Repowering a 54' Donzi Sportfish

Far from focusing on that. If anything, the opposite.
I only asked what the OD of the barb hose is, because from that follows the ID of the pipe that the engine manufacturer expected to be used.

I appreciate what you are saying ref commonly accepted ways of measuring pipes, and I'm aware that NPS+schedule is an industrial standard (though not so much in EU as in the US).
Also, when you say that this is what you deal with in the ship building and repair industry, I have no problem at all to take your word for it, because that is a sector I am not familiar with.
On the other hand, I came across more pleasure boats shipyards than I can remember, and I can assure you that all of them bar none normally talk of sizes related to fluid treatment in terms of ID, regardless of NPS and wall thickness.
And I mean that for all components: thru-hull fittings, valves, fittings, pipes for all sort of applications, like salt or fresh water, fuel, oil, exhaust, grey/black water tank... You name it.

Just to make a practical example to better explain what I meant when I referred to the OD of the barb hose, check out this webpage.
There are no less than 4 different versions of barb hoses, all compatible with the thread of a 3" valve (or pump intake, in your case), depending on the ID of the hose to be connected: 75, 76, 77, 90 millimiters.
And yes, all of these sizes are referred to the ODs of the hose end in the fitting, but only because that's what relevant for the ID of the pipe to be connected.
Now, the fitting that is typically used for a 3" raw water supply line is the one coded as "2156M*76", whose OD at the hose end is 76mm.
And that matches perfectly a hose with an ID of 3", which everyone and their dog in the pleasure boat industry would call a 3" hose, regardless of the fact that it isn't, when you look at it in terms of NPS and schedule.

But mind, I'm only trying to explain this just for sake of clarity, and there's no need to agree to disagree on the only point which really matters at the end of the day, i.e. whether your setup is OK for feeding enough raw water to your engines.
In fact, while I would have used a 3" ID pipe for all the reasons I just explained, I also said in my last post that I don't think you are going to have any problem with your 2.695" ID pipes, considering also their length and material.

As far as CAT agreeing, try to get something in writing. Protect that warranty.

Two plumbs that I always oversize: raw water and fuel. One must consider not only optimal flow for the piping and the engines, but then consider the impact of the slight blockage from growth, debris, etc that will always occur. My project's intake requirement was 2.5". I went 3". Fuel was 5/8. I went 1". Let the bastards drink, and your problems will be elsewhere...

Agreed, but that should be included in the normal process, as far as I know.
I mean, the warranty validation of marine engines on newly built boats requires an official dealer to assist the builder upon first commissioning and sea trial, checking that dozens of engine parameters are within specs in the actual installation.
And also anything that doesn't come with the engine but can affect its operation (typically, raw water and fuel supply, together with exhaust and e/r ventilation, must all be fit for purpose) should also be checked and validated.
I don't see why it should be any different in case of a full repowering like the one which is being debated.

That's radical. Fun if at sea. Run her to Bimini for lunch.

While hoping the date of the need doesn't arrive soon (despite the use), I'm really a bit stumped right now as to whether or not I'd rebuild versus replacing.

Positively +1!
I'm well aware that running WOT for a meaningful amount of time is part of these tests, but 1.5 hours sounds indeed OTT.
Btw, that's a whopping 180 gallons of fuel, according to Cat specs.
Just a drop in the ocean of the total repowering costs of course, but a pretty expensive seatrial nonetheless...
Best wishes in advance for enjoying the experience, anyway!

Any updates, Dockmaster?
Tell me you are not going to put your project on hold.
I'm now stuck onboard in Italy, with the whole Country fully locked down, and it's unlikely that the situation will improve quickly.
So, I'm looking for as much boat porn as I can find!

Yeah, that wasn't my intention of course.
I already have plenty of opportunities to debate CV (even if just remotely) with many other folks, both in Italy and elsewhere in Europe!

But thanks for your thoughts anyway, though my own situation is not bad, if I'm honest.
Yes, movement restrictions are annoying, but here in Sardinia the situation is under control, and I'm onboard a 70 footer of a friend of mine, which for just myself and my wife is akin to living in a seaside villa!

Back to the point, thanks in advance for your next post with pics, a boat porn fix will always be welcome from my part!
And all the best for being able to complete everything before any broader shut down should become necessary - if any.