Port side has no plenum box just open to engine compartment. Both terminations are non-directional.
https://cimg1.ibsrv.net/gimg/www.off...0ed85cb2c.jpeg

Starboard side does have these two small vents that may tie in somehow…
https://cimg7.ibsrv.net/gimg/www.off...5bbd6b940.jpeg
Starboard side 7’ forward of exit vent. Must tie together in behind upholstery.
https://cimg8.ibsrv.net/gimg/www.off...af9a9d6ca.jpeg
Starboard side non-directional termination.

I've seen the 'outlet' side vent system with multiple hose connections. Often 2 of them have dedicated air fans..and one hose was open, so it would flow air unobstructed from the other inlet side.

Often engine bays are not well ventilated, and don't even meet the demand of the engine's airflow...where you'll be sucking air in both side when running..as well as anywhere else it can draw air from. All depends on setup.

Might be worthwhile to contact Cobalt.

Padraig

You want bilge air exiting to be drawn from the lowest part of bilge since gas fumes are heavier than air. However, that Cobalt looks different than the ones I've delt with. I'd do like Padriag stated and contact Cobalt. Lot of liability if done wrong.

So did some more investigation today with an inspection camera…found a below deck cavity leading from the blower floor area to about a foot above the bottom of the bilge so I don’t need to run a 3” hose into the area…for now I plugged the 2 extra floor port so higher percentage of the air will pull from that side bilge port cavity. I’ll leave the two high plenum open ports open for now (don’t see any screw holes like they were ever used or plugged). I will contact Cobalt and see what’s proper on ventilation.

I would use the 2 round vents for blowers and the big vent and 'manifold' for make up air.
I bet somone stuck that hose in there and it used to go to the round vent , that`s my guess.