Seriously, your mechanics do not appear to know what they are doing. They should also be standing by their work. If they got paid but it is not fixed, they should be eating some work to get it fixed. Not charging
I know there are million ideas and theories coming at you. But, we know what the "problem" is. Now we just need to find the "cause".
The problem is that you do not have enough turbo boost to generate the HP you need.
This has been verified (as stated by you): 9 psi instead of 15 psi. This is a major cut in boost.
Knowing there is a lack of boost, we need to find the cause. Luckily there can only be a few things causing this...
1. Intake blockage (you state this has been checked and clearly is not the issue).
blockage (I asked about this, you did not say if it was actually checked. You only state that smoke and water
come out. But that does not mean there is not a restriction. This needs to be physically checked. Cheechako's suggestion to check the elbow
is a good starting point. But the system in full needs to be checked).
3. Bad Turbo (I know you don't want to believe it, but you turbos are very sensitive. Since we don't know what your cleaning
regiment was, we are skeptical).
3a. You didn't answer about the turbo wastegate. Does your turbo have one? If so, This is a critical adjustment. Not difficult to adjust, but critical that it be proper.
4. I would like to hear that the injection timing, fuel
pressure, and delivery
rate were actually tested. You only said that the mechanics didn't think these could cause this issue. I disagree: Ignition timing seriously effects power, just like it does on a gasoline engine.
Stop looking at compression
, this is not a lack of compression
Re-power is just a large dart at the problem. Waste. You just need a better mechanic.
Have you considered moving on to another yard? The boat moves. You need a different mechanic.
All this said, once you get this all running like it should. You might then want to look at the prop. You might be just slightly overpropped. You did say that you could get black smoke and soot at full throttle prior to all this work. This may be what clogged up your injectors to begin with.
However, I do not think the prop is the problem now. Period. Even if you had fouled the prop. You would see the turbo boost. But we don't, so turbo boost is the problem.