If, and that's a strong "if" you can do some of your own engine work, there are always decent used diesels to be found. I know of one local boat owner that replaced a tired but running Universal M25 with a new Betamarine. I seem to recall that someone came to the yard and picked it up, complete, for under 1K.
For this option, though, you need to network with boatyards within driving distance, and also try to have a friendly mechanic to answer questions...
Kind of a long shot solution, really.
Heck, if we keep our '88 boat another 15 to 20 years, I will likely replace the original Universal M25XP with a new Betamarine. whoever gets the good-running Universal will be getting a slightly-marginal-size transmission, mid-80's marine conversion technology, faded panel gauges, etc................
They'll get a "super deal", but they need to be ready for some wrench-turning and perhaps some hand wringing and head scratching.
I note that you've thought about how
much power you might need. IMHO the original A4 was used by all the boat builders because it
fit easily, being a low, flat-head engine design. It came in only a few HP sizes, and just about every boat, no matter how short, ended up with over twice the HP it needed.
In other words, I see no point in duplicating the HP when you change to a diesel (if you do). There is just not enough disp. and DWL in boats under 30 feet to "need" a 30 hp engine. :nerd:
Having said that, a good friend of mine took our a shot A4 originally installed in his Ericson 27 and replaced it with a 9 hp Yanmar single. He always said that while it was fine in smooth water, the boat would just momentarily come to a halt in big seas on coastal passages when several waves hit the bow in close order. It should have been a twin, at around 12 to 14 hp, he observed with 20-20 hindsight.
OTOH, that little Yanmar ran smooth and was totally reliable, getting the predicted (and much appreciated) fuel economy. Lot more room in the engine compartment, too!
Best,
Loren
