as the blue extrusion, through the domed red surface, but perpendicular to that same surface? I’m trying to form the vent opening as per the photo.

Note that the central axis of the blue extrusion is in the right location.Query.3dm (2.8 MB)

TIA