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Sunday, December 16, 2018

Mirror, Mirror, on the Wall, What's the Fairest Engine of All

I received a lot of questions about our Scania main engine and the thinking behind the decision, so here goes.

First, none of the engine choices we had would have been bad.  In fact, all are excellent engines with great reputation, and I wouldn't reject any boat just because it had one of these engines.  Quite the opposite.  But when faced with a blank (or almost blank) sheet of paper, the engine choice is worth some thought and consideration.

We have two engines, but not in the traditional sense of a twin engine boat where both engines are identical.  We have a main engine that is the primary propulsion engine, plus an auxiliary engine for hydraulic power for thrusters, windless, pumps, etc..  It also acts as backup propulsion in case of a main engine failure, using it's own drive shaft and a folding sailboat propeller to minimize drag when not in use.  It's location is offset to one side of the center line of the boat, and for that reason is typically referred to as a "wing" engine.

All this means we need two engines with different specs.  The wing engine needs to be around 150 hp, and the main engine around 400 hp, both with continuous duty rating.

Duty ratings are worth a little sidebar.  All engines are rated with a maximum horsepower or kw output power.  That's always part of the headline.  But elsewhere in the fine print are limits on how long you can run the engine at full power, or more specifically what portion of the run time can be at full power vs something less than full power.  Think of your car which might have an engine rated for 200 hp.  How long do you think it would last if you ran it at full power, peddle to the floor, all the time, never letting up for even a second?  Not very long.  But that's fine because that's not how we drive.

With industrial engines things are different because there are many application where the engine needs to operate at full power for sustained lengths of time.  Think about an irrigation pump that might need to pump water continuously, or a ferry that is underway at full power for 3hrs, then at dock for 2 hrs, then underway again...  To deal with this, industrial engines all have service ratings to help match them to the application.  Every manufacturer uses different terms with different definitions, but conceptually they are all the same.  By way of example, here are Deere's so-called "M ratings".

M1 - Unlimited full power hours, unlimited hours per year.  This is a "continuous duty" rating.  You can start the engine, load it up to full power, and leave it there for it's entire life, save maintenance time.  You can put almost 9000 hrs on it and still be under warranty, and continue to clock hours at 9000 per year.

M2 - Full power is allowed for 16 out of every 24hrs, and annual hrs are expected to be between 3000-5000.  This could run a ferry with two hrs underway at full power, 1 hrs at dock, then repeat for 12hs every day for the life of the engine.

M3 - Full power for 4hr out of every 12hrs, and annual hours of between 2000-4000.

M4 - Full power for 1hr out of every 12hrs, and 1000 to 3000 annual hours.

For many pleasure boats, any of these ratings would be fine, and very few can't be served just fine by an M2 rating.  In fact, many Nordhavn's are specified with M2 rated engines.  But others, especially if expected to operate wide and far, are specified with M1 rated engines.

All this brings us to requirement #1 for the engines:  They must be continuous duty rated.

Requirement #2 is that the engine needs to meet US, EU, and IMO emissions requirements.  For those in the US, that means Tier 3 which does NOT include special after treatment or catalysts, but is a very clean burning engine.

Requirement #3 is that the engine needs to provide the desired power output, 400 hp for the main, and about 150 hp for the wing.

Then there is a long list of stuff that I just assume is a given like a reputable manufacturer, parts availability, excellent reputation and service record in marine applications, etc. etc.

Wing Engine

Starting with the wing, the choices were:

1) Deere 4045
2) -----

It's a short list.  Caterpiller's smallest propulsion engine is 7 liters and 280 hp, which is just way too big.  Similarly, Cummins' smallest engine is 6.7 liters and 250 hp.  Yanmar has a much smaller 2.7 liter engine that operates at around 3500 rpm that puts out the right hp, but they caution about continuous full power operation.  They are really meant for lighter duty applications.  Someone asked about a "baby Scania', but the smallest Scania is a 5 cylinder, 9 liter engine, and it's not Tier 3 certified.  The bottom line is that there really isn't much choice.

