Resonators in 502 mpi exhaust
 

I have a pair of stock 502 mpi mercruisers with thru hull exhaust. The system has Corsa exhaust tips with built in flappers and clamp on rubber flaps on the mufflers. This set up came with plastics resonators midway inside the exhaust hoses. My understanding is they are there for water reversion.
My question is with the two flappers in the system are the resonators required.