Exhaust Noise

[Yachtieman]

I have a strange issue where the exhaust is louder than it used to be, making a loud boomy sound. As far as I can see the amount of water coming out is the same as it always was and impeller looks good.

I cannot link the change to anything I specifically did, although in the last couple of years, exhaust pipe has been replaced, exhaust elbow removed and checked (it was perfect), heat exchanger removed and cleaned, and engine mounts replaced, so perhaps some issue with these?

Engine is a Yanmar 4JH3E

If anyone has any thoughts, I would be most interested to hear

Thanks in advance

 

[jwfrary]

Is your hull heavily fouled? This could increase engine loading and associated noise.

Is the trim of the boat the same?

Exhaust is presumably secured well.

Quite a small reduction in water can cause more noise.

 

[anoccasionalyachtsman]

Have you done anything that has pushed the pipe more firmly against the structure of the boat?