MTU 12v183 Te93 Smoke?

I could understand the C32, but sticking 35xx engines in a fast powerboat is totally unheard of.
There's much more than power alone to consider, in fact.
Leaving aside the 3512 which is a 59 liters monster, also for the 3508 there is no place in any fast pleasure boat.
Just by heart, and without bothering to check the specs sheets, I'm pretty sure that it's MUCH heavier, taller and wider than the C32. Not to mention the narrower rpm range.
I'd rather have one in a tug than in a Baia, Magnum, Itama and the likes!

I was speaking of the 97' motoryacht.

Actually I read the 97' in your previous post as one example in the context of a more generic consideration:

"I generally don't believe in replacing engines that are phased out that are running fine in most cases. But in some cases, such as I ran a 97' with MTU 12 v 396's and they were due for W6 service that the owner didn't want to do because of the outrageous price, and outrageous price of parts for them, even though they ran fine, it would be better to just put C32's or 3508/3512's in the boat in the long run."

Anyway, that's OK, I was just saying.
BTW, I fully agree with your first sentence in the above paragraph.

"I generally don't believe in replacing engines that are phased out that are running fine in most cases. But in some cases, such as I ran a 97' with MTU 12 v 396's and they were due for W6 service that the owner didn't want to do because of the outrageous price, and outrageous price of parts for them, even though they ran fine, it would be better to just put C32's or 3508/3512's in the boat in the long run. Not to mention the boat had side exhaust near midship and smoked like you were fumigating for mosquito's. With the wind behind you, you literally stayed engulfed in a cloud of grey smoke. "
Post #40.

This is what I wrote and was referring to 12v396's. While the 97' boat would get on plane and do 20 knots at cruise RPM, the owner never had it run that way, we mostly did 11 knots at I forget which rpm.....perhaps 1200-1300 rpms...….

Fair enough.

I researched it as well, and when repowering a fast boat with MAN V10-1100 CRM motors, we had to get special approval from Twin Disc to have the installation with the larger ASD12L 's approved because we were just over the approved torque rating with a 2:1 reduction.
Because it's all about torque. If your application was a 1.75:1 ratio or thereabouts, that would keep it well within the rating limit. And might also explain why it was so hard to get the boat to perform.

I fully agree that torque is the driver and not power, but they must have given their approval based on the mated gearbox ratio rather than the ASD as such, I suppose.
In fact, all ASDs are 1:1, and their max input torque only depends on the model (10, 12, 14...), regardless of the g/box ratio, which is instead relevant for the g/box itself, of course.