Deere 4045AFM85

But only having the Deere isn't a bad thing because it's a really good engine.  The 4045 (4.5 liters) has been around for a very long time and has an excellent reputation, so I'm very happy with this engine.  It's continuous  duty rated (M1) producing 160 hp at 2300 rpm.  I'm told it will move the boat at about 6 kts which is excellent for a wing engine.

Deere, front view with clutched power take off

Main Engine

The wing engine was the easy decision, because there was no decision to make.  The main engine was a little tougher.  I was considering three, excellent engines, any one of which I expect would provide excellent service.  They were, in my ultimate ranked order:

1) Scania DI-13 (400 hp @1800 rpm)

2) Cummins QSM11 (400 hp @ 1800 rpm

3) Deere 6135SFM85 (425 hp @ 1800 rpm)

Absent from the list is Caterpillar.  They just don't have an offering in this power range and duty rating.  Also absent is Lugger, but they have been absent for a number of years after exiting the propulsion engine business a number of years ago.

Engine Room Heat

One particular technical aspect of all three engines ended up playing a major role in the decision;  heat, and engine room cooling.  I delved into this quite a bit on our 60, and am working hard to head is all off early in the 68.  For reasons that I can only guess, there is a huge difference in the amount of heat these three engines dump into the surrounding engine room.  That heat needs to be removed by ventilation, and that can be a challenge.  The difference isn't due to engine efficiency - they are all about the same.  The difference is WHERE the waste heat goes.  It exits the engine through one of three paths;

1) Out through the cooling system and into the surrounding sea water, either through a heat exchanger or a keel cooler.  This is where 90% of the heat goes.

2) Out the exhaust pipe in the hot exhaust gas.

3) Radiated into the surrounding environment, in our case the engine room.

Whatever heat doesn't go out one path, must go out another, and when it comes to engine room cooling, #3 is what we care about, and these three engines have radically different performance in this respect.

The Scania dumps a freakishly small amount of heat into the engine room.  14kw, to be exact.  In contrast, the Cummins dumps 23kw which is more normal, but still nearly twice the Scania.  Then the Deere dumps a whopping 40kw, which is freakishly large, and almost three times the Scania.  The result is a huge difference in the back flips required to vent the space, and the resulting temperature rise in the ER.  This alone was probably the dominant factor in the ranking.  Beyond this, each engine had characteristics that bumped it up a little, or bumped it down a little in the ranking.  It ended up being a very close call between Scania and Cummins, with Deere a distinct third.

Here's some random narrative on each.

Scania DI-13

Scania has very little presence in the US, but is a huge, $12B Swedish company.  They primarily build and sell trucks and buses, but build their own engines and have a separate business selling those engines into marine and other industrial application, much like Caterpillar and Deere.  And as of a few years ago, they became part of Volkswagon AG.

Scania DI-13

I have always favored Swedish engineering.  Older Volvos, Electrolux vacuums, Husqvarna chain saws are all brilliant in their simplicity, effectiveness, longevity, and serviceability.  Scania trucks and buses have a similar reputation, and that carries into the marine engines.  I spoke with a number of distributors, dealers, and owners of Scania marine engine powered equipment, and not a single one had anything but praise for the product.   And all the dealers and distributors deal in other brand engines as well, so had no incentive to favor Scania over anyone else.

Just looking it over, it's a very well thought out design with very well integrated marine accessories.  On many engines, the so-called "marinization" becomes it's Achilles heel, with heat exchangers and water pumps bolted on in ways that block service access to other parts, and creates a more complex package.  The Scania is very compact and streamlined, with excellent access to all servicable parts.

One thing I was concerned about was cost and availability of parts.  Volvo, another Swedish marine engine manufacturer, has a reputation for extremely expensive parts.  I owned one a while back and found that if you imagined an incredibly high price for a part, then doubled or tripled it, you would be in the right ball park.  So I made up a list of typical spares and service parts, and got a quote for price and availability.  Everything on the list was available either at the dealer or a day away in a central warehouse, and prices were all in line with other vendors.  So they passed that test.

