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Go Back   SailNet Community > On Board > Gear & Maintenance
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Old 02-25-2010
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Turbo Diesels

This article appeared on SailNet in 2001. Not much I've found that updates it so its my starting point.

How do people feel about Turbo Diesels today ? Are the pros and cons mentioned in the article still valid ?

I confess I have been quite negative re TDs not realising that in a sailing boat they are most likely to be very low boost and not the high boost intercooled type found in autos.

This is quote from the original article......I don't know who posed the original question...indeed I don't even know who Tom Wood is.

"Turbo Diesels

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 diesels—all of which have a displacement of 1.817 cubic inches—comes 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 tag—both 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 clank—and 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. "


Peoples....what are your thoughts ?
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Old 02-25-2010
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I shy away from them (on sailboats) too, but would not necessarily disqualify a desirable boat due to a turbo engine. Especially one with a low-boost version. I could live with it if adequately/properly heat shielded.

Also, there's boost and then there's boost. Our 31 footer has a naturally aspirated 3 cylinder 27 hp Yanmar. My brothers 31 footer has a 6 cylinder Yanmar turbo that puts out 440 hp. Now that's some boost!!
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Turbo diesels are good in the right application, unfortunately I do not think sail boats or any displacement boat are the correct application for such an engine, particularly when boost and electronic controls are applied to give a normally aspirated version two or three more powerful variant. Buy the norammly aspriated version, carefully maintained, it will last a long, long time......
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The information is not "out of date" but I there are a few points that I disagree on. The real advances recently have been in the fuel injection, not on the turbo side (it is somewhat effected). In the automotive world, variable vane or geometry turbos are becoming common and they are a different beast but most boats still use fixed blades. In my opinion, a moderately sized turbo makes a lot of sense on just about any diesel engine. Really large turbos will have too much lag and produce a lot of boost on the top end which increases cylinder pressures to undesirable levels. A moderately sized turbo will do a really good job of providing the necessary air to the cylinder.

The first place that I would disagree is on fuel consumption. If you look at a thermodynamic diagram, the biggest loss for turbodiesels is that they do not fully expand the gases in the combustion chamber (you would need infinite stroke). This means that the gases exiting the cylinder are still hot and can be used to power a thermodynamic device (turbo). By having a turbo, you ensure that you have enough air to fully burn the fuel in the combustion chamber and you can get more power out of a smaller displacement. Done properly, you will get better fuel economy out of a slightly smaller turbocharged engine versus a naturally aspirated one.

The other place that I would disagree is the carbon buildup. The exhaust needs to mix with something to lead to a really bad buildup and it is usually water or oil. A turbo will not introduce either of these to the exhaust stream (it has a problem if it is introducing oil). On an engine with a large laggy turbo, you can get a puff of smoke on throttling up but the engine tends to be less sooty in general than a naturally aspirated one due to improved airflow. I have never seen any exhaust tubing clogged due to having a turbo but I have seen plenty of piping clogged due to things like crankcase breathers being plumbed in.

In my opinion, turbos have made such large improvements for diesel engines (this is especially true for OTR engines). I have worked on a lot of both and the turbocharged engines do not give me any more problems than the naturally aspirated ones.
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Old 02-26-2010
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Quote:
Originally Posted by tdw View Post
. 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. "


Peoples....what are your thoughts ?
I have the same engine (and boat as Serengeti). All the pro's and cons you mention are real. It is expensive to maintain.
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Old 02-26-2010
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I agree with Klem's post with the exception that I still prefer a naturally aspirated small diesel. In larger diesels, such as OTR trucks turbos make much more sense where they need to generate 4-500hp with a minimum amount of weight. On most small (40' +- ) sailboats the weight savings is not a significant factor, and reliability is higher on the list of priorities. Turbos turn at up to about 75,000 rpm ( IIRC) and need a high volume of oil to lubricate the bearings and for cooling. While they are basically a simple device, they are an additional complication that is really not needed on a small, displacement style hull. In keeping with the KISS principle I would choose a NA engine over a turbo, but would not reject a boat strictly on that basis alone.
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Old 02-26-2010
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Quote:
Originally Posted by St Anna View Post
I have the same engine (and boat as Serengeti). All the pro's and cons you mention are real. It is expensive to maintain.
I'm assuming that means this particular engine is of the high boost, inter cooler variety ?
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4Jh2 - ute, on the Peterson 46. There is a very hot whatchamacallit on the end of the grey noisy, smelly bit and it makes a whirring sound over 2700 revs. The autostream thingamejig spins around a lot and we get plastered to the back rail.

It was on the boat and I agree exactly with JRD's last comment.
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Old 02-26-2010
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Quote:
Originally Posted by St Anna View Post
4Jh2 - ute, on the Peterson 46. There is a very hot whatchamacallit on the end of the grey noisy, smelly bit and it makes a whirring sound over 2700 revs. The autostream thingamejig spins around a lot and we get plastered to the back rail.

It was on the boat and I agree exactly with JRD's last comment.

Oh I do like it when I find someone who is seemingly as mechanically inept as moi !!

2700rpm ? Holy crap....our red noisy smelly thing would have conniptions if we even approached 2700rpm.

Then again slow measured progress is our way, the only way to get plastered on the Womboat is with me and the Wombet over dinner and a bottle or so of vino.
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Well

The tubro is a big issue as if your a bit lax at all on the upkeep the heat is a BIG fire issue
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