MAN LE403 engines

They used to build a V10 as well (2840).

In fact, if I should hazard a guess based on the vessel size, I think that's likely to be the one the OP is referring to.
A V12 would be even more appropriate for a 72 footer, but the LE403 version of the V12 is unheard of on pleasure boats, because it's a heavy duty rating engine, with a 720hp output @1800 rpm.
As opposed to 800 and 1050 hp @2300rpm respectively for the V8 and V10, whose LE403 version were both light duty.
And if that sounds like their models designation was a bit of a mess, it's because it was!

Anyway, happy to post MAN curves, if the OP specifies which engine he's interested in.

Bernd, happy to enter in more details by PM if you wish, but I think you're mixing up the V8 numbers/ratings (or possibly kW vs. Hp, not sure).
I happen to know the 90s MAN range pretty well because I came across many of them during my last boat search, eventually chosing one powered by the D2848 LE403.

And I'm pretty sure that this version was light duty rated, capable of 800hp.
But still 100% mechanical - in fact, the V8 was the very last MAN block to be converted to CRM, skipping the semi-electronic EDC versions that they fitted on the V10 and V12 for a few years.
The predecessor D2848 LE401 was capable of 680hp instead.

BTW, MAN never increased the bore of their engines - not even in the current lineup, which is still the same old 128mm that has been around forever.
The slightly higher displacement of V8 and V12 in the second half of the noughties (by which time the V10 had already been phased out) came from a redesigned basement+crankshaft, with a longer stroke.

If you're sure to have the medium duty V8 in your boat, the only one I'm aware of was the LE405, also mechanical and rated for 650hp @2100 rpm.
But I never studied their heavy and medium duty range in detail!

Always stroke. As I said, bore has been 128mm for decades, and still is in current days.
With the inline 6, stroke was upped from 155mm of the 2866 to 166mm of the 2876 - hence displacement from 12 to 12.8 liters.
With the V engines, stroke went from 142 to 157mm - hence displacement from 14.6 to 16.2 liters (V8) and from 22 to 24 liters (V12).
A longer stroke version of the V10 doesn't exist, because by the time they redesigned the V engines basement+crankshaft, they also dismissed the V10.

I was wondering if you were still interested.
Guys, Lets find this kid some answers.

Fuel burn does NOT depend just on the engine model and its RPM, but also on its load at that RPM - which in turn depends on the propeller demand of the specific boat you are considering.
And if you think this is just a useless analysis paralysis, well, think again: the same engine, at the same RPM, can show huge differences in fuel burn, between two different boats.

That said, according to MAN, one D2840 LE403 at 1900 RPM should burn 25 GPH.
You can see this and other relevant numbers in the bottom table of the second page, in the attached specs sheet.
But don't take this as gospel truth, because even the manufacturers have absolutely no way to know how much their engines will actually burn on each installation, and their "prop demand" numbers are just a theoretical average.

What the manufacturer know with a good level of accuracy is the output at full load that an engine is capable to produce, and in turn its full load fuel burn. Which, just to put things into context, is a whopping 47 instead of 25 GPH, for this engine.
But you should do a bit of math to calculate that, starting from the specific consumption in g/kWh.

As an aside, it's nice to see that my guess in post #3 was correct.
And FWIW, this is not a powerplant I'd be happy to have on any 72 footer, for various reasons.
But this is for another thread.

Hi and welcome.
Your post and your username make me guess that you're talking of a Sarnico 60 HT, right?
Very nice boat indeed, just perfect for Med cruising!

Mmm... Really BLACK smoke, I'd say very little, if any at all.
What is pretty normal is some grey smoke upon cold start, which can last anywhere from a minute to about 4 or 5, depending on the environment temperature.

Another normal occurrence is some black soot deposit on the hull around the exhausts, after running for some time at or just above idle.
This is due to the combination of two factors: first, the engines not reaching their optimal operating temperature, and second, the fact that in most boats (though I can't remember yours specifically), at very low speed the exhaust gas can't escape from the underwater outlet, and is forced through the lateral (or transom) bypass, hence sticking a bit on the hull around it.

But after say 5 minutes or so from startup, you should only have a minimal amount of grey-ish smoke.
Otherwise, it would be a good idea to pull all the injectors, have them calibrated, and their nozzles replaced.
How many hours did your engines clock (or how many since the last injectors check, if already done in the past)?
Most MAN engineers recommend to check the injectors every thousand hours, though many agree that they can last much longer (I made that at around 1500 hours on my boat, fwiw).