I sent you some pics Nemo.
My engine is a Deere marine engine with a coolant header tank and no external exhaust manifold as one would find on a non marine industrial engine. The engine is turbo charged.
I wrapped the exhaust with two inch thick ceramic insulation and wrapped the ceramic insulation in a fiberglass welding blanket to contain the ceramic. It looks pretty home made, but works well as you can wrap your arms around the exhaust when the engine is running. The turbo is wrapped with a custom blanket. The exhaust silencer whic in the engine room, is also wrapped, and is of the dump truck variety. All the exhaust piping in the stack itself is not wrapped and is cooled by air being forced up the funnel.
I did not wrap the exhaust pipe in the funnel on purpose as to get some heat out of the pipe so it does not damage paint as it exits the funnel on top of the boat. The funnel is obviously steel, and with it being insulated, it deals with radiant heat well. This aspect of my design seems to be working well as no paint is getting damaged and the exhaust pipe is relatively cool by the time it exits the funnel. The key here is the amount of cooling air flooding up the exhaust side of the stack from the funnel being partitioned and the ER being pressurized. The ER door has to be closed.
My exhaust funnel is about 2' x 2', and has a partition in the center of it. One side of the partition is intake air, and the other side if for the exhaust pipe and engine room hot air exhaust. The exhaust side of the funnel has high performance heat shielding lining the walls. I created a partition in the funnel as to not allow intake or exhaust air to short circuit and mix.
The ER is pretty air tight, and when the door is closed, I consider it pressurized. Intake air is provided by a quality axial fan I purchased from Delta T, and so far, that fan has done an amazing job. I do keep a spare fan on board.
I have a thermometer in the ER to keep an eye on the temperature, and do monitor it closely. On an 85 degree day after running the engine around 1600-1700 I'll see ER temps around 111 degrees Fahrenheit after about 6 hours of running. It seems to take the better part of the day for temperatures to climb over 110. The highest temperature I've seen was 115, and that was after an extended run at 2200 RPM while dealing with current on the Cumberland River. The ER temps seems to get to 103 fairly quickly, and then start a slow climb to top out at, like I said, around 111.
The engine is a Deere 6068TFM. I specified the engine to have 190 degree thermostats in it as I feel diesels need to be run on the warm side. Any temperatures under 205 but above 180 is fine with me. I'm happy with the ER temps I'm seeing given the mass of the main engine and generator, but I'd be interested in what kind of ER temps others see with similar set ups.
Conall