Cat 3408 800 HP Black smoke

The only MAN engine I can think of with a power rating of 820hp was the very last mechanical V10.
After that, on the V10 block, they built the electronic (non-CR) 1050hp first, and the 1100hp (CR) a couple of years later, before eventually phasing out the V10 altogether.
If it's indeed the 820 V10 that you have got, to my knowledge it didn't come with any EGT sensors.
Did you possibly retrofit them?
If so, I'd be interested to hear any technical details you might have about that job - thanks in advance!

yet you get a lot of soot on the transom ?
Black smoke on acceleration, how quickly (how many seconds) do you take to go from 1000 to say 1700/1800 and you get on plane? Personally regardless of engines I never increase power more than 100 RPM every 5 seconds or so

I'd be very interested to see that, if the search isn't too much of a hassle for you.
Thanks in advance, regardless of whether you will actually find it or not.

Anyway, that's indeed a nice panel to have, for mechanical engines. I fully understand why you wanted to fit it.
If by chance you could find also a pic of where the turbo pressure sensor was fitted on the engine, that would be great!

I have heard of a wet muffler full of barnacle fouling causing exhaust restrictions. I have checked for it thru the years but never found a real diesel failure because of this.
I did find an issue with a Chris Craft cast iron muffler full of rust so I've always been open minded on this issue.

Here's a good article on it:

"The process of blueprinting involves removing the turbocharger and disassembling it during a turbocharger overhaul. The exhaust housing is machined out to accept a CNC insert to perfectly match the turbine blades curvature and restore blade tip to housing clearances. The turbine housing is bored and readied for the new sleeve. A special material is chosen to match the heat characteristics of the cast iron turbine housing. The blueprinter can get the tolerance to meet production factory clearances and restore efficiency back to new or better."

www.scottmarinepower.com/techtips/2019/4/1/blue-printing

Sounds like this is (at least a big chunk of) the answer. All the pro skippers here advise against running it like a ski boat. Doesn't take much to get the black mist on the stern....

Thanks a lot MYlover, very interesting pic indeed.
Confirms that you are measuring EGT downstream of the turbine, as I already guessed based on the reading of your gauges.

And unless I'm missing something, it also confirms that you are only reading it from one cylinder bank, since I can't see the same probe on the left bank of the other engine. That's consistent with your "single" gauges, i.e. with one EGT for each engine, rather than one for each cylinder bank.

Nothing wrong with that, and MUCH better than nothing, as is normally the case with mechanical engines.
But since you already went the extra mile for monitoring your engines, you might be interested in a good reason for fitting the EGT on both cylinder banks - bear with me.
The premise is that the Bosch injection system of these engines is widely recognised as bulletproof, but a few blocks were wrecked by neglected injectors maintenance.
In fact, they are supposed to be pulled and inspected/tuned, replacing also their nozzles, every thousand of hours - a schedule often neglected, also because even MAN engineers consider it is VERY conservative.
One of them even told me of a commercial boat that clocked 3K+ hours before pulling the injectors for the first time, and according to him they were still in pretty good conditions when he pulled them.
On the other hand, I'm also aware of two pleasure boats which wrecked one engine well before reaching 2K hours, because one injector nozzle started dropping a bit instead of spraying as it should, their owners didn't notice the increasingly higher smoke and kept using the boat, and eventually had a wake-up call when the piston ended with a hole in it - no kidding!
Now, the first sign of such defect is an EGT increase - also because the smoke increase is "diluted", for lack of better wording, between all cylinders. So, it might take a while before you notice it, and by the time it's evident, that cylinder probably is on its last leg.

Bottom line, the EGT is by far the best early warning of unusual differences, also comparing the two engines (and/or their cylinder banks), since it's extremely unlikely that such defect pops up at the same time in two different engines, or in both banks of the same engine.
But with the pyro only on one cylinder bank, if this defect should materialize on the other bank, you have no way to spot it. Coming to think about it, the reading on just one bank could even be misleading, because whenever one cylinder of the other bank should be running way too hot, the gauge reading would still be fine.

All that said, don't get me wrong, I'm not dismissing your installation - very far from it.
The EGT reading on just one side is still great for spotting possible increases due to other factors (typically, overloaded boat and/or fouled hull/propellers).
But since you already made the effort to fit the sensors, snake the wires to the dashboard, and install the gauges, it seems to me that it would be worth monitoring both sides of each engine.
Oh, and if by chance it would be difficult to fit two more gauges in your dashboard, there are also gauges specifically designed for the two readings of V engines, like for instance the one you can see here
http://designatedengineer.com/Xhaust.html
No connections btw, it's just a website that was mentioned to me by a US friend of mine.
I hope the link doesn't contrast some forum policy, but just in case it should be removed, you can just google for "dual EGT gauges" or something like that, to find the instruments I'm talking about.

Wow, every 3 years? By "new", do you mean also the injector body?
Those Bosch injectors are part of what I called bulletproof, in these engines. I'm aware of engines that ran 15+ K hours before being overhauled, and even when they were, for the injectors they only replaced nozzles and fine tuned the opening pressure...
Anyway, yours is a very sound approach - if anything, just a bit OTT...
But I'm sure you will not regret that, in the long run!

Sorry, I can't give any suggestions on MAN service anywhere in FL.
But some folks here will be able to contribute, I'm sure.
Me, I'd be glad to help if and when you should bring your boat to the Med, instead!