Azimut 50 Fly Shorepower issue/diagram needed

The OP said that the dockside GFCI trips also with all onboard AC breakers off, so it doesn't sound like an appliance problem.
In fact, his assumption that the problem is somewhere between the cord and the main breaker makes good sense.
I believe that the shore power cord is connected to a transom socket, isn't it?
If so, I'd start checking/cleaning/drying that socket internally. I've seen it collecting enough humidity to allow for some current dispersion, and it doesn't take a lot to trip a GFCI (normally 30 mA in Europe, not sure about the US).
BTW, does the boat have also an onboard GFCI, downstream of the main AC breaker?

I'd be very surprised if there were any single pole breakers on a 2006 Azimut - for AC lines, at least.
I can't remember exactly when double pole breakers on AC lines became a standard requirement here, but I'm 99% sure it happened before the current century!

Out of idle curiosity, do you possibly know which is the current dispersion limit for GFCI devices in US?
It's 30 mA here, as I said...

Whoa! A cablemaster on a 50 footer sounds like a solution to a problem that doesn't exist...
Makes me wonder if that's part of US specs for Azimut or if it was retrofitted, 'cause I've never seen it on any of their "EU" boats under 60 feet or so - if not even larger.

Regardless, I agree with your expectation of what the culprit could be.
All the best for your hunting, and looking fwd to hearing the final result!

Interesting. Here that's not even compliant with the standards for AC electrical systems - not anymore, at least.
If Nathanw could confirm if the AC breakers fitted in the boat he's working on are single or double pole, I for one would be curious to know.

Azimut and most other Italian express cruisers I've worked on have a transfer box somewhere buried in the least accessible place. Usually I find them all the way aft behind a bunch of stuff.

You probably won't have much luck communicating with Azimut for new parts, I am sure the Italians are on holiday as per usual... Find a new set of contactors that fit the parameters of the system and replace all of them if you find one that is bad

Why would anyone want to drag a 42 pound shore cord around and on a 50' Azimut you're lucky to find storage for the life jackets, let alone a big coiled up shore cord.

How much does typical Euro-current shore cord weigh? This is 16A or 32A or something like that, single phase?

Yeah... Our current cord is 75' overall and at transient docks it almost always seems to need at least 50' of that to get from boat to pedestal.

When we bought our last boat it was a 50A/250V system with no Cablemaster. A Cablemaster had been an option the original buyer apparently declined. I wondered why Cablemasters exist. I'd never schlepped 50A shore cord around before, though, only the skinny/lightweight 30A cords.... which can also be handled one at a time. I began to discover early on that the extra weight for the 50A cord was becoming significant. We installed a Cablemaster.

-Chris

Each to their own of course, but between these two views I definitely tend to agree with Nathanw on the reason for having a Cablemaster on 50' (or even smaller) boats.
BTW, a major drawback of Cablemaster and its drum is the space it takes, so I'm puzzled by CJ comment about storage: if anything, you'd have more of it with NO Cablemaster, rather than the other way round!

Ref. weight, (also in reply to Chris), on my 56 footer I've got a 32A cord (230V single phase), 65 feet long give or take (20m), and it's nowhere near 42 pounds. I never bothered actually weighing it, but I don't think it's much more than half of that.
A Cablemaster for handling it would be beyond a joke, 'fiuaskme - not to mention how much longer it takes to handle the cord with it.
But as I said, each to their own!

Have you opened up the end that plugs into the dock and checked it’s connections ?
How you tried another dock pedestal? .
How easy is it to check the boat end of the lead ?

I expect that speaks to the difference in perception. A 50' Marinco 4-wire 50A/250V shorepower cord like we would use here (last boat was 42') weighs ~45 lbs.... so a 65' cord would weigh approx 59 lbs.

A 3-wire version, as would be useful with an isolation transformer (no neutral, as I understand it), would weight less, but I dunno how much less.

In either, it's usually #6 AWG wire, if it's copper...

FWIW, we find handling with the Cablemaster assistance is much faster; not as much "tangle and re-organize, argue with coils" and so forth.

-Chris