I was told both exhaust hoses were replaced in the not to distant past. I noticed the wrinkles/waves and figured it was because of the tight quarters. You're suggesting that is a sign that the hose is weakening at that point?
How low does your boat set in the water?
In view of the fact that it has arrows and an inspection/service cover on it in the "up" position and located between the engine and the exit... I would tend to think it is some sort of swing check or back flow preventer keeping sea water out of your exhaust engine manifolds.
I agree with Clyde. The minute I looked at the picture & saw the directional arrows I thought "Backflow Preventer", Usually one would expect to see something like this on a fishing vessel where they frequently are in reverse backing down on a fish. Sure your boat isn't an ex tuna fishing boat ?? :-)