how the wind catches underneath the cover when it is open, lifting and dropping it
We have a Maxxair in our bedroom area of the 2551 and find it to be an excellent product for all the reasons that Fred mentioned. We have the standard bathroom vent in in the bath area and from day one installed a vent cover over it so we can use it while raining. It works great for a bathroom fan.
In the galley area we have the Fantastic fan. We did a modification on it so that it has bidirectional air flow. This works great. We were always forgetting to close the vent cover and then stress about rain. We did not want to order the Fantastic vent cover for two reason, one because it requires drilling into the roof of the PC and two it was a bit pricey. Since the cover over the bathroom room fan works so great we ordered one for the Fantastic fan. This is the one we ordered https://www.amazon.com/Camco-40721-Aero-Flo-Cover-Smoke/dp/B0006JLU22/ref=sr_1_6?ie=UTF8&qid=1480375925&sr=8-6&keywords=camco%2Bvent%2Bcover&th=1
. We ordered it in white so as not to darken the galley area. It does not allow the fan cover to be opened fully but actually you can open the cover even more so then the Maxxair. It has air flow on all three sides of the fan and it stops the wind from catching underneath it thus eliminating the clunking noise as Ron mentions. Plus, no more stress about leaving it open in the rain.