I am currently replacing a diesel engine in a 41-foot sailboat. I would like your opinion on a turbo versus a non-turbo version of the same engine?
Tom Wood responds:
There are turbo chargers and then there are turbo chargers, so the answer depends on whether the engine in question has just a little blower to aid combustion, or whether it has a great big, intercooled, aggressive ram charger.
Consider that one of Yanmar's most popular sailboat engines, the 4JH series of four-cylinder dieselsall of which have a displacement of 1.817 cubic inchescomes in five flavors. They make five models on the same block with the 51-hp 4JH2-BE model being the only one naturally aspirated. Next up, the 4JH2-TE at 63 hp has a puny little blower that hardly qualifies as a real turbo charger, but is effective in getting almost 25 percent more power out of the same engine. From there we go up to the 4JH2-HTBE at 76 hp, the 4JH2-DTBE at 88 hp, and the 4JH2-UTE at 100 hp, all magically pulled out of the same little four cylinders. How do they do it? By increasing blower speed, intercooling the turbo to withstand the heat, and increasing air intake and exhaust port size to carry the combustion through the engine more efficiently.
Many years ago, turbos were finicky, hard to find repair parts or mechanics for, and generally enjoyed a bad reputation. Today, even some of their severest critics like me, have one in their own boat. Why? Turbos have become more reliable, and companies like Yanmar have offered better warranties and parts supplies.
The main advantage is, of course, more power when you need it without adding a great deal of weight to the boat by using a larger engine. Instead of using a six cylinder engine weighing 500 pounds more, a sailor can get 80 or 100 hp out of the same lightweight four cylinders. Except for the minor drawbacks of a high-pitched whine at high rpms on the aggressive turbos, and a tendency to lope, or hunt, at idle, from an operator's standpoint there will be very little difference.
So, what are the disadvantages? The bigger the turbo, the bigger the price tagboth for original installation and for repairs if they break. Installation costs can really soar with the big turbo since they may have larger water inlet sizes or exhausts or may need larger mufflers, strainers, and other parts. Naturally aspirated engines obviously use less fuel because they have less power.
Turbos add another piece to the maintenance schema on board. Since they sit as a bridge between the exhaust and intake sides of the airflow, the exhaust side tends to carbon up, especially if the engine is idled a good deal, is lugged by an mis-pitched prop, or is run at light loading (read charging batteries, refrigerator, or watermaker). This carbon needs to be removed periodically (Yanmar suggests every 50 to 200 hours, depending on the fluid used) in a painful process of injecting either water or expensive turbo cleaning fluid into the air intake while the engine is being run across the water at top speed. If a blob of carbon breaks loose, it can hit the high-speed blades of the "fan" causing a very expensive-sounding clankand the sound is not deceptive, because replacing an aggressive, intercooled turbo is a big job.
So, you can see, I've not given up my bias against turbos on boats entirely, only modified it a bit. The small, non-intercooled turbos have become reliable enough that I can live with one in my basement. If I felt I needed more power than was available in a naturally aspirated or small blower, I'd go on up to a large displacement engine before I'd go the aggressive-intercooler route. But this is only my opinion, and I note that Sue & Larry installed a 100-hp Yanmar on Serengeti.