The product checked out with flying colors, as did parts cost and availability, but what about service.  If there is any down side to Scania, that's it.  Pretty much anywhere you can find a Deere or Cummins service guy, but Scania?

For me, I'll be doing most if not all work on the engine myself, so in many ways access to techs is not an issue.  But in the event one is required, they do have a network, including Hatton Marine in Seattle who I have used in the past.  So worst case I'll be flying someone in from Hatton.  But in all honesty, if I need to get someone in to help, it would likely be serious enough that I'd be flying one of their guys in anyway, so not really a problem.

So I am very confident in the product, and am confident I can get parts.  The one risk is Scania's longevity in the North American engine business.  They have completely forfeited the North American truck and bus business, and it's not because it's a small market.  They made a go of it back in the 80s, but only lasted a few years before pulling out.  But really the bigger concern is the size of the engine business compared to their overall business, and the engine business's size in NA compared to their costs.  Unlike other regions where they have a large truck and bus business to carry the cost of spares and a dealer network, in NA it has to be carried entirely by the engine business.

Let's look at it via the numbers.  Scania reports that their world wide engine business is 1% of overall revenue.  Then, when they break down the engine business by geography, North America isn't even in the pie chart, and the smallest sliver in the chart is 3%, so we know NA is less than that.  So the NA engine business is less than .03% (3% of 1%) of Scania's business.  This was my only hesitation with Scania, and why Cummins was such a close second.  In contrast, Cummins is also a $12B company, and their whole business IS engines - 100%.  Or at least very close to 100%.  There's just no question where they will be tomorrow.

Sounds pretty scary, right?  Well, not really.  There have already been two Nordhavn't built with Scania engines, all running well.  And there are three of us currently building 68s with Scania engines.  And of the fleet of 70 or so Scania-powered commercial boats operating in Bristol Bay, Alaska, the only reported problem is a broken oil spinner.  The engine was installed with poor access and it got man-handled and broken.  So I really do think we are getting a superior product.  And even if Scania departs the NA market, there are plenty of ways to get parts, most of which we keep on board anyway.  And if it turns out to be a total, unmitigated disaster, I can always pull it out and install a Cummins for a small cost relative to the value of the boat.  So ahead we go.

Scania DI-13


The Cummins candidate was the QSM11, continuous duty rated at 400hp, 1800 RPM.  Most of the QSM11s out there are higher HP rated, pleasure duty engines.  They have a good reputation, but a well known issue with the exhaust manifold to head joint leaks.  But that issue is only in the higher output rated models, and not the commercial duty version.  It's a well proven engine, with an excellent commercial duty track record.  Parts and service are available on nearly every street corner, so no problem there.  It was a very strong candidate, and frankly lower risk than Scania, but that was offset by the superior heat rejection of the Scania.  Had Cummins had similar heat performance, I probably never would have looked further.

Cummins QSM11


The Deere under consideration was the 6135SFM85 which is the raw water cooled, heat exchanger version of the 6135.  Nordhavn specs the 6135AFM85 as standard equipment, which is the keel cooled version with an M2 (16/24 hrs full power operation), 425hp at 1900 rpm rating.  I wanted wet exhaust and cooling, hence the SFM version, which also has the benefit of an M1 (continuous duty) 425hp at 1800 rpm rating.  It's a touch more HP than the Scania and Cummins, but not enough to make any difference.

Deere 6135AFM85

The real killer was the heat rejection.  It makes for a challenging engine room venting design vs an easy and breezy one.  Plus there were some pesky issues I had with the Deere 6090 on my 60 that made me less than confident in the marinization of the 6135.  I think they are stellar base engines, but pesky problems can add up to a real annoyance and erode confidence in the over all package.  Here are some of the issue that I encountered.

1) Excessive belt dusting and shedding.  All the 6090's seem to have this issue shedding profuse amounts of dust and shrapnel.  I checked alignment of all the pulleys, tension, belt wrap, belt loading, and consulted everyone and anyone I could find, and never figured it out.  What I do know is that all the  other 6090s I know of in boat service experienced the same thing.  It does seem to reduce considerably somewhere in the 800-2000 hrs range, with ours finally subsiding at close to 2000 hrs.

