Question about exhaust flaps.
 

Are they nessessary in my case? The after market silent choice tip has one built in. I think they effect the sound, look like crap and turn the exhaust hit the transom sides and turn it yellow/brown.

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You don't need the external flapper as long as you have an operable internal flapper.

I have the same internal flappers as you. I was debating about putting the external flappers on too. My transon is black so they would not be as noticable.

I imagine they distort the sound (which I enjoy) a bit.

Update: Ran at idle with and with out. They do sound better without them. With them they cycle loading up then dumping water while almost sounding like they are going under water.

I don't believe that type of tip needs them or came with them.

We use the external flaps on a 25 Elim Cat, and they seem to help stop the spray of water coming up and misting over the back transom or hatch area bcuz its above the water line,, especially in reverse......

They are doing the oppistie for me. My transom is resessed and the flaps deflect the gasses toward the glass. Without them the exhaust would blow straight out.

Do you trailer your boat or leave it in the water?

I had the internal flappers in my boat and both flappers burnt out . A real bad metal on metal knocking sound ensued. I had them taken out and had the tips laser cut as I found that the exhaust was reduced to less than 3 inches beyond the flapper and wasn't needed. I think if you leave your boat in the water you may want them to eliminate any water back flowing into the exhaust. If you take your boat out every time you use it , you may not need them.

Always trailer. Never in the water longer than 7-8 hours.

Q&Q helps reduce the possibility of water washing in and over the hump since it will dump down the Y-pipe instead. If you don't have Q&Q it might be wise to keep both flappers! All JMO, I'm no expert on this.