Aircooled manifold, water cooled exhaust?

I hope you guys wont mind me jumping in on the subject. Ive seen a 1.9 vw tdi marinized. He works for some metal foundry and cast his own water cooled manifold. I believe he noted a g22 turbo on it. A little bigger than stock. His specs in the id of the manifold matched stock. The cooler manifold temps hindered the spoiling of the turbo causing it to smoke and would not allow the turbo to fully spool. The boat is a sea ray 25. Once replaced with non cooled manifold she would plan out quickly and run smoothly.

I'm interested in the wrapping of the copper tubes over the manifold.

To prevent it from getting too cool would it help to first ceramic coat the outside of the manifold then run the copper tubes under a layer of ceramic wool then wrapped in a quality heat tape?

Im using a 2.0 tdi so my manifolds are on the same side.

I will be injecting water into the downpipe.

 

I'm looking at converting a sailboat diesel auxillary to a skeg-cooled dry exhaust system, for simplicity and low service requirements.

It seems to me ;

Extensively wrap the exhaust manifold and muffler, and bellows it into the calorifier and anti-syphon loop, then directly through and out the under-side the steel hull, and then externally to a high point at the rear of the boat (solar panel rack) and then rain hat it.

Run the engine coolant from the skeg tank (plenty of cooling) first to the exhaust manifold outer skin (over top of the insulation) and then to the engine cooling jacket and then returning to skeg tank.

The calorifier can be (foul) water cooled or pressure-vented overboard if it over-temps, or else the crew can have long hot showers and get their legs and whatever else well shaved..

Engine Coolant is fed to the exhaust BEFORE the engine cooling jacket, so that if the engine is started cold and full-throttled it cannot overheat the exhaust cooling. (May be some minutes before the thermostat opens, but the exhaust will get hot quick..)

Dry exhaust through-hull fitting is steel and is mounted near the engine and well below the waterline and exposed directly to the exterior flow of seawater.

External exhaust galvanised and anoded exhaust pipework is exposed directly to seawater. May not need to be antifouled due "high" temperature.

Gotchas ;

What if the rain hat lets a TINY bit of water in, on an ongoing basis? Eventually the engine gets a drink over the top of the syphon loop, or else the solar panels and anyone on rear-deck gets a big blast of black sooty water on engine start. There cannot be a bleeder hole near the waterline (lower than the syphon loop) because any water in the exhaust at all will give a nasty and messy engine start.

Yes, there is still a small salt water pump to chill the calorifier if it hits around boiling point and other general duties (thermostats / solenoid valves), but there is one of those on EVERY boat. Shrug.

What is the situation with the sea-exposed exhaust pipework and the through-hull fitting? Will this be ok made from welded or flanged steel pipe? If it gets hit and damaged it should still be usable. If it fills with seawater, the internal syphon loop prevents engine damage. Will the through-hull fitting have enough cooling bolted to the steel hull, as well as being exposed to seawater?

If I can remove all the gotchas, it should be a nice cool-running, quiet system with a nice high-up exhaust exit.

TIA

 

I find that wrapping the exhaust with copper pipe and running water through it is the easiest and cheapest way to cool the exhaust. If the copper pipe ever corrodes or leaks, the water won't go into the engine.