2) Oil seepage from various engine joints and seems.  I was always getting oil seeping from valve cover seems, the oil pan seem, and other joints.  I just don't understand why this should be.  Oil just shouldn't ooze out of an engine.

3) Turbo gasket coolant leaks.  For the first couple of years I had a very slow loss of coolant, with no trace of where it was going.  I had heard of issues on the 6090's predecessor, the 6081, where coolant would leak past the turbo gasket and disappear out the exhaust in unnoticeable quantities, other than long term.  The master of all things Diesel, Bob Senter, suggested a sealing procedure on the turbo gasket, so I set about to do it.  The gasket alone suggests that the joint is difficult to seal.  It's a layered gasket, riveted together in a sandwich. The center layer is a typical gasket material, and the two outer sandwiching layers are thin steel each with a molded in rubber seal, kind of like a built-in o-ring.  The procedure was to further seal using Permatex Red high temp sealant.  I actually drilled out one of the rivets and fanned opened the layers like you would fan out a hand of cards.  That allowed me to get a film of the sealant on all the mating contact surfaces, then carefully fold it back up.  I put it all back together and presto, no more slow coolant leak.  Problem solved, but not a confidence builder.

Special turbo gasket with riveted layers

Unfolded gasket layers

Magic Permatex sealant

4) Coolant pump leak.  The cooling pump, like many, has a weep hole to detect leaks.  If the coolant seal is leaking, you will get cooling out of the weep hole, and if the drive side of the pump is leaking, you will get oil out of the weep hole.  It's a gear driven pump off the timing gears, hence the side exposed to oil.  Early in the engine's life I was getting drips of coolant from the weep hole, so the pump was replaced under warranty. 

Coolant drips from coolant pump

That sort of thing happens, but it exposed another issue which is accessibility due to the marinization of the engine.  To change the coolant pump, something that would be a couple of hours max on the tractor or industrial version of the engine, was a solid two day job for two guys.  Endless amounts of stuff had to be removed from the front of the engine to gain access, all of it added as part of the marinization package.  It just wasn't well thought out. 

Stripped engine to access coolant pump

Large pile of removed parts to access coolant pump

Frustrating, but that was only the beginning.  About 20 hrs into the new pump, and I was getting drips of coolant again.  So after the season was done, I pulled it all apart again, this time doing the work myself because it seemed logical that the guys doing the first replacement had done something wrong.  After I got the pump out, there was no sign of poor workmanship by the other guys, so I went to get another pump under warranty.  Well, warranty only provides for a rebuilt pump, so I decided to take the rebuilt pump and keep it as a spare, and sprung for a new pump on my own dime, just in case.  After two days of solid work it was all back together and ready to go.  But to my horror, after about 20 hrs (same as the last two times), it was dripping again.   Escalation of the issue through the distributor to Deere just went in circles and kept pointing back to an inapplicable tech bulletin that had the words "coolant pump" in it.  I finally gave up and decide to just live with it, like the oil seeps.  I went for well over a thousand hours and it never changed or progressed, so I just kept on going.  There was no way I was going to tear the front of the engine apart again unless someone had a very convincing explanation for the problem, and an equally convincing solution, and nobody ever did.

So the engine never missed a beat in 2000 hours, but these little things bugged me the whole time, and made me less than thrilled about another Deere engine.

There you have it. Scania is the fairest of them all.

Scania DI-13


  1. Peter, did you look at Steyer for the wing? I know nothing about them, other than they look cool, are lightweight, and I believe have an excellent rep.

    Carl Loeb

  2. Just took a look at the Steyr. All they offer is a "medium continuous duty" for up to 3000 hrs per year, and at that only up to 120 hp. The rpm rating is typically a give-away on an engine's rating. Anything over 3000 rpm is unlikely to be anything other than a lighter duty rating.

