Medium speed diesel - maintainability

Some of the vessels I’ve run across in my searches have had a medium speed diesel main. Most of the vessels which seem possibly realistic for my needs are newer than the early 1970’s. I am fascinated by a single medium speed main for several reasons, but I do wonder how well supported they are in terms of spare parts (rings, bearings, liners, etc.) Presumably it would vary from unit to unit.

The makes I have run across, or less commonly, am simply interested in by have not seen, include: Allen, Callesen, Duetz, MaK, MWM, Nohab Polar, Wartsila, Wichmann. I wonder if anyone can speak to a particularly high level of support, or particularly low level of support for any specific brands.

In a similar vein, I wonder if there are shops who will just make the parts one would need for an overhaul. Or even if that is the norm in the business for some of this kind of work?

From the tone of your question I guess you’re not really looking to use the boat professionally? If you are, it becomes a rather involved business decision that can only be made with local conditions in mind. If not, we have plenty to talk about.

A lot depends on if the factory is still operating or not. Wichmann made beautiful engines, but the factory got shut down and restructured so many times before what’s left of it got bought out by Wärtsilä that you only have access to used spares. There are plenty of those in West Norway, but not really anywhere else. See what I mean by local conditions?

On the other hand, I used to run a B&W Alfa 406 until about a decade ago, and enjoyed pretty much full factory support. They happily shipped me all the tricky little parts, like injector tips and high pressure air components, etc. Some stuff I had to get made, like scavenging air pump reed assemblies. There are absolutely people who will make replacement parts, especially if you do the CAD work, but of course that’s far from free.

You should realize that running old medium speeds is an expensive undertaking in any case. For example, a set of six pistons and liners for that old Alfa came to around 100k USD. You can have a brand new high speed of similar output for less than that, reduction gear and all.

Anyway, if you do all the work and respect all the gauges, you can always squeeze out one more run cycle, until you suddenly can’t. How big of a problem that is depends entirely on your use case.


@Klaveness: You read my tone correctly. You also managed to touch on a bunch of stuff that I find very useful and informative. Thank you very much for that. In my present conception of things I would do at most one major voyage per year, and I doubt that it would exceed 1200 hr. If I did zero voyages the total time would be perhaps a quarter of that.

One of the things which fascinates me about these engines is the possibility to take one cylinder somewhat off-line or repair it on a voyage. I was reading about it on one of threads here. Do you know off-hand if that is a characteristic of most of these ‘Alpha-like’ medium speed engines?

What might make sense would be to favor a vessel where the odds of a main having some time left in it seemed relatively higher and consider the eventuality of needing to modernize when it became impractical to nurse the engine along. In the mean time I could keep my eye open for spares to see if I could make that an option as well. Having some worse-case ‘limp-home’ capability is part of my plans, but I would definitely not like to have to rely on it. The flip side would be that I may use the vessel so little that such a day when the main is not seaworthy would never come (within my own service-lifetime.)

In that case I can’t recommend that you get into it with a medium speed, no matter how cool I think they are or how much I’d want another one saved from the smelters. If we were talking about doing up to a few hundred hours a year, and given plenty of time to learn the ropes, I’d be all for it. Things get very different if you want the boat to fill more needs than a learning opportunity, especially as it doesn’t sound like you’ll have experienced crew on hand.

1000+ hrs is a non-trivial amount of run time, and will require significant maintenance. Not all of it is highly qualified labor, but it must be overseen by someone with working knowledge of the system. Depending on budgetary constraints you will have enough on your hands with keeping the rest of the boat together.

If you’re concerned with limp-home capabilities, look no further than a twin screw boat. Given a finite maintenance budget, a single high speed will be more reliable than an aging medium speed anyway.

As for off-handedly characterizing these engines, I don’t quite know what to tell you. The Alfa is a loop scavenged trunk engine with either 34 or 40 cm bores, available in 2-9 cylinder inline configurations and various ratings. They typically do 15k hrs on the top ends and 50k hrs on a bottom end. However, there is huge variation in the small medium speeds typical of the post-war European fishing fleet, and far from all of them are even remotely “Alfa-like.” If you want to know more, I suggest you read a book or get involved in your local marine engine historical society.

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I do not dis-agree with you assessment. I am also highly dubious that there would be a any availability of personnel in my area who were competent at working on almost any system which they were not thoroughly and specifically trained to work on. I’m routinely horrified by the practices I see here when it comes to both mechanics and welders, though I’ve not worked with anyone who I know to have more international marine industry experience. (Here being The Philippines.)

I’ve worked on and off as a mechanic with the longest stint specializing in VW diesels. They are a different thing for sure, but there are certain standards of precision, cleanliness, etc, and certain theoretical understandings that one develops and which are somewhat universal to most mechanical work.

In researching things more, I may have mis-understood that medium speed diesels are ever reconfigured at sea to cut off a cylinder unit. That may be unique to low speed engines. One document I found describes the process, but it is for cross-head engines and involves undoing the connecting rod.

On general documentation about processes, procedures, etc, it seems to me that it is much more difficult to find research content on-line than it had been a decade or two ago. On almost any topic! Many collections of information seem to be a relatively dis-organized data dumps clumped together to attract ‘eye-balls’ and thus win more ad revenue. Additionally, more and more data is being claimed as intellectual property. But that’s life I suppose. The goals and requirements of the ‘new normal’ promise to make the situation much worse I fear.

In general I would say that if medium speed diesels benefit notably by having a highly experienced attendant in their presence much of the time to monitor their operation, that alone quashes much of my interest in them irrespective of the maintenance costs and hassles. I was responsible for a couple of TAMD Volvo’s on a tender for a season in Alaska, and they did require rather extensive attention and monitoring, but they had been amazingly neglected. Everything else on the craft had been as well, and most of my time was spent keeping the other systems operational (especially the refrigerated sea water system which was the life-blood of the mission.) I had time and was able to source an oil cooler and get some of the gunk cleaned out of one of the Volvos, but that was about it. I hated those engines, but mostly because they were in such dismal condition and I could do little about it.

I had a BRAND NEW Volvo TAMD turn out to be a huge PITA, so I can only guess how bad a neglected one is.