Pictures of my Catalina 30 exhaust project. Please consider 3/8"-16 stainless set screws with washers and hex nuts instead of flange bolts for the attachment to the manifold. The strategy on a Catalina 30 is to get as much rise as possible within the limitations of the galley cabinet. It will never be ideal but we do what we can.
Old black iron pipe and new stainless pipe..Note that the USCG and ABYC require schedule 80 pipe which I would not expect to find at Home Depot.
And the finished stainless pipe installed