I wish to thank everyone who has responded to my turbocharger survey, both on this list and off the list via private E-mail; and also I want to thank those of you who have helped me to learn much about the use of turbochargers on small engines in private trawlers. This will be a summary of what I have learned by this endeavor. My first surprise was that many of you have turbochargers on your engines. I had not expected this. Immediately, my second surprise was that almost none of you need them. I say this because by the fuel consumption data that you have provided, I can see that you are all using your engines at a small percentage of it total power most of the time. Some of you have expressed surprise that I could know this so easily. It is really very simple. For the average diesel, turbocharged or not, take your fuel consumption rate in gallons per hour and multiply it by 20. That will give you a very close estimate of the power you are actually using when you are consuming that amount of fuel. Five gallons per hour is close to a hundred hp, regardless if the manufacturer rates that engine at a hundred hp or at two thousand hp. (This rule of thumb begins to break down at very low power rates, especially for two stroke diesels; but other than that, it is a good rule that will give you a close estimate.) The primary reason for adding a turbocharger to a diesel engine is to get more power out of that engine. If you do not need more power, then you do not need the turbocharger. I'm not sure why every trawler that responded to my survey has a whole lot more power available to it than it is actually using most of the time. Perhaps there are times when you actually need all this power. That might make a good topic for further discussion. Possible reasons might be wind loads in a storm, or an occasional need to move much faster than normal. This second reason would not apply to a traditional full displacement trawler, but could apply to a modified semi-displacement "fast trawler." If you have reasons to hold so much power in reserve, then a turbocharger is a very wise choice. The diesel engine industry has much data about how long engines will last as a function of how hard they are worked. Generally, the harder you work an engine, the quicker you will wear it out. If you add a turbocharger to an engine to get more power, and then you demand that extra power out of your engine frequently, then you will wear it out quickly. Turbochargers are best suited to applications in which you only need that extra power occasionally; and are running at a much lower power level most of the time. If this is how you use your boat, then a turbocharger is a wise alternative to simply buying a larger engine. Suppose for example that your engine is good for 200 hp naturally aspirated, and 300 hp with a particular turbocharger on it. If you then use this engine at 80 hp most of the time, then adding the turbocharger has not effected the life of the engine at all. It is sort of just going along for the ride. Likewise, if you never have a need to demand more than 200 hp out of your engine, then you have wasted your money on the turbocharger. It is not doing a thing for you. The only justification for the turbocharger would be if you occasionally needed more than 200 hp out of your engine. If you needed more than 200 hp out of this same engine most of the time, then you would be better off buying a larger engine rather than turbocharging a smaller one-- unless other design objectives forced you into using a smaller engine rather than a larger one. The efficiency of an engine is measured by its specific fuel consumption. This is given in terms of the amount of fuel burned per hp per hour. Example units would be grams of fuel per hour per kW; or pounds of fuel per hour per horsepower. The one gallon per hour per hp that I gave earlier is just a good all around average of how these units would convert into something that would be more useful to us. The actual specific fuel consumption of an engine can vary according to a number of factors, though modern engine manufacturers have done a very excellent job of optimizing it under most common operating conditions. It is a common misconception that a turbocharger will make an engine more efficient, or that it uses "free energy" that would otherwise be dumped out the tail pipe. The fact of the matter is that if you do nothing else to a diesel except add a turbocharger to it, then your specific fuel consumptions will increase, which is to say that the engine will be less efficient. There is no such thing as "free energy." The engine performs work to turn the turbocharger, and this work is extracted out of the diesel fuel. The big advantage of a turbocharger is that it is a very efficient air compressor. Other types of air compressors, like for example the big belt driven superchargers that you see on dragsters, are not nearly as efficient. This is why turbochargers are much more common in "real world" engines than superchargers. Perhaps the reason many people believe that a turbocharger makes an engine more efficient is because many engines with turbochargers are more efficient than older engines without them. In actual fact, this is because the manufacturers have done many things to their engines to improve the specific fuel consumption. All these things work together as part of the entire system, so that no one item can be separated and singled out as the cause of the improved fuel economy. A turbocharger is just part of the overall system, which is a whole lot more efficient today than in the past. Two changes that a manufacturer will make to an engine when they add a turbocharger is the addition of an intercooler and/or the reduction of the compression ratio. Both have the same effect, which is to bring actual pressures during the compression stroke back down to what the engine was designed for; and in so doing reduce internal frictional loses. It is common for the addition of a turbocharger to cost about three percent in specific fuel economy; but for an intercooler and/or a lower compression ratio to increase efficiency by about 5-6 percent, for a net gain of perhaps two or three percent. Actual numbers for specific engine examples can vary somewhat. One reason for me to bring this up at all is to show that one way or another, the changes in actual fuel specific consumption will be small with the addition of a turbocharger. Perhaps the greatest improvement in engine technology to improve fuel efficiency is to get rid of that detestable indirect injection, a result of the 1970 era clean air requirements, which can cost up to 20 percent in fuel economy for the purpose of cleaning up the air. Fortunately, we have learned to make direct injection diesels run clean in recent years by doing two things. First, we are running much higher injector pressures. Whereas 1500 to 1800 psi used to be a typical injector pressure, some engines are now running as high as 35,000 psi. The purpose of the indirect injection was to promote atomization and mixing; but these higher pressures promote that just as well. Then we are also tailoring the injection charge, such that about three percent of the charge is injected at about 35 degrees BTDC to get the fire started, and then the rest is slowly injected starting about at TDC and continuing down for about 30 degrees. This burns the fuel much more efficiently. It also gets rid of most of that traditional diesel knock. You will find this technology on all larger engines, but not on all smaller ones. Look for buzz words like "direct injection," or "common rail" when buying your engines. BTW, these very high injection pressures have also enabled some modern diesel engines to spin much faster than they used to. Diesel is a flame front burning fuel, whereas gasoline is a mass burning fuel. Diesel therefore takes more time to burn completely, hence the lower crank speeds in traditional diesel engines. The better atomization of the fuel that results from these higher injection pressures will make the diesel fuel burn more quickly; hence closing the gap between the burn rates of gasoline and diesel fuel. Raising the crank speeds is another highly effective way of getting more power out of a smaller engines. Continued on Part II Boatless, but building M/V Doulos Paul Kruse plkruse@iu.net Port Canaveral, FL, USA