Exhaust sys

[Dick]

I have a monel pipe, perhaps 8" in dia, which runs behind each 8-71. Raw water and exhaust gas is fed into the pipe (I believe gas feeds into an "inner" pipe and is cooled by raw water in the "outer" pipe. The pipe is "T" shaped. Raw water and gas flow outboard to the "T," combine and then head into the rubber exhaust pipe (or whatever material it is).

The monel pipe has pitted and is leaking at the "T." I tried welding a couple years ago. It worked for awhile, but now, I'm back to square one.

I'd appreciate any experience with repair or replacement. Steve McP suggested talking w/Marine Exhaust, which I did. They indicated that they typically use fiberglass today rather than monel or stainless.

Any thoughts on using monel (very expensive but rugged), v. stainless (not as rugged but cheaper) v. fiberglass would be appreciated.

Dick

[Genesis]

I replaced the 45 degree down-elbows on my exhaust system this spring with new ones from Marine Exhaust. Mine were also made of Monel and were leaking.

They fabricated the replacements out of fiberglass with a SS "crush ring" to take the torque from the clamps.

The pieces they made are works of art. Seriously. They're freaking gorgeous.

Marine Exhaust out of Riviera Beach is a class act; the built me a complete setup of collectors from the turbos back to the hoses connecting to the fiberglass expansion chambers under the cockpit deck (I supplied the hose and did the install myself.) My collectors were leaking as well, and I had welded them once already - it was time to replace them.

The work was done on time, exactly to quote, and is both absolutely beautiful and functional. I'd use them again in an instant.

[Dick]

Karl:

Not sure if we're talking about the same part (I don't even know what it's called!). I have a couple 45 down elbows from the top of the engine. They run into this T shaped monel pipe. It's about four feet in length (6" dia) and runs just behind the eng. The T portion is outboard of the engine, 8" dia and is about 22" in length. It connects to the exhaust hose.

If I understood you correctly, you called this a "collector" and Marine Exhaust rebuilt it from fiberglass. Contrary to my first post, I think this is simply a single pipe (no "inner/outer"), exhaust gasses and raw water are fed directly into it.

When you converted to fiberglass, any concerns over exhaust gas temp and potentially melting the fiberglass? Did Marine Exhaust give you any estimate on how long this lash-up would last (my monel has been there almost 35 years)?

You also mentioned a fiberglass expansion chamber. Showing my ignorance, I'm not sure what that is either. My impression is that I have a straight exhaust. Runs from the back of the T to the transom.

Dick

[jim rosenthal]

My entire exhaust system from beyond the water injection elbow down is fiberglass with rubber hose connectors, and I have had no trouble with it. We used tubing made for the purpose from Oceana Ltd in Annapolis- I think it is made by Centek. They use heat-resistant resin and the tubes are filament-wound. They are intended for hot seawater and exhaust gases. The exhaust components need to be cradled where they sit on something and they need to be supported- when water is flowing through them, especially, they weigh a lot. But I have seen these materials used in a lof of boats and they hold up well. They can also be cut, rebonded together, etc, with epoxy or vinylester resin to make custom shapes.
When my boat was repowered, the man who did the install removed the old bronze exhaust pipes from the transom and fabricated new SS exhaust pipes at the transom. They are nice, and have held up well, but if I were doing this again I'd just glass pieces of the above tubing material right into the transom and fair it and paint it.

[Genesis]

The exhaust from the 6V92TAs looks like this, from the turbo back.

At the inboard turbo outlet there is a SS crossover pipe, which is clad in insulation (no blankets any more.) This has an expansion joint in it, and joins to the outboard piece (also made of SS and dry-clad), which continues to a 90 degree bend - just below that is the water injection "shower head". Installed, the shower head portion is angled down and aft at approximately 45 degrees.

This connects to a single-bellows silicone (high temp) hose, which is about a foot long. At the bottom of this there is a 90 degree elbow, which is the piece that is now fiberglass - and was originally Monel. It lasted 20 years - I suspect the replacement will as well.

The exit from this is approximately 2' long and connects from the outlet of the elbow to the fiberglass expansion chamber through the forward cockpit bulkhead (or aft engine room bulkhead, if you prefer) - this is also a hose connection. There are supports under the elbow tabbed to the hull.

From the cockpit bulkhead back to the transom the entire exhaust is fiberglass on my boat. There is a large surge/expansion chamber, with the exit from that being the tube to the side of the hull right near the transom.

[rtrafford]

note: be certain that any metal pieces in the chain are grounded to the engine block and eventually to the battery.

[Genesis]

There are multiple ground points.

1. The turbos are part of the engine "metal chain", and the elbows are clamped to the turbo outlets with V-band clamps. Good connection there.

2. There are two support brackets on the pipes in a "V" shape which bolt to the gear, to "unitize" the exhaust to the engine. Those are necessary so you don't stress (and possibly break!) the aforementioned V-clamps, which would be REAL BAD underway (can you spell F.I.R.E.)?

The entire system is quite solidly part of the engine block ground connection.... no way around it. Indeed, you'd have to work darn hard to avoid that if you wanted to for some reason.

[rtrafford]

my point is that the situation changes dramatically if/when you introduce fiberglass or rubber into the mix.

[Genesis]

... replacing the Monel elbows with fiberglass actually REMOVES one bonding requirement (the elbows) which otherwise required bonding wires (as they were otherwise isolated by hose on both ends.)