Rubber hose or fiberglass exhaust tube??

I have worked with both. I really prefer the glass tubes. Tab in a couple of knees to help support the tube in a few places and reduce resonating (vibrating a chord).
Wrap them with heat and sound foam. Never worry about them again. No clamps buried to worry about also.
Bring the tubes out past your transom a few inches. Stronger bond on both sides of the transom and in the future you can ad deflectors or external baffles if needed.

Use a premium double bump silicone hose between your dump can and the muffler.
Exhaust temp alarm on the dump can also.

Sleep well.

Are you using stock dump cans or custom builds?

Did you think about thru the hull, below the water line exhaust with just an idle relief tube astern (or sides)?

Simple is usually the best route. Your hands are full of enough work.

Don't forget to add a couple of feet at the engine room end to form a surge tube. It will help reduce the chance of water reaching the engine when waves hit the transom.

Do you have lift mufflers in the ER now Pascal? If you do straight tubes aft would be just fine, if not I'd suggest a liner muffler tube for the first section to reduce noise throughout. Glass together (with high temp resin if possible) the sections and a short piece for the transom penetration connected with hose (if accessible) makes the install much easier with transom curve). I also like to isolate hard tubing (and mufflers) from the hull to reduce noise rather than glassing them in. A simple ring of the same diameter exhaust hose where they pass through bulkheads.

The Cummins guy doesn't think you'll need mufflers??? Granted they will be quieter than the 53's but still... I can't wait till our rep stops in next time and I ask him that question. If you're switching from 6" to 8" diameter the old in line mufflers won't work anyway but I wouldn't consider not using some type of muffler and the close to the engines you can get it the better. If you can't get it close, wrapping the tubing (like Hatteras often does) with sound absorbing insulation would definitely be a good idea.

I understand the transom has a curve. Just bore new hole straight back.
Bill106 has a pretty pic. If the tube is supported, I do not understand the need for hose and clamps.
You think your ole Hatt hull flexes and would twist the tubes at a different rate?

That's actually two separate pieces rcrapps, the transom tube is glassed in and the "tube" is a linear muffler. This is the same thing on the 64' "Still Kickin" from that other thread. (I hope I resized it correctly Carl!)

Ah, That is a muffler. Got ya now.

Still thinking, can you do away with the hose and clamps? The linear muffler looks glassed in or near permanently installed. Glass it all in and reduce an inspection/maintenance item, those clamps and hoses.

I guess the sections could be glassed together but the muffler is isolated with rubber and those are trim rings covering them. In the fishing game unwanted radiated sound is considered a no-no so everything that can be done to isolate noisy components is attempted.

I'm sorry Pascal for taking up your post. We both may learn something.

Old school thoughts I was raised with; some boats raised fish with their sounds. The target was not a bad tone or excessive resonating ring. Of course, nothing scientific or verified. But the old tubs did not have those fancy thoughts of your stealth fisher. Of course old tubs had old engines. Who knows now days what really turns a fish on / off. They did raise fish. **** well, there were more fish also...

Meanwhile, in keeping Pascal happy, would solid glassed in tubes, no hosed and clamps be quieter or make more noise for humans.
I did recommend in post #2 a wrap on the tubes as I have done before for some of my (so far) happy customers.

Ha! The best fish raising boat I built had 12V71TI's hard mounted with the exhaust solid as well, no torsion couplings on the shafts either. It was noisy but there's something about the sound of those two strokes humming along that brought them in!

If I was doing solid tubes on a budget, I'd glass and wrap them and run with it. I would try to muffle the noise with some kind of muffler as far forward as possible but that would be plenty.

pascal, on my 58yf the tube is glassed in to the transom, it is only about 8 inches inside the transom then a short piece of hose then glass tube, the second length of tube is connected with a short piece of hose. from the factory the glass tubes are within one inch of the other but the hose piece is 18 inches long at the connection. be sure to use the ss crush sleeve from centek inside of the glass so it doesn't crush at the clamp area

Hey Pascal, for reference on the muffler/no muffler issue... If you remember, Panacea has the exhaust elbows dump right into the un-baffled 15 foot splash rails (aluminum of course). No muffler on Cummins the 6CTAs. Ride isn't whisper quiet, but quiet enough and practical.

Added photo for reference.