DD 8V-92 DDEC III (760 HP) for long-range cruising

Hi all,

We’re seriously considering a yacht that checks nearly every box for us — layout, build quality, condition — but it’s powered by twin Detroit Diesel 8V-92TA DDEC III engines (760 HP, 1250 operating hours). Before we go further, I’d love to hear from anyone with direct experience running or maintaining these engines in a marine application.

Our cruising plans are to run the boat from Alaska down to Mexico, spending long periods aboard and typically cruising slow and steady in the 8–10 knot range. We’re not in a hurry and value reliability and range over speed.

Our only prior diesel experience was with Cummins QSBs (on our previous boat), so these older two-stroke Detroits are new territory for us. I’ve done a fair bit of reading and understand the basics — they’re not as fuel-efficient as modern 4-strokes, can be prone to wet-stacking if under-loaded, and need diligent maintenance. That said, we’re trying to figure out if these engines are a deal breaker or simply a quirk we can manage with proper care.

A few specific questions for anyone familiar with this setup:

• How do these engines behave when run at lower RPMs for extended periods (8–10 knots cruise)?
• What kind of fuel burn and RPM have you seen in real-world cruising conditions?
• Have you run them long distances at modest speeds — if so, how did they hold up?
• Any common failure points or maintenance headaches specific to the DDEC III version (electronics, injectors, cooling systems, etc.)?
• Are parts and support still reasonably available?
• How concerned should we be about the DDEC electronics in terms of reliability and future serviceability?
• If you were us — looking at a boat you otherwise love — would the 8V-92s stop you, or would you go ahead with eyes open and a good maintenance plan?

We’re not opposed to a higher fuel burn if everything else about the boat works for us — we just want to go in with realistic expectations and understand any potential long-term limitations of these engines for slow-speed cruising.

Any insights, stories, or hard data from owners or mechanics would be hugely appreciated.

Thanks in advance for your time and experience — we’ve learned a lot from this forum and value the collective wisdom here.

Justin

Thanks for the info! Interesting to note that are actually more efficient at lower RPM, would running them at 1000 RPM or slightly lower be suitable like you mentioned on 12v71's? They are in a PH Motoryacht, 64', semi planing hull, I think vessel is about 80,000 lb dry.

Ok, good to know, thanks! Boatpoor noted concerns with the DDEC system, I started down that rabbit hole as well. Have you experienced any issues with DDEC system itself? It seems like there are plenty of posts about inherent issues with the DDEC system failing.

Thanks! Yes, we were under contract on a vessel with Cat 3306's, unfortunately other issues presented and we walked away. Too bad this new option has these old two strokes.