Why do Princess/Sunseeker install 2 large zincs on the hull bottom?

PB, to my knowledge, MAN engines always relied on a bonding to large external zincs also for the protection of the internal components which must go in contact with raw water, and which don't have any specific zincs.
That's a different approach vs. say Cat engines (at least traditionally - not sure about the latest common rail like the 12.9 that CaptJ mentioned), which rely on specific, engine-mounted anodes.

Ref. MAN specs, below you can see the relevant page of an installation manual.
With a disclaimer: this is pretty old, meant for their pre-common rail engines - cue: Morse control cables.
But interestingly, while looking for this page among my old files in order to (hopefully) clarify your doubt, I only just noticed that in their drawing, awful as it is, the shape and placement of the external zinc reminds the one in the Princess 62 photo.
On the other hand, I'm pretty sure that most if not all yards who adopted mechanical MAN engines used to fit transom anodes, like the one which you can (barely) see in the second photo, in between the trim tabs plates.
And I'm equally sure that MAN never argued with any boatyard against that solution, which aside from being equally effective at rest and at low speed, is undoubtedly more hydrodynamic, though as I said I wouldn't be concerned by the other alternative. Surely not in a 30 something kts boat, anyway.

Now, this is as far as I can go with facts.
But all considered, bearing in mind also what I already mentioned about CR engines using components with several dissimilar metals, I believe it's reasonable to assume that in recent years MAN became more strict about the placement of engines-relevant anodes in a position where they can be effective also at planing speed.
I would just be curious to understand if the same principle applies also to the latest CR Cat engines, regardless of the fact that they are actually designed and built by FPT, or if it's just a matter of standardizing the production of boats available with different engines.
If nobody knows better, there is a very good engines specialist at the yard where my boat is stuck at the moment who probably knows the answer. Hoping that the conditions for releasing this lockdown thing will materialize, possibly sooner rather than later...

Waddumean none of the MAN's have zincs? Engine mounted, yep, they sure don't, as I said.
But the external zincs bonded to the engines internally have been a strict MAN requirement for more years than I can remember.
Surely more than a quarter of a century, anyway.

PS: in other words, the only doubt/assumption is about whether they recently became more strict on a placement under the hull rather than on the transom. But the principle of engine-bonded zinc as such, that certainly ain't breaking news.

Ok, so we are saying exactly the same thing.
But don't be mistaken (they usually separate the metals with saltwater in them via O-rings or other non metallic materials):

The reason why they can do without internal zincs is that they are bonded to the external one, not because they have O-R or whatever separating the components inside them.
Just as one example, the heat exchanger box is made of aluminum, while the tube bundle inside it is bronze.
You might have seen its side round cover open, which is necessary for cleaning them.
And there is indeed a very large O-R pressed by that cover.
But that's meant to keep the cooling liquid separate from raw water, and does absolutely nothing to avoid the contact between the two metals, which for all intent and purposes are 100% electrically connected.

Correct.
In fact, in the previous (awful) drawing, you can see also the dedicated starting battery.
And the domestic grounding should be separate from the powerplant.
But I'm saying "should" purposedly, because in practice I've very rarely seen a MAN powered boat whose engines weren't (one way or another, it could be almost impossible to understand how) also grounded to the rest of the DC circuit.

As an aside, I've never seen a MAN engine whose HE external box wasn't made of aluminum.
Including the 1991 D2842LZE powered boat from where I'm writing.
But yes, the tube bundle is very solid.
I actually believe it's bronze rather than CuNi, but very good stuff anyway, as for the aftercooler.

Actually J, the diagram does show that also the engine must be bonded - see below.
And trust me, bonded they always are for good, also in practice.
Don't ask me why they show connections for BOTH the block and the gearbox, though.
As if they weren't bolted together...?!?
Must be the German way of applying the better safe than sorry principle, I guess!

If that's how Industry would read the diagram, well, "Industry" would be wrong.
In fact, the connections which I highlighted in the previous post belong to those that the manual describes as "indicated in bold print", and nothing in that page is qualified as a suggestion.
Let me guess J, you are not very used to deal with Germans, are you?

No worries, anyway.
Everybody involved in the installation of MAN engines can access the whole installation manual of course, not just to the page I previously posted.
So, hopefully they will have read also the page below, before reaching the previous one (the red underline is mine, obviously).

All that said, I'm frankly a bit surprised that this thing of MAN engines bonded to an external hull zinc seems to be not well known/understood in this forum, considering the otherwise pretty high expertise level.
This is in fact widely known in Europe even among owners of MAN powered boats, let alone yards (including non-official MAN services).
If I may give a suggestion, aside from obviously replacing any worn out anodes, in MAN powered boats it's worth including in periodical maintenance also an engine bonding check.