I have been spending a lot of time recently studying information about diesel engines, as we're considering buying a different boat. The size boats we are looking at are too large for gas engines and all have diesels. This has led me to do some comparison among different models and manufacturers of engines typically built in the 1980s. Let me say first, I am no mechanic and there are several people who contribute to this group who are, so I'm writing only as a consumer, not an expert.
There's a lot to digest but the short story is this, two cycle engines are inefficient, smelly and leaky but reliable and easy to maintain and rebuild - EXCEPT Detroit V9 series. These engines represent early engineering efforts to increase horsepower and RPMs in diesels to make "go fast" boats. Unfortunately the result turned out to be short- lived engines. Rebuilds at 1500 hours are the norm. This decreased life holds true for four-cycle engines too. Many diesel people scoff at two-cycle engines and will explain the value of modern four-cycle diesels. However, when one begins to look into it, the true benefits are relatively recent and are based on problems encountered early in the designs, especially from the era of boosting HP. Even today, there are faults to be found. For example, fuel quality or cleanliness is critical in new four-cycle diesels as they tend to clog much more easily than older two-cycles. This is an important factor for anyone considering long-distance cruising and likely to encounter careless fuel facilities. What we see nowadays are four cycle engines being lightened considerably and run at almost twice the RPMs to acheived HP and speed. This equates to higher engine temperature with less metal to withstand it. What about fuel consumption? Well, that seems to be a hard one to pin down, mostly I suspect because diesel owners are reluctant to reveal the true facts. Apparently, it takes a certain amount of energy to push a boat through the water at a certain speed - no kidding! The higher the speed, the higher the fuel consumption. So, when diesel owners were talking about 10KT boats cruising at 1500 RPMs, the torque of a diesel was a significant advantage. However, pushing a diesel engine to 2500 RPMs to get 22KTS changes things significantly. Usually the number I hear for normal crusing with diesels is about 1NM/ 1GAL. Like everything else, each manufacturer has it champions and its detractors. (Note: Cummins 555 are engines to be avoided because they are not supported any longer and parts are difficult to obtain and expensive.) The rules for engine life - diesel or gas - remain the same: change the oil often and don't run them hot. Experts will say monitoring diesel exhaust temperature is the best way to protect an engine. The point of my comments is to suggest we might present a more positive attitude with respect to gas engines. There are lots of negative feelings out there towards gas engines that are, I think, unjustified. The long term reliability, initial cost, quiteness of operation, ease of repair, lower rebuild costs, etc. easily outweigh the added fuel costs for gas engines. In fact, the fuel cost differences are not as great as they used to be. Diesel or gas, the answwer I keep running into is: to save money, slow down. Still, I keep imagining us cruising on Sturdy Girl at 22KTS...aaah. That's my two cent's worth (and you get what you pay for). Rocco --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "UnifliteWorld" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/UnifliteWorld?hl=en -~----------~----~----~----~------~----~------~--~---
