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No. A 4-108 is a great, easily serviced and common diesel, but it's neither light on a horsepower per pound basis nor is it particularly economical. It is best used where you anticipate motoring at a constant, not particularly high RPM (say 2,200 or less) for hours and hours, inferring a fuel supply to feed that. The smallest boat I've seen one in was a 36 foot full keeler, and I've seen most in 40 footers.

You are far better off with a 20HP or less diesel or a rebuilt Atomic 4. If you can acquire a running Perkins for peanuts, I have no doubt that you can trade it as is for a newer, lighter, and more appropriately powered engine for your needs.

From what I recall of the C30 engine space, if you could even jam a 4-108 in there, you'd need half-inch thick fingers to service it, and it would melt the glass with its fiery warmth.
 

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We pulled it out and had a ceremony, where I shot it, called it names (including Dieselbub), and threw things at it. It responded by squirting oil at me one last time. Oh, how I hated that engine.
Dieselbub. Classic. Your pain, maybe, but my laughter as that was a very funny post.
 

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HS: The need to push your boat at 6.8 knots (which is at or slightly above the hull speed of a C30, I would think, as my 33 footer is 6.9 knots, above which I'm "surfing" or in a current) is vanishingly rare. The fastest I've regularly gone in my 33 footer is 5.8 knots, because that last knot, while possible, was obtained at great cost in fuel consumption, noise, heat and vibration.

It isn't worth it.

Sailboats sail. Prop whatever engine on the basis of its power curve and your desired stopping power and backing down thrust. Sailboats usually only ever go "loud and proud" trying to back down, stop or while making a sudden move (sarcasm intended) while docking. My engine is best left idling in neutral if I can glide into dock without using reverse. I really don't need it to push the boat at hull speed, if only because motoring a sailboat that fast is gravely missing the point of owning a sailboat at all.
 
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