Re: Which diesel mnf. shall I choose
Yeah ^^^^ that's why I asked about BHP. Many of the trawlers, even single screws, are semi-displacement type now (and then) and may even run twin 425's 3208TA. Some of the single screw true displacement hulls will run 135 Lehman's so . . .
I slapped the 3208 a little too hard up there, it will be in most of the CAT powered boats in the vintage range you are searching. Thing is that the service comments reminded me that this is never just about the engine design. Also, being in the power side, at the L.A. area Dealer, from the late 70's to '01, I saw more splattered 3208s than you can imagine. Most due to poor maintenance of course, but the engine does have a few oddities that I'll try and elaborate on.
3208s were the "big CAT" in the pleasure craft industry for a loooong time. Interestingly enough, for perspective, it was the little CAT within the engine world, truck, marine, power gen and industrial. It had a 4 cylinder cousin too, but never mind that

They came out as the 3160 (1160 truck) in '68 or so and hung around well into the 80's maybe 90's (in trucks they went to engine heaven in '83). V8, 4.5 x 5" bore 636 CID 10.3 liter. It was rated @ 210 naturally aspirated to the first turbo'ed ones in say '80 at 250 and then up to 425 turbo'ed and aftercooled. There may have been a 435 or 450 even after I stopped paying attention. They were 2800 - 3200 RPM typically and had one issue that always made them a weak stepsister to me. The one "issue" that most will think I am concerned with is a parent bore block . . . same as a gasoline engine, no cylinder liners. The block had the cylinders cast in and they were bored. Again just like a BBC or all the other stuff we talk about here. Most diesels then had removable wet cylinder liners and the parent bore block was not considered worthy of diesels. That's not my issue, they are borable to .010, .020, and .040 over, and you can do one hole if necessary with no problems. They can also be resleeved.
My issue with them is they used a unique fuel injection pump called Sleeve Meter. Forget the Sleeve Meter description, but they were 100% fuel lubricated which caused them issues. Like anything, again, if properly maintained, they are fine, but ANY water, even trace, in the fuel system and they go to shi+ fast. If I was to own one (I would), I would have the biggest, baddest Racor or similar, water separator and watch them like a hawk. I'd also have the pump's top cover lifted for an inspection before I'd buy one. The pumps can easily be rebuilt, they may even still have Reman ones available. 3208's also use Pencil injection nozzles. Sometimes incorrectly called injectors, but that's another lesson . . . The good news is that they are easily changed by a novice, and can be carried as spares. Same thing, they don't like any water in the fuel!! (actually applies to all diesels).
Other than that all of these engines suffer from the same issues as all marine engines. Cooling system stuff. Yes, manifolds, heat exchangers, raw water pumps. Basically anything dealing with raw water. Zincs of course. Ya know, impellers, the same ole list of stuff . . .
With proper maintenance the 3208 was considered a 6000 hour engine and would do it easily. As a parts and service sales guy, then parts manager, then service manager, I saw all the bad stuff. 3208s were everywhere, especially in truck. We sold 500 complete engines a year, just as replacements, just in L.A. and Orange Counties. My opinion needs to be considered in that context. Most of the marine techs will probably think of it as a good engine, and the Yacht Brokers will be splashing it's name everywhere as a strong feature. They are not wrong. I am just a little more jaded than most. BTW, I used to defend it big time in truck. It was the first successful replacement for gasoline power in medium-duty, and people learned a lot of tough lessons at it's expense.
Let us know what you find and we'll go from there. As noted above you can NOT beat CAT Dealer service. It is amazing, and I could get you any part, anywhere in the world in 24 hours. Maybe even Antarctica. They have the best parts system on the planet, and marine service techs that do everything from replacing zincs to complete 5000 bhp overhauls on a cruise ship while she's underway. If you've never been to a major dealer, you should just take a little stroll around one. Amazing places for what is really just a big flippin' car dealer.