dorade vent with vetus mushroom

[captainal]

I have an '88 Crealock 34 and I think the Vetus mushroom vents, inside the dorade vents, are supposed to open and close. Can anyone tell me how they work before I break something trying?

[CapnHand]

If it's like this:
There should be a knob in the cabin under the dorade with which to close it. Lefty loosey, righty tighty.

[captainal]

My black knobs just unscrew from the bolt. I guess the bolts have corroded enough to not be turning and the knob should not be coming unscrewed (?)

[JohnRPollard]

Correct. The knobs should not come unscrewed. Maybe apply a little Mystery Oil or Liquid Wrench on the shaft above where it passes through the threaded hole. Let it soak a few days and then work it with a vice grips. In the meanwhile, you can turn the cowl vent away fromt he breeze to reduce the inflow of air.

Except in very cold or bumpy weather, we rarely close ours. But it's a good idea to give them a spin up and down every so often so they don't cease up.