Yanmar 3YM20 exhaust diameter

[Drumroll30]

On my C&C 30-2 then hose is 2" from exhaust outlet to the muffler and 1 1/2" from the muffler to the thru hull exit.

[Searles]

What don’t you understand, do not restrict a Diesel engine exhaust,if it starts at 2 inch then finish it at 2 inch ,the health and life of your engine not to mention your wallet may rely on it .⛵️⚓️

[Boatyarddog]

Originally Posted by Drumroll30

On my C&C 30-2 then hose is 2" from exhaust outlet to the muffler and 1 1/2" from the muffler to the thru hull exit.

It too is undersized, if it starts out 2" and reduces to 1 1/2".
It's done because it's the cheap way to go.
But it is restricting your outlet flow.

You may not notice it, but check for carbon build up, and run your diesel hard for a period of time regularly to keep it clear.

Maybe yours is a good Canidate for a pressure test inline as mentioned by some here.
Boatyarddog

[Drumroll30]

Originally Posted by Searles

What don’t you understand, do not restrict a Diesel engine exhaust,if it starts at 2 inch then finish it at 2 inch ,the health and life of your engine not to mention your wallet may rely on it .⛵️⚓️

First off I answered a question as to how my boat is equipped not about something I didn't understand. My boat was built that way by C&C Yachts in 1988 and hasn't given me any problems to date. I am planning on changing my exhaust hose in the near future, are you suggesting that I replace the pot muffler and increase the factory sized thru hull exhaust outlet to 2" while I'm at it? I'd be more inclined to replace the existing size hose and leave things OEM as intended by the manufacturer.