  3. I am a little puzzled by your radiant heat rejection data. Did the engine manufacturer's supply that data?

    But as a retired chemical engineer I have a hard time understanding, much less believing the wide disparity in radiant heat rejection rates among the three. Radiant heat rejection in btu/hr for a body is roughly related to its area and the temperature of its external surface (in absolute values in Kelvin or Rankin scale) and moderately related to color.

    I suspect that all three engines have roughly the same area. So does that mean that the Deere operates its block, head, manifold and turbo at three times the temperature of the Scania? That just isn't possible given that those components are all coolant cooled (except for the Cummins which some are insulated.

    The Cummins does have a non cooled exhaust manifold and turbo. But both are insulated so the appropriate temperature for radiant energy is the aluminum insulation cladding not the block. The Deere is built like the Scania with cooled manifold and turbo.

    I would love to see some IR gun readings on these engines running at wot. I bet they are within 10% of each other.


    1. Yes, it's all manufacturer supplied data, meant for people designing the engine into some application where it needs to be cooled. So although I too am surprised by the wide ranging numbers, have to believe they are the most credible data available.

      And I agree with you on the fundamentals for heat rejection, i.e. surface area and surface temp. On first inspection I would arrive at the same assumption too, namely all engines have roughly the same surface area, and all have surface temps approximating coolant temp. My previous Deere demonstrated exactly that, with IR surface temps across the engine in the 170-200F range, i.e. coolant temp, give or take.

      Here are the things that I expect contribute to the difference, but I can't quantify any of them:

      1) Any parts that are not coolant jackets, especially exhaust parts, can run significantly hotter. On some engines, for example, the pipe stubs coming off each exhaust port are not jacketed until they enter the main exhaust manifold. Those pipe stubs run real hot, and the paint is always discolored on them. But as best I can tell, the exhaust manifolds and all three engines are fully jacketed.

      Turbos are another example, where some are coolant cooled, and others are not. But the un-cooled turbos are always insulated. Ironically, the Deere is the only engine of the three with a coolant cooled turbo. Both the Scania and Cummins are dry and insulated. So perhaps the insulated turbos reject less heat? It's possible, but I won't know until I run it and can measure the insulation surface temp.

      One of the hottest parts is the intake air pipe exiting the turbo and leading into the after cooler. On the Scania it's maybe a foot total length. Perhaps the others are longer and/or run hotter?

      The after cooler is another big one. On the Deere, it's a coolant cooled aftercooler, so the whole thing runs at or above coolant temp, and it a large mass with large surface area. On the Scania it's sea water cooled, so I expect runs at a much lower surface temp.

      The Scania is a very tightly packaged engine, and physcially a bit smaller than the Deere. As such, perhaps the unfolded surface is measurably smaller.

      Looking at the specs, I see now that they tell a significant part of the story. Both engines send almost identical amounts of heat out through their combined cooling system, and ambient rejection. The Deere is a bit less at 197kw coolant, and 40kw ambient for a total of 237kw. The Scania is 227kw through the coolant, and 14kw to ambient for a total of 241kw.

      The big difference is that the Scania gets rid of a lot more heat via the cooling system rather than the ambient air.

      It's also worth noting that the difference between the ambient heat rejection for the two engines is only about 10% of the total heat being carried away from the engine. So a small shift in how the heat gets carried away can make a significant difference in the absolute number for the ambient heat.

  4. I was wondering if you compiled a spare parts on hand cost comparison for the three.Also if the service intervals were comparable.


    1. Not formally, no. What I did was spot check a bunch of the Scania parts against the corresponding Deere and Cummins parts. All were in the same ball park, and certainly not enough different to sway any decision.

      As for service intervals, the Scania has a 500 hr oil change interval which is really nice. The others are 250 hrs. But I wouldn't make the decision on that alone.

  5. OK, I understand some of the differences such as sea water/vs coolant cooled after cooler that may be making the difference. Didn't realize that the Scania has a dry turbo, so you may be right- insulation is better than coolant jacketing for radiant heat.


    1. It's still interesting that it's such a big difference.


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